Ci7< '?>.
NASA Conference Publication 3258
Second NASA Aerospace
Pyrotechnic Systems
Workshop
Compiled by
William W. St. Cyr
John C. Stennis Space Center
Stennis Space Center, Mississippi
Proceedings of a workshop sponsored by the
Pyrotechnically Actuated Systems Program
Office of Safety and Mission Quality
National Aeronautics and Space Administration
Washington, D.C., and held at
Sandia National Laboratories
Albuquerque, New Mexico
February 8-9, 1994
National Aeronautics and
Space Administration
Office of Management
Scientific and Technical
Information Prgram
1994
Workshop Management
NASA Pyrotechnically Actuated Systems Program
Norman R. Schulze, NASA Headquarters - Program Manager
Host Representative
Jere Harlan - Sandia National Laboratories
Workshop Coordinator
William W. St. Cyr - NASA, John C. Stennis Space Center
Workshop Program Committee
Norman R. Schulze
National Aeronautics and Space Administration
Code QW
Washington, DC 20546
James Gageby
The Aerospace Corporation
P. 0. Box 92957
Los Angeles, CA 90009
Laurence J. Bement
National Aeronautics and Space Administration
Langley Research Center
Code 433
Hampton, VA 23665
Anthony Agajanian
Jet Propulsion Laboratory
Code 158-224
4800 Oak Grove Drive
Pasadena, CA 91109
William W. St. Cyr
National Aeronautics and Space Administration
John C. Stennis Space Center
Code KA60 - Building 1 100
Stennis Space Center, MS 39529
Table of Contents
WELCOMING ADDRESS 1 " 9
Dr. John Stichman, Director, Surety Components and Instrumentation Center,
Sandia National Laboratories
NASA Pyrotechnically Actuated Systems Program 1 3 " ^ I
Norman R. Schulze, NASA, Washington DC
SESSION 1 - Laser Initiation and Laser Systems
Laser Initiated Ordnance Activities in NASA 29 ^ d
Norman R. Schulze, NASA, Washington DC
Laser-Ignited Explosive and Pyrotechnic Components 49 - Q
Al Munger, Tom Beckman, Dan Kramer and Ed Spangler,
EG&G Mound Applied Technology
A Low Cost Ignitor Utilizing an SCB and Titanium Sub-Hydride Potassium Perchlorate
Pyrotechnic 61—^5
Robert W.Bickes, Jr. and M. C. Grubelich, Sandia National Laboratories
J. K. Hartman and C. B. McCampbell, SCB Technologies, Inc.
J. K Churchill, Quantic-Holex
Optical Ordnance System for Use in Explosive Ordnance Disposal Activities 65 - 4~
John A. Merson, F. J. Sa/as and F. M. Helsel, Sandia National Laboratories
r-
Laser Diode Ignition 71"*^
William J. Kass, Larry A. Andrews, Craig M. Boney, Weng W. Chow,
James W. Clements, Chris Co/burn, Scott C. Holswade, John A. Merson,
Fredrick J. Salas, and Randy J. Williams, Sandia National Laboratories
Lane Hinkle, Martin Marietta Specialty Components
Standardized Laser Initiated Ordnance System 79 — £
James V. Gageby, The Aerospace Corporation
Miniature Laser Ignited Bellows Motor 83 ~ f
Steven L. Renfro, The Ensign-Bickford Co.
Performance Characteristics of a Laser-Initiated NASA Standard Initiator 93 - %
John A. Graham, The Ensign-Bickford Co.
Four Channel Laser Firing Unit (LFU) Using Laser Diodes 101 \
David Rosner and Edwin Spomer
Pacific Scientific, Energy Dynamics Division
LIO Validation on Pegasus (Oral Presentation Only) 115 — Q
Arthur D. Rhea, The Ensign-Bickford Co.
in
SESSION 2 - Electric Initiation
EBWs and EFIs - The Other Electric Detonators 117 - I
Ron Varosh, Reynolds Industries Systems, Inc.
Low Cost, Combined RF and Electrostatic Protection for Electroexplosive Devices ... 125 - '/
Robert L. Dow, Attenuation Technology, Inc.
Unique Passive Diagnostic for Slapper Detonators 131 ™ * 1
William P. Brigham and John J. Schwartz, Sandia National Laboratories
Applying Analog Integrated Circuits for HERO Protection 143 - \\
Kenneth E. Willis, Quantic Industries, Inc.
Thomas J. Blachowski, NSWC, Indian Head MD
Cable Discharge System for Fundamental Detonator Studies 149 h
Steven G. Barnhart, Gregg R. Peevy and William P. Brigham,
Sandia National Laboratories
Improved Test Method for Hot Bridgewire AII-fire/No-fire Data 165 ^ (S
Gerald L. O'Barr, Retired (formerly with General Dynamics)
SESSION 3 - Mechanisms & Explosively Actuated Devices
Development and Demonstration of an NSI Derived Gas Generating Cartridge (NSGG) 177 ~lQ
Laurence J. Bement, NASA, Langley Research Center
Harold Karp, Hi Shear Technology Corp.
Michael C. Magenot, Universal Propulsion Co.
Morry L. Schimmel, Schimmel Company
Development of the Toggle Deployment Mechanism 191 -it
Christopher W. Brown, NASA, Johnson Space Center
The Ordnance Transfer Interrupter, A New Type of S&A Device 213 ^
John T. Greensfade, Pacific Scientific, Energy Dynamics Division
A Very Low Shock Alternative to Conventional, Pyrotechnically Operated Release
Devices 223 ~~!^
Steven P. Robinson, Boeing Defense & Space Group
Investigation of Failure to Separate an Inconel 718 Frangible Nut 233 ~ ^O
William C. Hoffman III and Carl W. Hohmann, NASA, Johnson Space Center
SESSION 4 - Analytical Methods & Studies
Bolt Cutter Functional Evaluation 243
S. Goldstein, S. W. Frost J- B. Gageby, T. E. Wong, and R. B. Pan,
The Aerospace Corporation
Choked Flow Effects in the NSI Driven Pin-Puller 269
Joseph M. Powers and Keith A. Gonthier, University of Notre Dame
IV
-2£
Finite Element Analysis of the 2.5 Inch Frangible Nut for the Space Shuttle 285 ^Z ^
Darin McKinnis, NASA, Johnson Space Center
Analysis of a Simplified Frangible Joint System 297 " £ 4-
Steven L Renfro and James E. Fritz, The Ensign-Bickford Co.
Steven L Olson, Orbital Sciences Corp.
Portable, Solid State, Fiber Optic Coupled VISAR for High Speed Motion and Shock
Diagnostics 309
Kevin J. Fleming and O. B. Crump, Jr., Sandia National Laboratories
Development and Qualification of a Laser-Ignited, All-Secondary (DDT) Detonator ... 317 ~ 2 .Q>
Steve Tipton, Air Logistics Center (AFMC)
Thomas J. Blachowski and Darrin Krivitsky, NSWC, Indian Head MD
SESSION 5 - Miscellaneous «
Pyrotechnically Actuated Systems Database and Catalog 331
Paul Steffes, Analex Corporation
Fire As I've Seen It 337
Dick Stresau, Stresau Laboratory
SESSION 6 - Panel Discussion/Open Forum
Moderator: William W. St. Cyr, NASA, John C. Stennis Space Center
Panel Members:
Norm Schulze, NASA Headquarters - Code QW
Larry Bement, NASA Langley Research Center
Tom Seeholzer, NASA Lewis Research Center
Jere Harlan, Sandia National Laboratories
Jim Gageby, The Aerospace Corporation
Ken VonDerAhe, Pacific Scientific Corporation
Discussion topics:
Topics submitted from the audience.
What's the future of pyrotechnics?
What are the predominant issues pertaining to pyrotechnics?
Pyrotechnic failures - lessons learned.
Pyrotechnic coordination - is it needed?
Are standards and standard specifications needed?
Note: The panel discussion and open forum commenets were not recorded and are not
included in this conference publication.
APPENDIX A - List of Participants A-1
omit
1994 NASA AEROSPACE
PYROTECHNIC SYSTEMS WORKSHOP
February 8-9, 1994
Sandia National Laboratories
Albuquerque, NM
Welcoming Address - John Stichman, Director
Surety components and Instrumentation Center
Sandia National Laboratories
■ 1 -
'paceJA..,-.-
Welcome
■
Primary purpose of this conference is to promote communications
between government agencies and private industry.
Conference is Organized in Four Sessions
■
CO
Optical Ordnance
- New, exciting and potentially significant safety improvements.
Electrical Initiation
- Backbone of pyrotechnics.
- Continued safety improvements (ESD & EMR).
Mechanisms & Explosive Activated Devices
- Details of device designs are important for specific technology
transfer.
Analytic Methods & Studies
- Computer analysis & improved test methods lead to a deeper
understanding & improved performance characterization
Five Decades of National Service
4*
-x;>: : :%^ ....;. ■$■; '/'. ^.| : '" :: ".:•:. ..'.-.
National Laboratories have had opportunity & privilege to support
U.S. nuclear weapons programs where we must provide long life &
high reliability components. Performance is characterized by
studies of fundamental mechanisms of explosive & pyrotechnic
phenomena.
Sandia has two major laboratory locations
Cl
New Mexico
California
The Defense Programs Sector is responsible for a
significant fraction of the Laboratories' activities
o>
Other
Intelligence
Nuclear
safeguards
and security
Research and
development
Nuclear
testing
Technology
transfer
initiative
Verification and
control
technology Stockpile
support
Inertial
confinement
fusion
m
Our programmatic efforts address
changing national needs
DOLLARS IN MILLIONS
1400
70 72 74 76 78 80 82 84 86 88 90 92
Fiscal Years
Engineering and physical sciences are the
backbone of our multidiscipline laboratories
61 Support
D Other Professionals
□ Technicians
M Electrical Engineering
H Mechanical Engineering
H Computer Science
H Other Engineering
M Physics
H Chemistry
IS Other Science
Modern process development and
prototype fabrication facilities
■
iProcess
[Development
Laboratory
Manufacturing
Technologies Facility
Integrated
Manufacturing
Technologies
Laboratory
Improved Industrial
Competitiveness
o
I
mmmmmmm
: .- ----- - . ■ -: ---- -■ -
Technology transfer in the past has been controlled
for security reasons, however, today it is becoming a
mission of the national laboratories to help other
government agencies and private industry in order to
improve our economic security.
Sandia undertakes new programs that enhance national
security and industrial competitiveness
National security
• Military
• Energy
• Economic
• Environmental
1
a *
r Mi;
i
Teaming with industry
"All federal R&D agencies will be encouraged to
act as partners with industry wherever possible.
All laboratories managed by the Department of
Defense that can make a productive contribution
to the civilian economy will be reviewed with the
aim of devoting at least 10-20 percent of their
budgets to R&D partnerships with industry. In this
L way, federal investments can be managed to
? benefit both government's needs and the needs
of U.S. Business"
President Bill Clinton
"Technology for America's Economic Growth"
February 22, 1993
si-si
f' 1
V
Update: NASA
Pyrotechnically Actuated
Systems Program
Norman R. Schulze, NASA Headquarters
Second NASA Aerospace Pyrotechnic Systems Workshop
Sandia National Laboratory, Albuquerque, NM
February 8, 1994
13
=0$MA*
February 8, 1994
=mMA=
Agenda
I. Program Origin
II. Program Description
III. Summary
I. Program Origin
14
Introduction - Pyrotechnic Systems
=mM A
• Routinely perform wide variety of mechanical functions:
- Staging
- Jettison
Control flow
Escape
- Severance
• Mission Critical
• Are required to have near perfect reliability
• But failures continue, some repeatedly
February 8, 1994
Definition
By example, pyrotechnic devices and systems include:
- Ignition devices
- Explosive charges and trains !
- Functional component assemblies, e.g., pin pullers, cutters, explosive j
valves, escape systems !
- Systems, i.e., component assembly, ignition circuitry, plus the interactions
with the environment such as structure, radio waves, etc.
February 8, 1994 - 1 5 -
—osmA'
Summary of Survey
23 year span covered
Failure categories
- Initiation
- Mechanisms
- Spacecraft separation systems and linear explosives
Firing circuits
Reviewed by Steering Committee
Report prepared
- Bement, L. J., "Pyrotechnic System Failures: Causes and Prevention,"
NASA TM 100633, Langley Research Center, Hampton, VA, June 1988
February 8, 1994
—0$MA*
Assessment of Survey Results
Deficient Areas
Recommended Tasks
• Design Approaches
- generic specification
- standard devices
• Design Approaches
- prepare NASA specification handbook
- select/verify existing hardware types
• Pyrotechnic Technology
- research/development technology base
- recognized engineering discipline
- training/education
- test methodology/capabilities
- new standard hardware
• Pyrotechnic Technology
- endorse and fund plan's technology tasks
- fund training and academic efforts
- R&D for new measurement techniques
- develop new h/w for standard applications
• Communications
- technology exchange
- data bank & lessons learned
- intercenter program support
• Communications
- continue Steering Committee meetings
- initiate symposia
- establish pyro reporting requirements for NASA PRACA
- perform as a Steering Committee function
• Resources
- funds
- research/development staff and facilities
• Resources
- implement pyrotechnic program plan
February 8, 1994
■ 16
—0SMA*
II. Program
• PAS Program Goals
• Program Flow
• PAS Program Organization
1.0 Program Requirements and
Assessments Element
• Implement projects necessary to address management aspects of the
Program's objectives
• Emphasize documentation and communications
• Prepare policy and planning documents to ensure products used
• Analyze NASA's future program requirements and current problems
• Provide computerized data base
• Produce documentation related to reviews, proceedings, analyses, etc.
February 8, 1994
- 17
1.1 Future Pyrotechnic Requirements
Project Mgr: N. Schulze, Headquarters
• Determine new pyrotechnic technology requirements
• Define efforts to:
- Improve PAS quality
- Meet more demanding environments
- Extend service requirements
• Evaluate new diagnostic techniques
• Provide functional understanding using computational modeling
capabilities - enhance specifications
• Product:
- Report on analysis of future requirements
STATUS:
On hold pending program review
February 8, 1994 10
1 .3 PAS Technical Specification
Project Mgr: B. Wittschen, Johnson Space Center
• Develop common procurement specifications
• Provide consistent technical reference for common technologies
• Use shared experience
• Make applicable to design, development, demonstration, environmental
qualification, lot acceptance testing, and documentation
• Assure critical concerns addressed using expertise of pyro community
• Provide common in-process quality assurance measures
• Product:
- NASA Handbook (NHB)
STATUS:
On hold pending action by Pyrotechnic Steering Committee to complete
review of the document
February 8, 1994 - 1 ft - 1 1
1 .4 PAS Data Base
Project Mgr: T. Seeholzer, Lewis Research Center
• Include past and current programs in terms of a hardware database
incorporating system requirements, designs developed, performance
achieved, specifications, lessons learned, and qualification status
• Present sufficient detail to provide guidance for users
Pyrotechnic Catalogue:
• Describe PAS devices used on prior programs
• Make available single data source to provide information on applications
of pyrotechnic devices including:
- their requirements
- physical envelopes
- weights
- functional performance
- lessons learned
- environmental qualification
- flight history
February 8. 1994
12
1.4 PAS Data Base (continued)
• Provide available information on pyrotechnic flight failures
• Coordinate with industry
• Product:
- Catalogue to be made available upon request
STATUS:
• Project is underway, content selected, data being complied, first draft
submitted to Committee for review, comments being incorporated
• Workshop paper to provide details
• Project completion expected in 1995
February 8, 1994 ■ 1Q ■ 13
1 .7 NASA PAS Manual
=mMA
Project Mgr: L. Bement, Langley Research Center
• Develop detailed "how-to" document to provide guidance on all aspects
of design, development, demonstration, qualification (environmental),
common test methods, margin demonstrations, etc. of pyrotechnically
actuated devices and systems
• Scope: Applies to pyro life cycle from creation of PAS/component
design to final disposition of device
• Product:
- NASA Handbook (NHB) for reference
STATUS:
• Project is underway, content selected, text/data being complied
• Project completion expected in approximately one year
February 8,1994 14
1 .8 Pyrotechnically Actuated Systems
Workshop
Project Mgr: W. St. Cyr, Stennis Space Center
• Create opportunity for technology exchanges at national level
• Perform planning for review by the Steering Committee
• Presentations by government and industry personnel on latest
developments
• Informal to facilitate communications
• Product:
- Workshop organization, preparations, implementation, and preparation of
proceedings in a timely manner
STATUS:
• First Workshop held on June 9-10, 1992
• Workshop proceedings published and distributed, NASA CP-3169
February 8,1994 - 20 - 15
2.0 Design Methodology Program Element
• Applied technology focus
• Hardware developed
• Emphasize design standards and analytical techniques
• Decrease chance of failure of new hardware design approaches or of
proven hardware in new operational regimes
• All aspects of pyrotechnic component and systems applications
covered
• Provide guidelines, handbooks, and specifications for design and
development of pyrotechnic components and systems
February 8, 1994 15
2. 1 NASA Standard Gas Generator (NSGG)
=Q3MA : : = =
Project Mgr: L. Bement, Langley Research Center
• Develop where the use of gas output is needed to perform a function
rather than serving as ignitor:
- Separation nuts, valves, cutters, switches, pin pullers, thrusters, mortars,
bolts, etc.
• Common NASA GG
- Based on NSI (NASA Standard Initiator) to provide pedigree
- Important for safety
- Saves $, NSI
- Wide variety of cartridges - lack "pedigree" inherent with a "Standard"
February 8, 1994 17
- 21 -
2.1 NSGG (continued)
=mM A — =
• Develop sizes to meet wide range of performance requirements
• Products:
- Qualified NSGG
- Design specification (NHB)
- Test reports
STATUS:
• Project has been successfully completed
• Two sources
• Workshop paper to provide details
February 8, 1994 18
2.2.1 NASA Standard Linear Separation
System (NSLSS)
Project Mgr: Joe B. Davis. Marshall Space Flight Center
• Develop standard linear separation system
- Improved, more reliable, high performance hardware
- Lower cost
• Characterize functional performance, effects of system variables,
including scaling
• Specify process controls to assure consistency and reliability
• Qual test for flight
• Establish operational functional margin
• Solicit design approaches from industry
- Prepare NASA-wide technical specification
STATUS:
• Project has been terminated due to lack of funds
February 8, 1994 _ «0 _ 19
2.5 Advanced Pyrotechnically Actuated
Systems (PAS)
=mMA=
• Define and pursue advanced design concepts to bring NASA programs
up to the state-of-the-art in pyrotechnic technology
• Maintain currency
STATUS:
• Project has been terminated due to lack of funds
February 8, 1994 20
3.0 Test Techniques Program Element
=QSMA
Address all aspects of testing: manufacturing, lot
acceptance, qualification, margin validation, accelerated life,
ground checkout, and in-flight checkout
Provide better characterization of component and system
performance
February 8, 1994 _ aa ^ 21
3.1 NSGG Performance
'€>SM A
Project Mgr: L. Bement, Langley Research Center
• Test to demonstrate NSGG for flight
• Develop test procedures
• Quantify performance
• Qualify NSGG
• Prepare design and test specifications
• Products:
- Design and test specification
- NSGG qualification test report
STATUS:
• Project has been successfully completed
• Functional performance and qualification completed
• Workshop paper to provide details
February 8, 1994 22
3.2 Standard System Designs
• Provide improved, more reliable, high performance standard
hardware designs
• Establish functional performance, effects of system
variables, scaling
• Prioritized selection of candidate hardware to become
"standards"
• Products:
System designs flight qualified and reports
Process controls specified in a technical specification
February 8, 1994 _ 24
3.2.1 NSLSS Performance
Project Mgr: L Bement, Langley Research Center/J. Davis, MSFC
• Demonstrate functional performance of the NSLSS developed in Project
2.2.1.
• Develop test procedures for the NSLSS that confirm its intended
operation
• Quantify performance output and update design specifications
• Products:
- System design(s) flight qualified
- Process controls specified in a technical specification
- Comprehensive final report
STATUS:
• Project has been terminated due to lack of funds
February 8, 1994 24
3.6 Service Life Aging Evaluations
Project Mgr: L Bement, Langley Research Center
• Evaluate effects of aging on pyrotechnic devices and degradation from
storage in the intended operational environments
• Determine relationships between storage environments and device
shelf life
• Evaluate accelerated life test approaches I
• Find performance characteristics that can be measured during I
qualification to ensure that function and margins are not impaired by
long periods of storage
• Product:
- Guidelines for estimating service life
February 8, 1994 oc 25
=€)SMA=
3.6.1 Service Life Evaluations -
Shuttle Flight Hardware
Project Mgr: L. Bement, Langley Research Center
• Determine effects of aging on Shuttle flight pyrotechnic devices
- Ensure that function and margins not impaired by long periods of storage
- 42 units tested
• Compare actual space flight hardware with older hardware stored on
the ground under controlled conditions
• Test phase recently completed
- Results look good. Five year extension.
STATUS:
• Project has been successfully completed
• Service life extended
February 8,1994 26
4.0 Process Technology Program Element
Put science into design and analysis of pyros
Develop approaches for analytically characterizing device performance
sensitivities to manufacturing tolerances and "faults," or deviations, in
component ingredients
Perform tests that verify analysis
Address problems caused by inadequately controlled specifications or
introduction of unanticipated substances into manufacturing process
Establish proper degree of controls for assuring product quality and
reliability
Emphasize process understanding and controls to assure that specified
hardware performance is realized during manufacturing processes
Support product inspection criteria and acceptance testing criteria
February 8, 1994 _ 2g . 27
4.2 NSI Model Development
Project Mgr: R. Stubbs, Lewis Research Center
• Provide better understanding of NSI's sensitivities to the effects of
process variables on performance
• Develop model
- Contract with Dr. J. Powers and Dr. K. Gonthier, U. of Notre Dame
• Verify by testing
• Present necessary technical details to control device's function
providing consistently high reliability level of performance
• Products:
- Validated model
- Report describing model in specification format
STATUS:
• Project has been successfully completed
• Feasibility of modeling demonstrated
• Workshop paper to provide details
• Work given international recognition: International Pyrotechnics
Society Award, to be presented February 20-25, 1994 at Christchurch
New Zealand
February 8. 1994 28
Summary
—&SMA
• Program presented in the 1992 has been substantially phased down
• Funded projects in work/completed as planned within cost and
schedule constraints:
- Data Base (in work)
- Pyro manual (in work)
- Workshop (no funds)
- NSI Derived Gas Generating Cartridge
- Shuttle Pyrotechnics Service Life Extension
- Laser ordnance demonstration (Pegasus) (in work)
- Laser ordnance demonstration (Shuttle Cargo Bay) (in work)
- Modeling NSI
- Modeling Linear Separation System (in work)
February 8, 1994 *— 29
Summary (continued)
—dDSMA
Programs eliminated:
- Linear Separation System
- Improved safe and arm system
- Advanced standard hardware
- Standard components and detonator
- Training
Goal was to reduce risks on future programs through better engineering
understandings of pyrotechnic deveices
Pyrotechnic problems persist - one of the most likely causes for the
failure of the Mars Observer
New program initiatives may be forthcoming as a result of that failure
Plan to be given senior management attention
Only advocacy at NASA Headquarters for pyrotechnics resides in Code Q
February 8,1994 30
- 28
Laser Initiated Ordnance (LIO)
Activities in NASA
Norman R. Schulze, NASA Headquarters
Second NASA Aerospace Systems Workshop
Sandia National Laboratory, Albuquerque, NM
February 8, 1994
29 -
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
LASER INITIATED ORDNANCE BENEFITS
[GOALS FOR ANY PROGRAM]
• GREATER RELIABILITY
• ENHANCED SAFETY
• LIGHTER WEIGHT
• LESS COSTLY PRODUCTS
• IMPROVEMENTS IN DESIGN LEADING TO HIGHER
OPERATIONAL EFFICIENCY
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
APPLICATIONS
• INITIATION OF SEQUENCING FUNCTIONS
• FLIGHT TERMINATION
• PROGRAM APPLICATIONS
- new launch vehicles
- selected use on existing fleet designs
- spacecraft
• LASERS HAVE LONG DEVELOPMENTAL HISTORY BUT LACK
OPERATIONAL PEDIGREE
— 15+ years
- small ICBM rod lasers, first laser ordnance flight test
3 - 30 -
January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
ADVANTAGES OF LASER ORDNANCE
• PHYSICS OF PHOTON NOT SUSCEPTIBLE TO HAZARDS OF ELECTRON:
ELECTROSTATICS, EMI, RF
• LASER DIODES HAVE THE POTENTIAL FOR DESIGN OF ALL SOLID STATE
SYSTEM
• POTENTIAL FOR BUILT-IN-TEST (BIT)
• PERMITS LESS SENSITIVE INITIATION ORDNANCE
• ELIMINATES POSSIBLE HAZARD TO ELECTRONIC EQUIPMENT FROM
FIRING OF HOT BRIDGEWIRE CARTRIDGE
- Mars Observer failure option
- Magellan
• BOTTOM LINE: THE ABOVE FEATURES, WE SAY, FOR LASER DIODES
EQUATE TO IMPROVEMENTS IN SAFETY, RELIABILITY, OPERATIONS,
COST, POWER, MASS
• CONCLUSION: ADDRESS LASER DIODE ORDNANCE
DEVELOPMENT FOR OPERATIONAL FEASIBILITY
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
DISADVANTAGES OF LASER DIODE INITIATED
ORDNANCE
• TECHNICAL
- Low voltage to activate laser
- concern over electronics setting off laser accidentally
- BIT not proven
- development of requirements necessary
• MANAGERIAL:
- Hardware not proven with operational experience
- application not mandatory for program success
- new programs wait for others to "break the ice" to reduce risks with cost, performance,
schedule
- Incomplete understanding of requirements
5 - 31 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
IN THE BEGINNING
PAS PROGRAM PLAN
LIO PROGRAMS
2.4 NASA STANDARD LASER DIODE SAFE AND ARM
2.5.1 NASA STANDARD LASER DETONATOR
3.4 LASER DIODE SAFE/ARM PERFORMANCE
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
PAS PROGRAM PLAN FOR LIO
2.4 NASA STANDARD LASER DIODE SAFE AND ARM
Project Mgr: B. Wittschen, Johnson Space Center
• Develop, qualify, and demonstrate in flight a standardizable solid state laser safe and arm system
- Flight demonstration - TBD
- Joint HQS. activity with JSC
• Determine criteria for what constitutes an acceptable S&A
- Closely involve range safety in the design and testing
- Place operational considerations up front in the design
• Enhance safety and reduce risk
- Enhance functional reliability
- Simplify design
- Eliminate problems with current electromechanical designs
• Reduce power, explosive containment, and costs
• Make design more easy to manufacture/checkout
• Products:
- Flight performance demonstration-TBD
- Guidelines for incorporating features into flight units
- Design specification for standard safe/arm devices
STATUS:
• Project has been terminated
7 - 32 - January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
2.5.1 NASA STANDARD LASER DETONATOR
Phase I - Developmental Investigations
Project Mgr: B. Wittschen, Johnson Space Center
• Advance pyrotechnic technology - develop laser detonators
- Supports Project 2.4, NASA Standard Laser Diode Safe and Arm
- Conduct off-limits testing of developmental hardware
- Phase II task qualifies a NASA Standard Laser Detonator
• Goals include optimizing optical interface between the fiber and the pyrotechnic charge,
publishing a specification, and the procurement and test of devices to provide a data base
• Products: Qualified NASA Standard Laser Detonator and design/test specification
STATUS:
• Project has been terminated
January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
3.4 LASER DIODE SAFE/ARM PERFORMANCE
Project Mgr: B. Wittschen, Johnson Space Center
• Develop test procedures
• Quantify performance
• Confirm specification performance
• Demonstrate safe/arm devices for flight
• Update design and test specifications
• Products:
- Publish test specification for use by programs
- Prepare qualification report
STATUS:
• Project has been terminated
9 - 33 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
THEN
RE-EVALUATE
10 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
IMPLEMENTATION of a FEASIBILITY APPROACH: -
BACKGROUND-
• EVALUATED BY STEERING COMMITTEE FOR MANY YEARS
- concern about maturity
• AUGUST 1991: OSC/EBCO UNSOLICITED PROPOSAL TO
CONDUCT DEMONSTRATION ABOARD PEGASUS
- NASA performs one-time mission demonstration for a complete vehicle ordnance change
- OSC performs fleet change
• OBJECTIVE WAS "QUICK DEMONSTRATION" USING AVAILABLE
TECHNOLOGY
- delayed for two years
- Pegasus vehicle contracted under services contract, not R&D
- lacked clear contractual means to conduct a technology demonstration
ii - 34 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
IMPLEMENTATION APPROACH
• MANAGERIAL ASPECTS OF LIO INITIATION POINTED TOWARD:
- lack of technical requirements for LIO systems
- no practical operational experience
- lack of quick, simple, contractual instrument to implement new technology
MANAGERIAL SOLUTION NECESSARY TO PURSUE TECHNICAL
ISSUES
• ABOVE ANALYSIS POINTED NEED FOR NEW LIO
PROGRAMMATIC PATH
12 January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
STEPS REQUIRED FOR LIO IMPLEMENTATION
1. VALIDATE FEASIBILITY
a. ARE THE TECHNOLOGY CLAIMS CORRECT?
b. WHAT ARE THE SAFETY, RELIABILITY PROGRAMMATIC
DESIGN REQUIREMENTS TO FLY LASER ORDNANCE?
IF FEASIBLE WITHIN COST COMPETITION OF EXISTING
ELECTROMECHANICAL SYSTEMS, THEN ADDRESS THE:
2. IMPLEMENTATION OF LIO INTO OPERATIONS
13 - 35 -
January .10, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
A. VALIDATE LIO FEASIBILITY:
« REDUCE THE RISK «
1. PERFORM FLIGHT DEMONSTRATIONS
PHILOSOPHY:
a. TAKE THE MANAGERIAL APPROACH OF COMMENCING WITH A MINIMUM
SAFETY IMPACT PROJECT - THEN PROGRESS TO THE MOST DEMANDING:
- low hazard level in a controllable application, but safety impact exists and is such that the
LIO hazard must be controlled
- LIO serves an active function in flight - not along just for the ride
- ultimate application range is from unmanned to manned applications
- ultimate system range is from flight sequencing to flight termination
b. PERFORM SIMPLE, QUICK, DO-ABLE PROJECTS, ADDRESSING ISSUES AS
PROGRESSION OCCURS
2. DEVELOP REQUIREMENTS
a. PREPARE SPECIFICATION REQUIREMENTS
b. DEVELOP RANGE REQUIREMENTS
14 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
B. OPERATIONAL IMPLEMENTATION
« REMOVE THE RISK «
1. DEVELOP A "STANDARD"
- discussions held with Aerospace/Air Force:
- definition of "Standard" - build to print or to performance specification
2. QUALIFY FOR TOTAL OPERATIONAL ENVIRONMENTAL
SPECTRUM: - CAPTURE MARKET
3. HAVE A PRODUCT READY FOR PROGRAMMATIC USE,
ACCEPTED BY THE PYRO TECHNICAL COMMUNITY
4. MAINTAIN TWO QUALIFIED SOURCES AS A MINIMUM-NO SFP'S
is - 36 -
January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
STATUS:
THIS IS WHAT WE DID AND ARE DOING WITH
REGARD TO THE ABOVE PROCESS
16 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
1. PERFORM FLIGHT DEMONSTRATIONS
a. DEVELOP A NEW PROCUREMENT PROCESS:
COOPERATIVE AGREEMENT
WITH PROFIT MAKING ORGANIZATIONS
b. IMPLEMENT VIA QUICK, CHEAP FLIGHT DEMONSTRATION
PROGRAM
n - 37 -
30.1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
COOPERATIVE AGREEMENT WITH PROFIT
MAKING ORGANIZATIONS (CAWPMO)
• NEW PROCUREMENT PROCESS
- grants normally performed with universities
- cooperative agreement previously limited by policy to non-profit organizations e.g. think-tanks,
universities, etc.
• CAWPMO: FROM FIRST THOUGHT UNTIL SIGNATURE = 2 MONTHS
• FROM: RECEIPT OF PROPOSAL UNTIL SIGNATURE = 1 MONTH
• THIS INSTRUMENT IS BASICALLY A PARTNERSHIP WITH BOTH
GRANTEE WITH GOVERNMENT HAVING ACTIVE ROLES
• COOPERATIVE AGREEMENT ACCOMPLISHES COMMON BENEFIT
• NO HARDWARE IS DELIVERED
• NO FEE
• INTERNAL COMPANY FUNDING HELPS BUT NOT REQUIRED
• RED TAPE REDUCED
lg January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
PROJECTS
A. PEGASUS EXPERIMENT
B. SOUNDING ROCKET FTS DEMONSTRATION
C. SHUTTLE
EFFORTS AIMED AT THE DEVELOPMENT OF REQUIREMENTS:
- Specification
- Range Safety
19 - 38 -
January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
A. PEGASUS EXPERIMENT
TWO TESTS OF LIO CONDUCTED DURING ORBCOMM MISSION:
• CONDUCT A FLIGHT SEQUENCING FUNCTION: IGNITE TWO OF
THE NINE FIN ROCKET MOTORS USING LIO
- safety hazard to operational personnel: accidental motor ignition. Control by design and
procedure
- not mission success dependent. Fin rocket motors not required for mission success
- qualitative information. Go-no go information.
• FIRE LIO INTO A CLOSED BOMB
- not a safety hazard. Accidental ignition pressurizes a metal container designed to take the load
- not mission success dependent. Separate experiment
- quantitative information. Pressure measurements performed during flight with be compared with
ground test data.
• FLY ABOARD COMMERCIAL MISSION
- current date is June 1994
20 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
ENSIGN BICKFORD COMPANY TASKS:
1 . Conduct necessary design and research to demonstrate feasibility of LIO
2. Manufacture equipment
3 . Perform testing in coordination with NASA testing
4. Conduct analyses
5. Coordinate program activities closely with NASA
6. Conduct program tasks per E-B Proposal
21 - 39 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
NASA TASKS:
As necessary:
1 . Perform technical review, analyses, and test support
2. Involve Range Safety Offices
3. Conduct off-limits/overstress tests & evaluations to support Range Safety objectives
4. Establish requirements for NASA-wide application
5 . Provide test equipment support such as OTDR
6. Provide overall planning for incorporation of LIO into flight programs
7. Conduct analyses sneak circuit analyses
8. Conduct validation testing of sneak circuit analysis
9. Perform FMEA, safety, and reliability analyses
10. Conduct evaluations of program test planning
1 1 . Conduct safety and reliability ordnance initiation evaluations
12. Provide consultation regarding operational processes
13. Provide guidance on generic flight operational procedures
14. Assist in technology transfer
22 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
B. SOUNDING ROCKET FTS DEMONSTRATION
• OBJECTIVE: TAKE THE NEXT STEP WITH UNDERSTANDING
REQUIREMENTS AND GAINING CONFIDENCE
• INSTALL A FLIGHT TERMINATION SYSTEM ABOARD A TWO
STAGE SOUNDING ROCKET AND DESTRUCT DURING THRUST
- Nike Orion - second stage destruct flown out of Wallops
• IGNITE FIRST AND SECOND STAGES USING LIO
- maximize experience
• ACTIVATE FTS BY TIMER-THIS DEMONSTRATION NOT A TEST
TO VALIDATE NEW RF COMMAND SYSTEM
• HIGHER LEVEL OF SAFETY REQUIRED BEYOND PEGASUS
• 6 MONTH PROGRAM
• AWAIT UNSOLICITED PROPOSAL FOR CAWPMO
23 - 40 "
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
COMPANY TASKS:
1 . Design and manufacture termination ordnance
2. Provide LIO ignition for Nike and Orion motors
3. Provide laser firing unit, the fiber optic cable, connectors, detonators, and initiators
4. Perform testing in coordination with NASA testing
5 . Conduct analyses
6. Install ordnance and integrate FTS/payload into launch vehicle
7. Participate in flight operations and post flight analysis
8. Testing at company's discretion but expected for demonstrating compatibility of
laser initiation with current motor ignition system
24
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
NASA TASKS:
1 . Launch vehicle: Nike-Orion
2. Vehicle drawings
3. Provide environmental test requirements and WFF range safety requirements
4. Pyro interface such as mounting platform for LIO electronics
5. Instrumentation defining key events and body accelerations
6. 3-axis accelerometer
7 . FTS activation timer
8 . FM-FM transmitter
9. Build-up and integration of the motor and stage assembly
10. Flight performance analysis
1 1 . Radar coverage
12. Launch operations
13. Post flight analysis support
14. Photographic coverage
25 - 41 "
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
C. SHUTTLE
• Payload (Solar Exposure to Laser Ordnance Device)
- LIO opens shutter in space
- Exposure of LIDS and LIS:
- 4 different initiators
- 2 different detonators
- 2 different laser firing units
- Exposure to solar radiation:
- direct exposure to sun
- 10:1 magnified exposure to sun
- no exposure to sun
- LIO subjected to Shuttle payload safety review process
• STS Equipment (potential project not started - hazardous gas detection
bottles)
- Will subject LIO to Shuttle vehicle safety review process
26 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
EFFORTS AIMED AT THE DEVELOPMENT OF
REQUIREMENTS:
• SPECIFICATION: UNFUNDED IN-HOUSE ACTIVITY
• COORDINATION WITH RANGE SAFETY STAFF
- preliminary set of requirements developed
- work continues
27 - 42 ~ January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
PRELIMINARY
RANGE REQUIREMENTS FOR LIOS:
GENERAL CATEGORY "A" REQUIREMENTS:
System Level Requirements:
1 . Single fault tolerant (two independent safeties) before and after installation of SAFE/ ARM type connectors
Cleared pad during power switching, power-on, and RF radiation operations
To allow operations during these conditions, LIOS must be at least two-fault tolerant and meet the Man-Rated design
requirements defined in RSM-93 Paragraph 5.3.4.4.5
2 . At least one of safety controllable from pad
3 . Design to allow power-control operations remotely from blockhouse
4. Component (if electrical type) adjacent to the laser system must be single/double fault tolerant
5 . Component adjacent to the lasing device (either in the power or return leg of electrical circuit), shall not be activated
until programmed initiation event
6. LIOS must not be susceptible to external energy sources, such as stray light energy, static and RF
7 . Design to preclude inadvertent initiation due to singular energy sources, such as unplanned energy in power leg of
circuit or due to short circuits or ground loops.
8 . Design to allow for ordnance connection at the latest possible time in the countdown process
28 January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
Tri gger Circuit Requirements
9 . Design such that voltage required to initiate laser is at least 4 times the VCC of solid state logic circuits
10. Design to output energy after application of a 20 ms pulse
Monitor and Test Capability:
1 1 . Provide circuits to allow for remote control and monitor of all components in the Category "A" system. Application of
±35V in the monitor circuit shall not affect the Category "A" circuit
12. Recommend Built-in-Test (BIT)
Allow remote testing at energy levels of 10" 2 below no fire for both normal and failure modes. Use different
wavelength than main firing laser, separated by at least 100 run
1 3. Design to allow for "no-stray energy" type of tests prior to performing ordnance connection
14. Employ pulse catcher system to detect inadvertent actuation of laser prior to ordnance connection
Monitor 1/100 no-fire and be capable of determining a valid all-fire (power, energy density, frequency, pulse-width)
Laser Output Requirements;
1 5 . Energy delivered to LID shall be 2x all-fire
Ordnance Requirements;
16. All ordnance used with LIOS must be secondary explosive.
29 - 43 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
Power Supply Requirements:
1 7 . Install charged ("Hot") batteries into Category "A" circuits only if at least one of the following design approaches is
utilized. Otherwise, charge battery at latest feasible point in countdown process with no personnel in danger area
17.1 Electromechanical device utilized which mechanically misalign ordnance train
17.2 Optical barriers utilized which mechanically misalign initiation power from either LID or laser
1 7.3 Capacitive Discharge Ignition (CDI) system used meeting circuit criteria in RSM-93 Paragraph 5.3.4.4.4
1 7.4 Designed to be Man-Rated and meets circuit requirements in RSM-93 Paragraph 5.3.4.4.5
PRELIMINARY
SPECIFIC CATEGORY "A" REQUIREMENTS (PARTIAL LIST):
1 . Shielding for electrical firing circuits shall meet:
1 . 1 Minimum of 20 dB safety margin below minimum rated function current to initiate laser and provide a minimum
of 85% optical coverage. (A solid shield = 100% optical coverage)
I.2Shielding shall be continuous and terminated to the shell of connectors and/or components. Electrically join
shield to shell of connector/component around 360° of shield. Shell of connectors/components shall provide
attenuation at least equal to that of shield
1 .3Shield should be grounded to a single point ground at power source
1 .40therwise, employ static bleed resistors to drain all RF power on shield
2 . Wires should be capable of handling 150% of design load. Design shall assure that latched command will remain
latched with a 50 ms dropout pulse
3 . Bent pin analysis shall be performed to assure no failure modes
4 . Analysis/Testing shall be performed to determine debris contamination for blind connection sensitivity on optical
connectors
5 . All components in the Category "A" initiation system shall be sealed to Kr^cc/sec
30 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
PRELIMINARY
FTS REQUIREMENTS:
1 . FTS circuit must meet all requirements defined under Category "A" requirements
2. Circuit must requirements in RCC STANDARD-319-92, FTS Commonalty Standard, Chapters 1, 2, 3, and 4
3. All LIOS components must meet test requirements in RCC STANDARD-31992, FTS Commonalty Standard,
Chapters 5.1 and S.2
4 . Meet design requirements specified in WRR- 127. 1 (June 30, 1993) Chapter 4:
a. Circuit requirements in Sections 4.6.7.4.5, 4.6.7.4.8, and 4.6.7.4.9
b. Optical connector requirements in Section 4.7.5.2
c. LFU requirements in Section 4.7.7.4.1
d. LID requirements in Section 4.7.8.3
5. System must meet test requirements specified in WRR-127.1 (June 30, 1993) Chapter 4:
a. Appendix 4A.7: LFU Acceptance testing
b. Appendix 4A.7: LFU Qualification testing
c . Appendix 4A.7: Fiber Optic Cable Assembly Lot Acceptance Testing
d . Appendix 4A.7: Fiber Optic Cable Assembly Qualification Testing
e . Appendix 4A.7: LID Lot Acceptance Testing
f . Appendix 4A.7- LID Qualification; Testing (need to revise numbers)
g . Appendix 4A.7 : LID Aging Surveillance Test
h . Appendix 4B : Common Tests Requirement
31 - ZjZj - January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
6. Incorporate a Built-in-Test (BIT) feature which allow remote testing at energy levels of 10 2 below no-fire for both
normal and failure modes and must also be at a different wavelength than main firing laser. The wavelengths for the
main firing laser and the test laser must be separated by at least 100 nm
7. Piece parts shall be IAW ELV specs
8 . All ordnance interfaces shall allow for 4 times (axial, angular max. gap) or 0. 1 5" and 50% minimum design gap
9. Connectors per IAW MIL-C-38999J
10. Perform analysis/design on: LIOS FTS-FMECA, bent-pin analysis, LID heat dissipation due to SPFs
32 January 30. 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
SAFETY POINTS
• GENERAL REQUIREMENTS:
- avoid introduction of new hazards,
- avoid inadvertent ignition,
- functions upon demand
• LOW VOLTAGE FOR DIODE TO LASE CONCERN
• POSITIVE CONTROL OF PERSONNEL SAFETY AT PAD
ESSENTIAL
• RANGE STRAWMAN REQUIREMENTS
33 - 45 -
30.1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
ISSUES TO WORK
• SAFETY REQUIREMENTS
• BUILT-IN-TEST
• COSTS
• DEMONSTRATED RELIABILITY UNDER VARIETY OF
APPLICATIONS AND ENVIRONMENTS
34 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
WHERE DO WE GO FROM HERE?
WORK NEEDED AND NEXT STEPS
• BUILT-IN-TEST
• SPECIFICATION
• DEMONSTRATED RELIABILITY UNDER A VARIETY OF
APPLICATIONS AND ENVIRONMENTS
• STANDARD DESIGN: BUILD TO PRINT VERSUS BUILD TO
SPECIFICATION
• MARKET ANALYSIS
35 - 46 -
January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
SUMMARY
• PROGRAMS MORE LIKELY TO USE IF CONCEPT IS PROVEN VIA
DEMONSTRATION
•
•
PROGRAMS WILL USE LIO IF QUALIFIED AND IS COST
COMPETITIVE
NO PROGRAM DESIRES TO MAKE USE OF LIO AND PROCEED
DOWN THE LEARNING ROAD, UNLESS MANDATORY FOR
PROGRAM SUCCESS OR SAFETY
• WITHOUT A PROCESS WHEREBY THIS TECHNOLOGY IS
DEMONSTRATED AND COST FACTORS VERIFIED, THERE IS
NOT ANTICIPATED TO BE A DEMAND
36 January 30, 1994
Second NASA Aerospace Pyrotechnic Workshop
Laser Initiated Ordnance Activities in NASA
•
CONCLUDING THOUGHTS
A TECHNICAL COMMUNITY NOT UNITED IS NOT ANTICIPATED
TO MEET WITH THE SUCCESS NECESSARY FOR LIO
IMPLEMENTATION ON A REASONABLE TIME FRAME.
A WELL-COORDINATED, JOINTLY-CONDUCTED, AND CO-
FUNDED INITIATIVE BETWEEN GOVERNMENT AND INDUSTRY
OFFERS THE BEST OPPORTUNITY FOR TECHNOLOGY
IMPLEMENTATION.
- One example is the Pegasus demonstration.
- Another is laser gyro demonstration.
THERE ARE ISSUES TO BE WORKED WITH SUCH AN APPROACH
SUCH AS: PROPRIETARY INFORMATION, DEGREE OF FUNDING
PARTICIPATION VERSUS RETURN EXPECTED, WHO DOES
WHAT, GETTING AGREEMENT ON TECHNICAL ISSUES, ETC.
BUT THESE MUST BE CONSIDERED WORKABLE WHEN VIEWED
FROM THE PERSPECTIVE OF THE VALUE OF THE EFFORT AND
THE IMPACT OF SUCCESS.
37 - 47 -
January 30, 1994
LASER-IGNITED EXPLOSIVE AND
PYROTECHNIC COMPONENTS
A. C. MUNGER, T. M. BECKMAN, D. P. KRAMER
AND E. M. SPANGLER
AEROSPACE PYROTECHNIC SYSTEMS WORKSHOP
FEBRUARY 8, 1994
J^EGzG
=4
- 49 -
o/V'."i
EG&G MOUND APPLIED TECHNOLOGIES HAS PURSUED
LASER - IGNITION TECHNOLOGIES SINCE 1980
• EVALUATED FUNDAMENTAL EXPLOSIVE PROPERTIES
• TESTED OPTICAL FEED-THROUGH DESIGNS
• SHOWN FEASIBILITY OF PROTOTYPE DEVICES
• FABRICATED & TESTED PRE-PRODUCTION QUANTITIES
n
EBelB
MOUND HAS PERFORMED LASER IGNITION TESTS ON A
VARIETY OF PYROTECHNIC AND EXPLOSIVE MATERIALS
EXPLOSIVES PYROTECHNICS
BARIUM STYPHNATE BCTK d
CP° Ti/KCI0 4
CP/CARBON BLACK TiH .65/ KCI0 4
HMX b TiH 165 /KCI0 4
HMX/CARBON BLACK ZrKCIOVGRAPHITE/VITON
HMX/GRAPHITE
HNS C
a) 2-(5-CYANOTETRAZOLATO) PENTAAMINE COBALT (III) PERCHLORATE
b) CYCLOTETRAMETHYLENETETRANITRAMINE
c) HEXA-NITRO-STILBENE
d) BORON CALCIUM CHROMATE TITANIUM POTASSIUM PERCHLORATE
- 50 -
COMPARISON OF THE IGNITION THRESHOLDS
OBTAINED ON VARIOUS ENERGETIC MATERIALS
50% ALL-FIRE IGNITION THRESHOLD
700 mH
100/140 STEP INDEX FIBER
10 MS LASER DIODE PULSE
125 mH
75 mW
50 mH
CP BCTK Ti/KCIO, TiH. eg COARSE CP/ HMX/3X FINE CP/
4 ,„'?! IX CARBON CARBON 3. 2X CARBON
/KL1U 4 ^CK BLACK BLACK
ENERGETIC MATERIAL
COMPARISON OF THE THREE PRINCIPAL DESIGNS
UNDER CONSIDERATION FOR LASER-IGNITED COMPONENTS
(1)
CHARGE CAVITY
IS
SHELL ^V
'i
^m^
OPTICAL FIBER
(2)
CHARGE CAVITY
SHELL S>
J
R3
iS]^
FIBER PIN
/ ^ x CHARGE CAVITY
(3) IS I 153
SH " 1 i
^n^
WINDOW
- 51 -
COMPARISON OF THE 50% ALL-FIRE THRESHOLDS
USING SAPPHIRE AND P-GLASS WINDOW DEVICES
"3
o
lu
4.0-1
3.0-
2.0-
w 1.0-
0.0
SAPPHIRE
P-GLASS
1 1 1 —
0.0 0.2 0.4 0.6
WINDOW THICKNESS (mm)
MOUND HAS DESIGNED AND FABRICATED OVER
TEN DIFFERENT LASER-IGNITED COMPONENTS
• 3 "FIBER PIGTAIL" PROTOTYPES
• 5 "WINDOW"
• 6 "FIBER PIN"
• LOT SIZES - UP TO 400 COMPONENTS
&>
- 52
MOUND IS ACTIVELY ENGAGED IN LASER DIODE
IGNITION (LDI) COMPONENT DEVELOPMENT
SEALED
SEALED
HIGH
WINDOW
FIBER
STRENGTH
DETONATOR
DETONATOR
ACTUATOR
^O
EGkG
HERMETIC, LASER-IGNITED DEFLAGRATION
TO DETONATION TRANSITION (DDT) DETONATOR
- 53 -
IGNITION THRESHOLD DATA ACQUISITION SYSTEM
FIBER FOCUSING SHUTTER
COUPLER LENS
BEAM CHOPPER
EXPANDER
CW Nd:YAG LASER
BARRICADE WfTH OPTICAL WINDOW
STC CONNECTER
OPTICAL
FIBER
HIGH SENSITIVITY
PHOTODIODE
w&
-^
PHOTODIODE
TEST DEVICE
«a»
DIGITIZING OSCILLOSCOPE
DlGmZING OSCILLOSCOPE
IPS92-10
SEVERAL PARAMETERS MUST BE CONSIDERED WHEN
REFERRING TO COMPONENT THRESHOLD VALUES
• LASER BEAM/POWDER INTERFACE
- SPOT SIZE
- SPOT SHAPE
• LASER BEAM
- PULSE LENGTH
- PULSE SHAPE
- WAVELENGTH
• THERMAL CONDUCTIVITY
- POWDER/FIBER/SHELL/WINDOW
- 54 -
THE DDT DETONATOR HAS BEEN SUCCESSFULLY
LASER-FIRED USING A VARIETY OF TEST PARAMETERS
Maximum 50% All-Fire Standard
Laser Fiber Dia. N.A. Pulse Length Threshold Deviation
Nd:YAG
1000(1
0.22
12 msec
30 mJ
8 mJ
Nd:YAG
200|i
0.37
150 i^sec
34 mJ
16 mJ
Nd:YAG
200^
0.22
12 msec
50 mJ
11 mJ
A
ONE OF THE SEALED FIBER DEVICES HAS BEEN
SUCCESSFULLY CHARACTERIZED
• HMX/CARBON BLACK
• HERMETIC
• 50% ALL-FIRE IGNITION
THRESHOLD ~1.4mJ
• MAINTAINED STRUCTURAL INTEGRITY
MAXIMUM PRESSURE -20,000 psi
A
HMX
OPTICAL FIBER
HMX LASER SQUIB
- 55 -
The Laser Fired Pyrotechnic device
was derived from the well tested
" Hot-Wire" Device
ELECTRIC PYROTECHNIC SQUIB
TiH /KCIO.
1 1.65 4
BRIDGE WIRE
RTVPAD
LASER PYROTECHNIC SQUIB
A
™ i-66 «cio 4
EXAMPLE OF A HIGH-STRENGTH LASER
IGNITED PYROTECHNIC ACTUATOR
■ ■».-»
fH'-r'iifM 1 '
im 10 2
i.l.ilfllli.
Conversion Rule ?f
.iitlUtJtiillllt.lt
- 56 -
THRESHOLD PERFORMANCE INDICATES THAT A
RELIABLE DEVICE CAN BE FABRICATED
THRESHOLD DATA WITH 10 ms PULSE
ENVIRONMENT
NONE
TS.TC
TC.TS
NONE, MYLAR
TC, MYLAR
ENERGY
TEMP C
5.3 mJ (0.05)
•55
5.02 mJ (0.7)
4.50 mJ (0.2)
•55
-55
3.3 mJ(1.2)
2.7 mJ (0.5)
-55
-55
&**
ZERO VOLUME FIRING TEST SETUP USED TO DETERMINE
PRESSURE OUTPUT OF LASER-IGNITED FIBER PIN DEVICE
DATA ACQUISITION
DIODE DRIVER
-0
OPTICAL
FIBER \
*r
LASER
DIODE
TRANSDUCER
FIBER PIN
j DEVICE \
»»»>»jjjiit>*i»\>iii*j*\jjjt
PRESSURE BLOCK
""""TV.
EXPLOSIVE TEST CHAMBER
-57 -
ZERO VOLUME FIRING TEST RESULT OBTAINED
ON A LASER-IGNITED FIBER PIN DEVICE
1200
174
120 160
TIME (microsecond)
ii
COMPACT" RIGHT-ANGLE LASER-IGNITED
DEVICES CAN BE MANUFACTURED
fcNIIIIM
in xVio , I
im I
rfffii.
o
,iii
M I | | I I \ M M I \ \
Conversion Rule 2|
2 3 4 5I0 6<
6\0
\
- 58
LASER-IGNITED DETONATORS HAVE BEEN
DESIGNED TO BE BON-FIRE SAFE
• TWO PROTOTYPE STYLES HAVE BEEN TESTED
TESTS HAVE SHOWN THAT DETONATION DID NOT
OCCUR DURING THERMAL EXCURSION
DEVICE WILL NOT RECOVER
J^EB&B
LDI COMPONENTS HAVE BEEN FABRICATED
AT MOUND TO SUPPORT A VARIETY OF TESTING
MOUND TESTING
THRESHOLD DETERMINATION
HOT, COLD, AMBIENT
ENVIRONMENTAL CONDITIONING
THERMAL AND MECHANICAL
KED TESTING ( ZERO VOLUME )
VALVE ACTUATOR
SANDIA TESTING
LIGHTNING STRIKE
ESD - FISHER MODEL
- SANDIA STANDARD MAN
- 59 -
LASER DETONATOR MANUFACTURING REQUIRES
THE APPLICATION OF SEVERAL KEY TECHNOLOGIES
GLASS PROCESSING
NONDESTRUCTIVE
EVALUATION
FURNACE
TECHNOLOGY
GLASS MACHINING
LASER DDT-
DETONATOR-
/ \
LASER WELDING
GLASS SEALING
- POWDER PRESSING
HEAT TREATING
EXPLOSIVE POWDER
PROCESSING
- 60 -
1994 MhBA PYROTEOHNI© SYSTG
A LOW COST IGNITER UTILIZING AN SCB AND TITANIUM
SUB-HYDRIDE POTASSIUM PERCHLORATE PYROTECHNIC
R. W. Bickes, Jr. and M. C. Grubelich
Sandia National Laboratories
Albuquerque, NM 87185-0326
J. K. Hartman and C. B. McCampbell
SCB Technologies, Inc.
Albuquerque, NM 87106
J. K. Churchill
Quantic-Holex
Hollister, CA
ABSTRACT
A conventional NSI (NASA Standard Initiator) normally employs a hot-wire ignition element to ignite ZPP
(zirconium potassium perchlorate). With minor modifications to the interior of a header similar to an NSI
device to accommodate an SCB (semiconductor bridge), a low cost initiator was obtained. In addition, the
ZPP was replaced with THKP (titanium subhydride potassium perchlorate) to obtain increased overall gas
production and reduced static-charge sensitivity. This paper reports on the all-fire and no-fire levels
obtained and on a dual mix device that uses THKP as the igniter mix and a thermite as the output mix.
ll^lii;:
1 . INTRODUCTION
The Explosive Components Department at
Sandia National laboratories was assigned the
task of designing actuators for several different
functions for a Department of Energy (DOE)
program. The actuators will be exposed to
personnel as well as to a wide variety of
mechanical, temperature and electromagnetic
environments. In addition, required outputs vary
from a high pressure gas pulse for piston
actuation to a high temperature thermal output
for propellant ignition. In order to minimize
complexity, the firing sets for all the actuators
must be the same, and the firing signal must be
transmitted via a cable over lengths as long as
thirty feet.
Our solution was to modify an existing Quantic-
Holex component (similar to a conventional NSI
device) with a semiconductor bridge, SCB. Our
prototype device used titanium subhydride
potassium perchlorate (THKP) as the
pyrotechnic. Our second (dual mix) design used
THKP as the igniter mix and CuO/AI thermite as
the output charge. The low firing energy
requirements of the SCB substantially reduced
the demands on the firing system; indeed, the
present firing system design could not
accommodate conventional hot-wire devices.
The reduced static sensitivity of THKP 1 helped
mitigate the electromagnetic environment
requirements for exposure to radio frequency
This work performed at Sandia National Laboratories is supported by the U. S. Department of Energy
under contract DE-AC04-76DP00789. Approved for public release; distribution unlimited.
- 61 -
(RF) signals and
discharges (ESD).
human-body electrostatic
2. SCB DESCRIPTION
An SCB is a heavily doped polysilicon volume
approximately 100 urn long by 380 urn wide and
2 |im thick with a nominal resistance of 1 Q. It is
formed out of the polysilicon layer on a
polysilicon-on-silicon wafer. Aluminum lands are
defined over the doped polysilicon; wires are
bonded onto the lands connecting the lands to
the electrical feed-throughs of the explosive
header. The firing signal is a short (30 lis) current
pulse that flows from land-to-land through the
bridge. The current melts and vaporizes the
bridge producing a bright plasma discharge that
quickly ignites the THKP pressed against the
bridge. 2
Figure 1. Simplified sketch of an SCB.
The main advantages of an SCB igniter versus
conventional hot-wire igniters are that (1) the
input energy required to obtain powder ignition
is a decade less than for hot wires; (2) the no-fire
levels are improved due to the large heat sinking
of the silicon substrate; and (3) the function
times (i.e. the time from the onset of the firing
pulse to the explosive output of the devices) are
only a few tens of microseconds or less. 3
3. IGNITER DESIGN
Our SCB igniter is similar to the NSI device. It
consists of a metal body containing a glass
header, charge holder and pyrotechnic material.
3/8-24 UNF threads allow the device to be
installed into test hardware and an O-ring under
the hexagonal head provides the gas seal. The
internal charge cavity was reduced to a diameter
of 0.156" by utilizing a threaded fiber glass
composite (G10) charge holder. The threads
help prevent separation of the powder from the
bridge due to mechanical shock. The pins are
hermetically sealed by glass-to-metal seals and
extend approximately 0.020" past the header
base into the charge holder. The SCB chip is
bonded to the header base between the pins
with a thermally conductive epoxy. Aluminum
wires, 0.005" in diameter, are thermalsonically
bonded to the header pins and the aluminum
lands on the chip. For the prototype device, a
charge of 85 mg of THKP is pressed at 12,500
psi into the charge holder. A G10 disk, 0.156"
diameter and 0.010" thick, is placed on top of the
pressed powder, followed by an RTV disk,
0.150" diameter and 0.016" thick. A G10 plug,
0.065" thick, is then pressed on top of the RTV
at a pressure sufficient to compress the RTV pad
to half its thickness, which maintains a pressure
of approximately 5,000 psi on top of the THKP
column. A high temperature epoxy seals the
interference fit G10 plug in place.
CLASS-TO- METAL SEAL
IGNITER BODY. 304L CRES
IX PM. 302 ORES
C- ID PHENOLIC SUEVE
OUTPUT CLOSURE. WELDED
J7ft-24liMF-2A
Figure 2. The SCB igniter outline.
4. FIRING SET DESCRIPTION
The firing set for our application is low voltage
capacitor discharge unit (CDU) with a 50 \iF
capacitor charged to 28 V (nominal). 4 Because
the SCB dynamic impedance changes
significantly during the process that produces
the plasma discharge, two FET switches in
parallel are required to discharge the 35 A
current pulse into the SCB. In addition a test
current pulse is included that passes a 10 mA
pulse through the bridge to verify igniter
integrity.
- 62 -
WW IN 14-J1V •
i — | mutis 'f twit
n
-rn Wi
n
Figure 3. Wiring schematic for the SCB low voltage
CDU firing set.
As noted in section 1. ( some of the igniters may
be located as far as thirty feet from the firing set.
The use of either large diameter wire pairs or
ordinary BNC cable reduced the transmitted
current pulses to levels below threshold for
ignition. However, Reynolds Industries "C" cable
was able to transmit the current pulse with only a
small attenuation of the peak current.
5. PROTOTYPE TESTS
Figure 4. shows the voltage, current and
40.
O 30.
X
O
c
CO
O £0.
Q.
£
I
E
| u>.
0.0
/ ' \
v."
A V I
'
' Z
1
1.0 2.0
3.0 4.0
time (us)
5*0
6.0
7.0
Figure 4. Current (I), voltage (V) and impedance (Z)
wave forms across the SCB. At 4.8 //s the peak
current was 37.4 A, the corresponding voltage was
19. 1 V and the impedance 0.5 Q.
impedance wave forms across a device fired
when connected to the firing set through 30 feet
of "C" cable. At ambient conditions, the device
functioned in 83 |is (determined by a
photomultiplier tube looking at the end of the
device thorough a fiber optic cable).
Ten units were tested using the NEYER/SENSIT
scheme. 5 The units were fired at ambient and
connected to the firing set with 30 feet of "C"
cable. AnASENT 6 analysis of the data indicated
a mean all-fire voltage of 17.8 V + 0.2 V;
confidence limits on the mean were 17.7 to 19.2
V at a 95% confidence level and a probability of
function of 0.999. See table I for a listing of the
data in the shot order prescribed by SENSIT.
TABLE I: ALL-FIRE DATA
Cap Voltage
Go/Noqo
Energy
(V)
(X/O)
(mJ)
18.0
X
5.01
17.0
4.36
17.5
4.63
18.2
X
4.63
17.7
X
4.77
17.2
4.54
17.9
4.90
17.3
4.54
18.2
X
5.08
17.4
4.66
All Fire: 17.8±0.2 V, 4.8±0.1 mJ
Six THKP units underwent 3 temperature cycles
over a twenty-four hour period. Each cycle
consisted of 4 hours a 74C and 4 hours at -54C.
The devices were fired as soon as possible after
the cold cycle at approximately -15C. All of the
units function when fired using the firing set
without the 30 foot cable.
We subjected a THKP unit to a 1 A Current for 5
minutes. There was no indication of device
degradation and the unit functioned properly
when tested. Based on the no-fire tests in Ref.
3, which used the same bridge as tested in this
paper, we are confident that these units will have
similar no-fire levels similar to those reported in
Ref. 3(1.39±0.03A).
6. DUAL MIX DEVICE
Because composite propellants require a
relatively large amplitude long duration thermal
- 63 -
input for reliable ignition, we developed an SCB
igniter employing two discrete pyrotechnic
compositions. First, 25 mg of THKP is pressed at
12.5 kpsi against the SCB and is used as a starter
mix to pyrotechnically amplify the low energy
SCB signal. The THKP in turn ignites and ejects
150 mg of a high density thermite composition
composed of CuO and Al pressed onto the
THKP.
We briefly describe the advantages of this device
over a device composed of only a single load of
THKP or CuO/AI. THKP has excellent and well
known interface, ignition and pyrotechnic
propagation properties. It also is an excellent gas
producer providing zero volume pressures
greater than 150 kpsi. Unfortunately, the short,
high pressure output pulse of THKP is not ideally
suited for the ignition of a composite propellant.
CuO/AI on the other hand is an ideal material for
the ignition of composite propellants. Hot
copper vapor condensing and molten copper
impacting on the surface of the propellant
provides an excellent source of thermal energy
for ignition. Furthermore, copper and copper
oxides catalyticaily enhance the ignition and
combustion of ammonium perchlorate.
Unfortunately, CuO/AI thermites exhibit poor
ignition characteristics at high density and are
sensitive to header and charge holder thermal
losses. Thus, CuO/AI at high density requires
large input energies for ignition and the reaction
once started can be quenched as a result of
radial heat losses. The THKP ignition charge
eliminates both of these problems by providing
an overwhelming thermal input to the CuO/AI.
Although the CuO/AI is itself a poor gas producer
(the copper vapor rapidly condenses), the THKP
produces a sufficient gas pulse for this device to
be used to operate small, lightly loaded, piston
type actuators. In addition, the thermal output of
the CuO/AI helps to maintain the temperature of
the gases produced by the THKP. We have
tested both piston actuator and propellant
loaded gas generators with this dual mix device
with good results.
using a 50 \xF CDU firing set was 17.8 V; the 5
minute no-fire level is estimated to be greater
than 1 A with no device degradation. Future
research will examine the tolerance of this device
to mechanical shock and electromagnetic
environments.
8. ACKNOWLEDGMENT
The testing expertise of Dave Wackerbarth,
Sandia National Labs, is acknowledged with
grateful thanks.
9. REFERENCES
1 E. A. Kjelgaard, "Development of a Spark
Insensitive Actuator/Igniter," Fifth International
Pyrotechnics Seminar, Vail Colorado (July
1976).
2 See for example, D. A. Benson, M. E. Larson,
A. M. Renlund, W. M. Trott and R. W. Bickes, Jr.,
"Semiconductor Bridge (SCB): A Plasma
Generator for the Ignition of Explosives," Journ.
Appl. Phys. 62, 1622(1987)
3 R. W. Bickes, Jr., S. L. Schlobohm and D. W.
Ewick, "Semiconductor Bridge (SCB) Igniter
Studies: I. Comparison of SCB and Hot-Wire
Pyrotechnic Actuators," Thirteenth
International Pyrotechnic Seminar, Grand
Junction Colorado (July 1988).
4 Firing set designed by J. H. Weinlein of the
Firing Set and Mechanical Design Department,
Sandia National Laboratories.
5 B. T. Neyer, "More Efficient Sensitivity Testing,"
EG&G Mound Applied Technologies, MLM-
3609, (October 20, 1989)
6 H. E. Anderson, "STATLIB," Sandia National
Laboratories, SAND82-1976, (September
1982).
7. SUMMARY
We have developed two SCB igniters housed in
an assembly with an outline similar to the
standard NSI component. Our prototype design
utilized THKP to provide for a pressure output
static-insensitive device. Our second design
used a THKP and thermite mix to provide an
output sufficient for piston actuators as well as
propellant loaded gas generators. All-fire voltage
- 64 -
b
ft •'«
Optical Ordnance System For Use In Explosive Ordnance Disposal Activities*
J. A. Merson, F. J. Salas, and F. M. Helsel
Explosives Subsystems and Materials Department 2652
P. O. Box 5800
Sandia National Laboratories
Albuquerque, NM 87185-0329
ABSTRACT
A portable hand-held solid state rod laser system and
an optically-ignited detonator have been developed
for use in explosive ordnance disposal (EOD)
activities. Laser prototypes from Whittaker
Ordnance and Universal Propulsion have been tested
and evaluated . The optical detonator contains 2-(5
cyanotetrazolato) pentaamine cobalt III perchlorate
(CP) as the DDT column and the explosive
Octahydro - 1,3,5,7 - tetranitro - 1,3,5,7 - tetrazocine
(HMX) as the output charge. The laser is designed
to have an output of 150 mJ in a 500 microsecond
pulse. This output allows firing through 2000
meters of optical fiber. The detonator can also be
ignited with a portable laser diode source through a
shorter length of fiber.
1.0 INTRODUCTION
Sandia National Laboratories has been actively
pursuing the development of optically ignited
explosive subsystems for several years concentrating
on developing the technology through experiment 1 ' 3
and numerical modeling of optical ignition. 4 * 5
Several other references dealing with various aspects
of optical ordnance development are also available in
the literature. 6 " 1 ^ Our primary motivation for this
development effort is one of safety, specifically
reducing the potential of device premature that can
occur with a low energy electrically ignited explosive
device (EED). Using laser ignition of the energetic
material provides the opportunity to remove the
bridgewire and electrically conductive pins from the
charge cavity, thus isolating the explosive from stray
electrical ignition sources such as electrostatic
discharge (ESD) or electromagnetic radiation
(EMR). The insensitivity of the explosive devices to
stray ignition sources allows the use of these
ordnance systems in environments where EED use is
a safety risk.
The Office of Special Technologies under the
EOD/LIC program directed the development of a
portable hand-held solid state rod laser system and
an optically-ignited detonator to be used as a
replacement of electric blasting caps for initiating
Comp C-4 explosive or detonation cord in explosive
ordnance disposal (EOD) activities. The prototype
systems that have been tested are discussed in this
paper. Laser prototypes were procured from both
Whittaker Ordnance (now Quantic) and Universal
Propulsion Company and tests were conducted at
Sandia National Laboratories. An optical detonator
was designed at Sandia National Laboratories and
built by Pacific Scientific - Energy Dynamics
Division formerly Unidynamics in Phoenix (UPI).
2.0 THEORY OF OPERATION
The intent of the optical firing system is to provide
the same functional output performance of an
electrically fired blasting cap without the use of
primary explosives. Electrical detonation systems
use current to heat a bridgewire which in turn heats
an explosive powder to its auto-ignition temperature
through conduction. In contrast, an optical system
uses light energy from a laser source that is absorbed
♦This work was sponsored by the Office of Special Technologies under funding documents NO464A92WR07053
and NO464A91WR10380 and supported by the United States Department of Energy under Contracts DE-AC04-
76DP00789 and DE-ACO4-94AL85000.
- 65 -
by the powder, thus raising its temperature to the
auto-ignition temperature. The primary advantage
of optical ignition is that there are no electrically
conductive bridgewires and pins in direct contact
with the explosive powder. This removes the
potential electrostatic discharge pathways and
eliminates premature initiations which can be caused
by stray electrical signals. This is illustrated by the
comparison of the electrically and optically ignited
ordnance systems shown in Figure 1.
ELECTRICAL
DEVICE
BRIDGEWIRE
POWER
SOURCE
ELECTRICAL
LEADS
y^OWDE^\
W
HERMETIC WINDOW
OR FIBER OPTIC
OPTICAL
FIBER
standard SMA 906 optical connector. The
connector positions the optical fiber in contact with a
sapphire window as shown in Figure 2. This optical
interface and the use of optical fibers instead of
electrical wires completely de-couples stray electrical
sources from the detonator by removing any
electrical path to the explosive.
E-BRfTE 26-1
HMX Output Chwg*
CP DDT Column 1.7 oVce
1.5 glee
H
Figure 2. SMA compatible optical detonator with
doped CP ignition charge, undoped CP DDT column
and a HMX output charge.
Figure 1. Comparison of electrically and optically
ignited ordnance systems.
3.0 SYSTEM DESCRIPTION
The optical system is intended to be an additional
tool for EOD applications which provides a HERO
(Hazards of Electromagnetic Radiation to Ordnance)
safe system with a detonation output sufficient to
directly initiate Comp C-4 or detonation cord
without the use of primary explosives such as Lead
Azide. The system contains an optical detonator, a
portable, battery operated laser, and optical fiber to
couple the laser output to the detonator. Each part of
the system will be discussed individually.
3.1 Detonator Description
A drawing of the detonator design is shown in
Figure 2. The detonator relies upon the deflagration
to detonation transition or DDT. The detonator
contains approximately 90 mg of 2-(5-
cyanotetrazolato) pentaamine cobalt III perchlorate
or CP (see Figure 3 for chemical structure) for the
DDT column and 1 g of HMX for the output charge.
The detonator wall around the HMX output charge is
thin in order to minimize the attenuation of the
shock produced by the detonation of the HMX. The
detonator incorporates threads that will accept a
N C-CN
II II
N N
\ /
N
H J
H ^
Y±7
NH
NH
(CIO
4' 2
Figure 3. 2-(5-cyanotetrazolato) pentaamine cobalt
III perchlorate or CP.
The optical ignition of explosives depends on the
optical power delivered and the energy absorbed by
the explosive. This dependence is important at low
power as shown Figure 4.
At low power, it is necessaiy to dope some
explosives with other materials such as carbon black
or graphite in order to increase their absorptance of
the optical energy and thus lower their ignition
threshold. We have chosen to use CP doped with
1% carbon black so that these detonators can be fired
from lower power laser sources such as laser diodes.
- 66 -
At high powers, such as that provided by the Navy
EOD system, a minimum energy must be delivered
to the explosive in order for it to ignite. As seen in
Figure 4, this minimum energy for doped CP is on
the order of 0.25 mJ. The Navy EOD system uses a
solid state rod laser capable of delivering 100 to 200
mJ of optical energy in a fraction of a millisecond.
Explosive doping is not required in this detonator
when utilizing the high power rod laser but was
implemented so that the detonator could be used for
a wide range of applications.
30,000
Energy (mJ)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Power (watts)
Figure 4. Optical ignition threshold for doped CP at
low laser powers.
Successful ignition and function of the optical
detonator has been achieved with both portable solid
state rod laser systems powered by a 9 V supply and
by a portable semiconductor laser diode system
powered by five 9 V batteries (45 V total). The
operational goals of the detonation system require
the use of long optical fiber lengths (up to 2000 m)
which may have optical attenuation or loss near 90
percent with fibers that have 4-5 dB/km loss.
Fibers with higher loss per kilometer will enhance
the optical attenuation problem. The portable laser
diode is capable of delivering 2 W of optical power,
well within the ignition requirements, but
insufficient to overcome the cable losses in 2000 m
of optical cable. For this reason, the EOD system
uses solid state rods for the optical energy supply
which are discussed in the next section.
3.2 Solid State Rod Laser
Two laser firing unit designs have been built by
Whittaker Ordnance (now Quantic) and by Universal
Propulsion Company in Phoenix. The Whittaker
design was the first generation prototype followed by
the second generation prototype design from
Universal Propulsion. Both systems have been
shown to be effective at igniting the optical detonator
through 1000 meters of optical fiber. Both laser
designs are discussed below.
The first laser firing unit for the Navy EOD laser
ordnance system was built by Whittaker Ordnance
and was designed to be portable, rugged, water-proof
during transport, and battery operated. The laser
unit contains a 9-volt battery which supplies voltage
to a DC/DC converter to step up the voltage to
approximately 500 volts. This voltage charges the
300 nf capacitor which supplies current to the flash
lamps. The functioning of the flashlamps excites the
laser rod material, Nd doped YAG, and causes the
laser to function. The system is designed to deliver
between 100 and 200 mJ of optical energy during a
500 microsecond pulse. This exceeds the energy
required for the ignition of the detonator by at least 2
orders of magnitude. The laser output is coupled
into a 200 urn optical fiber which can be connected
to the laser firing unit using the SMA 905 connector
port on the top of the laser.
The laser can be easily transported in the field. It is
contained in a cylindrical container which is
approximately 3.5 inches in diameter and 6 inches
tall. The package weighs about 2 pounds. The laser
is not eye safe and care must be taken to properly
protect the operator and any casuals from exposure
to the beam. Laser safety glasses with an optical
density of 4.6 or greater are required for personnel
within 10 feet or 3 meters of the laser or the output
end of a fiber when it is coupled to the laser. During
operations, one person maintains positive control of
the laser and the optical detonators. It is the
responsibility of that person to assure that all
personnel within the exposure radius of 3 meters
have the proper eye protection. Once this is verified,
the laser can be armed by depressing the arm button
on the top of the laser firing unit. After 10 to 30
seconds, the fire light will begin to blink. The laser
can then be fired by depressing the fire button. The
optical fiber can then be disconnected from the laser
and the protective cover placed back on the optical
port on the laser.
The second generation laser was designed and built
by Universal Propulsion Company. It improved
upon the packaging, specifically with respect to
environmental protection, and maintained a
comparable laser output to the Whittaker laser. This
- 67 -
laser uses either six 1.5 V AA batteries or three 3 V
AA batteries to power the laser with a 9 V supply.
The 9 V supply is stepped up to 360 V to charge a
200 |if capacitor. The body of the laser is more
rugged and environmentally sealed. The housing is
similar to a flashlight housing and is 10.1 inches
long and 2.75 inches in diameter. The laser weighs
2.1 pounds. Operation of the laser is similar to that
of the Whittaker design. The design utilizes a rotary
arm/fire switch located in the rear of the laser
housing. The laser delivers 200 - 300 mJ optical
energy in a 200 usee pulse. The optical energy is
coupled into a 200 jam fiber using a press fit SMA
906 connector which attaches to the front of the laser
housing.
3.3 Optical Fiber and Connections
The optical energy from the laser is coupled to the
optical detonator with the use of optical fiber. The
fiber contains a core glass and either a glass or
plastic cladding depending on the manufacturer.
The mismatch of the index of refraction of the core
and cladding is such that all of the optical energy in
the core glass is internally reflected by the cladding
in a process known as total internal reflectance.
Each optical fiber is described by a size and
numerical aperture (NA). The size of the fiber is
determined by the core glass diameter. The Navy
EOD system uses 200 urn fiber and could easily be
adapted to larger diameters such as 400 urn. The
NA of the fiber describes the acceptance angle of the
light that can be coupled into the fiber such that the
light in the fiber does not exceed the critical angle
and is totally internally reflected. The core and
cladding are coated with an organic buffer to add
strength. Additional layers of plastic and other
strength members including Kevlar are used in the
optical fiber cable to give it additional strength. The
overall cable diameter can vary depending upon the
jacketing and strength member materials but is on
the order of 0.125 inches.
The optical fiber is relatively durable, however it can
be broken. Care should be taken to avoid sharp
bends less than 0.5 inch radius. Using a visible light
source which should be eye safe, the operator can
check for breaks in the optical cable by shining the
light through the fiber. During system setup, the
light can be transmitted through the fiber to verify
continuity. If the light does not appear at the other
end, then there is a break in the fiber cable. Only an
eye safe, low power, light source should be used for
checking fiber continuity. The fiber continuity
cannot be checked by the laser firing unit as it is not
eye safe, and the laser light is invisible to the human
eye.
Connections to optical fibers can be made with
standard optical connectors. This procedure can be
done in the field if required but is easier if done
ahead of time. The polish on the optical fiber is
important on the laser end. The polish on the
detonator end is not as critical and a simple cleave of
the fiber is sufficient. During explosive shots, the
last portion of the optical fiber is destroyed.
Therefore, it is recommended that optical cable
jumpers be prepared ahead of time and used in the
field to minimize the number of connectors that are
made in the field.
4.0 SUMMARY
The optical ordnance system utilizes laser light
energy to ignite an explosive powder contained in a
detonator. The detonator is HERO safe and
produces a detonation output sufficient to detonate
Comp C-4 or detonation cord. The detonator does
not contain primary explosives. The laser is portable
and powered by batteries. The optical energy from
the laser is coupled into standard optical fiber which
is connected to the detonator. Jumpers are used to
minimize the number of optical fiber terminations
that must be made in the field with multiple shots.
The system has been shown to be effective at
detonating Comp C-4 through 1000 meters of optical
fiber.
5,0 REFERENCES
1. S. C. Kunz and F. J. Salas, "Diode Laser
Ignition of High Explosives and Pyrotechnics",
Proceedings of the Thirteenth International
Pyrotechnics Seminar, Grand Junction, CO,
11-15 July 1988, p. 505.
2. R. G. Jungst, F. J. Salas, R. D. Watkins and L.
Kovacic, "Development of Diode Laser-Ignited
Pyrotechnic and Explosive Components",
Proceedings of the Fifteenth International
Pyrotechnics Seminar, Boulder, CO, 9-13 July
1990, p. 549.
3. J. A. Merson, F. J. Salas and J. G. Harlan, "The
Development of Laser Ignited Deflagration-to-
Detonation Transition (DDT) Detonators and
68 -
Pyrotechnic Actuators", to be published in
Proceedings of the Nineteenth International
Pyrotechnics Seminar, Christchurch, New
Zealand, 20-25 February, 1994.
4. M. W. Glass, J. A. Merson, and F. J. Salas,
"Modeling Low Energy Laser Ignition of
Explosive and Pyrotechnic Powders",
Proceedings of the Eighteenth International
Pyrotechnics Seminar, Breckenridge, CO, 12-
17 July 1992, p. 321.
5. R. D. Skocypec, A. R. Mahoney, M. W. Glass,
R. G. Jungst, N. A. Evans and K. L. Erickson,
"Modeling Laser Ignition of Explosives and
Pyrotechnics: Effects and Characterization of
Radiative Transfer", Proceedings of the
Fifteenth International Pyrotechnics Seminar,
Boulder, CO, 9-13 July 1990, p. 877.
6. D. W. Ewick, "Improved 2-D Finite Difference
Model for Laser Diode Ignited Components",
Proceedings of the Eighteenth International
Pyrotechnics Seminar, Breckenridge, CO, 12-
17 July 1992, p. 255.
1. D. W. Ewick, T. M. Beckman, J. A. Holy and
R. Thorpe, "Ignition of HMX Using Low
Energy Laser Diodes", Proceedings of the
Fourteenth Symposium on Explosives and
Pyrotechnics, Philadelphia, PA, 1990, p. 2-1.
8. D. W. Ewick, T. M. Beckman and D. P.
Kramer, "Feasibility of a Laser-Ignited HMX
Deflagration-to-Detonation Device for the U. S.
Navy LITES Program", Rep. No. MLM-3691,
EG&G Mound Applied Technologies,
Miamisburg, OH, June 1991, 21 pp.
9. C. M. Woods, E. M. Spangler, T. M. Beckman
and D. P. Kramer, "Development of a Laser-
Ignited All-Secondary Explosive DDT
Detonator", Proceedings of the Eighteenth
International Pyrotechnics Seminar,
Breckenridge, CO, 12-17 July 1992, p. 973.
10. D. W. Ewick, "Finite Difference Modeling of
Laser Diode Ignited Components", Proceedings
of the Fifteenth International Pyrotechnics
Seminar, Boulder, CO, 9-13 July 1990, p. 277.
- 69 -
Laser Diode Ignition (LDI)
William J. Kass, Larry A. Andrews, Craig M. Boney, Weng W. Chow,
James W. Clements, John A. Merson, F. Jim Salas, Randy J. Williams
Sandia National Laboratories
Albuquerque, NM
and
Lane R. Hinkle
Martin Marietta Speciality Components
Clearwater, FL
/
i
ABSTRACT
This paper reviews the status of the Laser Diode Ignition (LDI) program at Sandia National Labs.
One watt laser diodes have been characterized for use with a single explosive actuator. Extensive
measurements of the effect of electrostatic discharge (ESD) pulses on the laser diode optical
output have been made. Characterization of optical fiber and connectors over temperature has
been done. Multiple laser diodes have been packaged to ignite multiple explosive devices and an
eight element laser diode array has been recently tested by igniting eight explosive devices at
predetermined 100 ms intervals. A video tape of these tests will be shown.
INTRODUCTION.
Laser diode ignition of explosive
ordnance[l],[2] is an active program at
Sandia [3]. Optical ignited ordnance
enhances safety both on a component and
system level. Electrically initiated devices
can be sensitive to electrostatic discharges
which dictate special handling care.
Accidental initiation could cause personal
injury or death. Optical ignition eliminates
the possibility of this occurrence. Other
advantages of optical ignition are resistance
to triggering by electromagnetic radiation, no
electrical conductance after fire and the
absence of corrodible electrodes or
bridgewires.
The goal of this program is to develop a
laser diode based optical firing system to
ignite an octahydro- 1,3,5, 7-tetranitro-
1,3,5,7-tetrazocine (HMX) /carbon mixture
in an explosive actuator. Several
components and systems have been built and
tested. Among these are a single laser diode
system, a three laser diode system, a high
power laser diode igniting several actuators
"simultaneously", and an addressable array of
laser diodes used to ignite multiple
detonators. The building blocks of these
systems, environmental testing of the
components and the various systems and
their function will be described.
SINGLE LASER DIODE FIRING
SYSTEM.
The simplest system which we have
developed consists of a single laser diode, an
optical fiber, a connector and an explosive
Laser
Diode
f X14.5TC
Las
X2.0 T-t-
Optical
Fiber
Connected
Optical
Optical Power
TOTAL 11.8d B
Laser Degradation
" ' Environmental3.0dB
UD1
Fib
er
X2.0 Coupling Loss 3 QdB
X1.01FiberLoss 01dB
X1.2 Connection Loss 0.8dB
X1.01FiberLoss 0.1dB
Explosive ■ X3.0 Fire Reliability 4.8dB
Figure 1. Power budget for laser diode ignition.
- 71 -
PAGE.
±
actuator. This system along with a power
budget for each loss element is shown
schematically in Figure 1.
The losses indicated in Figure 1 are
referenced to the nominal (50%) fire level of
the explosive actuator. A factor of 3 .0
(4.8dB) is arbitrarily used to achieve a higher
fire reliability. The actual fire reliability will
require a measure of the spread in the
measurement of the fire threshold. Fiber
losses (0.1 dB) and connector losses (0.8dB)
are estimated from our experience with
commercial connectors and fibers. The
coupling loss (3.0 dB) represents the worst
case coupling between the laser diode chip
and the integrated optical fiber with which it
is packaged. Degradation over time,
temperature and thermal and mechanical
environments is taken as a factor of two (3.0
dB) over the expected lifetime (20+ years) of
the laser diode ignition system. The result of
this analysis is that the laser diode chip
power, before coupling, necessary to ignite
the explosive is approximately 15 times the
nominal fire threshold. For HMX/C, the
nominal threshold for a 10ms optical pulse is
70 mW, hence, a 1.0+ watt uncoupled laser
diode chip is required. Commercially
available laser diode chips delivering greater
than LOW coupled power have been
LMHMtdfl RAIM; Wrt »*p 1T M
Figure 2 Hermetically sealed-fiber optic
coupled 1W laser diode for optical ignition.
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Figure 3. Optical power vs. drive current
at tempertures between -55C and 75C for
a typical 1W laser diode.
obtained and evaluated.
The single laser diode firing system also
includes an electronic drive circuit used to
convert 28 V-10 ms input power pulse to the
1.6-2.0 A- 10 ms drive current pulse required
to deliver 1 W optical power from the fiber
coupled laser diode.
LASER DIODE.
The laser diodes used for these tests have an
optical output of approximately 1 W in the
spectral range of 800-850 nm. The laser
diode is an AlGaAs single quantum well
device manufactured by Spectra Diode Labs.
The laser diode is hermetically packaged
with an integrally coupled 0.22 numerical
aperture- 100 |im diameter optical fiber
which is terminated in a commercial optical
connector ferrule. A photo of this device is
shown in Figure 2.
Figure 4 Spectrum for a typical AlGaAs
quantum well laser diode.
- 72 -
1 T
0.9
0.8
0.7
\ 0.8 • ;
! 0.5 • •
JO.*-
0.3
0.2
0.1 ■:
-
Y/vWvW
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Temperature Sequence
Figure 5 Optical transmission during
temperature cycling for an ST type connector.
Figure 3 shows the optical power vs. drive
current for a typical 1 W laser diode used for
this system. The coupling efficiency from
the chip to the fiber is greater than 50% and
the nominal power at room temperature is
about 0.8 W at 1.5 A drive current. At 75°C,
however, the power has been degraded to
0.6 W, still in excess of the power required
from the power budget.
Because of the broad band absorptance of
the HMX/carbon [4] mixture used for LDI,
the output spectrum of the laser diode is less
important than the output power. However,
the spectrum is an indicator of the proper
function of the diode [5], Figure 4 shows
the spectrum for a typical diode laser.
OPTICAL FIBER AND CONNECTORS.
The diode package fiber is connected to the
explosive actuator via commercial optical
connectors and fiber. The optical connectors
have been tested over temperature by cycling
between -55°C and 100°C multiple times.
As can be seen in Figure 5, the transmittance
degrades through the first two cycles and
then oscillates between high and low
temperature values. The optical fiber used
was 0.22 NA, 100 |am diameter, pure silica
core, doped silica cladding obtained from
Polymicro Technologies. The results of
temperature testing only this fiber are shown
Figure 6 Optical transmission vs.
temperature for Polymicro optical fiber.
in Figure 6. It can be seen that a reversible
transmission loss occurs as the fiber is cycled
to low temperature. The loss is consistent
with losses predicted from microbending due
to the mismatch in thermal expansion
between the fiber and the polyimide coating
[6]. A larger diameter Polymicro fiber and a
fiber from General Optics (with a loose
acrylate buffer) were also tested as shown in
Figure 7. The losses from the 400 \im
Polymicro fiber were less pronounced than
the 100 \im while the losses from the
General Fiber were negligible.
EXPLOSIVE ACTUATOR.
The majority of the explosive
1 T
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! 0.4
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Genere) Rber Optic* 100/140 Ffc*r **i Aciyfate
Pdyrrtcre 40W440 fiber wHh PdyknMa Buflbr
I Rbwt ar«32 FmI Long In 10 bich Dtwnttor coil
-20 -10
Figure 7 Optical transmittance vs. temperature
for two kinds of optical fiber.
- 73 -
characterization done at Sandia National
Labs has been for 2-(5 cyanotetrazolato)
pentaamine cobolt III perchlorate (CP) and
TiH 165 KC10 4 ignition charges. TheCP
ignition charges are normally the first
element in a detonation column consisting of
1.7 g/cm 3 CP doped with carbon black,
1.5 g/cm 3 CP, 1.7 g/cm 3 HMX. The charges
are 20 mg of material in a 2. 1 mm diameter
by 2.5 mm long cylinder. They are unsealed
and the fiber is placed in direct contact with
the explosive powder. The LDI system was
designed to operate with explosive actuators
to generate gas and perform mechanical
work. The actuators consist entirely of a
mixture of HMX and 3% carbon black. The
carbon increases the material absorptance in
the near IR where the laser diode emits.
ESD TESTING
Laser diode ignition derives its immunity to
ESD and electromagnetic radiation (EMR)
because of the absence of electrical
conductors within the region where the
energetic material is located. A related issue
in ESD safety, however, is what the optical
output of the laser diode is when it is
subjected to an ESD pulse. Is the optical
energy or power generated sufficient to
ignite the energetic material? To address this
issue we measured the optical output while
subjecting the laser diode to an ESD pulse.
This pulse is defined by an electrical circuit
25
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Figure 9 Optical output power for a laser
diode subjected to a series of Sandia Severe
Human Body ESD pulses.
designed to simulate a human body spark
including a hand (small capacitance) and
body discharge [7]. The schematic of the
measuring equipment is shown in Figure 8 .
A series of measurements were made by
increasing the voltage on the SSET (Sandia
Severe ESD Tester) circuit and monitoring
the current through the laser diode. The
optical output from the laser diode was
coupled to an optical fiber and measured
with a fast response photodetector. The
early time results are shown in Figure 9.
The peak output is reached in 2 ns followed
by signal decay with two time constancts
The first decay constant is a few
nanoseconds and the second is 300 ns.
These decay constants result in a total signal
HIGH
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Figure 8 Test setup for measuring laser
diode output power with an ESD pulse
current input.
A
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V
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200 H0 400
Figure 10 Long time decay of optical output
for 25kV, 15.5kV and lOkV circuit input
voltages.
- 74 -
30
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25
125
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in
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25
10
12
14
10 18 20 22
Charge Voltage (kV)
24
26
Figure 11 Peak output power (broken line)
and current (solid line) vs. charge voltage on
ESD test circuit.
decay in about 1000 ns. As the input voltage
to the ESD circuit is increased from 10 kV
to 25 kV, the peak current increases from
60 A to 140 A. The optical output tracks
this current until degradation of the diode
begins. This occurs at about 125 A with a
circuit input voltage of 23 kV. The peak
optical output power is 25 W while the
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ESD
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1E-09 -
1E-09 1E-07 1E-05 1E-03 1E-01 1E+01
Time (s)
Figure 13 Comparison of optical energy
necessary to ignite TKP and CP with the
maximum optical energy available from an
ESD source.
1E+02 r
1E+01
1E+00
8
O
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1E- 1E- 1E- 1E- 1E- 1E- 1E- 1E- 1E-
09 08 07 06 05 04 03 02 01
Time (s)
Figure 12 Optical power necessary for
explosive ignition and optical power
generated by ESD pulses vs time.
maximum energy found from integration of
the complete decay is 5 ^J. The optical
decay until 1000 ns is shown in Figure 10.
Figure 11 shows peak optical power and
diode current plotted vs. circuit input
voltage. The behavior of this laser diode and
others tested indicates that even though the
current through the diode continues to
increase with higher circuit drive voltages,
the optical power levels off and begins to
decay as the laser diode is degraded. This
phenomenon becomes a safety advantage
because the diode will not be able to deliver
sufficient power to ignite the explosive.
Figure 12 shows the optical power available
from a laser diode driven by an ESD source
- 75 -
been built and tested in various
configurations. We have estimated a power
budget for reliable ignition and the individual
loss terms are being characterized. Fiber
losses and connector losses can be
accommodated with proper choices of
connectors and fibers. Currently available
commerical high power laser diodes provide
ample power to ignite a variety of explosives
under extremes in temperature and
mechanical environments. The behavior of
these laser diodes is being characterized over
temperature, mechanical environments and
time (aging). ESD testing demonstrates that
the laser diode is inherently safe from
producing optical power or energy which
exceeds the explosive ignition threshold.
ACKNOWLEDGMENT
The authors would like to express their
appreciation to John Barnum for making the
ESD measurements.
vs. time and compared to the power-time
combination required to ignite titanium
potassium perchlorate or CP. The HMX
threshold falls slightly below that for CP. It
can be seen from this plot that even though
there is ample power for ignition, the
duration is too short to ignite the explosive
material.
The integration of the power vs. time curves
gives a maximum available optical energy of
3-5 ^J from this type of ESD pulse. This
energy also probably represents the
maximum energy available under other high
current conditions. Figure 13 shows the
available optical energy plotted vs. time
compared to the energy required to ignite CP
or TKP. When plotted in this manner it is
apparent that too little ESD generated
optical energy is available to ignite these
explosives.
CONCLUSION
A complete laser diode ignition system has
REFERENCES
1. S. C. Kunz and F. J. Salas, "Diode Laser Ignition of High Explosives and Pyrotechnics, Proc.
of 13th International Pyrotechnics Seminar, Grand Junction, CO, 1 1-15 July 1988, pp505
2. D. W. Ewick, L. R. Dosser, S. R. McComb and L. P. Brodsky, "Feasibility of a Laser Ignited
Pyrotechnic Device", Proc of the 13th International Pyrotechnic Seminar, Grand Junction CO, 1 1-
15 July 1988, pp 263
3. J. A. Merson, F. J. Salas, W. W. Chow, J. W. Clements and W. J. Kass, "Laser Diode Ignition
Activities at Sandia National Laboratories", Proceedings of the First NASA Aerospace
Pyrotechnic Systems Workshop, Houston, TX, 9-10 June 1992, ppl79-196.
4. R. J. Jungst, F. J. Salas, R. D. Watkins and T. L. Kovacic, "Development of Diode Laser-
Ignited Pyrotechnic and Explosive Components," Proc. of the 15th International Pyrotechnics
Seminar, Boulder, CO, 9-13 July 1990, pp549-568.
5. L. F. DeChiaro, S. Ovadia, L. M. Schiavone, C. J. SandrofF, "Quantitative spectral analysis in
semiconductor laser reliability," SPIE Technical Conference 2148A, Los Angeles, CA, 24-26
January, 1994.
- 76 -
6. Powers Garmon, "Analysis of Excess Attenuation in Optical Fibers Subjected to Low
Temperatures", Proc. of the International Wire and Cable Symposium, 1983, ppl34-143.
7. R. J. Fisher, "The Electrostatic Discharge Threat Environment Data Base and Recommended
Baseline Stockpile-to-Target Sequence Specifications," SAND88-2658, November 1988.
- 77 -
STANDARDIZED
LASER INITIATED ORDNANCE
James V. Gageby l
Engineering Specialist
Explosive Ordnance Office
The Aerospace Corporation
Abstract
Launch vehicles and spacecraft use explosively initiated devices to effect
numerous events from lift-off to orbit These explosive devices are electrically initiated by
way of electro-mechanical switching networks. Today's technology indicates that
upgrading to solid state control circuits and laser initiated explosive devices can improve
performance, streamline operations and reduce costs. This paper describes a plan to
show that these technology advancements are viable for Air Force Space and Missile
System Center (SMC) program use, as well as others.
Introduction
A plan to develop, qualify and flight
demonstrate a laser initiated ordnance system
(LIOS) has been accepted by the SMC Chief
Engineer and The Aerospace Corp. Corporate
Chief Engineer as part of their horizontal
engineering program. The Chief Engineers'
horizontal engineering effort includes a task for
standardization of systems and components
common to a variety of programs. The objective of
standardization is to reduce costs by eliminating
duplications in development and qualification often
seen when vertical engineering prevents cross
pollination.
The LIOS is intended as a state-of-the-art
solid state replacement for the present day
electrically initiated ordnance firing circuits for
future space launch vehicle and satellite systems.
The LIOS eliminates the need for electro-
mechanical safe and arm devices and latching
relays that are presently used in today's ordnance
firing circuits.
This plan will result in confirmation of LIOS
suitability for SMC applications. It will establish a
performance and requirements specification for
standardization on SMC programs. Flight system
performance enhancements and cost savings will
result from the safety improvements, streamlined
operational flow, weight savings, improved
reliability and hardware interchangibility features of
this new technology. It is expected that a family of
LIOS's having various multiple output
configurations will be developed to fit SMC
program needs.
A typical SMC launch vehicle and satellite
uses at least 40 explosively initiated events to get
into proper orbit. The majority of these are
redundant, therefore, 80 explosive initiations can
occur from engine ignition and lift-off to final
appendage deployments in orbit. At the extreme
NASA's space shuttle uses more than 400
explosive events from lift-off through deployment
and release of their drag parachute on landing.
Shown below is a simplified description of
the conventional ordnance firing circuits used on
most SMC programs to effect these explosive
initiations.
Conventional Ordnance Firing Circuit
Electro-mechanical device with EED
and explosive train Interrupt (moving
parts) - Range Safety requirement for
FTS and SRM ignition
Power/Control
Input
Cu Wire
Electro Explosive Device (EED) (no moving parts)-*
Range Safety assessment needed for potentially
hazardous applications
In the conventional system, sequenced
power and control inputs from system computers
are routed to a switching network that allows safe,
arm and fire commands to be sent to the explosive
devices. Mechanical latching relays are used to
effect these commands.
The commands are sent via copper wire to
either an electro explosive device (EED) or to a
safe and arm device that contains an EED. The
EED has an electrically conductive path directly to
the explosive materials internal to it. Electrical
energy in this path, at predetermined thresholds,
causes EED ignition. The EED contains no moving
parts.
The safe and arm device (S/A) is an
electro mechanical component required for
- 79 -
.fttSc.
1«
compliance with safety regulations in flight
termination and solid rocket motor ignition systems
only. It contains moving parts. It provides a barrier,
or interrupt, in the explosive train so that premature
ignition of the EED will not cause an unplanned
event. This interrupt is remotely removed during
the mission sequence to allow end item function.
The safe and arm device also contains a
component called a safing pin which must be
manually removed before remote arming and firing
can be effected. Removal of the safing pin is done
late in the pre-launch cycle and usually requires
the launch site to be cleared of all but essential
personnel.
The LIOS replaces the EED used in the
conventional ordnance system with a device that
uses laser diode energy to ignite the same
explosives. The primary advantage is the
elimination of electrically conductive paths to the
explosive mixes. This drastically reduces concerns
of premature ignition since external environments
like static electricity, electro-magnetic interferences
as well as radio frequency (R-F) fields are isolated
from the explosives.
The new explosive component is called a
laser initiated device or LID. The LID will be
designed to use secondary explosive materials as
ignition sources rather than primaries as used in
EED's. This reduces handling concerns. The LID
could be considered in the same category as small
arms ammunition for handling and shipping
purposes. This will result in a significant, although
indeterminate, cost savings.
The LID outputs can be configured to be
nearly identical to the EED outputs; therefore,
interfaces with present day explosively actuated
components will be compatible. Requaiification of
explosively actuated components with LID's, that
were previously qualified with EED's, should be
minimal.
LIOS Concept
A description of the LIOS is given below.
LFU (LASER GENERATOR)
ELECT POWER t
SIGNAL CONTROL I
LIOS
_- e LID (EXPLosrvE)
ETS (FIBER OPTIC PATH) l
Z^-\
Laser firing unit (LFU) - receives control signals and power
(28VDC) for sequencing. Laser diodes in LFU produce single
or multiple laser outputs. Contains no moving parts.
Energy transfer system (ETS) - conveys laser light through
fiber optics and connectors to LID.
Laser initiated device (LID) - allows laser energy (heat) to be
absorbed into chemical mixture causing deflagration/
detonation of explosive.
The LIOS contains no moving parts. The
switching network in the LIOS uses solid state
electronics to accomplish the functions mechanical
latching relays and S/A's provide in the
conventional ordnance system.
Advantages of LIOS are in reduced
handling and safety concerns during ground
operations. During most pre-launch operational
cycles, R-F silence and limited access conditions
are in effect while ordnance installations are in
progress. These down times could be eliminated or
drastically reduced by use of the proposed LIOS.
The reduced safety concerns may allow for
installation of ordnance items at the factory instead
of the launch site, thus reducing pre-launch
operational costs by streamlining ground
operations.
The use of lasers for ignition of explosives
is not new. Research in this area began more than
twenty-five years ago. In fact, the small
intercontinental ballistic missile (SICBM) program
developed and flight demonstrated a crystalline rod
laser system a few years ago. The SICBM laser
ordnance concept is shown below.
SICBM Laser Ordnance Concept
Fiber
V OP**"/ LID
For clarity
features are not shown
(moving parts required)
Rod Laser
Motor Driven Sequencer
Safe/Arm with optical shutter
The SICBM concept served it's purpose
well. Unfortunately, it is more complicated than the
conventional ordnance firing system. It requires
numerous electro-mechanical components for
safety and operational reasons.
Power to the rod laser is sequenced
through an electro-mechanical switching network
similar to that used in the conventional system. For
system function an optical shutter is remotely
actuated to allow lased light to be directed onto a
motor driven sequencer. The sequencer has
optical prisms on a rotating wheel that allow for
splitting of the laser beam for multiple output
functions.
Included in the system, but not shown in
the schematic, is a built-in-test (BIT) feature. The
BIT feature requires additional electro-mechanical
devices to bypass the rod laser and let a light
emitting diode (LED) be pulsed into the fiber optic
transmission line. To verify health of the
transmission line, the LED's pulse is reflected at
- 80 -
the LID and it's total travel time measured by
means of an optical time domain reflectometer
(OTDR). This transmission line check-out is done
as late in the pre-launch cycle as practical. The
OTDR is not part of the flight hardware.
The use of semiconductor laser diodes as
an ignition source is a new, emerging technology.
Their use is, by all indications, a viable alternative
not only to the present day electrically initiated
systems but also to the SICBM approach. At the
onset of the SICBM effort, laser diode technology
had not developed sufficiently to provide output
energies needed to meet LID ignition margin
requirements. Today the technology has
progressed to a point that laser diodes can provide
high energies with ample margin.
Using laser diodes in place of crystalline
rod lasers is a quantum leap in miniaturization.
This miniaturization allows for multiple outputs
without having to use a mechanical prism
sequencer as in the SICBM system. All mechanical
components are removed. It also allows for the
introduction of solid state control logic circuits to
further advance explosive ignition technology in
space applications.
SMC LIPS
The SMC LIOS standardization plan is
broken down into six major tasks shown
below.
LIOS Major Tasks
Task
1. Acquire Range Cmdrs
Council approval for
use of solid state
UOS
2. System and circuit
modeling
3. Determine system
compatibility with
RF/EMI/ESD
4. Verify compatibility
with SMC programs
5. Determine cost
benefit of LIOS use
6. Qualify and flight
demo an SMC
compatible LIOS
Accomplishment
Eliminate mechanical
components In
ordnance firing circuits
Validate circuit
performance
Validate system
energy margins
Assess BIT designs
Compatibility validated
Interfaces validated
Cost benefits defined
LIOS technology ready
for SMC use
Exit Criteria
LIOS not approved or use
of moving components
with LIOS mandated
Solid state logic cannot
meet performance/
safety requirements
Lack of margin
BIT not compatible
with designs
System not compatible
UOS not compatible
No cost savings
Funding not available
The following discussion will outline the
key points of each task. Note that the exit criteria
shown for each task is not task completion. It is
criteria that will prevent LIOS from becoming a
standard for SMC programs, i.e., criteria that would
cause cessation of the SMC LIOS standardization
effort.
The first Task is to obtain an agreement
with the Range Commanders Council allowing use
of LIOS at all launch sites. To be specific, the
agreement must allow use of a LIOS, without
moving parts, i.e., remotely controlled shutters,
etc., on any ordnance system, at any launch site.
This includes both flight termination and
operational ordnance firing systems.
If the Task 1 agreement cannot be attained
the SMC LIOS effort will stop. The cost advantages
of a LIOS using mechanical components compared
to the cost of today's conventional ordnance firing
system are not of sufficient magnitude to warrant
implementation.
The remaining tasks will provide technical
rational to support safety and performance
requirements of the Task 1 agreement. These must
satisfy any Range Commanders Council or SMC
program concerns.
The second task is to analyze the solid
state circuits to verify that they can meet safety and
performance requirements. This will be followed by
an effort to model the entire LIOS and assess
performance margins. The margin analysis must
show that there is at least 50% more energy
available than necessary to ignite the LID when all
system parameters and external environments are
at their extremes. If the designs can not show
sufficient margins for safety and performance
needs, the SMC LIOS effort will be stopped.
Circuit concepts will be analyzed and be
validated by bench tests of designs that are
representative of the optimum configurations.
These tests are considered a key element in the
validation of the LIOS concept. Contributing
expertise to these tasks are Dave Landis and Don
Herbert of the Electronics Division.
During the course of the modeling BIT
designs will be evaluated. The BIT feature will be
used to check continuity of the ETS path between
the laser diode and the LID only. Full power system
checks will be done prior to final connection of the
LID and be performed as late in the pre-launch
cycle as deemed practical. A key feature of the
LIOS implementation is an ability to perform
remote check-out of system health without
interfering with other pre-launch activities.
Therefore, the LIOS effort will be stopped if an
adequate BIT feature cannot be found.
The third task is to determine the LIOS
compatibility with external environments that may
cause premature ignition or prevent ignition of the
LID. These environments include lightning induced
electro-static discharges (ESD), R-F and electro-
magnetic interferences (EMI). These are the same
- 81 -
environments that are concerns for conventional
ordnance firing circuit designs. As previously
noted, current designs are influenced by these
while the LIOS is not. Verification of LID
compatibility with reasonable limits of these
environments is obtainable. Much work has been
done in this area and will be evaluated for
applicability.
The LFU must also be shown to
adequately shield these environments from the
sensitive components within it. If the LID or the
LFU can not be shown to survive reasonable limits
of these environments, and designs cannot be
altered to do so, the SMC LIOS effort will be
stopped.
The fourth task examines the compatibility
of LIOS with common SMC program interfaces. An
attempt will be made to determine the optimum
LIOS configuration in terms of the number of LID
outputs, control circuit configurations and BIT
options. This will, more than likely, result in several
configurations and create a family of LIOS options.
Determining the number of changes to the LIOS
design to suit interface needs and maximize
standardization will be a major part of the task.
All of the above will have a direct impact
on Task 5 which will evaluate cost benefits of LIOS
implementation. Task 5 is also affected by other
factors including ground operations and flight
performance improvements. In ground operations
costs, procedural changes in handling and check
out of conventional ordnance systems versus LIOS
need to be assessed.
It is anticipated that use of LIOS on SMC
programs will be limited to new programs and to
those undergoing major changes. The non
recurring costs of a blanket change to use a LIOS
on existing programs is prohibitive. No other
justification would out weigh these cost differences.
If the fifth task indicates that there is no
cost savings the effort will be stopped. Likewise, if
Task 4 shows that the LIOS is not compatible with
SMC programs the LIOS effort will be stopped.
The sixth task will be the ultimate proof of
the LIOS concept and it's compatibility with SMC
programs. The work of the other tasks will result in
creation of a performance and requirements
document that will be used to solicit multiple
suppliers for qualification of LIOS designs. This will
be followed by a flight demonstration on an SMC
program. Success will demonstrate the usefulness
of LIOS for space and launch applications. Task 6
will not be executed if funding is not made
available.
Acknowledgments
The author wishes to thank Col. J.
Randmaa, Col W. Riles, Maj. K. Johnson, Capt. R.
Anderson and W. Evans of the SMC Chief
Engineers office, and Dr. J Meltzer, Dr. R. Hall and
J. Gower of The Aerospace Corp. Chief Engineers
office for sponsoring the pursuit of the LIOS plan. I
also need to thank Norm Schulze of NASA Hqtrs
for the opportunity of being a member of his
NASA/DOD/DOE Pyrotechnic Steering Committee
where the LIOS concept was initiated.
- 82 -
1-2%
~1
v/1
MINIATURE LASER IGNITED BELLOWS MOTOR
Steven L. Renfro
The Ensign-Bickford Company
Simsbury, CT
Tom M. Beckman
The Ensign-Bickford Company
Simsbury, CT
Abstract
A miniature optically ignited actuation device has
been demonstrated using a laser diode as an
ignition source. This pyrotechnic driven motor
provides between 4 and 6 lbs of linear force
across a 0.090 inch diameter surface. The
physical envelope of the device is 1/2 inch long
and 1/8 inch diameter. This unique application of
optical energy can be used as a mechanical link
in optical arming systems or other applications
where low shock actuation is desired and space
is limited.
An analysis was performed to determine
pyrotechnic materials suitable to actuate a
bellows device constructed of aluminum or
stainless steel. The aluminum bellows was
chosen for further development and several
candidate pyrotechnics were evaluated. The
velocity profile and delivered force were quantified
using an non-intrusive optical motion sensor.
Intrpduptipn
A small optical to mechanical link has
been developed for uses where low
velocity force is required. This device
uses a small B/KN0 3 charge to actuate
a miniature rolling bellows. This laser
diode ignited system provides
approximately 4 lbs of force over 0.1
inches of displacement. The device was
designed to move a small barrier either
into or out of the way to provide means
for a miniature optical arming feature.
The overall size of the device is less
than 1/2 inches long and 1/8 inches in
diameter. A mounting feature allows
simplified integration into new or existing
systems.
Design Analysis
The challenges of this development
program are to balance the gas output to
desired force, ignite with a 1 Watt rated
laser diode, and to downsize processes
to manufacture such a small complex
device.
The force is dictated by the material used
for the bellows. This analysis assumes
that in order to sufficiently move the
bellows, plastic deformation must occur.
This requires that the yield point of the
selected material be exceeded without
violating the ultimate strength. Following
these guidelines, the pressure required
for actuation can be calculated. The
results are summarized in Table 1.
The burst pressure for hardened
aluminum alloys is less than the pressure
required for actuation. Annealed 302
Stainless Steel, Aluminum 1100-0, or
Aluminum 3003-0 are suitable bellows
candidate materials. Using this
information, the resultant force developed
by a fully actuated bellows can be
calculated. The force results are listed in
Table 2.
In order to produce the desired force,
- 83 -
several candidate pyrotechnic materials
and stoichiometrics were considered.
Size restraints required that the selected
pyrotechnic use the space allocated for
the charge holder precisely. This
analysis was crucial due to space
restraints for the charge allocated given
the overall size envelope.
The amount and type of pyrotechnic
material was calculated based on the
pressure required for actuation using the
NASA-Lewis equilibrium thermochemistry
code. The results of this analysis are
normalized to Ti/KCI0 4 and are listed in
Table 3.
The mass calculations were used to
select materials for prototype testing.
Based on these mass calculations, the
first candidates selected for prototype
testing were B/KN0 3) Ti/KCI0 4 , and
B/BaCr0 4 /KCI0 4 .
Initial Prototype Testing
In order to gain information isolated to
function of the bellows, larger prototypes
were used for the initial test series. The
results of the first two groups of five
prototypes each are listed in Table 4.
The B/KN0 3 resulted in an acceptable
charge weight for the desired extension.
The other candidates did not perform
successfully. The B/BaCr0 4 /KCI0 4
loaded devices would not ignite using
the output from a 1 W laser diode. The
Ti/KCL0 4 loaded devices resulted in
burst of the bellows. The burn rate of
the Ti/KCL0 4 did not provide the low
velocity required for this application.
Sensitivity of B/KNO,
The B/KN0 3 material ignites consistently
using full power 840 nm diode with a 10
ms pulse width. An interface sensitivity
test was used to verify reliability. The
results of this testing using 200 micron
fiber are listed in Table 5. These results
are listed based on the calibrated output
from the diode and do not include line
losses.
Process Development
The success of this miniature component
depends highly on an integral charge
holder / fiber optic subassembly. In
order to offset losses expected in fiber
optic interfaces, a smaller core fiber was
chosen to increase the power density of
the available optical energy. This allows
for the fiber to be prepared prior to final
assembly into the charge holder.
Polishing would not be possible given the
restricted space. The Ensign-Bickford
Company developed a cleaving
technique capable of limiting losses to
less than 1dB at the final assembly level.
These losses are acceptible for reliable
ignition without polishing the fiber in the
final assembly.
The charge for the test units was
pressed directly onto the fiber to ensure
intimate contact between the fiber and
the B/KNO3.
The development units were assembled
using processes developed for
miniaturization. These early development
units were then functionally tested to
verify analysis and prototype work and to
determine force and velocity output.
Force Output Testing
The units are designed to function under
axial load, therefore, is is desirable to test
them in that mode. A crushable foam
- M -
was selected to determine the
approximate output force developed by
each test unit. The bellows must develop
at least 2.64 lbs to actuate. The goal for
total nominal developed force is 4.02
lbs. A polyurethane foam was selected
with a minimum compressive strength to
require at least 2.0 lbs to crush in order
to assess the total nominal force output.
Figure 2 illustrates the test setup and
Figure 3 illustrates the results of the four
units tested using this method.
Each of the test articles were bonded to
the test block utilizing the existing
mounting flange and two part epoxy.
This bonding method successfully held
each test unit during function. Three of
the units extended approximately 0.060
inches into the foam block and the fourth
did not actuate. The failed unit was
inspected and revealed that the bellows
had been inadvertently bonded in place
during assembly. This unit burst under
the developed pressure. This lesson
learned resulted in careful inspection of
the bellows area after final assembly.
The area filled with epoxy cannot be
readily viewed with the unaided eye.
Future assembly will necessarily require
magnification.
Velocity Testing
To assess the overall impulse of the
delivered force, a simple velocity
measurement sensor was devised. This
article is illustrated in Figure 2.
The velocity fixture is quite simple. Two
donor fiber optics are aligned across a
channel with acceptor fiber optics. Each
donor / acceptor pair is placed at a
known distance from the unextended
bellows. Using white light as a source,
the acceptor fiber picks up the light and
is then connected to a photo-diode to
produce a small voltage. Upon function
of the unit, this optical path is broken
resulting in a voltage drop across the
photo-diode. This voltage is monitored
using an oscilloscope to determine a time
difference between the donor / acceptor
pairs. This measurement scheme allows
for determination of average bellows
velocity without interrupting the function.
The results of three of these test units
are presented in Figure 4. During
function of the bellows motor into air, the
test bellows for the first unit did not stay
intact. This indicated that the unit
probably is producing too much gas for
function without axial load. The resultant
velocity is not for the entire bellows for
this test unit, but for the aluminum end
free from the assembly. The second and
third units functioned correctly and the
velocities measured are for the bellows.
Further Development Work
The Ensign-Bickford Company is
continuing to develop this product under
contract for Los Alamos National
Laboratory. The ideal miniature bellows
will function under load to produce the
desired force and be able to function in
air without expelling products of reaction.
The final development phase is to
concentrate on optimizing the charge
size in order to meet these goals.
Discussion
The analysis and prototype phase
contributed to development of the
miniature bellows motor. More work
needs to be done to refine the design. A
pyrotechnic device to deliver a small
amount of force is possible and has been
demonstrated.
- 85 -
Table 1. Pressure Requirements for Bellows Actuation and Burst
Bellows
Material
Alloy and Temper
Minimum
Actuation
Pressure
(psi)
Burst
Pressure
(psi)
Aluminum
1100-0
389
577
Aluminum
1100-H12
1089
689
Aluminum
1100-H14
1555
977
Aluminum
3003-0
467
711
Stainless Steel
302, Annealed
2722
4000
Table 2. Force Developed for Various Bellows Materials
Bellows
Material
Alloy and Temper
Actuation
Force
(lbs)
Target
Force
(lbs)
Aluminum
1100-0
2.64
4.02
Stainless Steel
302, Annealed
17.32
25.45
Table 3. NASA Lewis Calculation Results
Candidate Pyrotechnic
Formulation
Calculated Flame
Temperature
(K)
Normalized Mass
Required to
Produce 500 psi
Ti/KCI0 4
5006
1.00
Ti/KCI0 4 + RDX
4155
0.63
RDX + C
3083
0.67
B/BaCr0 4 /KCI0 4
3872
1.19
BKN0 3
4044
0.79
- 86
Table 4. Results of Initial Prototype Testing
Pyrotechnic
Material
Charge
Mass
(mg)
Ignition
Source
Maximum
Extension
BKNO3
6
Laser Diode
0.08
Ti/KCLCy
6
Laser Diode
Bellows
Burst
B/BaCr0 4 /KCI0 4
6
Nd:YAG
Table 5. Ignition Threshold Test Results Using 840 nm Diode
Test Results
No. of Tests
10
Threshold (50% Level)
536 mW
Standard Deviation
56 mW
All-Fire Level (.999/95%)
909 mW
- 87 -
Figure 1 Minature Laser Ignited Bellows
- 88 -
. Donor Fiber Optic
^ r^
1
\
It
. Acceptor Fiber Qptic
, Foan Block
.Bellows Extension
Figure 2 Force and Velocity Test Setup
- 89 -
Figure 3 Force Output Test Results
- 90 -
0.012
0.011
^.^
o
0)
f/1
0.01
**■•<■•,,,
E
0.009
E
**— *
^
0.008
o
O
(D
0.007
>
(D
O)
(0
0.006
<D
3
0.005
"D
0)
0.004
8
0)
0.003
2
0.002
0.001
Ligh t Leak
Figure 4 Results of Velocity Tests
- 91 -
- 92 -
PERFORMANCE CHARACTERISTICS OF A LASER-INITIATED
NASA STANDARD INITIATOR
John A. Graham
Senior Project Engineer
The Ensign-Bickford Company
Aerospace and Specialty Products
698%
INTRODUCTION
The Ensign-Bickford Company has been
actively involved in the design and
development of a laser equivalent to the
electrically initiated NASA Standard
Initiator (NSI). The purpose of this paper
is to describe the present design and its
performance characteristics.
Recommendations for advancement of this
program are also presented.
DESIGN DESCRIPTION
The Ensign-Bickford Laser-initiated NASA
Standard Initiator (LNSI) design consists
of an Optical Connector, Optical Fiber
and a Propellant that is hermetically sealed
in a Squib Housing (see Figure 1). The
LNSI is equivalent to the NSI, using the
NSI propellant and matching the
installation envelope so that it can be used
to function present NSI initiated devices.
A standard ST or SMA connector is used
and attached to the optical fiber with a pot
and polish technique. The present design
uses 200 micron Hard Clad Silica optical
fiber but is not limited to that size; larger
or smaller diameter fiber can be
incorporated if dictated by system level
requirements. The fiber is installed and
sealed into an optical header using Ensign-
Bickford proprietary fiber seal technology.
The Ensign-Bickford seal has demonstrated
hermeticity after exposure to a 40,000 psi
proof pressure; also hermeticity is
maintained post-function. This seal
technology has been successfully employed
in devices functioned from -62 °C to
+93°C (-80"F to +200°F) and has
successfully endured exposure to the same
level of thermal shock without
performance degradation.
The propellant is the NSI-defined blend of
Zirconium, Potassium Perchlorate,
Graphite and Viton "B". Powdered raw
materials are wet blended in a high shear
blender followed by application of Viton
"B" via a precipitation process. The mix
has been examined by Scanning Electron
Microscope and found to be uniform. The
blending process does not alter particle
morphology.
The optical fiber is polished in situ and dB
loss characteristics verified prior to
propellant loading. The propellant is in
direct contact with the exposed polished
fiber face thus allowing laser diode power
to reach the propellant without power
density loss due to beam divergence.
Hermetic sealing is provided by laser
welds. A closure disc is laser welded onto
the output end of the squib housing. The
disc has a chemical milled "flower pattern"
which "blossoms" when the device is
functioned. The flower pattern prevents
expulsion of large metallic particles from
the squib and into devices which would be
detrimental in some applications.
PAS.
kt; : ;?:.miy el
- 93 -
Two versions are available, one using a
stainless steel housing and another using
Inconel 718. In either design, the charge
cavity is proof pressure tested at 15,000
psi prior to loading propellant.
ALL-FIRE POWER
Reliability testing has been done to
establish the all-fire power requirement at
room temperature. Testing was done
using 200jim fiber. The "pass" criteria
was that the time from the start of the
laser pulse to first pressure had to be less
than or equal to 10 milliseconds, although
the actual laser diode pulse width was 50
milliseconds. The long duration pulse was
used to get a better characterization of the
relationship between power and time to
ignition (Figure 2). The 0.9999 all-fire
power at 95% confidence is 595
milliwatts. This corresponds to an all-fire
power density of 1900 watts/cm 2 .
LASER IGNITION TRANSIENT
THERMAL FINITE ELEMENT
ANALYSIS (FEA)
The reliability test data suggests that
ignition time repeatability is a function of
the laser power. At high laser power, the
function time (i.e. time to ignition) is short
and repeatable, but as power is decreased,
function time slows and is less predictable.
Transient FEA was done over a range of
input powers to gain a qualitative
understanding of this phenomena. The
computer model included the propellant,
fiber optic core/cladding, epoxy and
surrounding metal structure. Upon initial
application of laser energy, the heating
rate is high, but slows and asymptotically
approaches a limit that is a measure of the
LNSFs ability to reject heat to the
surrounding environment. If the
autoignition temperature of the mix is
reached quickly, then the function time
will be very repeatable because only the
propellant is heated and therefore only the
variability of the propellant comes into
play (eg mix homogeneity, density
gradient within the pressed powder, etc).
As the time to ignition increases, the
thermal effects of the surrounding
materials become significant. Sources of
variation include the amount of epoxy and
the concentricity of the optical fiber to the
ferrule. Conditions such as these increase
the variability of the thermal time constant
resulting in greater function time jitter.
This has system level implications. The
specification for the laser diode firing unit
pulse duration needs to balance the output
power of presently available laser diodes
versus the inherent increase of non-
repeatability of function time as the pulse
duration is lengthened to allow for lower
net laser diode power. Another way to
state this is function time jitter will be
minimized when the laser diode with the
highest output power is used. Also,
thermal isolation of the propellant from
surrounding materials will result in more
repeatable ignition and, therefore, lower
all-fire power level which in turn means
laser diode output power requirements are
reduced.
PRESSURE PERFORMANCE
For many NSI users, the interest is in
output pressure characterization since the
NSI is used as a cartridge to actuate
pressure driven devices (eg bolt cutters,
pin pullers, etc). The LNSI has
demonstrated a nominal output pressure of
654 psi over the last several lots of
LNSI's; within each lot, the Coefficient of
Variation has ranged from 3 to 5%.
- 94 -
Also of concern is the response time and
time to peak pressure. At 800 milliwatts
net power applied at the opto-propellant
interface, function times (i.e. time from
application of laser diode power to first
pressure) has been 1.5 milliseconds with a
Coefficient of Variation of 12%; time to
peak pressure has been 0.13 milliseconds
with a Coefficient of Variation of 20%.
This data is difficult to compare with the
NSI specification since requirements are
tied to the applied current level. What can
be said first of all is the energy source,
whether it be a hot bridge wire or a laser
diode, does not effect the pressure
performance of the NSI propellant.
Secondly, the pressure rise rate to 525 psi
can be inferred to be equal to or better
than the rise rate performance reported
above for attaining peak pressure.
Further, all of the NSI pressure-time
requirements at 3.5 amps can be met:
(1) Time to first pressure of greater
than 1.0 milliseconds
(2) Time to 525 psig shall not exceed
6.0 milliseconds
(3) Peak pressure shall be 525 to 775
psig
(4) Range of time to first pressure shall
not exceed 3.5 milliseconds
(5) Range of pressure rise from first
pressure to 525 psig shall not
exceed 0.5 milliseconds
Random Vibration will consist of 1
min/axis exposures to the level indicated
on Figure 3 .
Thermal cycle exposure will be from
-16°C to +56°C (3°F to 133°F) for a
total of 6 cycles with a 2 hours minimum
dwell at temperature.
The final two test groups will be used in
reliability tests to establish all-fire power
at hot and cold temperatures.
RECOMMENDATIONS FOR FUTURE
DEVELOPMENT
Further development of the LNSI is
needed to expand the performance
envelope. No problems are anticipated
from vibration due to the mechanical
similarities between the NSI and the LNSI.
The thermal environment does however
raise some questions regarding low
temperature performance of optical fibers.
A parallel task is to develop a specification
for an LNSI. Specific areas needing
attention are: (1) all-fire power and pulse
width, (2) no-fire power and pulse width
(which also requires credible stray light
sources to be identified and quantified)
and, (3) pressure versus time performance.
PLANNED TESTING
Development testing is on-going at Ensign-
Bickford. The next test series includes
exposure to random vibration and thermal
cycling along with high and low
temperature all-fire power reliability tests.
The requirements were customer driven
based upon satellite requirements. The
test matrix is shown in Table 1.
- 95 -
TTDd© Ensign-Bickford
LASER WELD
3 7 5-24 UNJ F - 3A
OPT I CAL
FIBER
OPT I CAL
HEADER
LASER WELD
PETAL L I NG
CLOSURE D I SC
NS I
PROPEL L ANT
SOU I B
HOUS I NG
TABLE 1-- FLIGHT READINESS TEST MATRIX
CO
00
Itest
GROUP
A
9 Units
B
9 Units
C
9 Units
D
9 Units
E
20 Units
F
20 Units
INSPECTION
•
•
•
•
•
•
THERMAL
CYCLE
•
•
RANDOM
VIBRATION
•
•
FUNCTION
High Temp
Ambient
Low Temp
3
3
3
3
3
3
3
3
3
3
3
3
20
20
Figure 2
LASER INITIATED NSI PERFORMANCE
200ji Optical Fiber Pigtail
Room Temperature Data
Function Time (msec)
Figure 3 — Random Vibration Spectrum
Q
u
&
L.
O
On
U. 1
H .
H
I
\
....
\
\
\
■-
\
n ni
\
1
U.U1
...
0.001 -
10
100
1000
10000
Frequency (Hz)
si- n
U^
Four Channel Laser Firing Unit Using Laser Diodes
David Rosner, Sr. Electrical Development Engineer
Edwin Spomer, Sr. Electrical Development Engineer
Pacific Scientific/ Energy Dynamics Division
ABSTRACT
This paper describes the accomplishments and
status of PS/EDD's internal research and devel-
opment) effort to prototype and demonstrate a
practical four channel laser firing unit (LFU)
that uses laser diodes to initiate pyrotechnic
events. The LFU individually initiates four ord-
nance devices using the energy from four diode
lasers carried the over fiber optics. The LFU
demonstrates end-to-end optical built in test
(BIT) capabilities. Both Single Fiber Reflective
BIT and Dual Fiber Reflective BIT approaches
are discussed and reflection loss data is present-
ed.
This paper includes detailed discussions of the
advantages and disadvantages of both BIT ap-
proaches, all-fire and no-fire levels, and BIT
detection levels. The following topics are also
addressed: electronic control and BIT circuits,
fiber optic sizing and distribution, and an
electromechanical shutter type safe/arm device.
This paper shows the viability of laser diode
initiation systems and single fiber BIT for typi-
cal military applications.
1. INTRODUCTION.
1.1 Purpose . This paper presents the accom-
plishments and status of Pacific Scientif-
ic/Energy Dynamics Division (PS/EDD) internal
research and development effort to prototype
and demonstrate a practical Four Channel Laser
Firing Unit (LFU) incorporating laser diodes. In
this program, PS/EDD is developing and de-
monstrating laser diode initiated safe/ami tech-
nology for commercial, space, and defense ap-
plications.
1.2 Design Goals . PS/EDD designed the LFU
as a Safe and Arm Device (SAD) shown in
Figure 1 for a typical missile application requir-
ing flight functions like stage separation, motor
ignition, and shroud removal. We designed it to
operate in typical missile environments.
EMI/EMP protection features, and systems for
built-in-test (BIT) of the optical and electronic
subsystems were incorporated. We chose a sim-
ple electronic interface using redundant elec-
tronic controllers that can be tailored to support
a more sophisticated interface.
As much as practical, we designed the LFU to
address the typical Military safety specifications
and guidelines for in-line SAD. The LFU uses
one electromechanical energy barrier in the opti-
cal path, several static switches in the arm and
firing circuits, and no mechanical barrier in the
ordnance train.
1.3 Typical Safety Requirements . Ordnance
subsystems must often meet certain documented
safety criteria. The following documents are
some of the specifications that can be applied to
ordnance subsystems in military and aerospace
systems:
• MIL-STD-1316D titled "Military Standard,
Fuze Design, Safety Criteria For"
• MIL-STD-1512 titled "Military Standard,
Electroexplosive Subsystem, Electrically
Initiated, Design Requirements and Test
Methods"
• MIL-STD-1576 titled "Military Standard,
Electroexplosive Subsystem Safety Require-
ments and Test Methods For Space Sys-
tems"
• MIL-STD-1901 titled "Military Standard,
Munition Rocket and Missile Motor Ignition
System Design, Safety Criteria For"
• WSERB Guidelines Titled "WSERB Tech-
nical Manual For Electronic Safety and
Arming Devices with Non-Interrupted Ex-
plosive Trains"
- 101 -
3.50
J2 Fiber Optic
Connector
J1 Control & Power
Connector
Figure 1. Four Channel Laser Firing Unit
Both MIL-STD-1316D and MIL-STD-1901
address interruption type and in-line ordnance
subsystems. The WSERB Guidelines specifical-
ly address in-line ordnance systems and are of-
ten specified in addition to MIL-STD-1316D
and MIL-STD-1901. However, these specifica-
tions do not directly address laser initiation sys-
tems. The LFU is designed to address these
requirements and guidelines as much as practi-
cal.
2. LFU OVERVIEW.
2.1 Introduction . The LFU uses laser diodes
and solid state electronics to initiate ordnance
devices via fiber optics. It contains a Laser Di-
ode Safe/Arm Module (LDSAM) to provide the
safety -reliability of a movable barrier or shutter.
It also contains a built-in test system that per-
forms an end-to-end test of the fiber optic.paths.
The size of the LFU shown in Figure 1 is
6.80 in. x 4.25 in. x 3.50 in. and it wfeighs 3.8 lb
excluding connectors and cables. The LFU is
equipped with MIL-C-38999 Class IV connec-
tors for both electrical and fiber optic interfaces.
The input power requirements are 28 Vdc at
0.4 Adc average and 3.6 Apeak for 10 ms when
firing a laser.
The input commands enter the LFU through Jl.
Each uses an opto-isolated pair of connections
that can be driven by 5 V TTL logic. The input
commands are:
• Master Reset Command resets the LFU log-
ic and starts operation in the selected
Test/Launch mode. This is essentially a
powerup reset without cycling power.
• Test/Launch Mode Command instructs the
LFU either to perform an automatic BIT
sequence (Test) or to execute the normal
operational sequence (Launch) after power-
up or master reset.
• Pre-arm Command energizes the Pre-arm
Switch Circuit to make electrical power ava-
ilable to the electronic switches for the high
power laser diodes and LDSAM arming
solenoid.
- 102 -
Arm Command energizes the Arm Switch
Circuit to power the LDSAM arming sole-
noid using power available via the Pre-arm
Switch Circuit.
Select 1, Select 2. and Select 3 Commands
act as a three bit code to select between the
four LFU outputs before each fire
command.
Fire Command commands the LFU to sup-
ply the high power laser pulse from the se-
lected output provided that the LFU is
armed.
The two output status signals, BIT Pass and BIT
Fail, exit the LFU through Jl. Each uses an
opto-isolated pair of connections providing an
electronic switch closure.
The four laser outputs exit the LFU through J2.
Each uses 100 nm core 0.37 numerical aperture
(NA) fiber and provides a 904 nm wavelength
10 ms pulse of approximately 1.0 watt.
2.2 LDSAM Characteristics . The LDSAM is
a 24 output electromechanical shutter assembly
with only four outputs fully assembled. It pro-
vides an optomechanical safety feature for ord-
nance initiation power. As show in Figure 2, all
critical optical elements in the LDSAM are rig-
idly mounted to eliminate misalignment in harsh
environments.
Shutter Aperture
High Power Laser
Collimating Lens
Alignment Collar
Fiber Optic
Focusing Lens
Figure 2. LDSAM Cutaway View
- 103 -
For each output, a rigidly mounted laser diode
and collimating lens illuminates a rigidly mount-
ed focusing lens and 100 ^m core fiber optic ca-
ble. An aluminum shutter, located between the
collimating and focusing optics, acts as an ener-
gy barrier. A solenoid rotates the shutter be-
tween Safe and Arm positions with a spring
loaded return to Safe.
An electro-optical sensor monitors the Safe po-
sition of shutter. Visual indication is provided
by a shutter driven flag and window. The flag is
labeled "S" for safe and H A H for Armed. A re-
movable safing pin locks the shutter into the
Safe position when installed.
2.3 Built-in-Test (BIT) System . The LFU also
contains a BIT system that performs the follow-
ing tests on the LFU subsystems;
Continuity of fiber optic paths between the
LFU and ordnance devices
Firing of high power laser diodes
Operation of Pre-arm circuits
Operation of LDS AM.
To develop an optimal design, PS/EDD investi-
gated two different approaches to performing
the optical continuity BIT. The LFU is
equipped with two channels of each type. They
are:
Single Fiber Reflective BIT . A low power
laser signal is sent to the ordnance device
through the same fiber optic used to initiate
that device. This signal reflects off the di-
chroic mirror deposited on the window in
the ordnance device and returns to the BIT
system through the same fiber optic. A pho-
todiode and electronic circuit measure its
intensity.
• Dual Fiber Reflective BIT . A low power
laser signal is sent to the ordnance device
using the same high power diode laser and
fiber optic used to initiate that device. The
output power of the high power laser diode
is limited to a level safely below the no-fire
level by an aperture in the shutter. A small
fraction of this signal reflects off the ord-
nance device window and returns to the BIT
system through a second fiber optic. The
BIT system uses a photodiode and electronic
circuit to measure the intensity of this refle-
ction.
2.4 Electronic Subsystem . The Electronic
Subsystem controls and sequences the BIT fea-
tures and the laser initiation system. It also in-
terfaces to other missile systems. The Electron-
ic Subsystem consists of the following elements
shown in the LFU Functional Block Diagram
(Figure 3):
• Input and Output Circuits
• Power Converters
• Redundant Controllers
• Pre-arm Switch Circuit
• Arm Switch Circuit
• High Power Laser Drive Circuit
BIT Laser Drive Circuit
BIT Sense Circuits
2.4.1 Input and Output Circuits . We used
optocouplers and transient suppressors for all
electronic input and output (I/O) signals. Each
input command enters the LFU through Jl and
uses an opto-isolated pair of connections that
can be driven by 5 V TTL logic.
Each output signal exits the LFU through Jl and
uses an opto-isolated pair of connections provid-
ing electronic switch closure. All electrical in-
puts and outputs, including power, are equipped
with semiconductor transient suppressors to
protect against electrostatic discharge (ESD) and
electromagnetic pulse (EMP).
2.4.2 Power Converters . The LFU is equipped
with two DC/DC power converters that provide
regulated sources of 5 Vdc for logic circuits, and
of 15 Vdc for the analog circuits and the BIT
lasers. Unregulated 28 Vdc provides power to
both DC/DC converters and to the Pre-arm Cir-
cuit. Note, the DC/DC Converters operate when
28 Vdc is present no matter whether the Pre-arm
Switch Circuit is open or closed.
The power returns for the 28 Vdc, 5 Vdc, and
15 Vdc sources are separately routed. They are
connected to the chassis at a single point
through 47 kfl resistors bypassed by 0.01 nF
capacitors. This minimizes cross talk between
the digital, analog, and laser fire circuits.
- 104 -
Channel Select Inputs
Pre-Arm Command
Arm Command
Master Reset
Launch/BIT Select Input
p/o Jl
BIT Pass Status
BIT Fail Status
Fiber Optic
Outputs to
Ordnance
Devices
Channel 1 Output
(Single Fiber BIT)
Channel 2 Output
(Single Fiber BIT)
Channel 3 Output
(Dual Fiber BIT)
Channel 4 Output
(Dual Fiber BIT)
Figure 3. LFU Functional Block Diagram
2.4.3 Redundant Controllers . PS/EDD chose
to use hard logic implemented with application
specific integrated circuits (ASIC) instead of
using microprocessors or stored program devic-
es. This choice eliminates the costs involved in
developing, debugging, and eventually qualify-
ing software.
Each Redundant Controller consists of a single
ACTEL brand factory programmable logic array
(FPGA). Both controllers are identical and op-
erate from a common clock. A common power-
up reset circuit resets the logic circuits in each
FPGA and initiates the automatic BIT testing of
the LFU.
The BIT logic circuit part of each FPGA is basi-
cally a string of latches fed by logic gates. This
forms a state machine that sequences through a
set of predefined steps. Each step sets the
FPGA's outputs to predefined levels and per-
forms a boolean logic test of all inputs. If the
test passes then the logic proceeds to the next
state, if it fails the logic indicates a BIT failure
and stops.
The fire control logic circuit part of each FPGA
consists of logic circuits to decode the channel
selection and fire commands originating form
outside the LFU. It also consists of timing cir-
cuits to control the duration of the High Power
Laser outputs.
105 -
Each FPGA monitors the following commands
originating from outside the LFU: Master Reset
Command; Test/Launch Mode Command; Pre-
arm Command; Arm Command; Channel Select
Inputs (Select 1, Select 2, and Select 3 Com-
mands); and Fire Command. Each FPGA also
monitors the following internal signals: Pre-arm
Switch Circuit monitor; Arm Switch Circuit
monitor; Safe position status of LDSAM; and
output of the Bit Sense Circuit.
Each FPGA generates the Bit Pass and Bit Fail
status commands for use by missile systems
outside the LFU. Each also generates com-
mands to arm the Arm Switch Circuit and to fire
High Power Laser Diode Drive Circuits. The
FPGA's command outputs are ANDed together
by the subsystems they control. In other words,
both FPGAs must issue identical output com-
mands before a subsystem uses that output
command. The BIT Fail status outputs are
ORed together so that either controller can issue
a BIT failure signal.
2.4.4 Pre-arm and Arm Switch Circuits . The
LFU uses unregulated 28 Vdc to energize the
LDSAM solenoid and to power the High Power
Laser Diodes. The unregulated power is first
routed through the Pre-arm Switch Circuit to
provide the first static switch function for arm-
ing and ordnance initiation power.
The Pre-arm Switch Circuit uses MOSFET
switches to switch both the +28 Vdc and 28 Vdc
return lines, and is commanded by the Redun-
dant Controllers through two series connected
optocouplers. This arrangement requires that
both Redundant Controllers issue the Pre-arm
command to turn on the Pre-arm Switch Circuit.
The Pre-arm Switch Circuit also provides a sin-
gle monitor signal to both Redundant Control-
lers through an optocoupler.
The switched +28 Vdc and 28 Vdc return out-
puts of the Pre-arm Switch Circuit is then routed
to the High Power Laser Drive Circuits and to
the Arm Switch Circuit.
MOSFET switches to control both the +28 Vdc
and 28 Vdc return lines, and to energize the
LDSAM solenoid. It is also commanded by the
Redundant Controllers through two series con-
nected optocouplers and provides a single moni-
tor signal to both Redundant Controllers through
an optocoupler.
2.4.5 High Power Laser Drive Circuit This
drive circuit consists of four individual
MOSFET switches to control each of the four
High Power Laser Diodes. These MOSFET
switches receive switched +28 Vdc power from
the Pre-arm Switch Circuit through a common
current regulator circuit. The current regulator
compensates for variations in the unregulated
28 Vdc power source and provides a constant
current to the High Power Laser Diodes. It is
designed to operate the lasers within their rated
power limits.
The MOSFET switches provide the second stat-
ic switch function for ordnance initiation power
and are controlled by the Redundant Controllers
through two series connected optocouplers. As
with the Pre-arm and Arm Switch Circuits, this
arrangement requires that both Redundant Con-
trollers issue the fire command to turn on a laser
diode.
2.4.6 BIT Laser Drive Circuits . This drive
circuit consists of two individual MOSFET
switches to control each of the two BIT Laser
Diodes used in the single fiber BIT system.
These MOSFET switches receive regulated
15 Vdc from the Power Converters through a
common current regulator circuit. The current
regulator provides a constant current to the BIT
Laser Diodes and operates the lasers within their
rated power limits.
The MOSFET switches are controlled by the
Redundant Controllers through two series con-
nected optocouplers. As with the High Power
Laser Drive Circuits, this arrangement requires
that both Redundant Controllers issue the fire
command to turn on a laser diode.
The Arm Switch Circuit provides the second
static switch function for arming power. It uses
2.4.7 BIT Sense Circuit This circuit supports
the optical continuity BIT function by sensing
- 106 -
the reflected light and by providing a simple
digital signal to Redundant Controllers. The
BIT Sense Circuit supports both Single and Dual
Fiber BIT systems, and consists of:
Photo diodes to sense the reflected BIT sig-
nals
• Analog circuits for amplification and level
detection
Optocouplers for output to the Redundant
Controllers
The sensitivity of the BIT Sense Circuit is limit-
ed by the photo diode's rated dark current while
the response time is limited by the photo diode's
total capacitance rating. In other words, the
optical BIT signal must be bright enough to be
reliably detected above the photo diode's worst
case dark current and must be present long
enough for the photo diode's capacitance to
charge up.
3. LASER DIODE INITIATION SUBSYS-
TEM.
3-1 Introduction . The basic mechanism for
laser ignition is thermal in nature. The laser
ignition system must deliver a sufficient intensi-
ty to raise the temperature of the ordnance com-
pound above its ignition temperature. This de-
pends on the properties of the ordnance com-
pound such as: ignition temperature, thermal
diffusivity, specific heat, surface optical
properties, and particle size.
The Laser Diode Initiation Subsystem uses con-
tinuous type lasers that are typically rated in
watts. For this reason, it is best to specify the
all-fire and no-fire levels in units of power
(milliwatts) instead of units of energy
(millijoules). Since the all-fire and no-fire lev-
els depend on spot size, the type of fiber used to
deliver the laser energy to the ordnance device
must be specified.
For this design we used a 100 ^m core step in-
dex fiber optic inside the LFU and 1 10 ^im core
step index fiber for the external cables. This
conserves the intensity of the laser diode as it is
delivered to the ordnance device.
The optical path starts with a 920 nm wave-
length High Power Laser Diode coupled to a
collimating lens and mounted in the LDSAM,
shown in the Initiation Subsystem Functional
Block Diagram Figure 4. The collimated laser
light passes through the LDSAM shutter and is
refocused into a 100 nm fiber using another lens
in the LDSAM. For channels one and two, the
coupler is the next item in the optical path. Fi-
nally the J2 connector on the LFU is the last
item in the optical path. Table 1 lists the typical
output delivered to an ordnance device through
the external 110 nm cables.
3.2 Requirements . There are no established
industry-wide all-fire and no-fire standards for
laser ordnance. However, PS/EDD has designed
several diode initiated devices. As an example,
we designed and manufactured a miniature pis-
ton actuator that had a 320 raw all-fire and a
130 mw no-fire using 1 10 ^m diameter fiber.
We used these levels as a guide in developing
the LFU.
This actuator used titanium potassium
perchlorate for the ignition/output charge and
incorporates a fiber optic pigtail. A Neyer sta-
tistical analysis was used to determine the all-
fire and no-fire levels. Table 2 shows the test
data from the Neyer test performed on the piston
actuator. The power levels listed in the table
were measured prior to each test shot using the
fiber that connects to the pigtail of the device.
3.3 Design Trades . The main goal in designing
the LFU is to maximize the efficiency of deliv-
ering power to the ordnance devices. This usu-
ally requires selecting a fiber optic cable with
the smallest diameter practical and usually be-
comes a trade between launch efficiency and
spot size. In other words, one must select a
combination of laser diodes and fibers that sup-
ply the largest power per unit area. Minimizing
the quantity of connector interfaces is another
design goal.
In designing ordnance devices, the main goal is
to minimize the spot size at the ordnance com-
pound while meeting other requirements like
cost, proof pressure, and sealing. Fiber optic
- 107 -
Table 1. Measured LFU Output
Output
Channel
Typical
Output
Power
Margin
(based on
320 mw all-
fire)
1
27.1 dBm
(517 mw)
162%
2
26.6 dBm
(452 mw)
141%
3
27.0 dBm
(500 mw)
156% |
4
26.8 dBm
(482 mw)
151%
cables emit light in a diverging cone that causes
the spot size to grow with distance. To mini-
mize the spot size, the ordnance device must
either put a fiber in contact with the ordnance
compound or use optics to refocus the spot onto
the ordnance compound. Plane parallel win-
dows are not typically used in devices initiated
by laser diodes. However, a gradient index
(GRIN) lens or an integral fiber can efficiently
couple a fiber's output to the ordnance com-
pound.
3.4 Outnut Tests . We measured the LFU out-
puts at the ordnance end of external 1 10 nm
cables. The results are listed in Table 1. Note,
the LFU can delivers sufficient laser intensity to
initiate ordnance devices with 141% to 162%
margins above an 320 mw all-fire requirement.
This margin means that the LFU operates from
4.3 to 6.4 times the 30.7 mw sigma over the
0.999 reliability all-fire level shown in Table 2.
Table 2. Neyer Analysis of Laser Initiated Pis-
ton Actuator
Stimulus in
milliwatts
Successes
133.0
172.0
190.0
213.0
1
241.0
243.5
279.0
289.0
298.0
460.0
Note:
The Mu was 222.9 mw with a sigma of
30.7 mw. The calculated 0.999 all-fire
level is 317.8 mw and the 0.001 no-fire
level is 128.1 mw.
- 108 -
r
Laser Firing Unit
l
High Pwr
Laser Drive
Circuit
High Pwr
Laser Drive
Circuit
fO
Safe
30
Channel 1
Channel 3
Channel 4
(same as Channel 3)
Shutter in
Arm T u Arm Position
Laser Diode S/A Module
l
Figure 4. Initiation Subsystem Functional Block Diagram
J2
Connector at
Ordnance Device
All-Fire
Power
Connector at
Ordnance Device
All-Fire
Power
J
4. SINGLE FIBER BIT SUBSYSTEM.
4.1 Introduction . The Single Fiber BIT Sub-
system is meant to detect broken fiber optics or
mismated and contaminated optical connections.
Each Single Fiber BIT channel consists of fol-
lowing elements shown in Figure 5:
• A 1.0 mw BIT Laser Diode operating at
780 nm wavelength
A fiber coupler that has three inputs and one
output
A common BIT Sense Circuit to detect the
reflected optical BIT signal.
• An ordnance device with a dichroic coating
on the window that reflects 780 nm wave-
length light.
The Optical Coupler provides paths for injecting
the BIT laser signal into the output fiber and for
extracting the return signal from the output fi-
ber. The three inputs of the coupler are connect-
ed to the High Power laser diode, BIT laser di-
ode, and the BIT photodiode.
During Single Fiber BIT operation, the LDSAM
is in the safe position with the output of the
High Power Laser Diodes blocked by the closed
LDSAM shutter. A BIT laser is fired to provide
a low power laser pulse to illuminate the ord-
nance device through the single output cable.
The dichroic coating on the ordnance device
window reflects 90% of the BIT laser output
back to the LFU through the same cable. The
fiber coupler directs this reflected signal to the
BIT Sense Circuit.
4.2 Requirements . To keep with the spirit of
the monitor circuit requirements of MIL-STD-
1516, the power of the BIT signal should be
kept 20 dB below the rated no-fire of the ord-
nance device. Note, MIL-STD-1516 para-
graph 5.10.7 limits the monitor current for
electroexplosive devices to one tenth of the no-
fire level. This corresponds to a one hundredth
factor for power or a margin of 20 dB.
- 109 -
F
BIT
Sense
Circui
7>
it —J
BIT Laser
[
Ci
IT Laser "IL
Drive \l
Circuit — '
780 nanometer
High Pwr
Laser Drive
Circuit
920 nanometer
L
Laser Firing Unit
~i
J
Safe
I V Optical
I ^^ 4 ^Coupler
J2
- Shutter in
Safe Position
Arm T
Laser Diode S/A Module
SMA Connector
Connector at
Ordnance Device
J
Figure 5. Single Fiber BIT Subsystem Functional Block Diagram
The BIT Laser Diodes are rated at 1.0 mvv
which is 21 dB below the no-fire level of
130 mw. This 1.0 mw output is attenuated by
the 1 1 dB loss in the coupler and the coupling
loss to the fiber. In other words, the laser inten-
sity at the ordnance device is at least 31 dB be-
low the no-fire level of 130 mw or 12 dB lower
than the MIL-STD-1516 requirement. Note, this
does not include the losses associated with the
connectors (typically 0.7 dB to 1.5 dB loss per
connector) and with the dichroic coating (10 dB
loss i.e. it passes 10% at 780 nm).
4.3 Design Trades . Unwanted reflections are
the main limiting factor for the Single Fiber BIT
system. These are caused by the connectors in
the optical path and by the coupler's internal
reflections. These reflections are sensed by the
BIT Sense Circuit and appear as background
noise that the BIT reflection must over come.
For connectors, the fresnel reflection at each
glass-to-air interface is 4.0% of the incident
light. The intensity of the coupler's internal
reflections are approximately 25 dB below (or
0.32% of) the BIT Laser intensity. The main
design trade is to optimize the coupler design to
minimize reflections while still providing an
adequate optical path for initiation energy.
4.4 BIT Tests . We performed some testing to
detenu ine the reflection losses that we can ex-
pect at the ordnance device during Single Fiber
BIT. A mirror and GRIN lens simulated the
ordnance device with dichroic coating. A
1 10 um fiber optic with an SMA connector was
routed from the LFU and mated with the GRIN
lens/mirror combination. Using an optics bread-
board we could vary the gap distance between
the SMA connector and the GRIN lens. Using a
HeNe laser in place of the BIT laser diode, we
measured the reflection loss for a variety of
gaps. Figure 6 is a plot of the relative loss vers-
es gap distance. The loss values are referenced
to the BIT output intensity of the LFU.
As Figure 6 shows, there is a 1.5 dB dynamic
range for discriminating between pass and fail.
However the intensity of the reflection is only
about 22 dB to 24 dB below the LFU's BIT out-
put. In the spirit of MIL-STD-1516, the BIT
reflection could be as bright as 44 dB below the
rated no-fire of the ordnance device. This could
be as much as 5.2 jiw for a system using
130 mw no-fire ordnance devices. Silicon
photodetectors have a typical sensitivity of
0.5 nA/jiw and would generate a 2.6 \iA signal
that is easily detectable.
- no -
-22
-22.2
CD £
"D ti
</> o
-22.4
</)
O 3
—I u.
-22.6
sz ->
"co 2
-22.8
C CD
.2 g
-23
o <u
© a5
-23.2
a> <5
a: oc
-23.4
-23.6
0.00 100 2.00 3.00 4.00
Gap between Fiber & GRIN/Relfector Combination (mm)
5.00
Figure 6. Reflection Loss Verses Gap Distance for Single Fiber BIT
5. DUAL FIBER BIT SUBSYSTEM.
5.1 Introduction . The Dual Fiber BIT Sub-
system is meant to detect mismated and contam-
inated optical connections. It uses two separate
fibers from the LFU that are terminated together
in the connector that mates with the ordnance
device. One fiber connects to a LDSAM output
while the other connects to a PIN diode
photodetector in the BIT Sense Circuit as shown
in Figure 7.
During BIT, the LDSAM is in the safe position
and a high power laser diode is fired to provide
a low power laser pulse to illuminate the ord-
nance device. Note, the output power of the
high power laser diode is limited by an aperture
in the shutter. A small fraction of this signal
reflects off the ordnance device and returns to
the BIT Sense Circuit through a second fiber op-
tic.
We wanted to minimize costs by making the
ordnance interface simple fabricate. The cable
interface at the ordnance device consists of an
SMA type fiber optic connector with two fibers
bonded side-by-side and polished. The fiber
core diameter was 1 lO^im with an overall diam-
eter of 125 nm, and a numerical aperture (NA)
of 0.37.
5.2 Requirements . To keep with the spirit of
the monitor circuit requirements of MIL-STD-
1516, the power of the BIT signal should be
kept 20 dB below the rated no-fire of the ord-
nance device. Note, MIL-STD-1516 para-
graph 5.10.7 limits the monitor current for elect-
roexplosive devices to one tenth of the no-fire
level This corresponds to a one hundredth fac-
tor for power or a margin of 20 dB.
The High Power Laser Diodes have a 13 dB
dynamic range from 0.1 W at threshold to a
maximum of 2.0 W. This dynamic range is not
large enough to use current limiting alone to
reach the 20 dB safety margin. Therefore a
shutter with either an aperture or other type of
optical attenuator was required. We found that
an aperture of about 0.005 in. provides 27 db to
30 dB of attenuation.
- in -
r
Laser Firing Unit
High Pwr
Laser Drive
Circuit
£
\
BIT
Sense
Circuit
■> BIT Aperture
- Shutter in
Safe Position
Arm T
Laser Diode S/A Module
J2
3q
SMA Connector
Connector at
Ordnance Device
I
Figure 7. Dual Fiber BIT Subsystem Functional Block Diagram
5.3 Design Trades . The main design trade for
a Dual Fiber BIT systems is cost verses the in-
tensity of reflected signal. For example, we
could have used a coupler, a separate BIT laser
operating at 780 nm, and a dichroic coating on
the ordnance device. This would have increased
the reflected signal however the system cost and
configuration are very similar to the Single Fi-
ber BIT configuration. Alternately, we could
have complicated the ordnance interface to im-
prove the intensity of the reflected signal. How-
ever this would significantly increase the cost of
the ordnance devices.
For our low cost approach, the critical design
trade is to maximize the reflected BIT signal
while providing adequate initiation power.
Figure 8 shows the ray diagram associated with
a pair of fibers up against a reflector. The re-
flecting surface represents the ordnance com-
pound and fresnel reflections from and imaging
optics associated with a practical ordnance de-
vice. Unlike the single fiber BIT approach, di-
chroic coatings can not be used since this ap-
proach uses the same laser for BIT and initia-
tion.
As mentioned in section 3.3, any laser diode
initiated ordnance device would use optics be-
tween the fiber and the ordnance compound to
re-image the laser spot while providing a seal.
Ideally, the net effect of such optics would be
the same as not having any optics. For simplici-
ty, Figure 8 does not show any re-imaging op-
tics.
The bottom fiber illuminates the reflector while
the top fiber gathers the reflected light. Both
fibers emit or accept light in diverging 43.4 de-
gree cones that overlap at the reflecting surface.
The intensity of the reflected BIT laser signal is
directly effected by this overlap area and by
reflectivity of the ordnance compound.
Note that the area of this overlap varies with the
gap between the reflector and the fiber ends.
For a given set of fiber core diameters and fiber
spacing, there is a range of usable gaps with
specific minimum and maximum gap distances.
One can expect the intensity of the reflected BIT
to increase with gap distance to a peak value and
then decrease with larger gap distances. To
avoid the ambiguity of having an intensity value
indicate two different gap distances, a designer
would select a gap that is ate or beyond the
peak.
- 112 -
.110 mm core dia
0.125 mm overall dia
NA=0.37
Half angle - 21.72 deg
Acceptance &
radiation angle
determined by NA
Reflecting surface
Acceptance &
radiation angle
determined by NA
Usable range for
Reflecting surface
Figure 8. Dual Fiber BIT Sense Geometry
As mentioned in section 3.1, any gap in the
fiber-to-ordnance interface increases spot size
requiring more all-fire power from the High
Power Laser Diodes. With this type of fiber
geometry, one must select the BIT laser, fiber
size, and ordnance interface geometry to maxi-
mize the reflected BIT signal while providing
adequate initiation power for the resulting spot
size.
5.4 BIT Tests . We performed some testing to
determine the reflection losses that we can ex-
pect at the ordnance device during Dual Fiber
BIT. A flat black surface and GRIN lens simu-
lated the ordnance device. A pair of 1 10 \xm
fibers were terminated in an SMA connector
mated with the GRIN lens/black surface combi-
nation. One fiber was routed from a HeNe laser
to simulate the LFU's BIT output and the other
fiber was monitored by an optical wattmeter.
Using an optics breadboard we could vary the
gap distance between the SMA connector and
the GRIN lens. Figure 9 is a plot of the relative
loss verses gap distance. The loss values are
referenced to the output intensity of the LFU.
The loss curve starts at a low level, peaks at -
25 dB, and the gradually drops to -40 dB. Note
that losses between -25 dB to -40 dB correspond
to two different gap values.
As discussed in section 5.3, the selected fiber
geometry has a range of usable gaps with specif-
ic minimum and maximum gaps. The effect of
the minimum gap can be seen in the steep rise
while the effect of the maximum gap is seen in
the curve's fall.
However, one would expect a steeper fall than
shown. We believe that the gradual drop is
caused by reflections from the test setup. Simi-
lar reflections might be expected from a connec-
tor that is partially mated to an ordnance device
with its clean reflective connector interface. In
any case, the such reflections effect the sensitiv-
ity of this BIT approach.
As Figure 9 shows, there is a 15 dB dynamic
range for discriminating between pass and fail.
However the intensity of the reflection ranges
from 26 dB to 40 dB below the LFU output. In
the spirit of MIL-STD-1516, the BIT reflection
could be as bright as 46 dB to 60 dB below the
rated no-fire of the ordnance device. This could
be as much as 3.3 nw to 130 nw for a system
using 130 mw no-fire ordnance devices. Silicon
photodetectors have a typical sensitivity of
0.5 nA/nw and would generate a 1.7 \xA to
65 nA signal that is not easily detectable.
- 113 -
f^&s?.
co O ou
O 3
.c -■
ection P<
fenced 1
D C
1
5= OJ ^
0) 0)
or rr
-60 h
i i I i
i i i i
i i i i
i i i i
i i i i
0.00
1.00
2.00
3.00
4.00
5.00
Gap between Fiber & GRIN/Black Relfector
Combination (mm)
Figure 9. Reflection Loss verses Gap Distance for Dual Fiber BIT
6. SUMMARY .
6.1 Conclusions . With this effort, PS/EDD is
demonstrating a viable laser diode based initia-
tion system that uses Single Fiber BIT and a
high degree of automatic operation. The LFU
delivers sufficient laser power with 141% to
162% margins above an 320 mw all-fire require-
ment. This margin is 4.3 to 6.4 times the
30.7 mw sigma over the 0.999 reliability all-fire
level shown in Table 2. PS/EDD is demonstrat-
ing a workable Single Fiber BIT System that
requires only one fiber per ordnance device for
both initiation and BIT.
two different wavelengths and dichroic coatings
on the ordnance devices.
6.2 What's Remains . In general, PS/EDD
plans to apply this technology to simpler and
lower cost units. We will perform some envi-
ronmental testing on LDSAM and BIT verifica-
tion tests of the Single Fiber BIT system. In
future laser diode initiation systems we will
reselect laser diodes to take advantage of the
newer high power lasers that have are now
available. In future Single Fiber BIT Subsys-
tems we will update the coupler design to fur-
ther reduce internal reflections.
Our aggressive approach to Dual Fiber BIT is
proving to be unsuitable for diode based initia-
tion systems. For simplicity, we used an
extremely simple fiber-to-ordnance device inter-
face that requires a gap to obtain reasonable BIT
return signals. This gap degrades the delivery of
initiation energy. Our approach, is better suited
for solid state laser initiation systems that use
- 114 -
QMir
LIO Validation on Pegasus
(Oral Presentation Only)
Arthur D. Rhea
The Ensign-Bickford Company
Simsbury, CT
- 115 -
5lO-'2fc
EBW'S AND EFI'S
THE OTHER ELECTRIC DETONATORS
RON VAROSH
RISI
INTRODUCTION
Exploding BridgeWire Detonators (EBW)
and Exploding Foil Initiators (EFI)
which were originally developed for
military applications, have found
numerous uses in the non-military
commercial market while still retain-
ing their military uses.
While not as common as the more
familiar hot wire initiators, EBW s
and EFI's have definite advantages in
certain applications. These advan-
tages, and disadvantages, are dis-
cussed for typical designs*
HISTORY
EBW 1 s were invented in the early
1940' s by Luis Alvarez as part of the
Manhattan project ( 1 ) . Alvarez ' s in-
sight was to use a rapidly discharg-
ing capacitor to fire a hot wire
detonator and thus obtain the re-
quired simultaneity for a nuclear
device. Further research showed that
this "exploding wire concept" could
also be used to initiate secondary
explosives such as PETN and RDX. The
concept remained classified for many
years until a patent was issued in
1962 to Lawrence Johnston, one of
Alvarez ' s co-workers . These detona-
tors were studied and used extensive-
ly by the former Atomic Energy Com-
mission. Although many of these
studies have never been declassified,
a good sampling of what was learned
was published in the proceedings of
the Exploding Wire Conferences (2).
Of particular interest in these
conference proceedings are many of
the reports of T.J. Tucker , especial-
ly his formulation of the "action"
concept (3) . The "action" concept
remains the basis for the design and
evaluation of both EBW's and EFI's*
EFI ' s (or slappers as they are fre-
quently called) were invented by John
Stroud of Lawrence Livermore National
Laboratory in 1965 (4) . In a report
on the acceleration of thin plates by
exploding foils, Stroud noted that
the pressures produced by these
"slappers" appeared to be sufficient
to initiate high density secondary
explosives*
DEFINITIONS OF EBW'S AND EFI'S
The same basic definition can
applied to both EBW's and EFI's.
be
An EBW (or EFI ) is an all
secondary explosive detonator
that requires a unique, high
ampl itude , short duration
electrical pulse for proper
functioning.
Both EBW's and EFI's require a unique
high amplitude electrical pulse, and
each contains only secondary explo-
sives. The differences are that the
explosive in an EBW is directly
against the bridgewire and is usually
at 50% of crystal density. The
explosive is "believed" to be shock
initiated by the exploding wire. In
an EFI, the exploding foil acceler-
ates a disc across a gap and the high
density explosive ( 90% crystal densi-
ty) is initiated by the kinetic
energy of the flying disc . For the
EFI , the explosive is not in direct
contact with the exploding foil.
WHY BOTHER?
These electric detonators appear to
be so much more complicated than
- 117 -
PAGE
likwiHTC:-
simple hot wire devices, that the
question must be addressed as to why
bother with this added complication?
Three major reasons why people bother
with EBW's and EFI ' s are:
Safety
Repeatability
Reliability.
Safety comes primarily from the fact
that no primary explosives are used
in either device. Both are electro-
statically safe as demonstrated by
the "standard man test (5). Nominal
values of RF are also not a problem
(6). Stray currents do not affect the
devices since approximately 3 amps DC
are required to melt open a common
type bridgewire and about 5 amps to
open a typical foil.
The second major reason for using
EBW's and EFI ' s is their excellent
shot to shot repeatability. Even
with different firing systems, shot
to shot repeatabilities under 5
microseconds are easily obtained.
Finally for applications where simul-
taneity is a requirement, both EBW's
and EFI's are easily fabricated with
standard deviations under 25 nanosec-
onds.
APPLICATIONS
Following are some of the applica-
tions where EBW' s and EFI ' s have
found substantial acceptance:
nize cameras, flash X-Rays, etc. with
detonations makes good use of the
inherent repeatability of EBW s and
EFI's. Much of the explosive welding
is performed on-site to electric
power plant boilers - a location
notorious for stray voltages. Not
only is the safety important here,
but in addition many of the welds
require the simultaneous detonation
of two charges. Safety is the prim-
ary requirement for the majority of
the other applications . Mining
applications are limited since most
mining requires "ripple" firing -
something extremely difficult to
accomplish with either EBW 1 s or
EFI's.
EBW CONSTRUCTION
Figure 1 shows a typical EBW detona-
tor and compares it with a typical
.VT77Z
1-HEAD
2-BRIDGEWIRE
3-INITIAL PRESSING
4-OUTPUT PELLET
HOT-WIRE
Plastic
Hi-resist
Lead Azide
PETN/RDX
E9W
Plastic
Lo— resist
PETN
PETN/RDX
Figure 1. Typical Bridgewire Detonators
Military Ordnance
Military R&D
Explosive Welding
Explosive Hardening
Seismic
Oil Fields
Forest Service
Mining
Power Plants
Military Ordnance is an obvious
application, although most conven-
tional weapons still use hot wire
initiators. The reverse is true with
Ordnance R&D. The need to synchro-
hot wire detonator. Heads and output
pellets are the same for both detona-
tors. The major differences are in
the bridgewires and initial press-
ings. EBW's generally use gold or
platinum wires, primarily for their
inertness, while hot wire devices use
high resistance materials such as
Nichrome. The explosive against the
bridgewire in an EBW is generally
PETN although RDX and "thermites"
have been used . Hot wire devices
generally have Lead Azide or Lead
Styphnate against the bridge wire.
- 118 -
In addition, the explosive in an EBW
is generally at about 50 percent of
crystal density. In the EBW, the
"explosion" of the wire starts a
detonation without any intervening
deflagration as is the case with a
hot wire detonator.
SAFETY DATA
Since EBW's have been around for
almost 50 years a great deal of test
data has been accumulated by various
organizations . Everyone has an opin-
ion on which safety tests are most
important, but the US Forest Service
is probably the most imaginative. In
their testing, which was conducted
for them by China Lake (7), detona-
tors were subjected to the following
"potential" hazards:
110 vac, 60 cycle
220 vac, 60 cycle
12 vdc battery
truck ignition coil
camera flash unit
chain saw magneto
campf ire.
In all the above testing, all detona-
tors dudded and none detonated .
These are obviously hazards which
they believe could occur in their
work areas.
The National Laboratories at Los
Alamos , Sandia and Livermore have
performed the most design studies on
both EBW's and EFI ' s and obviously
have the most test data on these
devices.
The length of the narrow section is
approximately equal to the width i.e.
about 0.008 inch long.
Tamper
Bridge Foil
Dielectric
Barrel
H E Pellet
Figure 2. EFI Major Components
The dielectric flyer is usually
polyimide, .001 inch thick, but other
materials have been used.
The barrel is usually a dielectric,
but a conductor could also be used.
If the diameter of the barrel hole
equals the length of the narrow
bridge foil length (0.008 inch), the
design is called a "finite barrel
design" . If the diameter of the
barrel hole is 2+ times the narrow
bridge foil length, the design is
called an "infinite barrel design".
EFI CONSTRUCTION
Figure 2 illustrates the major com-
ponents of an EFI . Tampers can be
any rigid dielectric material : plas-
tics , metals , sapphire , etc . have all
been used successfully. Next comes
the bridge foil. These may be any
conductor . Copper and aluminum are
the most common. Thicknesses are
usually about 0.0002 inch thick. The
thinnest width nowadays is about
. 008 inch wide , although previously
foils as wide as 0.025 were used.
The above four components are lami-
nated into one sub assembly, and
clamped against a high density explo-
sive pellet - usually HNS.
In operation, for the finite barrel
design, a high current explodes the
narrow section of the bridge foil,
which shears out a disc of dielectric
which accelerates down the barrel and
by means of kinetic energy initiates
the high explosive pellet. An infi-
nite barrel design works exactly the
- 119 -
same way except the rapid expansion
of the dielectric "bubble" is the
source of the kinetic energy.
Both, EBW bridgewires and EFI foils
"explode" because the electric cur-
rent is heating the conductor which
is trying to expand , but the conduc-
tor is being heated faster than it
can physically expand,
FIRING CIRCUITS
A typical firing circuit for either
EBW s or EFI ' s is shown in Figure
3. The circuits are similar except
SWITCH
r
W BLEED <
INPUT RESISTOR <
L
HIGH VOLTAGE
CAPACITOR
y EBW/BF1
TRIGGER s.
INPUT ^
TRIGGER
BUFFER
I
such as:
batteries
line voltage
piezoelectric generators
fluidic generators
etc.
Most circuits also have "safety" type
features such as bleeder resistors to
discharge the capacitor in case of an
aborted test , features to prevent
repetitive firing, etc.
TYPICAL CURRENT TRACES
Figure 4 shows typical current traces
through a bridgewire and a foil .
Exploding BridgeWire
Current Trace
Time, microseconds
Figure 3. Typical EBW/EFI Firing Circuit
EFI ' s tend to use lower ca-
pacitance values (0.1 microfarad)
because of their requirement for low
low inductance while EBW's usually
use about 1.0 microfarad. The low
inductance is necessary to "explode"
the foil rapidly enough to accelerate
the flyer to a high enough velocity
to initiate the explosive.
Exploding Foil Initiator
Current Trace
- Pofnt of Bu vt
1 2
Time, microseconds
Figure 4. Typical Current Traces
A wide variety of switches have been
used for both EFI's and EBW's. These
have included:
overvoltage switches
vacuum triggered switches
gas filled triggered switches
solid state switches
crush switches
etc.
Power supplies have included systems
Both work exactly the same way.
Current flows through the device,
when the bridge starts to heat the
resistance increases and the current
falls. At the inflection point,
burst occurs and an arc is created.
The arc being of lower resistance,
allows the current to recover.
Burst occurs when a constant action
(integral of current squared, from
zero to burst time) is accumulated.
- 120 -
Also, the current at threshold is
constant regardless of circuit param-
eters whereas the threshold voltage
varies with circuit parameters.
Burst, preferably should occur at
about 1 microsecond for an EBW, and
. 1 microsecond for an EFI . Longer
times allow the wire or foil to melt
open before exploding.
EXPLOSIVES
Most EBW • s use PETN which has a
reasonable threshold firing current
(200 amps) . RDX has a significantly
higher threshold firing current (450
amps) but is frequently used where
higher operating temperatures are
required. These threshold firing
currents work out to be 500 and 800
volts respectively on a 1 microfarad
capacitor. EBW's (and EF^s) can
also shock initiate (?) "Thermites"
to produce an initiator with a defla-
grating output (8). Other explosives
tested to date with EBW's have too
high a threshold voltage to make a
reasonable system (above 5000 volts
on a 1 microfarad capacitor).
CD
s
o
-C
(0
<D
JZ
H
LU
u
P8X-9407
MS
+
Q
PON
J I I L
J I I L
0.1 0.2 OJ 0.4 Oi Q.8 0.7 U 0.9
Drop Hammer Height
Figure 5. EFI Threshold vs Drop Hammer
MIL-STD-1316 which covers the safety
criteria for fuzes and Safety and
Arming Devices applies to all muni-
tions except:
EFI's can initiate just about any
explosive although PETN and HNS have
acceptably low thresholds (9). PETN
is frequently chosen as a "weak link"
in an explosive train because of its
ability to sublimate away at moderate
temperatures and dud the weapon
system* Most DOD systems use HNS for
two major reasons - its relatively
low threshold and its acceptability
by MIL-STD-1316.
Figure 5 shows one of the main rea-
sons why HNS is so popu 1 ar as an
initiating explosive for EFI's.
Plotting EFI threshold voltage versus
a measure of explosive sensitivity
such as Drop Hammer Height shows most
explosives following a straight line
(PETN-RDX-PBX9407) . HNS does not
follow the same general trend.
Instead it is quite insensitive as
indicated by its large drop height,
but still has a low threshold to EFI
initiation.
Nuclear Weapons
Hand Grenades
Flares
Manually emplaced ordnance
Pyrotechnic countermeasures .
For an in-line device, the only
permissible explosives are: ,
Comp A3
Comp A4
Comp A 5
Comp CH6
PBX 9407
PBXN-5
PBXM-6
DIPAM
HNS Type 1
HNS Type 2
HNS-IV.
Note that PETN is not an acceptable
explosive. Of the listed explosives,
HNS appears to be the best choice for
an in-line device.
- 121 -
ELECTRIC DETONATOR COMPARISON
Table 1 compares some of the electri-
cal characteristics of three differ-
ent types of electric detonators.
Hot Wire EBW
Current
Threshold 1 amp
Operating 5 amps
Voltage
Threshold 20 volts
Energy
Threshold 0.2 joule
Power
Threshold 1 watt
Function Time
Typical 1 millisec.
200 amps
500 amps
500 volts
0.2 joule
100,000 watts
1 microsec.
EFl
2000 amps
3000 amps
1500 volts
0.2 joule
3,000,000 watts
0.1 microsec.
Table 1. Electric Detonator Comparison
The values listed are nominal and ob-
viously detonators have been built
with lower energy and power require-
ments, but the comparison is still
useful*
For the EBW, values assume a 1 micro-
farad capacitor while a .15 microfar-
ad is assumed for the EFI. The 1 amp
1 watt hot wire device is what is
generally required for DOD devices
although detonators with an all fire
current of 50 milliamps have been
fabricated (10).
Of particular interest, is the fact
that all the energy values are ap-
proximately equal. This implies that
the same physical size fire set can
be used for all three types of deto-
nators. The major difference between
the three detonators is the power.
The higher power levels of the EBW's
and EFI ' s are related to the very
short energy spike associated with
these devices. A typical bridgewire
burst time is 1 microsecond for an
EBW and 100 nanoseconds for an EFI.
The equality of the energy has been
utilized in a recently developed
"Power Multiplier" which takes the
energy output of a normal capacitive
hot wire firing unit and steps up the
power to fire an EBW (11).
SUMMARY
Both EBW's and EFI's tend to have
definite advantages where safety,
reliability and repeatability are
required but EFI ' s have a clear
advantage in being able to initiate
HNS and PBX-9407 and thus are Mil-
Std-1316 acceptable.
As disadvantages , both tend to be
more expensive than hot-wire blasting
caps, but this is primarily because
of the limited manufacturing base.
Blasting caps are manufactured in the
10 ■ s of millions annually while the
total annual fabrication of EBW's is
about 100,000. Only about 10
20,000 EFI's are currently manufac-
tured annually in the US.
Two other major disadvantages of
EBW's and EFI's, are the small number
of detonators which can be fired per
shot and the difficulty in delaying
individual detonators . The ability
to delay individual detonators is
very important in the mining industry
where "ripple" firing is necessary
for efficient earth movement.
The final disadvantage is the re-
quirement for low inductance. This
is much more severe for EFI ' s than
for EBW ' s . EBW ' s can be reliably
fired over 100 feet of twin lead or
300 feet of coax at 3.5kv from a 1
microfarad capacitor. To fire EFI ' s
over 10 feet, generally requires a
flat cable, or some other method of
obtaining the low inductance required
for a fast rise time*
REFERENCES
(1) Luis W. Alvarez, "Alvarez: Adven-
- 122 -
tures of a Physicist," Basic Books,
Inc., New York, 1987, pp. 132-135.
( 2 ) "Exploding Wires , " Vol . 1-4 ,
edited by W . G Chace and H . K . Moore ,
Plenum Press, New York, 1959 - 1968.
( 3 ) T.J. Tucker , " Exploding Wire
Detonators : The Burst Current Criter-
ia of Detonator Performance," in
Exploding Wires, Vol. 3, edited by
W . G . Chase and H . K . Moore , Plenum
Press, New York, 1964, p. 175.
(4) "History," RISI Technical Top-
ics, San Ramon, CA. , Issue 05-93.
(5) R.S. Lee and R.E Lee, "Electro-
static Discharge Effects on EBW
Detonators," UCRL-ID-105644, Lawrence
Livermore National Lab, August 1991.
(6) Letter Report, R.H. Joppa, Los
Alamos National Laboratory to Eglin
Air Force Base, July 10, 1973.
( 7 ) Carl F . Austin and Carl C .
Halsey, "Safety and Durability Tests
of the Fireline Explosive Cord," TS
74-47
(8) "Secondary Explosive Initiators &
Accessories, " RISI Product Catalog,
San Ramon, CA. , April 1992.
(9) H.A. Golopol, et al., "A New
Booster Explosive, LX-15, " UCRL-
52175, Lawrence Livermore National
Laboratory, March 1977.
(10) Richard M. Joppa, et al, "Re-
sponse of Airborne Electroexplosive
Devices to Electromagnetic
Radiation, " Technical Report ASD-TR-
73-10, Los Alamos Scientific Labora-
tory, February 1973.
(11) "PM-25 and PM-100," RISI Data
Sheet, San Ramon, CA. , 1994.
- 123 -
LOW COST, COMBINED RADIO FREQUENCY AND ELECTROSTATIC PROTECTION
FOR ELECTROEXPLOSIVE DEVICES
Robert L.Dow
President, Attenuation Technology Incorporated
Attenuation Technology Incorporated
9674 Charles Street
La Plata, Maryland 20646
fie
Abstract : Attenuation Tech-
nology Inc. (ATI) has devel-
oped a series of ferrite
attenuators for protecting
electroexplosive devices
(EEDs) from inadvertent actua-
tion due to RF exposure .
ATI ' s first attenuator was
fabricated using the MN 67
ferrite formulation. That at-
tenuator protected EEDs from
both pin-to-pin and pin-to-
case RF exposure . Those at-
tenuators passed MIL STD 1385B
testing when used in electric
blasting caps (EBC) , electric
squibs, and firing line fil-
ters made for the US Navy.
An improved attenuator, fabri-
cated using ferrite formula-
tion MN 68™, protects EEDs
from both RF and electrostatic
inadvertent actuation . The
pin-to-pin and pin-to-case
combination protection previ-
ously demonstrated with MN 67
attenuators was maintained for
the RF and extended to the
electrostatic protection area.
In-house testing indicates
that the EED protection can be
extended to near-by lightning
protection using these new at-
tenuators.
Franklin Research Center inde-
pendently confirmed the in-
creased protection provided by
MN 68™ Ferrite Devices using
the Mk 11 Mod EBC which uses
a conventional bridgewire ini-
tiator. A new R&D MN 68™
Ferrite Device combined with a
Semiconducting Bridge (SCB)
passed MIL STD 1385B testing
for the first time. ATI is
continuing to extend the pro-
tection technology to other
EED initiator designs and uses
other than EEDs.
ATI has issued USA Patents on
the MN 67 and MN 68™ protec-
tion technologies and for many
individual applications. USA
patent applications are pend-
ing on SCB protection and
other newer EED applications .
US and overseas patent appli-
cations are pending on the ex-
tended coverage.
ATI developed the technology
for supplying ATI Certified MN
68 Ferrite Devices for each
application that has passed
the required qualification
testing . ATI has the Trade
Mark on MN 68™. The Certifi-
cation Mark application is
pending at the US Patent and
Trademark Office. Production
tooling is available to manu-
facture the .25 caliber MN
68™ Ferrite Devices.
Introduction : Attenuation
Technology Inc. (ATI) has de-
veloped a series of ferrite
protection devices using a new
and different basic technical
approach. That approach is to
modify the basic MN 68™ Fer-
rite Formulation in order to
- 125 -
\vi.
.,LY LiL-
get the desired combined RF
and electrostatic (ES) protec-
tion characteristics in the
final ferrite protection de-
vice , and then to place that
ferrite device inside the
electroexplosive devices
( EEDs ) in direct contact with
and electrically grounded to
the conductive case.
Background : Prior to our new
efforts in this area , prior
art EED RF protection applica-
tions used ferrite devices
with Curie Temperatures as low
as 150°C. The Curie Tempera-
ture of these prior art de-
vices was exceeded within a
few seconds when the EED was
exposed to RF energy levels
called out in MIL STD 1385.
The early prior art ferrite
devices also had cutoff fre-
quencies above 3 megahertz,
which made them unacceptable
when MIL STD 1385 required RF
protection at one megahertz.
These early failures gave
generic ferrite protection de-
vices a bad reputation that
they still have difficulty
overcoming. Many people still
automatically revert to think-
ing of these early failures
when the sub j ect of EED pro-
tection using any ferrite de-
vices is discussed. As a con-
sequence, they are still ex-
cluded as alternative EED
protection options even though
the technology has changed
significantly. As far as ATI
can determine , we are the
first company to specially
formulate a specific ferrite
formulation, MN 68™, for EED
protection and then make spe-
cific formulation modifica-
tions for individual EED ap-
plications.
New Technology : The first
ferrite formulation character-
istic that was changed was the
Curie Temperature. This phys-
ical property characteristic
is important because, when the
lossy ferrite device is ex-
posed to RF energy, it con-
verts that RF energy to heat.
If that heat cannot be removed
effectively , the ferrite de-
vice will increase in tempera-
ture. When the ferrite device
reaches its Curie Temperature,
it stops converting the RF en-
ergy to heat. If the ferrite
device reaches its Curie Tem-
perature, it can not protect
the EED. The RF attenuation
property is reversible in that
once the ferrite device cools
below its Curie Temperature,
it resumes attenuating RF en-
ergy until it repeats the tem-
perature cycle.
ATI has consistently increased
the Curie Temperatures of its
lossy , soft ferrite formula-
tion with 250 to 280°C modifi-
cations currently available
for manufacture. ATI is work-
ing toward a goal of at least
approaching 4 00°C on a second
ferrite formulation series .
Progress has been slow on this
new ferrite formulation, since
ATI appears to be the only
customer in the USA with in-
terest in the very high Curie
Temperature , lossy f err ites .
There is some interest devel-
oping in Europe in using these
very high Curie Temperature
formulations.
The second lossy ferrite for-
mulation characteristic that
was changed was to provide a
controlled DC resistance in
the ferrite device. Most of
the previous art EED ferrite
protective device applications
used lossy f err ites that were
- 126 -
not DC conductive . Further ,
most of these prior art lossy
ferrite devices were potted in
place in the EEDs with noncon-
ductive adhesives. We made
the conscious effort to go in
the opposite direction and
provide lossy, high Curie Tem-
perature ferrite device with a
controlled DC resistance
within an acceptable range.
The third lossy ferrite formu-
lation physical property that
is included in all our ferrite
formulations is cut off fre-
quencies below one megahertz.
MN 68™ Ferrite Devices suc-
cessfully attenuate RF energy
at 10 kilohertz.
Our lossy ferrite devices have
a sufficiently low DC resis-
tance to equalize the electro-
static energy that can build
up between the firing leads of
an EED (pin-to-pin) and/or be-
tween the firing leads and the
conductive case of an EED
(pin-to-case) . Our lossy fer-
rite devices have sufficiently
high DC resistance so that
they do not act as a DC shunt
for the EED's DC firing pulse.
Each EED application must be
tailored to work within those
DC limits. ATI has developed
the technology to provide this
acceptable range for each EED
application.
Improved EED Design ; Once the
three ferrite device require-
ments were met, the design of
the RF protective device and
assembly methods used for se-
curing it in the EED could be
greatly simplified. Noncon-
ductive potting materials were
no longer required during EED
assembly. The electrical in-
sulation previously used on
the firing leads passing
through the ferrite device was
eliminated. One lossy ferrite
device could provide both RF
and ES protection for the EED
for both pin-to-pin and pin-
to-case RF and ES energy expo-
sure modes.
It was also determined that
the ferrite device could be
inserted into EEDs, such as
electric blasting caps ( EBC)
thin conductive case , without
excessive breakage . It was
further determined that a good
electrical ground could be
achieved between the lossy
ferrite device and the conduc-
tive case using just the in-
sertion assembly method. All
of this work was done with
ferrite devices that were
right circular cylinders. New
manufacturing methods have re-
cently been developed, so that
a chamfer can be molded into
the finished ferrite device to
make assembly of other EED de-
signs easier.
Benefits of Design ; The first
synergistic effect of this as-
sembly procedure was that once
all of the electrically insu-
lating potting material was
removed from the EED design,
the heat conduction path
available to cool the RF at-
tenuating ferrite device were
great ly improved . Thus , sub-
sequent EED designs that con-
tained the higher Curie Tem-
perature lossy ferrite de-
vices , actually stabilized at
lower temperatures when ex-
posed to comparable amounts of
RF energy than prior art EED
designs.
This observation was at-
tributed to an improved heat
removal path directly to the
EED's conductive case, provid-
ing better cooling of the at-
tenuating, lossy ferrite
- 127 -
device. Thus, the safety fac-
tor of these new EED designs
were improved by two mecha-
nisms instead of the original
approach of simply using the
higher Curie Temperature ,
lossy ferrite devices.
The second synergistic effect
was that tieing the conductive
EED case to the firing leads
through the controlled circuit
ferrite allowed large amounts
of ES energy to be safely dis-
sipated without firing the
EED . Laboratory tests of the
ATI ferrite devices showed
that repeated exposures of the
wound ferrite devices with up
to 12 Joules of ES energy did
not destroy the ferrite device
or change its RF attenuation
properties. Most other compo-
nents in the EED when exposed
to that level of ES energy
only once, were completely
disintegrated , destroyed , or
failed to the duded mode.
The final discovery was that
the level of RF protection
could be changed by selection
of the winding pattern used in
the ferrite device. One and
one half turns of additive
choke windings on each firing
lead was necessary for the EBC
to pass MIL STD 1385B environ-
ments , but other winding pat-
terns can be used for commer-
cial applications where the RF
exposure hazards are lower.
It was independently deter-
mined that the improved fer-
rite devices did not signifi-
cantly attenuate the DC firing
pulse , even when they were
used to protect the semicon-
ducting bridge (SCB) igniters
that use microsecond DC firing
pulses . One design of the Mk
66 Igniter , containing a sin-
gle ATI high Curie Temperature
lossy ferrite choke , has been
reported as passing MIL STD
1385B RF testing as well as
the electrostatic testing.
Production Status : ATI is
currently working with three
USA ferrite device manufactur-
ers to produce these lossy ,
high Curie Temperature, con-
trolled DC resistance, ferrite
devices using high volume, low
cost production techniques .
So far, the largest production
lot has only been 25,000 bare
ferrite chokes . This quan-
tity, while very small by fer-
rite manufacturer's standards,
was produced without signifi-
cant production problems. ATI
is also working with an over-
seas source for potential ap-
plications in Europe.
Certification Approach ; Some
of the ferrite manufacturers
are offering their versions of
high Curie Temperature, lossy
ferrite devices that are pur-
ported to be as effective as
our MN 68™ Ferrite Devices.
We have been awarded the USA
Trademark on MN 68™ to dis-
tinguish our ferrite devices ,
certified by ATI , from those
produced with similar formula-
tions but not tested as com-
prehensively. ATI has a Cer-
tification Mark pending at the
US Patent and Trademark Of-
fice.
Since this technology niche
has not been investigated be-
fore , ATI was forced to de-
velop the techniques and
measurement equipment on its
own to measure the performance
and certify the effectiveness
of these ferrite devices. ATI
has developed these to the
point where, once a specific
ferrite device has been quali-
fied for a specific EED appli-
- 128 -
cation , subsequent production
lots can be certified to the
levels required.
ATI is maintaining certified
ferrite device samples from
each EED successfully quali-
fied. These samples are main-
tained to assure that new lots
of the ferrite devices pro-
duced in future years can be
directly compared to the orig-
inal and certified equivalent
in performance to the baseline
sample. If the project spon-
sor wants improved performance
(based on how the technology
has progressed in the mean-
time) or the projects safety
requirements have increased in
the interim, an improved ver-
sion ferrite device can also
be manufactured and made
available. It now appears
that it may be possible to
produce the improved perfor-
mance ferrite devices without
any modifications to the pro-
duction tooling.
US Patents : Since all of this
work has been funded solely by
ATI , patent protection is the
main form of intellectual
property rights protection .
ATI's issued patents are:
1. US 5.036,768 Basic Patent
on MN 68™ Applications
2. US 5,243,911 Near-by Light-
ning Protection for EED
The main, generic approach,
patent application revealing
the principles of EED protec-
tion regardless of the con-
trolled property ferrite for-
mulation used or the winding
pattern employed is expected
to be issued shortly. ATI has
other patent applications
pending in the areas of EED
protection and ferrite device
certification areas.
During the EED protection
technology evolution, ATI de-
termined that the technology
can be modified to protect
other devices as well . The
first medical protection de-
vice patent US 5,197,468 has
been issued. Other patent ap-
plications are pending cover-
ing many classes of equipment.
Conclusion : Since this is a
completely different approach
to protecting EEDs from both
RF and ES inadvertent ignition
with a single device , ATI is
prepared to discuss any poten-
tial applications of this new
technology area with anyone
interested . Each solution
must be tailored for each ap-
plication. The technology ap-
pears to have progressed suf-
ficiently so that can be done.
Please contact us if you are
interested in considering this
new approach.
- 129 -
SI z-z%
Unclassified
Distribution Unlimited
SAND94-0246C
UNIQUE PASSIVE DIAGNOSTIC FOR SLAPPER DETONATORS
William P. Brigham
Explosive Projects and Diagnostics Department
John J. Schwartz
Stockpile Evaluation Department
Sandia National Laboratory
Albuquerque, New Mexico
ABSTRACT
The objective of this study was to find a material and configuration that could
reliably detect the proper functioning of a slapper (non- explosive) detonator.
Because of the small size of the slapper geometry (on the order of a 15 mils),
most diagnostic techniques are not suitable . This program has the additional
requirement that the device would be used on a centrifuge so that it could not
use any electrical power or output signals. This required that the diagnostic
be completely passive.
The paper describes the three facets of the development effort: complete
characterization of the slapper using VISAR measurements, selection of the
diagnostic material and configuration, and testing of the prototype designs.
The VISAR testing required the use of a special optical probe to allow the laser
light to reach both bridges of the dual-slapper detonator. Results are given in
the form of flyer velocity as a function of the initiating charge voltage level.
The selected diagnostic design functions in a manner similar to a dent block
except that the impact of the Kapton disk from a properly- functioning slapper
causes a fracture pattern. A quick visual inspection is all that is needed to
determine if the flyer velocity exceeded the threshold value. Sub -threshold
velocities produce a substantially different appearance.
Introduction
Slapper-detonators are used in current
weapon systems because of their fast
function time , small j itter , and
relatively low energy requirements
compared to other types of detonators.
As part of the Sandia National
Laboratories (SNL) evaluation program,
detonators are typically tested in the
This work was supported by the United
States Department of Energy under
Contract DE-ACO4-94AL85000.
laboratory under realistic physical
and environmental conditions . The
unique operation and design of the
slapper requires sophisticated
diagnostics like VISAR or closure
switches to evaluate performance
parameters. The complexity of these
techniques makes their use difficult
in the evaluation lab. This paper
discusses a device developed to
provide a simple evaluation of slapper
function within the constraints
- 131 -
p/
\U: ..J.
|J0
j;:jV p! r-*i£
imposed by the laboratory environment.
It consists of a small glass target
that provides a unique visual record
when impacted by the flyer from the
slapper .
Slapper Detonator
The SNL slapper detonator is shown in
Figure 1. It consists of a central
"bullseye" connector for attachment to
the firing set with the flat copper
cables extending in opposite
directions to form a single loop. The
upper layer of thin copper narrows at
each end to form a "bridge" that
causes the current density to increase
significantly. The current through
each bridge is strong enough to drive
the copper into vapor. The pressure
of the gas causes the Kapton to shear
against the sapphire "barrel" forming
a rapidly-accelerating flyer with a
diameter of about 0.015".
Flyer velocity is a function of the
initial firing set charge voltage and
the resulting current . Typical
terminal velocity is on the order of
3-4 mm//is, although other designs are
capable of nearly 6 mm/^s . It is
assumed that the flyer begins to come
apart soon after it leaves the barrel,
but good data have been obtained for
distances up to 1 mm. The most common
practice is to place the explosive of
the next assembly in contact with the
barrel.
Slapper Characterization
Prior to the development of the
passive diagnostic , it was necessary
to determine the performance
(velocity-time history) of the slapper
detonator over a range of initial
firing set voltage. The best tool for
this measurement is VISAR (Velocity
Interferometer System for Any
Reflector) that uses Doppler- shifted
laser light from the slapper surface
to infer the velocity. Because this
slapper is a dual -bridge functioned
from a common firing set, it was
desired to measure both flyers
simultaneously. Most VISAR' s are
"dual -leg" to provide redundant
measurement of a single device using
two interferometers with different
experimental constants . A unique
optical probe was therefore developed
to convert the existing equipment into
a dual system to make the two separate
measurements .
The probe allows the light from a
single laser to be split into two
equal beams that are then fiber -
coupled to the target locations . A
simplified schematic of the probe is
shown in Figure 2 to demonstrate the
path of the light. The input fiber
connects to optics that allow the
light to be focused onto the target
surface . The target surface causes
the light to be scattered diffusely
where it is collected by other optics
within the probe. The light is then
collimated and focused onto the return
fiber located at the rear of the
probe. In this manner the image from
each slapper can be routed to a
different VISAR leg.
A unique feature of the optic probe is
the incorporation of a small camera to
give a TV image of the target surface.
The selective coating on the angled
mirror causes a portion of the
returned light to be transmitted to
the camera element. The TV image is
then present on a monitor within the
test area. This feature is essential
when testing slappers with a small
active area because it allows the
operator to precisely align the input
laser light onto the Kapton element in
the center of the barrel. Placing
each end of the slapper on a separate
translation stage allows adjustment of
the position just prior to the test.
Additional diagnostics include
detection of the charge voltage and
current waveforms from the firing set.
Each of these along with the VISAR
- 132 -
data were recorded on Tektronix DSA
602 transient digitizers. Data
reduction was performed following each
test and stored on computer disk.
Figure 3 shows VISAR data from an
experiment where the initial charge
voltage was 2.6 kV. The data are in
the form of flyer velocity and
displacement versus time where the
distance is obtained by numerical
integration of the velocity- time
record. The behavior is typical of
slapper detonators in that the
acceleration of the flyer is less
abrupt than a conventional
explosively-driven plate, although the
final velocity at the exit of the
barrel is over 3 mm//is . Note that the
record continues for a distance
approaching 0.75 mm. At the higher
initial charge voltage levels, breakup
of the flyer is assumed as manifested
by increasingly noisey signal quality.
The data of Figure 3 can be cross -
plotted to give velocity as a function
of displacement as shown in Figure 4 .
This is particularly useful in
assessing the velocity as a given
distance , such as the exit of the
barrel or the location of the next
assembly.
The firing set for all tests was a Hi-
Voltage Components, Inc. model CDU2045
with a 0.2 /ifd, 5-kV capacitor.
Initial charge voltage was varied from
1.6 kV to 3.0 kV. Two tests were done
at each voltage level to provide
redundant data.
Results for the characterization test
matrix are given in Figure 5 in the
form of flyer velocity as a function
of firing-set charge voltage. The
numerical results from the same tests
are shown in Table 1. The velocity is
obtained at a propagation distance of
0.5 mm, or just beyond the exit of the
barrel. The four data points at each
voltage represent the measurement of
each side of the slapper, with two
tests at each level . In all cases ,
the designation "A" refers to the
bridge that first receives the firing
pulse , based on the direction of the
current flow. The "B" suffix then
denotes the opposite bridge.
The results given in Figure 5 indicate
that the behavior of the detonator is
significantly more erratic at voltage
levels below 2 kV. It is thought that
at the lower voltage, minor tolerance
differences in the construction of the
bridges have a more pronounced effect
on the behavior. At the higher
voltage levels , sufficient energy is
available to overcome these
differences and the velocity achieved
by the two bridges is more consistent.
For both tests at 1.6 kV, the "B" side
of the unit failed to cause
acceleration of the Kapton to a
velocity sufficient to be measured by
the VISAR, which has a lower detection
limit of about . 2 mm//is . Inspection
of the bridge following the shot
indicated that the copper had failed
in the region of the bridge.
Results in the voltage range above 2.0
kV show a correspondence between the
applied voltage and the resulting
velocity. The greatest velocity, on
the order of 4 mm//is, was achieved at
the highest voltage level. Some
scatter is present above 3 . 5 mm//is
that is probably caused by breakup of
the Kapton flyer. There does not
appear to be a discernible trend to
establish that side "A" or "B" is
consistently higher in velocity at a
given voltage.
Passive Diagnostic
As mentioned previously , the purpose
of this work was to develop a passive
diagnostic for the slapper used during
evaluation testing. The specific
requirements were that the device
would not require any external
communication (input power or signal
cables) and that the visual indication
could be easily detectable. Previous
- 133 -
experience had shown that brittle -like
fracture could be introduced into some
plastic or ceramic materials using
metallic flyers from hot-wire
detonators. This observation
suggested that a similar arrangement
could be used for the Kapton flyer
from the slapper.
Initial screening tests looked at a
variety of material types, sizes, and
thicknesses . The presumed 50%
probability threshold velocity for
detection corresponded to an initial
voltage of about 2.1 kV, although
tests were done at higher and lower
levels to ascertain the sensitivity of
each configuration. Table 2 contains
the results from the initial screening
tests . Some of the tests used a
single -bridge and are shown as one
configuration only, while the
remainder are dual -bridge that may
have a different device on each end.
The screening matrix demonstrated a
number of viable candidates for
selection based on the appearance of
obvious cracks above the threshold
voltage level. The best material was
sapphire, but was rejected because of
prohibitive expense. The 0.036" thick
microscope slide also showed excellent
performance, but a source for this
material could not be located. The
next alternative was to obtain
standard fused silica material in
thicknesses in the range of 0.020" to
0.030". Although this is thinner than
typically produced, several vendors
were found that could grind 1"
diameter disks to virtually any value.
Disks were purchased in . 020" and
0.025" thicknesses of BK-7, a standard
fused silica composition made for the
optics industry. A total of 16 tests
were conducted, six using the 0.020"
thickness and the remainder with the
0.025" pieces. Table 3 shows the
results of the BK-7 tests.
The 0.020" thick BK-7 samples from
tests at 2.2 and 2.4 kV demonstrated a
large number of cracks at both voltage
levels, while the 0.025" samples only
showed cracks at the higher charge
voltage. The behavior described above
was relatively consistent throughout
the remaining tests . One additional
modification was made for the last
nine tests of the shot series . A
simple fixture of aluminum was made to
hold the glass against the slapper,
using a 1/16" thick 0-ring to provide
a mild compressive load. The other
side of the slapper continued to use
the glass glued to the sapphire
barrel. This was done to determine if
a fixture would have any effect on the
crack initiation and propagation.
The results with the fixture suggest
that i t may have induce a s 1 i ght
increase in the crack sensitivity of
the glass . This is not consistently
true for all the shots, but in no case
did the unfixtured end show greater
damage than the corresponding fixtured
side.
Conclusion
As part of the development of a
passive diagnostic for surveillance
testing of a slapper detonator, a
unique optical probe was constructed
that allows simultaneous VISAR
measurement of both flyers . The
characterization of the slapper was
done to establish the correlation
between applied firing voltage and the
resulting flyer velocity. At voltages
below 2 kV, significant differences
were seen between the two sides of the
unit and from one unit to another .
This was attributed to minor
differences in the construction of
each device.
A variety of materials were tested to
determine which would provide a
discernible crack pattern at flyer
velocities above a predetermined
threshold value . Standard fused
silica was selected based on
performance, availability, and cost.
For this slapper, a thickness of
- 134 -
0.020" to 0.025" and a diameter of 1"
provides acceptable performance .
Efforts are continuing using an
intermediate thickness and fixturing
to improve the device's behavior for
the intended application.
Table 1
Slapper Flyer Velocity Results
Table 3
BK-7 Test Results
Firing Set
Voltage (kv)
Velocity
Bridge A
(mm/ms)
at 0.5 mm
Bridge B
(ram/fis)
1.6
ti
2.37
2.20
-
1.7
tl
2.90
2.52
1.72
2.52
1.8
II
2.55
3.06
2.70
2.50
1.9
II
3.15
2.85
2.66
2.76
2.0
II
2.88
3.05
2.93
3.08
2.1
II
3.12
3.26
3.15
2.98
2.2
ll
3.36
3.27
3.52
3.33
2.4
II
3.58
3.52
3.52
3.44
2.6
II
3.68
3.50
3.88
3.60
2.8
II
3.78
3.68
3.96
3.84
3.0
ii
4.05
4.10
4.14
3.85
Charge
Voltage
(kV)
Sample
Thickness
(in.)
Number of
Cracks
(A) (B)
2.2
0.020
2.4
tf
4
6
2.6
II
5
6
2.2
0.020
6
many
2.0
«
4
2
1.9
II
3
5
1.8
■1
2.2
0.025
6
8*
2.0
It
0*
2.1
II
0*
2.2
II
o*
2.3
II
o*
2.4
■■
3
9*
2.3
it
2
0*
2.0
0.020
5
0*
2.2
■i
4
0*
* indicates fixture was used
on Side B
- 135 -
Table 2
Results From Initial Screening Tests
Shot
Number
Charge
Voltage
(kv)
Sample Configuration
Results
1
1.8
0.03" thk PMMA
surface damage
2
2.8
tl
surface damage
3
2.8
0.036" microscope
slide 1/2" x 3/4"
numerous cracks
4
1.8
tt
4 cracks from
contact point
5
2.0
.006" cover glass
22 mm square
4 cracks
.065" quartz glass
1" square
no damage
6
2.8
.006" cover glass
22 mm square
>10 cracks
.065" quartz glass
1" square
3 cracks
7
2.0
.039" microscope
slide 1" square
damage in center
no cracks to edge
silicon substrate
.016" x -1" square
6 cracks
8
2.8
.039" microscope
slide 1" square
damage in center
no cracks to edge
silicon substrate
.016" x -1" square
many cracks ,
center missing
9
2.8
plate glass 1/8"
no damage
.036" microscope
slide 1/2" x 3/4"
6 cracks
(continued)
- 136 -
Table 2 (Continued)
10
2
.8
.039" microscope
slide 1" square
.036 microscope
slide 1" square
minor damage
4 cracks
11
2
.0
.062" plain glass
-1" square
.020" x 3/4" dia
sapphire disk
no damage
no damage
12
2
.8
.062" plain glass
-1" square
.020" x 3/4" dia
sapphire disk
no damage
3 cracks , rear
spall
13
2
.4
.065" quartz -1"
square
.020" x 3/4" dia
sapphire disk
no damage
1 diagonal crack
edge to edge
14
2
.2
.038" quartz ~1"
square
.020" x 3/4" dia
sapphire disk
1 crack, edge to
edge
incipient fracture
no complete cracks
15
2
2
.018" quartz, -1"
square
.038" quartz ~1"
square
several cracks,
not from center
incipient cracks
16
1
95
.019" Dynasil, odd
shape
.019" Dynasil, odd
shape
6 cracks
5 cracks
17
1
95
.034" Dynasil, odd
shape
.034" Dynasil, odd
shape
no damage
no damage
- 137 -
V>4
OO
Isolator
2 ml Kapton XT
ImlPyrafcut
Saphire Barrel
IB ml 10
Adhesive
1 mlPyrafcix
Bridge/Flyer
1 ml Kapton Ryar
175 Mftcroinch Cu
Adhesive
2mlPyraiux
Top Cover Coat
2 ml Kapton
2miPyrafci*
Circuit "A"
1 oi. Cu
Epoxy
2ml Kapton
Inside Adhesive
1 ml PynAix
1 ml Kapton
1 ml Pyrahix
Circuit "BC"
1 oi. Cu
Epoay
2ml Kapton
Bottom Cover Coat
2 ml Pyrafci*
2 ml Kapton
SLAPPER DETONATOR
GB
Sanda
national
laboratories
figure 1
IMAGING FIBER OPTIC COUPLED SENSOR
INPUT FIBER OPTIC FROM LASER
TARGET
RETURN FIBER
OPTIC TO
VISAR
SECTIONAL VIEW OF SENSOR. LASER LIGHT FROM SOURCE ILLUMINATES TARGET, REFLECTED
LIGHT IS COLLECTED AND FOCUSED INTO RETURN FIBER OPTIC FOR ANALYSIS. PAT. PEND.
figure 2
lELOCITV/DISPLflCEMENT US TIME LEG "A" 2.6kU Date : 81/2B/94
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figure 3
JELOCITY US DISPLACEMENT LEG "A" 2.6 kU CHARGE Date: 81/28/94
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figure 4
SLAPPER DETONATOR
VELOCITY @ .5mm
4.5
(0
"e
E,
>-
H
O
o
_l
LU
>
4-
3.5-
2.5-
2-
1.5
1.4 1.6
1.8 2 2.2 2.4 2.6 2.8
CHARGE VOLTAGE (KILOVOLTS)
SHOT 1 A
-~EEH-
SHOT 1 B
SHOT 2A
SHOT 2B
3.2
figure 5
APPLYING ANALOG INTEGRATED CIRCUITS
FOR HERO PROTECTION
By:
Kenneth E. Willis
Quantic Industries/ Inc
990 Commercial Street
San Carlos, CA 94070
(415) 637-3074
Thomas J. Blachowski
Naval Surface Warfare Center
Indian Head, MD
(301) 743-4876
INTRODUCTION
One of the most efficient methods
for protecting electro-explosive de-
vices (EEDs) from HERO and ESD is
to shield the EED in a conducting
shell (Faraday cage). Electrical en-
ergy is transferred to the bridge by
means of a magnetic coupling
which passes through a portion of
the conducting shell that is made
from a magnetically permeable but
electrically conducting material.
This technique was perfected by ML
Aviation, a U.K. company, in the
early 80 ! s, and was called a Radio
Frequency Attenuation Connector
(RFAC). It is now in wide use in
the U.K. Previously, the disadvan-
tage of RFAC over more conven-
tional methods was its relatively
high cost, largely driven by a thick
film hybrid circuit used to switch
the primary of the transformer.
Recently, through a licensing
agreement, this technology has
been transferred to the U.S. and
significant cost reductions and per-
formance improvements have
been achieved by the introduction
of analog integrated circuits.
An integrated circuit performs the
following functions: 1) Chops the
DC input to a signal suitable for
driving the primary of the trans-
former, 2) Verifies the input volt-
age is above a threshold, 3) Verifies
the input voltage is valid for a pre-
set time before enabling the device,
4) Provides thermal protection of
the circuit, and 5) Provides an ex-
ternal input for independent logic
level enabling of the power transfer
mechanism. This paper describes
the new RFAC product and its ap-
plications.
BACKGROUND
Electro-explosive devices (EEDs)
must, in many applications, be pro-
tected against unintended initia-
tion by Electromagnetic Radiation
(EMR) or Electrostatic Discharge
(ESD).
A variety of methods are in use to
mitigate these problems; they in-
clude:
1) Low resistance bridgewires
which can dissipate some elec-
- 143 -
trical energy before heating to
ignition temperature.
2) Filters consisting of capacitive
or inductive elements which
can absorb or reflect RF energy.
3) Shielding to create a Faraday
cage around power source, con-
ductors and the EED.
4) Voltage spike dissipation or
"clamping" functions.
5) Switches or relays to discon-
nect/short the EED pins until
ready for function.
All of these solutions suffer from
one or more of the following defi-
ciencies:
1) Not completely effective.
2) Impose undesirable constraints
on the system, e.g., weight,
power, and envelope.
3) Adds cost.
Depending on the system require-
ments, these deficiencies can be
more or less annoying.
The ideal solution is to simply sur-
round the EED with a Faraday cage
- cheap and 100% effective. This so-
lution leaves only one problem:
how do you get the firing energy
into the bridgewire when it is sup-
posed to function. A practical im-
plementation of this concept is
shown in Figure 1.
The Faraday closure surrounds the
EED and the secondary of the trans
WTVT MLftt CAPAOTM
PRACTICAL IMPLEMENTATION
Figure 1
former. The material between the
transformer cores is a conducting,
but magnetically permeable, alloy.
The secondary of a narrow band-
pass transformer inside the Faraday
closure generates the firing current.
The conducting copper-nickel alloy
maintains the integrity of the Fara-
day cage. The primary of the trans-
former is driven with an AC signal
at the mid-frequency of the pass
band, generated by the DC-AC in-
verter.
This concept, of course, is not new.
The physics has been around a long
time. The application to EED pro-
tection, as near as I could trace its
origins, was proposed by Wing
Commander Reginald Gray of the
Royal Air Force in 1957. In the mid
to late 1970's, Mr. Raymond Sell-
wood of ML Aviation, a U.K. de-
fense company, adapted this con-
cept to a practical device called the
Radio Frequency Attenuating Con-
nector (RFAC). Mr. Sellwood was
then granted several patents for
these designs, including a U.S.
Patent in 1979.
The RFAC has been successfully
deployed on a number of U.K.
weapon systems, and has per-
- 144 -
formed flawlessly- These systems
include:
• Chevaline SLBM
• Airfield Attack Dispenser
(Tornado)
• Torpedoes (Spearfish and
Stingray)
• Stores Ejection Systems
• ASDIC (Cormorant)
In 1989, Mr. Tom Blachowski, this
paper's co-author, completed test-
ing of an RFAC equipped impulse
cartridge for a Naval Surface War-
fare Center (Indian Head) applica-
tion.
EVALUATION TESTING
The Indian Head Division, Naval
Surface Warfare Center (NSWC)
completed an evaluation of the in-
ductive coupling technology for
electrically actuated cartridges and
cartridge actuated devices (CADs).
This effort was performed as part of
the Naval Air Systems Command
Foreign Weapons Evaluation
(FWE)/ NATO Comparative Test
Program (CTP). The FWE Program
is designed to assess the applicabil-
ity for foreign-developed, off-the-
shelf technology for procurement
and implementation in the U.S.
Fleet. The FWE goal is production
procurement offering fleet users
enhanced performance while low-
ering the per item cost to the pro-
gram managers.
The FWE effort to analyze the in-
ductive coupling initiation tech-
nology was structured as follows: A
Navy standard electrically initiated
cartridge, the Mark 23 Mod im-
pulse cartridge, was selected to be
modified to accept the inductive
coupling initiation hardware. The
MK23 Mod cartridge was previ-
ously tested by the Navy in nu-
merous configurations and rated as
"susceptible" when subjected to
Hazards of Electromagnetic Radia-
tion to Ordnance (HERO) electrical
field strengths. There have been
several documented instances in
which MK23 Mod cartridges have
inadvertently actuated when sub-
jected to a HERO or electromag-
netic interference environment.
These inadvertent actuations re-
sulted in mission aborts, loss of es-
sential equipment, and an in-
creased threat to crew members and
ground personnel during an elec-
trical event. ML Aviation Limited
was contracted by NSWC to install
the inductive coupling hardware
into the existing MK23 Mod car-
tridge envelope maintaining the
same form, fit, and functions as the
Navy standard device. ML Avia-
tion packaged the existing RFAC
secondary transformer into the
MK23 Mod impulse cartridge and
designed a primary transformer
into an electrical connector which
must be installed in the cartridge
firing circuit.
These primary electrical connectors
and inductively coupled MK23
Mod impulse cartridges were sub-
jected to a specialized design verifi-
cation test series at the Indian Head
Division, NSWC. Two phases of
design verification test were con-
ducted: the first phase was electrical
requirements and analysis
(performed in accordance with
MIL-I-23659C, "General Design
Specification for Electrical Car-
- 145 -
bridges"), and the second phase was
the functional testing of the car-
tridges (performed in accordance
with MIL-D-21625F, "Design and
Evaluation of Cartridges and Car-
tridge Actuated Devices").
All of the inductively coupled
MK23 Mod impulse cartridge tests
were successful and the results ex-
hibited the potential to implement
the inductive coupling technology
in a wide range of electrically initi-
ated cartridges and CADs. The In-
dian Head Division, NSWC pub-
lished the results of this effort in
Indian Head Technical Report
(IHTR) 1314 dated 17 November
1989, "Evaluation of the Inductive
Coupling Technology Installed in a
Standard Impulse Cartridge Mark
23 Mod 0".
Based on the excellent test results,
and the Navy's desire for a U.S.
producer for the RFAC, Quantic
Industries and ML Aviation en-
tered into a license agreement for
U.S. and Canadian production and
sales of RFAC.
DESIGN
A typical configuration of the
RFAC, used in a connectorized ver-
sion is shown here (Figure 2). The
primary electronics module is
housed in a 7mm diameter x
35mm long tube. The magnetics in
this configuration will transfer a
minimum of five watts to the sec-
RFAC ASSEMBLY
Figure 2
ondary bridgewire. The electronics
can drive larger magnetics in a 9,
11, or 14mm outside diameter con-
figuration, to provide more power.
In the original ML Aviation design,
a self oscillating feedback circuit
was implemented in a thick film
hybrid. Quantic implemented sub-
stantial cost reductions and per-
formance improvements by replac-
ing the original thick film hybrid
circuit with an analog application
specific integration circuit (ASIC).
Relatively new technology in high
voltage analog array ASICs made
this economically viable.
The electromagnetic attenuation
performance of the RFAC is un-
changed by the change in electron-
ics. Sixty (60) to 80 dB attenuation is
achieved. A typical attenuation per-
formance is shown here in Figure
3.
- 146 -
i
I
j
M
/
\l\
lj
rJ
V
In
^ *
< J
/^
^
lV\ ^
/
^/
** "^
/'■-
o sc«o«oaoo»oaooMo«o«9cia
RFAC PERFORMANCE
Figure 3
Some additional safety and per-
formance features were added to
the ASIC, which, incidentally, adds
no cost to the product. These fea-
tures include:
1. Self contained oscillator.
- Stable over wide tempera-
tures and voltages
- Simpler magnetics: original
design used - feedback loop
to self oscillate
2. Programmable delay time - an
additional guard against voltage
transients.
3. Input voltage threshold test.
4. Output enable - separate logic
level input needed to transfer
power.
5. Thermal cut-off.
6. High current output - can be
used for larger units.
7. ESD and over voltage protection
(note that the ordnance section
is intrinsically SAFE from ESD.
8. Programmable turn-off time (0-
10 ms).
9. Designed to be nuclear hard.
A block diagram of the RFAC is
shown in Figure 4:
RFAC SIMPLIFIED ELECTRICAL
BLOCK DIAGRAM
Figure 4
CURRENT STATU?
At this time (November 1992) the
development and engineering tests
of the enhanced inductively cou-
pled MK23 Mod cartridge are
complete. The Indian Head Divi-
sion, NSWC is conducting a quali-
fication program to allow for pro-
duction procurement and imple-
mentation in a wide variety of fleet
applications. The inductively cou-
pled MK23 Mod cartridge has
been renamed the CCU-119/A Im-
pulse Cartridg e as part of this pro-
gram. The functional test phase of
the qualification program is again
based upon MIL-I-23659C and MIL-
D-21625. Successful completion of
these tests will allow Indian Head
to recommend approval for release
to service. The tests that will be per
formed as part of the qualification
effort are:
- 147 -
Visual inspection
Radiographic Inspection
Bridgewire integrity
Electrostatic discharge
Stray voltage
Forty foot drop
Six foot drop
Temperature, humidity, and altitude
cycling
Salt fog
Cook-off
High temperature exposure
High temperature storage
Low temperature (-65°F) testing
Ambient temperature (+70°F) testing
High temperature (+200°F) testing
APPLICATIONS
The potential applications of RFAC
include essentially all EEDs which
must operate in HERO and ESD
environments. We expect the re-
duced cost, made possible by inte-
grated circuit technology, will sub-
stantially expand these applications
in both the U.S. and U.K. However,
In closing, I would like to discuss
one novel application that may be
of interest to this audience.
The increasing availability of high
power diode lasers has sparked the
interest of the ordnance commu-
nity. A fiber optic cable can conduct
the optical energy into an initiator
which is totally immune to RF and
ESD hazards. Offering very
lightweight and potentially low
cost for safing and arming func-
tions, the diode laser is nearly ideal
for many applications. There is one
catch; the diodes laser generates the
optical energy with a low voltage
(typically 3 volts) source. This cre-
ates a single point failure safety
problem unless mechanical means
are used to block the light. How-
ever, using an RFAC to isolate the
diode power supply makes this
problem disappear. A system which
protects the diode and its power
supply inside a Faraday closure
should meet all safety require-
ments for diverse applications such
as crew escape systems, rocket mo-
tor arm fire devices and automo-
tive air bag initiation.
BIOGRAPHIES
Mr. Blachowski has held his pre-
sent position as an Aerospace En-
gineer in the Cartridge Actuated
Devices Research and Develop-
ment Branch at the Indian Head
Division, Naval Surface Warfare
Center for 5 years. In that time, he
has been involved in exploratory
R&D, advanced development,
product improvement, and pro-
gram support for cartridges and car-
tridge actuated devices throughout
the Navy. Mr. Blachowski received
his Bachelor of Science degree in
Aeronautical and Astronautical
Engineering from Ohio State Uni-
versity in 1985.
As division vice president at Quart-
tic Industries, Inc., Mr. Willis is re-
sponsible for directing internal re-
search and development activities,
developing new products and new
business activities. Product areas
include electronic, electromechani-
cal and ordnance devices used for
safety and control of systems using
energetic materials and processes.
Mr. Willis received his Master of
Science Degree in Physics from Yale
University in 1959 and a Bachelor
of Arts Degree from Wabash Col-
lege.
- 148 -
514-28
£1 14-
Cable Discharge System for Fundamental Detonator Studies 31
Gregg R. Peevy and Steven G. Barnhart
Explosives Components Department
William P. Brigham
Explosives Projects and Diagnostics Department
Sandia National Laboratories
Albuquerque, NM 87185
/o>
ABSTRACT
Sandia National Laboratories has recently completed
the modification and installation of a cable discharge
system (CDS) which will be used to study the
physics of exploding bridgewire (EBW) detonators
and exploding foil initiators (EFI or slapper). Of
primary interest are the burst characteristics of these
devices when subjected to the constant current pulse
delivered by this system. The burst process involves
the heating of the bridge material to a conductive
plasma and is essential in describing the electrical
properties of the bridgewire foil for use in
diagnostics or computer models. The CDS described
herein is capable of delivering up to an 8000 A pulse
of 3 |is duration. Experiments conducted with the
CDS to characterize the EBW and EFI burst
behavior are also described. In addition, the CDS
simultaneous VISAR capability permits updating the
EFI electrical Gurney analysis parameters used in
our computer simulation codes. Examples of CDS
generated data for a typical EFI and EBW detonator
are provided.
♦This work was supported by the United States Department of
Energy under Contract DE-ACO4-94AL85000.
1.0 INTRODUCTION
This paper describes the Cable Discharge System
(CDS) and its use in fundamental detonator studies.
The CDS is preferred over a conventional capacitor
discharge unit (CDU) that delivers a decaying
sinusoidal current pulse. The fast rising constant,
"stiff', current, provided by the CDS charged
cable(s) eliminated the uncertainty of a continuously
changing current density that comes from a CDU.
The CDS is actually two systems; the cable discharge
system which provides a square wave current pulse
to the detonator and the instrumentation system
which measures the detonator parameters of interest.
Fundamental detonator studies using the CDS
generates information to be used in diagnostics or
computer models. Computer modeling provides
electrical/mechanical performance predictions and
failure analysis of exploding foil initiator (EFI) and
exploding bridgewire (EBW) detonators. This
project is being performed in order to improve
computer modeling predictive capabilities of EFI and
EBW detonators. Previous computer simulations
predicted a much higher voltage across the bridge
than was measured experimentally. The data used in
these simulations, for the most part, was collected
two decades ago. Since this data does not adequately
predict performance/failure, and instrumentation and
measurement methods have improved over the years,
the gathering of new data is warranted.
- 149 -
2.0 SYSTEM DESCRIPTION
The cable discharge system (CDS) resides at Sandia
National Laboratories New Mexico in Technical
Area II and consists of the following hardware:
■ Four 1000 foot long rolls of RG218 coaxial cable
■ A high-voltage power supply (100 kV, 5 mA)
■ A gas pressurized, self-breaking switch
■ A gas system for pressurizing and venting the
switch
■ Custom output couplings with integral current
viewing resistor (CVR)
• Flat cable coupling for testing of exploding
foil initiators (EFI)
• Coaxial coupling for testing of exploding
bridgewires (EBW)
■ Instrumentation for measuring:
• System current - current viewing resistor
(CVR)
• Voltage across the EBW/EFI bridge elements
- voltage probes
• Free-surface velocity of flying plate and
particle velocities at interfaces for
determining device output pressure - velocity
interferometer system for any reflector
(VISAR) 1
■ Tektronix DSA602A digitizers
■ 486DX33 PC
The CDS is operated by pressurizing the output
switch with nitrogen, charging the cables up to a
pre-determined voltage which will deliver the
required current to the device being tested when the
switch is operated. The switch is operated by
venting the gas with a fast-acting solenoid valve.
Current from the CVR is used as a trigger source for
the data recording system. A photograph of the CDS
is given in Fig. 1 and a schematic of the CDS is
given in Fig. 2.
3.0 CAPABILITIES
The four 1000 foot long RG218 coaxial cables can be
configured to provide a current pulse ranging in
amplitude from 100 to 8000 A with a width of 3 \xs
and a risetime of 25 - 35 ns, Fig. 3 and 4. This wide
range of current is made possible by the parallel
connection of one to four cables.
The system current is measured with a series 0.005
Q CVR that is integral to the output of the CDS. A
voltage probe is used to measure the voltage drop
across the exploding element, either a bridgewire in
the case of the EBW or the foil of an EFI (slapper).
The voltage probe is a 1000 CI resistor placed in
parallel with the bridge and a Tektronix CT-1
current viewing transformer which measures through
it. This allows for decoupling the measurements
from ground and minimizes the possibility of ground
loop problems.
The VISAR is used to measure the free-surface
velocity of the flyers of an EBW or EFI. It also can
be used to measure particle velocity at a window
interface which in turn, through the use of Hugoniot
curves, can determine the explosive output pressure
of an EBW. Two separate and independent VISAR
modules can make these measurements
simultaneously. They have different sensitivities
therefore giving a high degree of confidence in these
measurements.
All three of these measurements (current, voltage,
and velocity) are recorded on Tektronix DSA602A
digitizing signal analyzers. These instruments have
high bandwidth (up to 1 gHz) and high sampling
rates (1 gHz for 2 channels of data). They also can
produce calculated waveforms from basic current
and voltage measurements representing:
■ Resistivity
■ Specific action
■ Energy
These calculated waveforms are produced from the
measured data automatically as soon as they are
recorded on the digitizer, see Fig. 5.
The 486DX33 PC can acquire up to 16 waveforms
on any shot and store it on a 90 megabyte Bernoulli
disk. Other custom software does VISAR data
reduction/analysis to give profiles of:
■ Flyer velocity vs. time
■ Flyer displacement vs. time
■ Flyer velocity vs. flyer displacement
Other commercial or custom software packages can
then be used to create tables and/or graphs for
presentation and report format.
4.0 FUNDAMENTAL DETONATOR STUDIES
This section briefly states the basic electrical/
mechanical theory of EBW and EFI detonators. For
a more detailed explanation see the referenced
reports 2 through 6. The CDS can be used to
observe both electrical and mechanical behavior of
detonators. From these observations, models with
their parameters can be generated. Tucker and
Toth 2 demonstrated that exploding wire (and foil)
- 150 -
resistivity, p, at fixed current density, j, may be
uniquely specified as a function of either of two
parameters: energy, e, or specific action, g. These
relationships and equations are summarized below.
p = /(e) or /(g)
(1)
The resistivity of the bridge is the voltage gradient
across the bridge divided by the current density
through the bridge. The resistivity is characteristic
of the bridge metallic material. Resistance of the
metallic bridge can be determined by accounting for
the bridge volume; cross sectional area, A, and
length, C
R = pr/A
(2)
The energy deposited to the bridge is the integral of
the voltage, V, and the current, i, over time.
e = |Vidt
(3)
The specific action deposited to the bridge is the
integral of the current density squared over time.
g-jj 2 dt or (l/A 2 )Ji 2 dt
(4)
The characteristic resistivity versus specific action
curve shows the resistivity of the bridgewire (foil) as
it passes through the material phase changes; solid,
liquid, and vapor, Fig. 6. Bridge burst is the
condition in which the bridge is vaporized and arc
breakdown occurs through the vapor. This
corresponds to the peak resistivity.
The characteristic resistivity as a function of energy
or specific action curve is obtained from the
instrumentation system by the measurement of the
current through the bridge and the voltage drop
across the bridge, Fig. 7. The voltage drop across
the bridge divided by the current through the bridge
gives the bridge resistance. Resistivity is calculated
by multiplying the resistance by the bridge cross
sectional area and dividing by the bridge length.
Specific action is calculated by squaring the current
and integrating over time while dividing by the
square of the bridge cross sectional area. Energy is
calculated by multiplying voltage and current and
integrating over time.
Tucker and Stanton 3 extended the Gurney method of
predicting the terminal velocity of explosively driven
projectiles to flyers driven by exploding foils in an
EFI detonator. This couples input electrical
parameters with EFI detonator mechanical output
parameters; namely flyer velocity. The Gurney
analysis of an explosive system is based on
conservation of momentum and the assumption that
the kinetic energy of the system is proportional to the
total energy released by the exploding foil. The
following is an approximate or simplified analysis
(known as a modified Gurney analysis). The ratio of
the system kinetic energy to the energy released is
the Gurney efficiency, r\, and the Gurney energy, Eg
is given by
Eg^e
(5)
where e is the energy deposited into the foil. The
solution of the momentum and energy equation
yields a prediction of the terminal flyer velocity, Uf
u f = (2 Eg) - 5 /(geometry)
(6)
where /(geometry) is a known factor dependent upon
the EFI geometry.
Tucker and Stanton 3 also showed that the Gurney
energy could be empirically related to the burst
current density of the foil.
E g = kj b n
(7)
where k is the Gurney coefficient and n is the
Gurney exponent. Measurement of the burst current
density and knowledge of the Gurney energy allows
the calculation of the Gurney coefficient and
exponent. Once the Gurney coefficient and exponent
are known, the terminal flyer velocity can be
calculated for a determined burst current density.
From the measurement of the flyer velocity, the flyer
pressure pulse magnitude, P, and duration, t,
imparted to the explosive receptor can be calculated
from Hugoniot pressure - particle velocity (P-u)
relationships. 4 Explosive initiation criteria can then
be calculated to determine initiation margin. Some
explosives are characterized by the relationship
P n x>K
(8)
where K is a constant and n is an exponent specific
to an explosive. 5 For explosive initiation
(detonation), this criterion must equal or exceed the
specified constant, K. Other explosives are
characterized by initial shock pressure, P, versus run
- 151 -
distance to detonation, x, plots or "Pop plots". 6
These plots can be expressed empirically by the
relationship
log P = A - B log X or
P = C + Dx" 1
(9)
(10)
where A, B, C, and D are constants for least squares
data fit.
4.1 SAMPLE DATA
A typical EBW and EFI detonator were selected and
tested in order to present typical data output. The
EBW is a 1.2 x 20 mil Au bridgewire in contact with
a PETN explosive DDT column (18.5 mg 0.88
g/cm 3 initial pressing, 9.3 mg 1.62 g/cm 3 output
pellet). The EFI is a 15 x 15 x 0.165 mil square Cu
bridge with a 1 mil thick Kapton flyer. An
investigation was conducted to observe the behavior
of the detonators over a range of operating current
density. The response of the EBW and EFI
detonators to a similar CDU burst current level pulse
was also investigated to verify that CDU and CDS
generated data are comparable. The data is
presented in a summary format at bridge burst
condition. Bridge burst resistivity, specific action,
and energy are plotted versus current density, Fig. 8
through 13.
Based upon these results, several observations could
be made.
■ Resistivity at bridge burst decreases with
increasing current density for the EBW, Fig. 8.
■ Specific action to bridge burst remains fairly
constant over current density range for both the
EBW and EFI, Fig. 9 and 12.
■ Energy to bridge burst increases with increasing
current density for both the EBW and EFI, Fig.
10 and 13.
■ Resistivity at bridge burst remains fairly
constant over current density range for the EFI,
Fig. 11.
■ CDU and CDS generated data are comparable,
Fig. 11 through 13.
From these observations, in order to adequately
model an EBW or EFI detonator, resistivity versus
specific action or energy data needs to be taken at
three current levels; slightly above threshold (50%
fire/no-fire), 1.5 times threshold, and 2 times
threshold (normal minimum operation).
Previous computer simulations always predicted a
much higher voltage across the bridge than was
measured. The "old" resistivity versus specific
action look-up table data for a gold EBW and a
copper EFI are compared to recently, "new",
generated data in Fig. 14 and 15. Since the peak
resistivity is much lower, predicted voltages now
closely match actual values.
The mechanical output of both the EBW and EFI
detonators was also observed over the range of
operating current density by using the VISAR. The
flyer velocity of the EBW closure disk was measured
at a PMMA window interface. Flyer velocity did not
change over the current range. This was expected,
Fig. 16. EFI flyer velocity increased with increasing
current density as expected, Fig. 17. The EFI
Gurney energy was calculated from the flyer velocity
and current density, Fig. 18. A least squares data fit
yielded a Gurney coefficient of 0.00125 and a
Gurney exponent of 1.28.
5.0 INTEGRATION OF DETONATOR
STUDIES DATA INTO PREDICTIVE
COMPUTER CODES
Detonator studies data are used in computer codes to
predict the electrical and mechanical behavior of
bridges as they burst. An electrical circuit solver
computes current as a function of time and then
"looks up" resistivity in a look-up table or calculates
the resistivity with an empirical relationship as a
function of computed energy or specific action to get
the instantaneous bridge resistance. Once a burst
current is known, for an EFI, a flyer velocity can be
calculated. A list of some of the electrical circuit
solvers available along with a brief description
follows.
■ AITRAC - complex circuit solver with bursting
wire & foil look-up table^
■ CAPRES - simple circuit solver with bursting
foil look-up table and electrical Gurney routine
■ PSpice© - complex circuit solver with bursting
elements added by Furnberg (empirical
function) and Peevy (look-up table) with
electrical Gurney and P 11 * initiation criterion^
■ Fireset - code by Lee with empirical resistivity
function 10
■ Slapper - code by R. J. Yactor, Los Alamos
National Laboratories, with empirical resistivity
function, electrical Gurney, and Pop plot
explosive initiation criteria.
Electrical Gurney and P^ initiation criterion are
implemented into the PSpice electrical circuit
- 152 -
simulator as custom circuit elements using the
Analog Behavioral Modeling capability.
5.1 COMPUTER PREDICTION VERSUS DATA
A computer simulation of a typical capacitor
discharge unit (CDU) firing system with a single EFI
detonator was performed using the latest CDS
generated resistivity versus specific action data look-
up table. The firing system lumped parameters are:
C = 0.2^F
R = 100 mQ
L = 17 nH.
Simulation output versus test data is shown
graphically in Fig. 19 and 20. As can be seen in
Table 1, simulations compare well to experiment.
6.0 CONCLUSION
The CDS has been fully documented. Newly
obtained data are more accurate and improves
computer simulation, electrical/mechanical
performance predictions and failure analysis of EBW
and EFI detonators. Future plans are to model other
EBW and EFI detonators of interest.
6. B. M. Dobratz, P. C. Crawford, LLNL
Explosives Handbook Properties of Chemical
Explosives and Explosive Simulants. Lawrence
Livermore National Laboratory, Report No.
UCRL-52997, 1985.
7. Berne Electronics Inc., Sandia National
Laboratories. Albuquerque. AITRAC
Augmented Interactive Transient Radiation
Analysis bv Computer User's Information
Manual . Sandia National Laboratories, Report
No. SAND77-0939.
8. PSpice (a registered trademark of) Microsim
Corporation, 20 Fairbanks, Irvine, California.
9. G. R. Peevy, S. G. Barnhart, C. M. Furnberg,
Sla pper Detonator Modeling Using the PSpice©
Electrical Circuit Simulator. Sandia National
Laboratories, Report No. SAND92-1944.
10. R. S. Lee, FIRESET. Lawrence Livermore
National Laboratory, Report No. UCID-21322,
1988.
7.0 REFERENCES
1. O. B. Crump, Jr., P. L. Stanton, W. C. Sweatt
The Fixed Cavity VISAR. Sandia National
Laboratories, Report No. SAND-92-0162.
2. T. J. Tucker, R. P. Toth, EBW1: A Computer
Code for the Prediction of the Behavior of
Electrical Circuits Containing Exploding Wire
Elements . Sandia National Laboratories, Report
No. SAND-75-0041.
3. T. J. Tucker, P. L. Stanton, Electrical Gurnev
Energy: A New Concept in Modeling of Energy
Transfer from Electrically Exploded
Conductors . Sandia National Laboratories,
Report No. SAND75-0244.
4. P. W. Cooper, "Explosives Technology Module
D, Shock and Detonation," Sandia National
Laboratories Continuing Education in Science
and Engineering, INTEC Course No. ME717D.
5. A. C. Schwartz, Study of Factors Which
Influence the Shock-Initiation Sensitivity of
Hexanitrostilbene (HNS) . Sandia National
Laboratories, Report No. SAND80-2372.
- 153 -
Fig, 1 Photograph of Cable Discharge System
— (heo) D=-U}-
( VBOTT \ / 1B88FT A
I RG218 J I R0218 J
J>:
GAS
WITO
i»*v
powet
SUPPLT
TOO
PULSE
GENERATOR
DELAY
GENERATOR
Fig. 2 Schematic of Cable Discharge System
- 154 -
DSA 602 A DIGITIZING SIGNAL ANALYSER
date: 5 -JAN- 9 4 tia«: 10:52:01
Tfek
1.125V
D
125mV
CABLE DISCHARGE SYSTEM
•OUTPUT INTOSHORT CIRCUIT-
Fig. 3 Typical DSA Current Waveform
DSA 602A DIGITIZING SIGNAL ANALYZER
data: 5-JAN-94 tim»z 10:55:13
Ttek
-12SiiV-
-ll.Bn«
7.68
! L-'M^T'I HI
125m\
: J •' '• ''■ : '■ = -'
: \.l CABLE DISCHARGE SYSTEM
/ OUTPUT INTO SHORT riPriITT \
LI
_J/ ^ ! ; \ \ \ \ \ I
X'
-1BBB AMPSi
lBns^dlv ET}
B8.2n»
.anHEHrcHM
Fig. 4 Typical Current Leading Edge
- 155 -
DSA 602A DIGITIZIHG SIGNAL ANALYZER
dot*: 6-AUG-93 tla*: 13:20:30
Ttek
675mUj
Fig. 5 Calculated Waveforms
6.00E-04 T
O.OOE+00
O.OOE+00 5.00E+08 1.00E+09 1.50E+09
Specific Action (A A 2-s/cm A 4)
2.00E+09
1,2x20® 400 A
Fig. 6 Typical Resistivity vs. Specific Action Profile
- 156 -
200 300
TIME(nSEC)
-CURRENT
Ufend
VELOCITY
- VOLTAGE
Fig. 7 Cable Discharge System Waveform for EFI
1000
900
800
E 700
o
§
600
g
500
£
400
£
CO
300
CO
UJ
cc
200
100
■r ~ "* " " " " ~ — " ~~ "
^
■
1 «H , m
_j_j l, ,
20 40 60 80 100 120 140 160
CURRENT DENSITY (amps/cm ~ 2)
(Millions)
180 200
Fig. 8 EBW Burst Data Summary of Resistivity vs. Current Density
- 157 -
<
CM ~
< °*
9 $
o
o
LU
a.
CO
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
— *— * - * -*-j - u-
■
_ __ «. __ I _,..„ _ _
— _ j_ 1
20 40 60 80 100 120 140 160 180 200
CURRENT DENSITY (amps/cm ~ 2)
(Millions)
Fig. 9 EBW Burst Data Summary of Specific Action vs. Current Density
D
O
>
o
cc
W
2
LU
100
90
80
70
60
50
40
30
20
10
' ' T m ir " l -
_ „*„■ „ ||f J L _
- - ■■— - — —
20 40 60 80 100 120 140 160
CURRENT DENSITY (amps/cm ^ 2)
(Millions)
180 200
Fig. 10 EBW Burst Data Summary of Energy vs. Current Density
- 158 -
2.50E-04
2.00E-04
E
V
J 1.50E-04
O
>
P 1.00E-04
55
UJ
5.00E-05
O.OOE+00
• #
• CDS DATA
■ CDU DATA
O.OOE+00 5.00E+06 1.00E+07 1.50E+07 2.00E+07 2.50E+07 J.00E+O7
CURRENT DENSITY (amps/cm A 2)
3.00E+09
T 2.50E+09
E
o
CM
<
2.00E+09
•2* 1.50E+09
Z
o
H
O
< 1.00E+09
O
O
UJ
£ 5.00E+08
(0
O.OOE+00
Fig. 11 EFI Burst Data Summary of Resistivity vs. Current Density
> CDS DATA
i CDU DATA
O.OOE+00 5.00E+06 1.00E+07 1.50E+07 2.00E+07 2.50E+07 3.00E+07
CURRENT DENSITY (amps/cm A 2)
Fig. 12 EFI Burst Data Summary of Specific Action vs. Current Density
- 159 -
150.0
120.0 -
3 90.0 -
o
g 60.0 -f
• CDS DATA
° CDU DATA
30.0 --
0.0
O.OOE+00
1
5.00E+06
-h
-h
H
1 .00E+07 1 .50E+07 2.00E+07 2.50E+07 3.00E+07
CURRENT DENSITY (amps/cm A 2
Fig. 13 EFI Burst Data Summary of Energy vs. Current Density
1.20E43 T
^ 1.00E-03 -
E
V
g 8.00E-04 -
^ 6.00E-04 --
>
to 4.00E-04
2.00E-04 -
0.00E+00 \ \ ><** *
1.2x20 ©400 A
Tucktrdata
i .i p~ — , ■ ~ — . -J — t- m ft » m —
0.00E+00 1.00E+09 2.00E+09 3.00E+09
Specific Action (A A 2-s/cm A 4)
4.00E+09
Fig. 14 New vs. Old EBW "Look-up" Table
- 160 -
O.OOE+00
O.OOE+00 4.00E+09 8.00E+O9 1.20E+10 1.60E+10
Specific Action (A A 2-s/cm A 4)
15x16x.165e3kA
Old look-up tabte
2.00E+10
Fig. 15 New vs. Old En "Look-up" Table
■t i r
> i i i
Orertay
i i i i
Nv
'^^^*^^
~ +T~°
°4— -
1! %%
200 300
TIME(iiSECONDS)
- VELOCITY, 6KA
VELOCITY, 4KA
Legend
■ VELOCriY, 8KA
- VELOCITY, IKA
Fig. 16 EBW Output Flyer Velocity vs. Current Density
- 161 -
« -r
4 --
E 3
E
8 2
1 "
-h
H-
-+-
PART OF CURRENT SHUNTED
AWAY FROM BRIDGE
• COS DATA
* CDUDATA
600 1000 1500
2000 2500 3000 3500
CURRENT (amps)
4000 4500 5000
Fig. 17 EFI Flyer Velocity vs. Current Density
>%
c
UJ
ST
c
3
o
ivv -
y
' m
10 -
/
m
1
1
■ .5*v A 2/fo*o
k*j*nFlt
1000
10000
Burst Current Density (GA/m A 2)
Fig. 18 EFI Gurney Energy vs. Burst Current Density
- 162 -
4.0K T
l.OK
Os lOOna
- I(RFS) • V(12)
Ti»
Fig. 19 Simulation Using New Look-Up Table Voltage and Current Traces
lMt.(! : Hl/Hh/!M
A
/
y
/
\
!
\
\
\
\
\
s
\
II
1 M
i n
1 11
i ii
A II
i li
i <n
i fl
■ ii
i
TM<n$>
Fig. 20 Test Data Voltage and Current Traces
- 163 -
Table 1
EFI Simulation Output vs. Test Data
CDU
Charge
Voltage
(V)
Calculated
Burst
Current
(A)
Calculated
Flyer
Velocity
(mm/us)
Burst
Current
(A)
Flyer
Velocity
(mm/us)
1950
3009
4.1
3020
4.2
2600
4072
4.8
3960
4.9
2800
4325
5.0
4170
5.1
- 164 -
INITIATION CURRENT MEASUREMENTS FOR HOT BRIDGEWIRE DEVICES
Gerald L. O'Barr (Retired, General Dynamics, 1 Oct 1993)
) ^
ABSTRACT One-shot type testing of hot bridgewire
explosive cartridges provides the weakest possible firing
characteristic data. One-shot type testing includes the
Bruceton and the Probit methods, and all their off-shoots.
One-shot testing is used for only one reason: the fear of
"dudding." Modern programmable power supplies and
oscilloscopes can now be used to obtain data with no fear of
dudding. Any continued use of these old, one-shot type test
methods is irresponsible behavior. Our society deserves
better testing methods and will get them through the courts
if we cannot make these changes on our own.
1 . INTRODUCTION
Explosive cartridges often use
a bridgewire initiation
system. A bridgewire is a
very small wire, approximately
0.005" in diameter and 0.2"
long, through which electrical
current can be forced to flow.
Because of the electrical
resistance of the wire, the
current can cause the wire to
become hot like the filament
in a light bulb. Around the
bridgewire is a sensitive
ignition mix that will ignite
with temperature. As the
bridgewire gets hot, it
ignites the ignition mix,
which then sets off the main
charge of the cartridge, often
through intermediate mixes
between the ignition mix and
the main charge.
The reliability of operation
of an explosive device is
critical. Being a destructive
event, one would not want an
explosive cartridge to go off
before it is needed (for
safety) and yet, when its
function is required, since
explosive devices are usually
used for critical operations,
it must work quickly and
reliably. Since the primary
initiation is by the flow of
current, the following
questions must be asked:
A. What is the maximum
current that can flow
through the bridgewire
and not have it ignite or
explode?
B. What is the minimum
current that can be used
and still be sure that it
will ignite or explode?
The answer to A provides what
is called the "no-fire"
current. It tells one the
degree of safety that might
exist in using this device.
If the current for A is so low
that random stray voltages
might induce sufficient
- 165 -
current to set it off, then it
would be unacceptable. Often,
a one-ampere current is
specified as being the minimum
acceptable no-fire current.
If the bridgewire resistance
could be less than one ohm, a
power minimum of one watt is
also sometimes specified.
The answer to B provides the
"all-fire" current. This
value must obviously be more
than A, and hopefully low
enough that the power supply
being used to set it off can
provide the current that is
required. Values of 3.5 to 5
amperes are often specified.
In statistical terminology,
the all-fire and no-fire
current requirements are often
stated as follows:
A. The cartridges shall have
a 1 ampere/1 watt or
greater no-fire current
with a reliability of
99.9%, at a confidence
level of 95%.
B. The cartridges shall have
a 3.5 ampere or less all-
fire current with a
reliability of 99.9%, at
a confidence level of
95%.
These statistical
requirements can be determined
if the firing currents are
normally distributed and the
mean and the standard
deviation of the lot's firing
current can be determined.
Basically, this report will
discuss a new test method for
measuring the mean and the
standard deviation of the
firing current for a lot of
explosive cartridges.
2.0 DIFFICULTIES IH MEASURING
THE INITIATION CURRENT
The phrase "firing current"
has many different meanings.
This results in certain
difficulties that we will take
care of now. The firing
current is often used to mean
the current being applied to
the bridge-wire. It is also
used for the minimum current
required to ignite a
cartridge. It is this minimum
current, along with its
distribution, that allows us
to determine the all-fire and
the no-fire. Therefore, when
we mean this minimum current,
we shall use the words,
"initiation current."
To measure the initiation
current, it would seem easy to
connect a cartridge up to a
variable power source and
manually turn up the current
until it ignites. Another
method would be to use a
series of ever increasing
steps or pulses of current.
The current at which it
ignites could then be the
desired data.
When cartridges were
originally made (over 30 years
ago), such efforts often
proved to be impossible. The
"sensitive" ignition mix, when
exposed to heat, could
degrade. If one raised the
current too slowly, or exposed
a cartridge to several firing
currents below that required
for ignition, the cartridge
could actually become
impossible to ignite. When
the chemicals making up the
- 166 -
ignition mix become
sufficiently degraded, the
cartridge becomes a dud.
Thus, the initiation current
was often dependent on the
rate at which the current was
applied, and could become
infinite. The industry
quickly learned that only
"virgin" cartridges could be
tested in a one-time-only
test.
For this reason, all tests for
explosive cartridges (Bruceton
testing, Probit testing, and a
multitude of testing based
upon these approaches) use a
one-shot approach. A
cartridge is exposed to one
pre-selected current value,
and a fire or no-fire result
is recorded.
The data obtained by this
approach is not good. If a
cartridge is tested at 2.30
amperes and it fires, no one
can say that this was the
initiation current for this
cartridge. The Bruceton and
Probit test methods would use
this data as a firing point,
but all one knows for sure is
that the true initiation
current for this cartridge was
this value or less. It could
have been much less. It could
have been so much less that it
could have skewed all the rest
of the data. But in the one-
shot method, one will never
know the true initiation
current for that particular
cartridge.
The same things are true if
the cartridge did not fire.
Again, the Bruceton and the
Probit test methods assume
that it is the no-fire point.
The actual no-fire point might
be much greater. It could
even be a dud, with an
infinite firing current value.
Neither the Bruceton nor the
Probit methods will be
sensitive to these situations.
Because the data that comes
from a one-shot test is not
normally the initiation
current for that cartridge (if
it fires), nor the real no-
fire current for that
cartridge (if it does not
fire), then the data is
extremely poor data. It has
almost no meaning except as
limits to the values being
sought, and these limits have
no value unless they are
repeated a great number of
times in a well controlled
lot. If you are making tests
on a lot that is not well
controlled, the limit data
will be entirely useless.
Worst of all, one can seldom
tell by looking at the
Bruceton or Probit data if the
data is from an adequately
controlled lot, or when the
number of limit tests are
really adequate.
3.0 NEW METHODS
Today, one jjoes not need to
manually turn up the current
to fire a cartridge. One does
not need to follow a moving
indicator to read what might
have been the initiation
current . Today , with
programmable current
generators, and oscilloscopes,
very controlled current
profiles and measurement
devices can measure the actual
initiation current of a
- 167 -
device. It can be done at a
rate where no significant
degrading will occur.
Thus, today, in any modern
laboratory, there is no need
to work with the out-of-date,
and very poor data generating
methods such as the Bruceton
or Probit one-shot methods. A
"dynamic ramp" test method can
supply reliable and specific
initiation data for all
cartridges tested.
It is also a fact that over
these many years, much more
stable ignition mixes are now
being used. For most modern
explosive cartridges, one
could probably even use a
manual method and obtain
better data than what a
Bruceton or Probit method
might provide.
4.0 THE DYNAMIC RAMP TEST
METHOD The dynamic ramp
test used a programmable power
supply that puts out a
controlled current ramp from
zero to five amperes. The
rate of the ramp, as used in
these tests, was approximately
3.5 amperes per second. The
current circuit included a
standard one-ohm resistor in
series with the explosive
cartridge. The voltage across
the one-ohm resistor was
recorded on an oscilloscope
with memory trace recording.
The scope was calibrated so
that within the expected
firing levels, currents could
be read to the nearest 0.01
amperes, with an overall
accuracy estimated to be
better than ±0.02 amperes.
The firing point of the
cartridges being tested
appeared to be a clean break
in the circuit, with the
voltage returning to zero when
the bridgewire initiated the
cartridge. If the
programmable power supply has
too high of a voltage
capability, current can
continue to flow even when the
bridgewire is "broken" by
flowing the current through
the ionized gas that is
created in an explosion. This
would indicate a higher firing
current then that actually
required. When ionization
flow is present, the trace is
usually very uneven without a
clean break.
5.0 RESULTS
The results for a series of
ten consecutive firings are
shown in Table I. The results
from a small Bruceton test of
17 firings is shown in
Appendix A.
The means determined from
these two tests were almost
identical, 2.43 amperes in the
dynamic ramp test and 2.44
amperes in the Bruceton. The
standard deviations, however,
are much different, 0.234
amperes for the dynamic ramp
test and only 0.070 amperes
for the Bruceton test. This
difference in the standard
deviation is over three to
one.
Table 2 shows the results
after 20 firings. The data
continues to confirm the
statistics that had been
obtained in Table 1. Figure
1 shows the distribution for
- 168 -
TABLE 1. DYNAMIC RAMP TEST
PART NO. :55-06018-2 LOT 13-37700 DATE: 1 FEB 1993
CARTRIDGE
NO.
PEAK
CURRENT (Xi)
(Xi-X) A 2
1
86845
2.50
0.0045
2
86811
2.14
0.0858
3
86881
2.39
0.0018
4
86850
2.32
0.0128
5
86854
2.71
0.0767
6
86864
1.97
0.2144
7
86991
2.66
0.0515
8
86883
2.55
0.0137
9
86866
2.60
0.0279
10
86816
2.49
0.0032
SUM Xi =
24.33
SUM(Xi-X) A 2 =
0.4924
N =
10
t (for90%,n= 9) =
1.83
MEAN = X =
SUMXi/ N
—
2.433
STANDARD DEVIATION = S.D. =
(SUM(Xi-X) A 2/(N-1)) A .5 = 0.234
STANDARD ERROR
OF THE MEAN (S.D.)/(N\5) = 0.074
STANDARD ERROR
OF THE S.D. = (S.D.)/(2N A .5) = 0.052
ALL FIRE =
X + t (S.D./N A .5) + 3.09 ( S.D. + t S.D./(2N)\5) = 3.587
NO FIRE =
X - t (S.D./N A .5) - 3.09 ( S.D. + t S.D./(2N)\5) = 1 .279
- 169 -
TABLE 2. DYNAMIC RAMP TEST
PART NO. :55-06018-2 LOT 13-37700 DATE: 1 FEB 1993
CARTRIDGE
NO.
PEAK
CURRENT (Xi)
(Xi-X) A 2
1
86845
2.50
0.0057
2
86811
2.14
0.0809
3
86881
2.39
0.0012
4
86850
2.32
0.0109
5
86854
2.71
0.0815
6
86864
1.97
0.2066
7
86991
2.66
0.0555
8
86883
2.55
0.0158
9
86866
2.60
0.0308
10
86816
2.49
0.0043
11
86826
2.50
0.0057
12
86907
2.50
0.0057
13
86815
2.35
0.0056
14
86863
2.54
0.0133
15
86888
2.02
0.1636
16
86885
2.58
0.0242
17
86814
2.05
0.1403
18
86829
2.47
0.0021
19
86956
2.65
0.0509
20
86926
2.50
0.0057
SUM Xi =
48.49
SUM(Xi-X) A 2 =
0.9101
N =
20
t (for90%,n=19) =
1.725
MEAN = X =
SUMXi/ N
—
2.425
STANDARD DEVIATION = S.D. =
(SUM(Xi-X) A 2/(N-1))\5 = 0.219
STANDARD ERROR
OF THE MEAN (S.D.)/(N A .5) = 0.049
STANDARD ERROR
OF THE S.D. = (S.D.)/(2N A .5) = 0.035
ALL FIRE =
X + t (S.D./N A .5) + 3.09 ( S.D. + 1 S.D./(2N) A .5) = 3.370
NO FIRE =
X - t (S.D./N\5) - 3.09 ( S.D. + t S.D./(2N)\5) = 1 .479
- 170 -
FIGURE 1. FIRING DISTRIBUTION
55-06018-2 LOT 13-37700 1 FEB 1993
D
TOTAL DISTRIBUTION
FIRST 10
LAST 10
1.85 1.95 2.05 2.15 2.25 2.35 2.45 2.55
FIRING CURRENT (AMPERES)
2.65 2.75
2.85
these firings. A deviation
from a normal distribution
does exist , but a larger set
of data would be desirable
before too much should be made
of these details. The
important point is made, the
distribution function is
obtainable by this test
method .
6.0 LIMITATIONS OF THE NEW
METHOD There are only two
limitations in using the
dynamic ramp test method. The
current ramp can be too slow
or too fast.
If one were to use a very fast
current ramp (possibly over 30
amperes per second) , a thermal
diffusivity effect might be
observed. This effect is due
to the amount of time it takes
the heat energy generated in a
bridgewire to distribute
itself out to the ignition mix
to ignite it. If during this
time, the current in the
bridgewire changes, the
initiation current will appear
to be slightly greater than
that actually required.
Because bridgewires are so
small, and are made of metals
that have relatively high
thermal conductivity values,
this time is very small.
This time can be estimated in
other ways. The cartridges
which we were testing normally
fire in one millisecond when
using twice their mean
initiation current.
Therefore, their time constant
is about 3.5 milliseconds.
Using a ramp rate of only 3.5
amperes per second, an error
of about .01 amperes would
occur due to these diffusivity
effects.
The other limit is being too
slow. The slower the ramp
rate, the greater could be the
degradation of the ignition
mix. With a ramp rate of 3.5
amperes per second, and all
firings being at a value of
less than 3.5 amperes, this
means that all the units fired
within one second of time.
Very little degradation could
be expected in conditioning
times as short as one second.
7.0 ADVANTAGES OF THE NEW
METHOD Explosive cartridges
are usually very expensive.
In order to obtain reliability
they must be made in large
lots under controlled
conditions, and a large
percentage of the lot tested.
The dynamic ramp test will
directly reduce the number of
cartridges required for
testing. Even better than
this, however, is a great
increase in reliability. The
dynamic ramp test will catch
all cartridges that might be
outside of the normal
distribution. Bruceton and
Probit type testing cannot
produce data specific to a
single cartridge, and
therefore abnormal cartridges
tested with these methods
cannot make much, if any,
change in the final results.
The real power of the dynamic
ramp test is providing, for
the very first time, the
specific initiation current
for individual cartridges.
This data will now make it
possible to actually confirm
- 172 -
the true current distribution
of a lot.
8.0 CONCLUSION
If one has modern test
equipment, there are no known
reasons why one would not want
to use the dynamic ramp test
method. It brings the testing
of explosive cartridges back
to standard statistics.
Books have been written on the
questionable assumptions and
misuse of data from the
Bruceton and Probit methods.
All those questions disappear
with the use of the dynamic
ramp test. The applications
of the Bruceton and Probit
methods require special charts
and calculations. The dynamic
ramp test uses the same
statistics that would be used
in any other normal approach.
It is true that the dynamic
ramp test is still a
statistical test. The
meaningfulness of the results
will, as always, depend upon
how well the test units
reflect the distribution of
the lot. If non-random or
incomplete selections are made
from a lot, the dynamic ramp
test data will be faulty to
the extent that this occurs.
But, this is true for all
statistics, and can be guarded
against in the same way that
all other statistical tests
are handled.
This new method actually
allows additional research.
If at any time a set of
cartridges are identified as
being "out-of-family, " having
seen some unexpected exposure
or has some other observed
anomaly, the dynamic ramp
test, with very few test
units, can quickly tell if
those anomalies are causing
any effect in their firing
characteristics. For Bruceton
or Probit testing, you might
need 30 or 40 units before you
could feel good as to whether
a difference exists between
two different groups.
Research into thermal
diffusivity effects and into
degradation effects could also
be easily accomplished. These
reasons make the dynamic ramp
test an exciting approach to a
problem that has existed for
over thirty years. It will be
a powerful and necessary
approach if we are to remain
competitive.
9 . RECOMMENDATIONS
Government regulations
requiring Bruceton or Probit
testing of bridgewire type
explosive cartridges should be
modified to include, as a
preference, the dynamic ramp
testing approach. The dynamic
ramp testing is a major
improvement. It provides
stronger, more direct
statistical data for
determining the mean and the
deviation of the initiation
current for bridgewire type
explosive cartridges. In
addition, the true
distribution of the data is
observable. For all previous
testing methods, assumptions
of the distributions were
required and could never be
actually confirmed.
Therefore, all previous
testing was always with some
- 173 -
uncertainty, especially where
projections of several
standard deviations were
required.
The dynamic ramp test method
allows the initiation current
of individual cartridges to be
measured. This greatly
increases the research that
can be done with explosive
cartridges. The effects of
any manufacturing variable or
any environmental exposures
can readily be assessed.
Also, by taking the ramp rate
to great extremes, the
diffusivity effects and the
degrading effects (if any) of
any particular design can be
quickly determined.
- 174 -
APPENDIX A
CALCULATIONS (55-06018-2, Lot 13-37700)
Fires No-Fires (NO i x Ni i 2 x Nj
10
5 12 4
3 4 4 4
12
Applied
I i
2.6
3
2.5
2
2.4
1
2.3
Mean
(XR)
Xr
=
10 N = 7 A=6 B = 8
10 + Al (A/N + 1/2)
2.3 + 0.1 (6/7 + 1/2)
= 2.44 amperes
Standard Deviation (or)
M = N x B - A 2
N 2
7 X 8 - 6 2
7 2
0.4082
Therefore,
S = 0.70 (from table)
or = S(AI)
(0.70) (0.1)
0.070
Sampling Error (o a )
a a = or H/N 1/2 (H from table)
0.07 (1.7)/7 1/2
.045
Sampling Error (o x )
o x = or G/N 1/2 (G from table)
0.07 (1.3)/7 1/2
0.0344
Confidence Intervals (single tail statistics)
Y + ta v (t = 1.94 from table at 95% level of confidence)
1. For the mean: Xr + to x
2. For the standard deviation: or + to a
- 175 -
APPENDIX A - Continued
No-Fire (0.999 reliability at 95% confidence)
(Xr - tax) -3.09 (or + ta a ) > 1 ampere
2.44 - 1.94 (0.0344) - 3.09 [0.07 + 1.94 (0.045)] > 1 ampere
1.88 > 1 ampere
All-Fire (0.999 reliability at 95% confidence)
(Xr + tax) +3.09 (aR + ta a ) < 3.5 amperes
2.44 + 1.94 (0.0344) + 3.09 [0.07 + 1.94 (0.045)] < 3.5 amperes
2.99 < 3.5 ampere
- I7B -
?■
DEVELOPMENT AND DEMONSTRATION
OF AN
NSI-DERIVED GAS GENERATING CARTRIDGE (NGGC)
by
Laurence J. Bement
NASA Langley Research Center
Hampton , Virginia
Morry L. Schimmel
Schimmel Company
St. Louis, Missouri
Harold Karp
Hi-Shear Technology
Torrance, California
Michael C. Magenot
Universal Propulsion Co.
Phoenix, Arizona
Presented at the 1994 NASA Pyrotechnic Systems Workshop
February 8 and 9, 1994
Sandia National Laboratories
Albuquerque, New Mexico
- 1/7 -
DEVELOPMENT AND DEMONSTRATION OF AN NSI-DERIVED
GAS GENERATING CARTRIDGE (NGGC)
Laurence J. Bement
NASA Langley Research Center
Hampton, Virginia
Harold Karp
Hi-Shear Technology
Torrance, California
Morry L. Schimmel
Schimmel Company
St. Louis, Missouri
Michael C. Magenot
Universal Propulsion Co.
Phoenix, Arizona
Abstract
Following functional failures of a number of small pyrotechnically ac-
tuated devices, a need was recognized for an improved- output gas gen-
erating cartridge, as well as test methods to define performance. No
cartridge was discovered within the space arena that had a larger output
than the NASA Standard Initiator (NSI) with the same important fea-
tures, such as electrical initiation reliability, safety designs, structural
capabilities and size. Therefore, this program was initiated to develop
and demonstrate an NSI-derived Gas Generating Cartridge (NGGC).
The objectives of maintaining the important features of the NSI, while
providing considerably more energy, were achieved. In addition, the
test methods employed in this effort measured and quantified the energy
delivered by the NGGC. This information will be useful in the appli-
cation of the NGGC and the design of future pyrotechnically actuated
mechanisms.
Introduction
Failures have occurred in several small pyro-
technically actuated devices, which attempted to
use the NASA Standard Initiator (NSI) as the
sole energy source. "Small pyrotechnically ac-
tuated devices" are defined here as those mecha-
nisms that require 500 to 1000 inch-pounds input
energy from a cartridge for reliable functioning.
The NSI has been used extensively within the
space community as both an initiator and a gas
generating cartridge. The NSI, shown in figure 1
and described in reference 1, is an electrically
initiated cartridge that contains a quantity of
pyrotechnic material. The output produced by
this material is heat, light, gas and burning par-
ticles, which can be used to ignite other mate-
rials and do work. An assessment was made of
the problems encountered in the use of the NSI
within the NASA. A survey was conducted to
determine if a cartridge existed or needed to be
developed to prevent these problems. A problem
that was immediately recognized in this survey
was the lack of test methods to define perfor-
mance of gas generating cartridges. Upon find-
ing no cartridge that met the requirements set
by this effort, an NSI-derived Gas Generating
Cartridge (NGGC) was then developed. The ap-
proach for this development was to modify the
NSI to produce more gas energy, to demonstrate
its performance through baseline firing tests, and
to demonstrate that it could meet the NSI envi-
ronmental qualification requirements. This sec-
tion has been divided into subsections to de-
scribe: (1) the failures that occurred with the
NSI, and the lack of test methods, (2) the survey
that was conducted to find candidate cartridges,
(3) the objectives to develop and demonstrate an
NGGC, and (4) the approach that was used to
develop and demonstrate the NGGC.
Failures and Lack of Test Methods
The failures that have occurred in critical
cartridge-actuated mechanisms, such as pin
pullers (ref. 2), separation nuts and explosive
bolts, can be attributed not only to insuffi-
- 178 -
WELD <REF)
TT
EPOXY
ELECTRICAL PIN
CUP. CLOSURE
DISK .INSULATING
DISK, INSULATING
BRIDGEWIRE
Figure 1. Cross sectional view of NASA Standard Initiator (NSI).
cient input energy, but also to a lack of under-
standing of pyrotechnic mechanisms and test-
ing methods (ref. 3). The energy output of
pyrotechnic gas generating cartridges is influ-
enced by the conditions into which they are fired.
For typical piston/cylinder configurations, these
conditions are volume (shape and size), mass
moved, resistance to motion (friction), and ther-
mal absorptivity/reflectivity of the structure.
The only existing standard for measuring car-
tridge output performance in the field of
pyrotechnics is the closed bomb, reference 4,
which is inadequate for measuring energy deliv-
ered by cartridges. The closed bomb is a fixed
volume into which the cartridge is fired. The
pressure produced in the volume is monitored
with pressure transducers and the data (pressure
versus time) are recorded. As described in ref-
erence 5, the closed bomb provides no quanti-
tative information that can be related to work
performed in an actual device.
The use of the NSI as a gas generating car-
tridge has both advantages and limitations. The
advantages are: (1) it is accepted in the com-
munity with no additional environmental qualifi-
cation required, (2) it has excellent safety fea-
tures, 1-amp/l-watt no-fire, and electrostatic
protection, (3) it has a demonstrated structural
integrity and (4) it has a demonstrated reliabil-
ity of electrical initiation and output as an ig-
niter. The limitations are: (1) it was not de-
signed for use as a gas generator, (2) the gas
output produced is inconsistent in different man-
ufacturing groups (ref. 2), and (3) it does not
- 179 -
provide sufficient work output for many small
mechanisms. To overcome these problems, the
NSI has been used with booster modules. These
modules are sealed assemblies that contain ad-
ditional pyrotechnic gas generating material and
are installed into the structure of the mechanical
device. This requires additional volume, mass
and seals, as well as additional costs for develop-
ment, demonstration, and qualification.
Survey of Gas Generating Cartridges
A survey of literature and personnel within
NASA and Air Force space centers was con-
ducted, using the following criteria:
1. Provide the following important features that
are the same as those in the NSI:
* safety
* reliability of electrical initiation
* high-strength construction
* small size
2. Output performance greater than that of the
NSI
3. Long-term thermal/vacuum stability for
space applications.
The survey revealed the following information.
Some cartridges do not have the NSI safety fea-
tures. None have the NSI demonstrated reliabil-
ity. Several use the same pyrotechnic materials
as the NSI. Several use gas generating materials
that are not stable under thermal/vacuum condi-
tions. None offer sufficient advantages for further
evaluation.
Based on this information, a decision was made
to develop a new, NSI-derived, Gas Generating
Cartridge (NGGC).
Objectives for Development and
Demonstration of the NGGC
The objectives of this effort were to demonstrate
the feasibility of designing/developing an NSI-
derived Gas Generating Cartridge (NGGC) by:
1. Maintaining the important electrical initia-
tion and structural reliability of the NSI
2. Providing significantly more energy than is
provided by the NSI
3. Characterizing the work performance of the
NSI and NGGC to assist in the design of
pyrotechnically actuated devices, and
4. Maintaining the same environmental surviv-
ability as the NSI.
Approach Used for Development and
Demonstration of the NGGC
The approach for this effort was divided
into designing/developing, demonstrating/
characterizing and environmental survivability.
Figure 2 shows the design for the NGGC, which
utilizes the NSI body and electrical interface.
The electrical interface is defined as the electri-
cal pins, bridgewire, bridgewire slurry mix and
the initial load of 40 milligrams of NSI mix. The
remaining volume within the NSI was filled with
a thermal/vacuum-stable gas-generating mix, in-
cluding the additional second load above the
ceramic cup. A joint development was con-
ducted with the two certified NSI manufactur-
ers, Hi-Shear Technology and Universal Propul-
sion Company (UPCO).
The performance of the NGGC was established
by measuring and recording input and output
characteristics for comparison to the same mea-
surements in other cartridges. That is, for in-
put electrical ignition performance tests, a direct-
current electrical circuit was used to apply input
electrical currents in discrete steps, measuring
the times from current application to bridgewire
break and to first indication of pressure. The
output performance of the NGGC was character-
ized with four test methods, the industry stan-
dard and three work-measuring devices: (1) The
Closed Bomb is the industry standard, which in-
volves firing the cartridge into a closed, fixed vol-
ume, measuring the pressure versus time in the
volume, (2) The Energy Sensor, which involves
firing the cartridge against a constant force, mea-
suring energy as the distance stroked times the
resistive force, (3) The Dynamic Test Device,
which involves firing the cartridge to jettison a
mass, determining energy by measuring veloc-
ity of the mass to calculate l/2mv 2 and (4) The
Pin Puller, which involves firing the cartridge to
withdraw a pin for release of an interface, deter-
mining energy by measuring velocity of the pin
to calculate l/2mv 2 .
To demonstrate the environmental survivability
of the NGGC, the input and output performances
of as-received (untested) units were used as per-
formance baselines for comparison to the perfor-
mances achieved by units that were environmen-
tally tested. Changes in functional performance
would indicate a sensitivity to environments.
- 180 -
DISK, INSULATING
GAS-GENERATING LOAD
85-90 MG
Zr/KC104
PROPELLANT
40 MG
Figure 2. Cross sectional view of NASA Standard Gas Generator (NSGG), showing changes to NSI configuration.
Cartridges Tested
Four cartridges were evaluated in this program,
the NSI the Viking Standard Initiator (VSI),
and two NGGC models, which were produced by-
different manufacturers.
NASA Standard Initiator (NSI)
The NSI units evaluated in this program were
manufactured by Hi-Shear Technology. Hi-Shear
Technology utilized the same Zr/KClC>4 in both
the NSI and their NGGC.
Viking Standard Initiator (VSI)
The VSI is functionally identical to the NSI
and was manufactured by Hi-Shear Technology
in 1972 for the Viking Program's lander on the
surface of Mars; Since very few NSI units were
available, the VSI functional performances were
used to represent that produced by the NSI.
NSI-derived Gas Generating Cartridge
(NGGC)
The NGGC units, manufactured by Hi-Shear
Technology and UPCO, are the same as the NSI,
except for the major changes shown in figure 2.
The electrical interface from the bridgewire re-
mained the same with the slurry mix, but the
first press was 40 mg of Zr/KC10 4 at 10,000 psi,
instead of the 57 mg for the NSI. The gas gen-
erating materials were selected by each manufac-
turer, based on a demonstrated stability against
elevated temperature and long-term vacuum en-
vironments. This material was pressed into
and completely filled the charge cavity of the
ceramic cup. An isomica insulating disc was
bonded across the face of the cup to prevent
an electrical path from the bridgewire through
the pyrotechnic material to the cartridge case.
A second increment of gas-generating material
was pressed on top of the insulating disc to fill
as much of the free volume as possible. The
- 181 -
CONSTANT
CURRENT
SOURCE
CURRENT
VOLTAGE
MONITOR
CARTRIDGE
MAGNETIC
TAPE
RECORDER
10 cc
CLOSED
BOMB
OSCILLO-
GRAPH
I
PERMA-
NENT
RECORD
J
PRES.
(2)
XDUCERS
Figure 3. Cross sectional view of closed bomb and schemtic of firing and monitoring system.
materials selected and the loading procedures
used were the suppliers' choice and are consid-
ered proprietary. Hi-Shear Technology loaded
90 mg of gas generating material, while UPCO
loaded 85, yielding a total pyrotechnic load of
130 and 125 mg respectively, as compared to the
114-mg load for the NSL The same electrical and
thermal insulation discs used at the output end
of the NSI load were also installed on the NGGC.
Test Apparatus and Methods
To characterize the input/output performance of
the test cartridges, an Electrical Firing Circuit
was used for input measurements, and four dif-
ferent test methods were used for output mear
surements. These output test methods were: the
Closed Bomb, the Energy Sensor, the Dynamic
Test Device, and the Pin Puller. All output test
hardware was made of steel and was reusable.
Electrical Firing Circuit
A direct current firing circuit, shown schemat-
ically in figure 3 and described in reference 4,
was employed to measure the electrical igni-
tion characteristics (function times) of cartridges
tested. Long-duration, square-wave electrical
pulses were applied at levels of 20, 15, 10, 5 and
3 amperes. The input current and the pressure
produced by the cartridges in the various out-
put test methods were recorded on an FM mag-
netic tape recorder with a frequency response
that was flat to 80 Khz. Electrical initiation
function times were measured from application
of current to bridgewire break and from applica-
tion of current to first indication of pressure from
the cartridge.
Closed Bomb
The closed bomb, shown in figure 3 and de-
scribed in references 3 and 4, is the industry
standard for measuring the output of cartridges.
The cartridge is fired into a fixed, 10-cc cylindri-
cal volume, and the pressure produced is mea-
sured with the pressure transducers, recorded on
the FM tape recorder. The data collected are
the peak pressure and the time to peak pres-
sure. This approach has limitations, as described
- 182 -
in reference 5, in trying to relate the pressure
produced to a mechanical or ignition function.
For example, the NSI performance requirement
in reference 1 is 650 +/— 125 psi peak pressure,
achieved within 5 milliseconds at direct-current
inputs of five amperes or greater. These data
provide no quantitative information that can be
related to work performed in an actual device.
Energy Sensor
The Energy Sensor, shown in figure 4 and de-
scribed in references 4 and 5, represents an appli-
cation where the cartridge output works against
a constant resistive force. This resistive force is
provided by precalibrated, crushable aluminum
honeycomb. The strength of the honeycomb se-
lected for this study was 500 pounds force. The
cartridge is fired on the axis of a piston/cylinder
as shown. The amount of work accomplished is
obtained by multiplying the length of honeycomb
crushed during the firing by the honeycomb's
crush strength to yield an energy value in inch-
pounds.
Dynamic Test Device
The Dynamic Test Device, shown in figure 5
and described in references 4 and 5, represents
the jettisoning of a mass. A one-inch diam-
eter, one-pound, cylindrical mass is jettisoned
through a one-inch stroke, when the o-ring clears
the cylinder. The velocity of the mass is mea-
sured electronically by a grounded needle on
the mass successively contacting spaced, charged
foils to trigger electronic pulses. These pulses
were recorded on a magnetic tape recorder to
measure the time interval between contact of the
needle with the foils. Velocity was calculated by
dividing the spacing distance (0.250 inch) by the
time interval. The energy of the mass was calcu-
lated as 1/2 mv?, where m is the total mass of
the 1-pound mass and the needle. The pressure
in the working volume was measured by a pres-
sure transducer installed in the port as shown,
and was recorded on the same magnetic tape
recorder. The data collected were the energies
delivered in inch-pounds and the peak pressures
achieved.
Pin Puller
The Pin Puller, shown in figure 6 and described
in reference 3, represents a pyrotechnic function
with a low-mass retractor. It also presents a tor-
tuous flow path of gases from the cartridge to
the working piston. The cartridge's output gas,
generated 90° from the working axis of the pis-
ton/pin, must vent through a 0.1-inch diameter
orifice into the working volume. Energy was ob-
tained and calculated by measuring the velocity
of the piston/pin, as described for the Dynamic
Test Device. Pressure in the working volume was
measured by a transducer installed in the sec-
ond port, as shown. The data collected were the
energies delivered in inch-pounds and the peak
pressures achieved.
Test Procedure
The testing effort was divided into three major
areas, as summarized in table I. This table shows
the number of units fired in each test, as well as
Table I. Allocation of Cartridge Test Units
Performance Baseline Firings
Test condition
VSI
NSI
NGGC
Hi-Shear
UPCO
Closed bomb
Energy sensor
Dynamic test device
Pin puller
13
5
8
5
3
3
6
5
7
7
5
5
5
5
Total
31
6
25
20
Environmental Testing
Temp,
cycling
Mech.
vibr.
Mech.
shock
Thermal
shock
NGGC
Hi-Shear
UPCO
Group 1
Group 2
Group 3
Group 4
2
3
4
3
4
4
16
16
16
16
12
12
12
13
Total
64
49
The units were visually, electrically and x-ray inspected
before and after exposure to each environment.
Post-Environment Firings
Test condition
NGGC
Hi-Shear
UPCO
Closed bomb
Energy sensor
Dynamic test device
Pin puller
16
16
16
16
12
12
12
13
Total
64
49
Units from the environmentally exposed groups were
equally subdivided into each functional test group.
Total NGGC test units: 89 69
- 183 -
Energy sensor
Initiator firing block
Cylinder p Anvil Honeycomb
retainer
Piston Adapter-
Piston seal
Figure 4. Cross sectional view of McDonnell Energy Sensor.
Pressure transducer face
Cartridge port
Cyl inder
Piston
Sealing ring
Figure 5. Cross sectional view of Dynamic Test Device.
- 184 -
Cartridge Port
Orifice (2)
Energy Absorbing Cup
O-Rings (5)
1/4" Pin
Pressure Transducer Port-
Figure 6. Cross sectional view of NASA Pin Puller.
the number of units subjected to the various en-
vironments. The Electrical Firing Circuit was
used to collect input electrical ignition charac-
teristics (function time) data for all units (except
the NSI) that were fired in the Performance Base-
line and in the Post-Environment tests. Elec-
trical inspections were accomplished on all units
at the start of the program with 50-volt bridge-
to-case and 10 milliampere bridgewire resistance
measurements.
Performance Baseline Firings
The performance baseline firings were conducted
with as-received cartridges to provide a func-
tional reference for comparisons among all
cartridge types and to compare with post-
environmental performance of the NGGC. Per-
formance data included input electrical ignition
and the four output measurements. The Elec-
trical Firing System was used as the input fir-
ing source for all cartridges, except the NSI.
(NSI firings were conducted prior to the use of
the Electrical Firing System). The cartridges
were subdivided as equally as possible for fir-
ings at current levels of 20, 15, 10, 5 and
3 amperes. As an example of output test fir-
ings described in table I, the Closed Bomb was
used for 13 VSI, 3 NSI, 6 Hi-Shear Technology
NGGC, and 5 UPCO NGGC units. Due to their
scarcity, no NSI units were functioned in the En-
ergy Sensor or Pin Puller. VSI units were used to
supplement the data collected on the NSI, since
their design and performance were essentially the
same.
Environmental Testing
Environmental tests, duplicating the qualifica-
tion levels and test order required for the NSI,
were conducted on the NGGC. The NGGC units
from each source were divided into four groups
for testing as shown in table I. Thermal stabi-
lization in these tests was established by thermo-
couples attached to several cartridges; once the
desired temperature level was indicated by the
thermocouples, the units were soaked for at least
15 minutes before the environmental tests began.
The units were visually, electrically and x-ray in-
spected before and after each environment. Elec-
trical inspection was accomplished with 50-volt
bridge-to-case and 10 milliampere bridgewire re-
sistance measuapftments.
The definition of each environmental test follows:
Temperature cycling. The units were placed in
a wire basket for transfer between chambers that
were stabilized at -260 and +300°F. The follow-
ing describes one of twenty cycles conducted:
1. Insert units into -260°F chamber, and once
stabilized, maintain that temperature for one
hour
2. Transfer units to +300°F, and once stabilized,
maintain that temperature for one-half hour
- 185
2. Transfer units to +300°F, and once stabilized,
maintain that temperature for one-half hour
Mechanical vibration. The units were
mounted into test blocks in a thermal chamber
for vibration tests on all three axes. Two series of
tests were conducted at +300 and -260°F. The
units were conditioned at each temperature and
the following spectrum, which produced an over-
all G rms value of 27.5, was applied for 7.5 min-
utes in each axis:
Frequency (Hz)
Level (G/Hz)
10 - 100
100 - 400
400 - 2000
0.01 to 0.8 (6 db/oct increase)
0.8 constant
0.8 to 0.16 (3 db/oct decrease)
Mechanical shock. The units were mounted
in the same test blocks used for the vibration
tests. The units were subjected to +/— pulses on
each axis to the following trailing edge sawtooth
pulse: 100 G peak with an 11 ms rise and a
1 ms decay. Tests were conducted at laboratory
ambient conditions.
Thermal shock. The units were placed in a
wire basket and immersed in a container of liq-
uid nitrogen and allowed to stabilize (no bub-
bles). The units were then removed from the
nitrogen and allowed to stabilize at room tem-
perature with no protection from water conden-
sate. The units were subjected to this process for
five cycles, except during the fifth cycle, follow-
ing stabilization, the units were held in the liquid
nitrogen for 11 hours.
Post-Environment Firings
Following the environmental exposures, the
NGGC units were subdivided equally and fired
with the electrical firing circuit using the four
test methods. That is, four units of the 16 envi-
ronmentally tested in Group 1 were fired in each
test method. The data collected were compared
to the performance baseline.
Results
The results of the tests are presented in the same
format as the Test Procedure section.
Performance Baseline Firings
The data collected for the functional performance
baselines (input electrical function time and out-
put tests) for each cartridge are summarized in
the top portions of tables II through VI and fig-
ures 7 through 10.
Table II. Electrical Ignition Performance Data
on Cartridges
(Average/Standard Deviation)
Current
Time to
Time to
applied
No.
BW break,
first press,
Cartridge
amperes
fired
ms
ms
Performance baseline (no environments)
VSI
20
6
.124/.005
.158/.014
15
3
.182/.007
.215/.013
10
2
.354
.389
5
1
1.431
1.480
3
1
121.020
121.060
Hi-Shear
20
1
.120
.175
NGGC
15
1
.190
-
10
1
.335
.362
5
1
1.350
1.370
3
1
12.400
12.425
UPCO
20
3
.130/.030
-
NGGC
15
1
.160
.225
10
2
.324
.373
5
3
1.295/.018
1.298/.020
3
2
8.355
8.373
Post environments
Hi-Shear
20
16
.135/.012
.187/.025
NGGC
15
12
.184/.020
.224/.029
10
12
.329/.044
.443/.199
5
12
1.245/.050
1.274/.063
3
12
10.653/5.452
11.315/5.789
UPCO
20
12
.121/.013
.792/.663
NGGC
15
12
.176/.012
.639/.481
10
10
.348/.045
.739/. 441
5
8
1.238/.100
1.327/.145
3
8
7.641/4.015
7.353/3.746
Table III. Closed Bomb Performance Data
on Test Cartridges
(Average/Standard Deviation)
Cartridge
No.
fired
Time to
peak pressure,
ms
Peak
pressure,
psi
Performance baselii
ae (no environmei
its)
VSI
NSI
Hi-Shear NGGC
UPCO NGGC
13
3
6
5
.09/.05
.23/.06
1.15/.34
.48/.13
675/81
660/53
1083/41
1120/58
Post environments
Hi-Shear NGGC
UPCO NGGC
16
12
1.11/.30
.28/.07
1076/25
1250/47
- 186 -
Table IV. Energy Sensor Performance Data on
Test Cartridges
(Average/Standard Deviation)
Cartridge
No.
fired
Energy delivered,
inch-pounds
Performance baseline (no environment)
VSI
Hi-Shear NGGC
UPCO NGGC
5
5
5
466/21
815/99
812/90
Post environments
Hi-Shear NGGC
UPCO NGGC,
16
12
869/80
927/58
V8I
HI-SHEAfl, NO ENV
HhSHEAfl, POST ENV
UPCO, NO ENV
UPCO, POST ENV
S 10 10
Current Applied, amperes
Table V. Dynamic Test Device Performance Data
on Test Cartridges
(Average/Standard Deviation)
Cartridge
No.
fired
Energy
delivered,
inch-pounds
Peak
pressure,
psi
Performance basel
ine (no environ:
ment)
VSI
NSI
Hi-Shear NGGC
UPCO NGGC
8
3
7
5
337/64
351/15
785/66
756/74
5580/940
5540/755
4983/993
9408/2002
Post environments
Hi-Shear NGGC
UPCO NGGC
16
12
667/45
777/50
6953/1866
8337/1980
Table VI. Pin Puller Performance Data on
Test Cartridges
(Average/Standard Deviation)
Cartridge
No.
fired
Energy
delivered,
inch-pounds
Peak
pressure,
psi
Performance baseline (no environment)
VSI
Hi-Shear NGGC
UPCO NGGC
5
7
5
154/20
450/36
526/39
7056/143
12313/797
16392/1514
Post environments
Hi-Shear NGGC
UPCO NGGC
16
13
462/21
514/17
11720/440
15532/680
V8I
-#- HI-SHEAR, NO ENV
-9- HI-SHEAR, POST ENV
-*~ UPCO, NO ENV
~9- UPCO. POST ENV
0.1 x
5 10 IS
Current Applied, amperes
Figure 7. Plots of current applied versus time to bridge-
wire break (top) and to first pressure (bottom).
Electrical ignition performance. The elec-
trical ignition performance baselines (no envi-
ronments) for the VSI and NGGC are shown in
table II and figure 7. As mentioned earlier, no
NSI data were collected. Each of the data points
on the plots is the averaged value of the func-
tion times for each cartridge type at each current
level. Very little difference in performance could
be detected among any of the cartridge groups.
Closed bomb. The closed bomb performance
baseline data are shown in table III. Typical
traces for each cartridge type are shown in fig-
ure 8. The times to peak pressure for the VSI
and NSI are smallest. The average time to peak
pressure for the Hi-Shear Technology NGGC is
considerably longer than for the UPCO units
(1.15 versus 0.48 ms). The NGGC peak pressures
achieved are comparable (1083 and 1120 psi).
Energy sensor. The Energy Sensor perfor-
mance baseline data are shown in table IV. The
- 187 -
1600 -
Hi-Shear t?CGC
UPCO NGCC
Figure 8. Typical pressure traces produced by the NSI, VSI and UPCO, and Hi-Shear NGGC in the closed bomb.
Figure 9. Typical pressure traces produced by the VSI and Hi-Shear and UPCO NGGC in the dynamic test device.
- 188 -
16000 -
-UPCO NCGC
12000
8000
4000-
Time, millisecond
Figure 10. Typical pressure traces produced by the VSI and Hi-Shear and UPCO NGGC in the pin puller.
NGGC performances are comparable (815 and
812 inch-pounds) and nearly twice that of the
VSI (466 inch-pounds).
Dynamic test device. The Dynamic Test De-
vice performance baseline data are shown in ta-
ble V. The performance of the VSI and NSI
are comparable (337 and 351 inch-pounds), as
are the two NGGC models to each other (785
and 756 inch-pounds). The NGGC performance
is over twice that of the VSI and NSI. Figure 9
shows typical pressure traces from each cartridge
type. The peak pressure for the UPCO NGGC
is appreciably higher and more dynamic than the
Hi-Shear Technology units.
Pin puller. The Pin Puller baseline data
are shown in table VI. The performance of the
NGGC models (450 and 526 inch-pounds) are
three times that produced by the VSI (154 inch-
pounds). Figure 10 shows distinctively different
pressure traces from each cartridge type.
Environmental Testing
The environmental testing was completed with
no evidence of physical damage through visual,
x-ray and electrical inspections.
Post-Environment Firings
The data collected for the post-environment
functional performance tests (input electrical
function time and output tests) for each cartridge
are summarized in the lower portions of tables II
through VI.
Electrical ignition performance. The elec-
trical ignition data are shown in table II and fig-
ure 7. The only change between pre- and post-
environment performance was a small increase in
times to first indication of pressure in the UPCO
NGGC units. All values were within the 5 mil-
lisecond delay times at 5 amperes or greater, al-
lowed by the NSI specification, reference 3.
Closed bomb performance. The data fol-
lowing environmental exposure are shown in
table III. No appreciable change in performance
was observed.
Energy sensor. The Energy Sensor baseline
data are shown in table IV. The apparent in-
crease in energy delivered (54 and 115 inch-
pounds) by the NGGC models following envi-
ronmental exposures is insignificant, considering
- 189 -
the standard deviations of the pre- and post-
environments data. These standard deviations
total 179 and 148 inch-pounds for the respective
NGGC models, which could include this range of
data.
Dynamic test device. The Dynamic Test De-
vice data are shown in table V. No significant
change in performance was observed following en-
vironments, again considering the standard devi-
ations.
Pin puller. The Pin Puller data are shown
in table VI. No change was detected following
environments.
Conclusions
All objectives of this effort were met, which
should allow for immediate consideration for the
application of the NGGC. The NGGC was man-
ufactured using the same body and electrical
interface as the NSI. The electrical initiation
characteristics are the same as the NSI. A slight
delay was observed in the time to first pressure
for the UPCO NGGC following environmental
exposures. This delay, caused by a decrease in
thermal transfer from the bridgewire, is accept-
able, since it is well within the NSI performance
specification. The cartridge functional evalua-
tions used in this effort clearly show that out-
put working energy is affected by the configura-
tion in which it is used. The Energy Sensor and
Dynamic Test Device measured the most energy
delivered by the NGGC, about 800 inch-pounds,
while the Pin Puller was much less efficient, de-
livering only about 500 inch-pounds. Although
the two NGGC manufacturers selected different
thermal/vacuum-stable gas generating materials,
as evidenced by the different pressure traces ob-
served, the output performance of the two models
was essentially the same in each of the four test
methods. Under the assumption that the NSI
produces the same output performance as the
VSI, the NGGC produces approximately twice
the output of the NSI/VSI in the Energy Sensor
and the Dynamic Test Device, and three times
that of the NSI/VSI in the Pin Puller. No signif-
icant change in output performance was observed
following exposure of the NGGC to the rigorous
thermal/mechanical environmental requirements
for the NSI.
A work-producing cartridge has been developed
with the key attributes of the NSI. Designers
of pyrotechnic mechanisms now have a cartridge
that is defined in terms of work, and they can
relate the test configurations and energy deliv-
eries documented in this report to their design
requirements. This cartridge performance can
meet the requirements of a substantial portion
of small aerospace pyrotechnic devices (including
many applications where the NSI with booster
modules are now employed), such as pin pullers,
nuts, valves and cutters.
A word of caution is warranted. The suc-
cessful completion of this developmental effort
does not "qualify" the NGGC for any appli-
cation. Users must conduct a developmental
effort, including demonstrating functional mar-
gins, environmental qualification, and system in-
tegration/operation demonstrations for devices
in which the NGGC is to be used.
The acquisition of the NGGC should be based
on performance, as measured by at least one of
the energy measuring devices described in this
report, the Energy Sensor, the Dynamic Test
Device or the Pin Puller.
References
1 . Design and Performance Specification for
NSI-1 (NASA Standard Initiator-1),
SKB26100066, January 3, 1990.
2. Bement, Laurence J. and Schimmel,
Morry L.: "Determination of Pyrotechnic
Functional Margin." Presented at the 1991
SAFE Symposium, November 11-14, 1991,
Las Vegas, Nevada. Also presented at the
First NASA Aerospace Pyrotechnic Systems
Workshop, June 9-10, 1992, NASA Lyndon B.
Johnson Space Center, Houston, TX.
3. Bement, Laurence J.: "Pyrotechnic System
Failures: Causes and Prevention." NASA
TM 100633, June 1988.
4. Bement, Laurence J.: "Monitoring of Explo-
sive/Pyrotechnic Performance." Presented
at the Seventh Symposium on Explosives
and Pyrotechnics, Philadelphia, Pennsylva-
nia, September 8-9, 1971.
5. Bement, Laurence J. and Schimmel,
Morry L.: "Cartridge Output Testing: Meth-
ods to Overcome Closed-Bomb Shortcom-
ings." Presented at the 1990 SAFE Sympo-
sium, San Antonio, Texas, December 11-13,
1990.
- 190 -
Coin
t
DEVELOPMENT OF THE TOGGLE DEPLOYMENT MECHANISM
Christopher W. Brown
NASA Lyndon B. Johnson Space Center, Houston, Tx
Abstract
The Toggle Deployment Mechanism
(TDM) is a two fault tolerant, single
point, low shock pyro/mechanical
releasing device. Many forms of
releasing are single fault tolerant
and involve breaking of primary
structure. Other releasing
mechanisms, that do not break
primary structure, are only
pyrotechnically redundant and not
mechanically redundant. The TDM
contains 3 independent pyro
actuators, and only one of the 3 is
required for release.
The 2 separating members in the
TDM are held together by a toggle
that is a cylindrical stem with a
larger diameter spherical shape on
the top and flares out in a conical
shape on the bottom. The spherical
end of the toggle sits in a socket
with the top assembly and the
bottom is held down by 3 pins or
hooks equally spaced around the
conical shaped end.
Each of the TDM's 3 independent
actuators shares a third of the
separating load and does not
require as much pyrotechnic
energy as many single fault
tolerant actuators. Other single
separating actuators, i.e.,
separating nuts or pin pullers, have
the pyrotechnic energy releasing
the entire preload holding the
separating members together.
Two types of TDM's, described in this
paper, release the toggle with pin
pullers, and the third TDM releases
the toggle with hooks. Each design
has different advantages and
disadvantages. This paper describes
the TDM's construction and testing
up to the summer of 1993.
Introduction
Numerous aerospace programs have
been a need for low shock, single
point separators that are multi-fault
tolerant and can separate without
breaking primary structure. In late
1987, such requirements were
applied on an Orbiter Disconnect
Assembly that is part of the
Stabilized Payload Deployment
System (SPDS). Two different types
of TDM's were developed. They
differed by way of solving an initial
design problem. Both TDM's had 3
pin pullers each and were
vulnerable to unexpected tensile
load spikes creating plastic
deformation. If the pins were bent,
they could not retract which would
lead to a separation failure with
little to no preload holding the 2
structures together.
In late 1988 a request for a TDM in a
different envelope shape was
considered, and a third concept, the
TDM20KS, was designed. This TDM
was met the envelope constraints
and was designed to function with
the inner parts deformed from
tensile load spikes. The TDM20KS
application dissolved, but the
development tests continued.
Most of the tests performed
considered the 2 fault tolerant case
by using only one of the 3
separation members.
The First Toggle Deployment
Mechanisms
- 191 -
The original SPDS requirements
were translated into the first pin-
puller configured TDM and resulted
in the United States Patent
4,836,081.!. The original concept,
shown in figure 1, had a problem
with the preload forcing the pins
back and causing the shear pins to
function as primary structure. The
less the angle "a" from the
horizontal on the toggle, the less
load there is pushing the pins back.
However, the less angle "a", the
harder it is for the toggle to swing
away from the unretracted pins. If
angle "a" was zero, there would be
no moment on the toggle, created
by the 2 unretracted pins, for the
toggle to swing away from.
The first NASA-JSC pin-puller
configured TDM, seen in figure 2,
has the axis of the pins parallel to
the conical surface of the toggle.
The tension of the toggle pushes the
conical surface perpendicular to
the pin ! s axis and does not act on
the shear pins.
Preloading the toggle was
completed by unscrewing the
preload collar that pulls the toggle
up. To prevent twisting of the
toggle wile preloading, a tool was
placed in the socket holes to hold
the toggle and socket from turning.
This TDM was designed to hold and
release a preload of 1000 pounds.
Testing was performed with
pneumatics and NASA Standard
Initiators (NSI). With pneumatics, a
static pressure of about 500 psi was
needed to release the 1000 pound
preload. Dynamic pressure
releasing was performed by
opening a solenoid valve into the
NSI port. Pluming orifices and
other dynamics required a higher
static pressure behind the solenoid
valve for separation. Figure 3
shows pressure versus preload with
two types of piston/pin coatings.
Friction coefficients of the TDM
parts play an important role in
releasing energy. Figure 3 also
shows a difference between the
original piston finish and a Teflon
impregnated nickel plate finish
called NEDOX from General
Magniplate Corp.. The NEDOX finish
shows a consistent improvement in
releasing energy.
The second TDM concept had a
different design to avoid
transferring the preload into the
axis of the pins. This resulted in
development of the double swivel
toggle and lead to United Stated
Patent 4,864,910. 2 . As seen in Figure
4, this TDM had the axis of the pins
running perpendicular the axis of
the toggle. When one pin was
retracted, the bottom of the toggle
could swivel down and clear itself
from the 2 unretracted pins. This
TDM was successfully developed and
qualified to meet SPDS
requirements.
Toggle/Hook D eployment
Mechanism TDM20KS
The TDM20KS was designed to
release a preload up to 20,000
pounds even if some internal parts
were plastically deformed. Figures
5 and 6 show the fastened and
released configurations of the
internal parts. In figure 5, the
toggle is held down with 3 hooks
that pivot in the body. Each hook is
held from pivoting by a piston. As
seen in figure 6, the piston has
moved up and the toggle is released
when a hook is free to swing back
into the void of the piston. 3,
Two TDM20KS's were made with
differences in the angle of
toggle/hook contact. One TDM20KS
had a 45 degree angle of contact,
and the other assembly had a 30
degree angle contact from the
- 192 -
horizontal. Both toggle stems had
full strain gauge bridges applied
inside holes going through their
axes. Each piston port had 2 NSI
ports. Most parts of the TDM20KS
were plated or coated with low
friction surfaces.
Tnyr?nK<s TVvPlnpment Test
Three sets of development tests
were completed. After initial
testing, the next 2 development tests
were performed with design
changes that were needed during
the initial testing. The initial
development tests were performed
with hydraulics and with NSI's, but
the first goal was applying the
preload. 4 . With 2 NSI ports per
cylinder, pressure monitoring was
easily accomplished.
TDM20KS Tnitial Dev elopment
Testing
Preloading was similar to the
original TDM by way of pulling the
socket up when unscrewing the
preload collar (otherwise known as
a preload bolt). Figure 7 shows the
setup used to get the maximum
preload. A tension machine would
pull the socket up by stretching the
toggle, and the preload bolt was
unscrewed until it was snug with
the socket. The bolts connecting
the tension machine to the socket
had a 17,000 pound maximum limit,
and the TDM20KS assembly would
settle down to about 12,000 pounds
preload. A future design was able to
obtain a 20,000 pound preload.
Releasing the preload with
hydraulic pressure in one cylinder
showed the difference between the
45 degree TDM and the 30 degree
TDM. Figure 8 shows 3 different
releasings at 3 different preloads
for the 45 degree TDM, and figure 9
shows the same tests with the 30
degree TDM. As expected, there was
less pressure needed to release the
30 degree TDM due to less force
between the hooks and pistons.
What was unexpected is the
inconsistency of releasing pressure
as a function of preload.
NSI firing showed similar
pressure/preload results after the
TDM's were exposed to vibration,
shock, and thermal environments.
Ambient firings revealed a design
problem in the piston stops. The
pistons traveled too far and leaving
the bottom of the piston voids
pushing the hook back up which
prevented toggle releasing. All
toggle releases, with the original
piston stops, were performed with
one NSI per piston. The second
phase of development testing, with
2 NSFs per piston, showed some
success in an improved design.
Figures 10 and 11 show pressure
and preload curves in the 30 and 45
degree TDM chambers during 275
degree F. firings. The TDM's were
successfully fired in -90 degree F.
environment. Figure 12 shows the
data on the 45 degree TDM cold
firing.
Both hydraulic and NSI tests showed
a preload increase when
separating. This is belived to be
caused by the piston bending in
toward the hook while traveling up.
A plastic deformation test was
performed with the 45 degree TDM
while the 30 degree TDM was saved
for testing improved piston stops
and preloading mechanisms.
The 45 degree TDM was first
preloaded, and the separating
members were tensioned to 29,000
pounds. There was a .040 inch gap
in the separation plane, but no
separation was noticed while the
tension was within the preload. The
29,000 pound load was released, and
the remaining preload in the TDM
- 193 -
was unknown due to strain gauge
damage in the toggle stem. Figure
13 shows the average permanent
change in the deformed parts. The
45 degree TDM was preloaded and
put back into tension. The toggle
stem finally broke at 34,000 pounds
tension. Besides the toggle, the
internal parts were deformed a
little more and were still able to
function in the TDM body.
TDM20KS Post Development Tests
The 2 post development tests
evaluated a redesigned piston stop
and a new type of preloading
mechanism.
Piston Stop Redesign
The initial NSI firing tests revealed
that the piston stops were not
stopping the piston with the
actuation of one NSI. The existing
stops, made of AL7075-T6, were set to
start taper locking the piston tops at
a position too high for the piston to
settle in the correct position. In
addition, the original piston stops
were cracking at the sides where
the bolts held them down. The
original piston stops were lowered
and extra side supports were bolted
down, but these created assembly
problems that led to the new piston
stop.
Besides making the new piston stops
out of 15-5 CRES, the design was
beefed-up on the outside, and the
interior dimensions had tighter
tolerances. Figure 14 shows the
difference in the piston stops.
Six firings of the TDM were
conducted at various temperatures,
preloads, and number of NSI'sA
Most tests were performed with 2
NSI's per piston unlike the initial
development tests. Tests proved the
piston stops did not deform, but the
original 1/4-20UNC-3A bolts,
holding the stops, elongated and
were bent. Figure 15 shows how the
deformed bolts allowed the piston to
travel too far, pushing the hook
back up, and wedging the piston
between the hook and cylinder.
Testing with bolts made of carbon
steel, instead of 300 series SST, also
resulted in stretched bolts but not as
deformed as the older ones. The
bottom surface of the piston void
was lowered 0.15 inchs to give room
for successful releasing with 2 NSI's
per piston.
Top Member Redesign
The last of the TDM20KS
development solved the preloading
problem by completely redesigning
the top preloading members. As
noticed in earlier TDM preloading,
one set of threads could apply a
certain tension regardless to the
diameter. Also, the tension
machine would have to load the
toggle about 1.4 times the desired
preload to get what the TDM would
settle down to. The theory behind
the new top TDM section is to design
in as many sets of threads as
possible, and the tensions from all
threads would sum up to a desired
preload.
Figure 16 shows the major parts
used in the new top members
designed to get up to 20,000 pounds
preload without using a tensile
machine. The only existing part
used is the socket. It sits in a
tensioner that contains 18 sets of
3/8"-24 threaded holes surrounding
the socket. Eighteen hex cap screws
were threaded into the tensioner
and sit in the base plate. This base
plate has 18 counter bores with the
same bolt circle as the tensioner
threads. Each base plate counter
bore has 2 SST washers with a brass
washer between. These washers act
as thrust bearings for the bolts.
Tightening the bolts in a star
- 194 -
pattern would separate the
tensioner from the base plate and
create tension on the toggle.
Testing of the new top member and
releasing over 20,000 pound preload
with one NSI was successful. 6 .
Each bolt was torqued at 20 in. lb.
increments, in a star pattern, until
the toggle's strain gauge failed at
18,000 pounds. Preload, as a
function of torque, was continued
until 20,000 pounds was estimated.
The maximum torque/preload tested
was 200 in.lb. on each bolt and
24,000 pounds preload. At ambient
conditions, one NSI was still able to
release the 24,000 pound preload.
Conclusions
Each of the three toggle deployment
mechanism concepts tested
successfully. Other designs were
considered which had different
hook shapes and pivot locations.
Besides pivoting hooks, sliding
members can also apply to fit
envelope constraints.
References
1. Patent Number 4,836,081 Jun.
6,1989 "TOGGLE RELEASE".
Inventors: Thomas J. Graves;
Robert A. Yang; Christopher W.
Brown. Assignee: The Unites
States of America as represented
by the Administrator of the
National Aeronautics and Space
Administration, Washington, D.C.
2. Patent Number 4,864,910
"DOUBLE SWIVEL TOGGLE
RELEASE". Inventors: Guy L.
King; William C. Schneider.
Assignee: The Unites States of
America as represented by the
Administrator of the National
Aeronautics and Space
Administration, Washington, D.C.
3. NASA Tech Briefs Vol. 15 No. 11
P. 71 "Redundant Toggle/Hook
Release Mechanism" Nov. 1991.
6.
NASA JSC Thermochemical Test
Area No. JSC 26486 "Internal
Note For the Toggle Deployment
Mechanism (TDM)" April 1993.
NASA JSC Thermochemical Test
Area No. JSC 25964 "Internal
Note For Toggle Deployment
Mechanism Piston Stop Test"
July 1992.
NASA JSC Thermochemical Test
Area Task History 2P809 " August
1993.
- 195 -
Shear Pin
^- F - Preload/Tan a
Figure I
Original Toggle Deployment Mechanism Concept.
- 196 -
Preload Collar/Bolt
Top Plate
Piston/Pin
Collar
Shear Pin
Toggle
«•- Separation Plane
O-Ring
O-Ring
Body
Figure 2
Toggle Deployment Mechanism, Pin-Puller Configuration.
- 197 -
CO
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2000
1000
1600
MOO
1200 -
1000
ooo
600
400
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—
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—
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—
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—
—
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—
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<_
—
S
S
—
i
i
-o- NEDOX(psi)
-+- 16 micro (p3i)
1 00 200 300 400 500 600 700 000 900 1 000
Load (lbs)
Figure 3
Pressure pulse v.s. preload for releasing the TDM,
Preloading Nut
Two Part Toggle
Socket
Bottom Swivel
Separation Plane
Piston/Pin
Figure 4
Double Swivel Toggle Release.
- 199 -
ST0P(3-TYP)
HOOK (3-TYP)
PISTON (3-TYP)
PYRO PORT (3-TYP)
TOP CAP
SOCKET
PRELOAD BOLT
LOCK PIN
TOGGLE
PISTON (3-TYP)
HOOK (3-TYP)
SECTION A-A
Fi gure 5
Toggle/Hook Deployment Mechanism TDM20KS before separation.
- 200 -
TOP CAP
STOPO-TYP)
PISTON (3-TYP)
PYRO PORT (3-TYP)
SECTION B-B
PISTON (3-TYP)
HOOK (3-TYP)
ELgUI£J&
Toggle/Hook Deployment Mechanism TDM20KS during deployment.
Separation plane is at section B-B.
- 201 -
TENSION
MACHINE
PRELOAD
PLATE
SOCKET
ADAPTOR
SOCKET
BOLTS
SOCKET
PRELOAD
BOLT
TOP PLATE
THREAD LOCK
HOLE
TDM
TENSION
TOOL
TENSION
MACHINE
Fi gure 7
Preloading the TDM20KS.
- 202 -
TOGGLE PRELOAD
lbf and psig
12,000
10,000
8,000
6,000
4,000
2,000
HYDRAULIC PRESSURE
Figure 8
Hydraulic release tests for the 45 degree TDM. Load cell and toggle gauge lines
were staggered due to pen locations on the strip chart recorder.
- 203 -
I
O
I
TOGGLE PRELOAD
lbf and psig
12,000
10.000
8,000
6,000
4,000
2,000
HYDRAULIC PRESSURE
Fi gure 9
Hydraulic release tests for the 30 degree TDM. Load cell and toggle gauge lines
were staggered due to pen locations on the strip chart recorder.
12x10
10-
PRELOAD RELEASED 280 uS
AITER PRESSURE RJSE
-PRELOAD INCREASED
252 lbf. DURING RELEASING
i
IV,
o
I
LEGEND:
NSI PRESSURE
TOGGLE PRELOAD
800nS
Fi gure 10
Forty-five degree TDM pyrotechnic release at 275 degrees F. Toggle preload
values are not compensated for thermal effects on toggle gauges.
10x10 -
8
o.
(/>
2
6
1
a
n:
■a
o
en
o
r— «
4>
i
fc.
4
2-
-PRELOAD INCREASnD
179 Ibf. DURING RELEASING
PRELOAD RELEASED 340uS
AFffiR PRESSURE RISE
2.0
-PEAK PRESSURE 5440 psi \
1 IOiiS AFTER RISE
1^
2.2
""T~
2.4
2.6
LEGEND:
NSI PRESSURE
TOGGLE PRELOAD
2.8
3.0mS
Figure 11
Thirty degree TDM pyrotechnic release at 275 degrees F. Toggle preload values
are not compensated for thermal effects on toggle gauges.
14x10 -
12-
CO
M
GO
^
•a
s
1
13
ro
O
O
^4
10-
8 -
6-
4 -
2-
PEAK PRESSURE 3896 psi
90uS AFTER RISE
1^
0.2
0.4
0.6
-PRELOAD RELEASED 410uS
AFTER PRESSURE RISE
LEGEND:
NSI PRESSURE
TOGGLE PRELOAD
0.0
1.0mS
Fi gure 12
Forty-five degree TDM pyrotechnic release at -90 degrees F. Toggle preload
values are not compensated for thermal effects on toggle gauges.
r
s.
y
1
i
1
i
.002 SHORTER
f i \
.001 WIDER
PISTONS
PISTONS
.003 OUT OF ROUND -i
007 TALLER
HOOKS
Figure 13
Dimensional analysis of the deformed 45 degree TDM parts after a
29,000 lbf structural load test. Dimensions are averages of all parts and in inches.
- 208 -
I
< I
Original Piston Stop
AL 7075-T6
Rpdpsigned Piston Stop
15-5PHCRES
Figure 14
TDM20KS Piston Stops.
- 209 -
Fi gure 15
TDM20KS Piston/Hook interference after excessive piston travel.
- 210 -
Bolts
Socket
Tensioner
Base Plate
Separation Plane
washers
Toggle
Figure 16
TDM20KS Redesigned Top Assembly
- 211 "
SI*-**
THE ORDNANCE TRANSFER INTERRUPTER. A NEW TYPE OF S&A DEVICE
John T. Greenslade, Senior Staff Engineer
Pacific Scientific Company, Energy Dynamics Division
ABSTRACT
A discussion is given in this paper of a new
approach to the Safing and Arming of
aerospace ordnance systems interconnected
by detonation transfer lines, in which the
conventional type of S&A device normally
used for this purpose is replaced by a
relatively simple electro-mechanical
switching device, referred to as an
"Interrupter. " In this approach the
Interrupter, which is interposed in the
transfer line between the system initiator and
output device, is completely passive in that
it contains no pyrotechnic devices or
materials. Being passive (therefore, non-
initiating), the Interrupter is much less
hazardous to handle and install, as well as
being significantly less complex and costly
than conventional S&A devices containing
EEDs and explosive leads.
Details are presented relative to the design,
development and qualification, by PS/EDD,
of an ordnance transfer Interrupter intended
for use on a commercial launch missile.
This device, which is capable of
simultaneously "switching" multiple
detonation transfer lines, incorporates a rod-
type rotary barrier with independent
transverse apertures for each transfer line.
Barrier actuation is bi-modal, i.e., the
barrier can be driven from safe-to-arm or
from arm-to-safe positions by independent
electro-mechanical actuators. The
Interrupter described also features visual and
remote status monitoring provisions and, in
common with range-approved conventional
S&A devices, a pre-flight safety locking
mechanism functioned by a removable safing
key.
Successful development of the Interrupter
required the resolution of such problems as
ensuring reliable detonation propagation
(between opposed booster tips in the transfer
lines) across unusually large airgaps within
the barrier apertures, and the damping of the
barrier drive train to prevent inadvertent
actuation during vibration and shock
extremes. The latter problem was solved by
the incorporation of in-line pneumatic
dampers in each of the barrier drive-trains.
INTRODUCTION
For safety reasons, all ordnance systems,
regardless of their level of complexity, must
be capable of being maintained in an
inoperative "Safe" state, prior to when they
are required to function. At the simplest
level , the Safing function could be
exemplified by the switching of a firing
circuit of a single electro-explosive device
(EED). In most missile and spacecraft
ordnance systems, the Safing function, and
its converse, the Arming function are
effected by a specifically designed, and
often complex, Safe/ Arm Device, or SAD.
A brief discussion relative to the
conventional usage and technology of these
devices will provide an appropriate
introduction to the subject of this paper.
The SADs employed in missile ordnance
systems have generally been classifiable in
either of two broad categories, namely, the
"Command" type and the "Inertial" type.
SADs of the former type are "commanded"
to change their state from Safe to Arm (and
reverse, in some cases) by the input of
electrical signals generated by a remote
controller. On the other hand, the Safe to
Arm transition is achieved automatically
- Z13 -
PAGE
JUL
.V liL,
with the "InertiaT type SAD, when it is
subjected to a specific level of vehicle
acceleration for a specific minimum
duration. The arming mechanisms in the
Command type SADs have most commonly
been electro-mechanical, although electronic
devices have become competitive, and laser
based Command type SADs have started to
make an appearance. The Inertia! SADs are
armed by inertia forces, resulting from the
missile acceleration, acting on a spring-
loaded "set-back" weight. With these
devices, the movement of the set-back
weight is controlled by an escapement
mechanism, similar in principle to the
escapements used in clocks.
Figure 1 tabulates some of the more
common types of SAD which have been
used in missile applications.
Conventional SADs, Command and Inertial,
are more than just a system safing and
arming mechanism; they are also the
ordnance system initiator. For that purpose,
they incorporate electro-explosive devices,
usually detonators, and very often explosive
transfer components such as "leads," or
confined detonating cords. This, of course,
increases the hazard potential associated
with pre-flight testing and installation of
TYPE
COMBINATIONS OF:
ENABLE
ARM
INTERRUPT
COMMAND
LANYARD
SOLENOID
GAS
PRESSURE
ROTARY
SOLENOID
LINEAR
SOLENOID
SPRING
GAS PRESSURE
ROTARY
SOLENOID
LINEAR
BARRIER
MOVABLE EDO
INERTIAL
AS ABOVE
INERTIA
AS ABOVE
OTHER
ELECTRONIC
ELECTRONIC
RELAY
Figure 1:
SADs Used in Missile Applications
conventional SADs. As such, it is one of
the factors which led to the concept of the
Interrupter, which contains no pyrotechnic
or explosive components, as a replacement
for conventional Command SADs in systems
employing linear ordnance transfer lines
such as shielded Mild Detonating Cord
(SMDC), or Confined Detonating Fuze
(CDF).
In the Safe mode, conventional Command
type SADs must either physically hold their
internal detonators out of alignment with
their output ports, or, interpose a barrier
between the detonators and ports. They
must also disable the firing circuits to the
electro-explosive detonators, and impose a
safety shunt across those circuits.
Conversely, when in the Armed mode, the
Command SADs must align their detonators
with the output ports (or remove the
barrier), and they must complete the firing
circuits to the detonators. In comparison,
the Interrupter, having no internal EEDs, is
not involved in disabling or enabling the
firing circuits to the system initiators. This
considerably simplifies its internal circuitry
and switching requirements. The Interrupter
would , as the name implies , have to
interrupt the system firing train, in this case
by a removable barrier. The functional
requirements for a typical conventional
Command SAD are compared, in Figure 2
with those for the Interrupter.
A number of the design requirements for
SADs have been dictated by the
Government' s Missile Test Ranges,
predicated primarily on safety
considerations. Such requirements relate,
for instance, to the minimum amount of
firing train misalignment needed, the
integrity of status monitoring provisions,
and the "hand-safe" capability of the device,
i.e., its ability to remain intact in the event
of an inadvertent detonation of its EEDs.
- 2m -
MODE
FUNCTION
CONVENTIONAL
SAD
INTERRUPTER
SAFE
PHYSICALLY BLOCK FIRING TRAIN
DISRUPT FIRING CIRCUIT
SHUNT FIRING CIRCUIT INDICATOR
X
X
X
X
ARM
PHYSICALLY ALIGN FIRING TRAIN
COMPLETE FIRING CIRCUIT
REMOVE INITIATOR SHUNT
X
X
X
X
MONITOR
PROVIDE INDICATION OF "SAFE"
PROVIDE INDICATION OF "ARMED"
X
X
X
X
SAFING
MANUAL SAFING FROM ANY POSITION
PREVENT MANUAL ARMING
LOCK IN SAFE PRIOR TO FLIGHT
PREVENT INADVERTENT SAFETY PIN
REMOVAL
X
X
X
X
X
X
X
X
FIRE
INITIATE INTERNAL EED
X
-
:^ : >
Figure 2: Functional Requirements: Conventional Command SADs Vs. Interrupter
One important aspect of the design criteria
influenced by the Test Ranges relates to
manual safing and the Safing Key. The
SADs must be capable of being manually
transferred to the Safe condition from the
Armed state (or any intermediate state), but
not vice-versa. The Safing Key used for
manually safing, normally doubles as the
Safety Pin used to lock the unit in the Safe
mode, prior to flight. Current range
requirements dictate that the installed safety
pin must not be removable if arming is
inadvertently attempted.
The Interrupter, shown in Figure 3, has
been designed to satisfy all Test Range
requirements relative to firing train
misalignment, status monitoring, manual
safing, and the "interlocking" of the Safing
Key to prevent its removal during
inadvertent arming attempts. Since the
device contains no EEDs, the "hand-safe"
requirement does not apply.
DESIGN CONSIDERATIONS
Before undertaking the design of any new
conventional SAD, certain issues must be
addressed relative to the functional elements
of the device. Several of these will be
defined in the product specification, the
others will involve trade-off studies to
Figure 3:
The Ordnance Transfer Interrupter
optimize the selection of functional
approaches. Examples of the specified
criteria might be as follows:
a) The general type of SAD (Command or
Inertial)
b) Single or dual firing trains?
c) Hermeticity?
d) Reversibility of the drive train?
e) Detonation or deflagration output?. . .etc.
Choices that can be made by the designer,
based on such factors as cost and reliability,
include the type of prime-mover in the
- 215 -
drive-train (e.g., solenoids, or springs, or
..), movable EEDs versus a movable
barrier, and the type of electrical switching
components to be used (e.g., rotary or snap-
action, or ...).
When generating the design of the
Interrupter, the ground rules had changed
slightly, and different choices were to be
made. This unit was to contain no EEDs,
therefore, questions regarding firing trains
only related to the external ordnance transfer
lines. The issue of SMDC versus CDF lines
arose, and the propagation characteristics
were found to be somewhat different for the
two types. Hermeticity was not specified,
which simplified the design of the
interlocking Safing Key, since a welded
metal bellows "pass-through" was not
required. It should be noted that the
Interrupter is environmentally sealed, with
and without the Safing Key installed.
Because the unit interrupts fixed transfer
lines, the interruption must be done by a
movable barrier. Design choices for the
barrier included a linear displacement type
and two rotary displacement types, one a
disc the other a shaft. Workable designs
could have been generated based on any of
these approaches, but the rotating shaft
option was selected because it was believed
that it would facilitate the interfacing of the
barrier with the drive train and the required
manual safing mechanism.
A linear solenoid/bellcrank solution was
chosen for the drive train, rather than a
more conventional rotary solenoid. The
selection was based on lower cost, and the
ability to readily obtain a reversible 90
degree rotation of the barrier without
resorting to a gear reduction train.
INTERRUPTER DESIGN
As shown in Figure 4, the Interrupter
housing is a complex rectalinear structure
with overall dimensions of 5 1/4 L x 3 5/8
W x 2 7/8 H inches. The lower LH view in
Figure 4 shows two of the four input/output
detonator ports (the other two oppose the
ones shown) in the aft section of the
housing, and two electrical connectors. One
of these interconnects with the drive train
power circuits, the other connector
interfaces with the remote monitoring
circuits. The two lower views depict the
Safing Key, which is located in a cylindrical
projection on top of the unit. The two
cylindrical projections at one end of the
Interrupter house the pneumatic damper
components.
Figure 5 shows the drive train components.
The prime movers are two identical pull
type solenoids, installed in parallel, one for
driving the mechanism from the Safe to the
Armed state, the other for reversing the
procedure. The plunger in each solenoid is
pinned to a rod extension on which a roller
is mounted. A low-inertia rotor is mounted
on a shaft aligned on an axis normal to the
solenoid axes and half way between them.
As shown in Figure 5, the rod-mounted
rollers contact opposite faces on the Rotor.
A retraction of the Arm solenoid causes its
coupled roller to cam-drive the Rotor in the
clockwise direction (viewed from the rotor
side of the unit). Conversely, the Safe
solenoid will drive the Rotor in the CCW
direction. An overcenter spring, pinned, to
the Rotor and housing , completes the
Rotor's full 90 degree rotation after it is
driven past top-dead-center by either
solenoid. The overcenter spring is also
designed to detent the Rotor in either the
Safe or Armed position.
- 216 -
.06 MAX-
2X .52 UAX-
^
1*
1-63
i I
i |
3
5.265
'5.235"
J^
/ 1
-©■
/
-©-
STATUS VIEWPORT -
n
\
Figure 4: The Interrupter Configuration and Envelope
2X .877
T | 1.412
. J L 1-382
-L I
_] L
3.637
3.607
J i.
i
3.902 MAX
i i
2.S75
.1
J L_^
SECTION D-D @7 Y©
Figure 5: Cross-Sectional Views of the Interrupter
- 217 -
Figure 6: The Pneumatic Damper
An unusual feature of the Interrupter drive
train is the incorporation of pneumatic
dampers, which are coupled in-line with
each of the solenoid actuated pull rods. The
purpose of these dampers is to prevent the
rollers from hammering on the rotor, during
shock and vibration exposure. Each
damper, as shown in Figure 6, consists of a
spring-loaded piston riding in the bore of a
tubular extension on the housing. The
damper-piston head and rod are sealed by
dynamic "labyrinth" glands designed to
minimize friction drag. The damping force
is controlled by an orifice through the head
of the piston. Figure 7 shows the calculated
effect of one of these dampers on the
rotational velocity of the rotor. The rotor
shaft, which is mounted in plain bearings at
each end, is the barrier which blocks (or
permits) detonation propagation between the
input (donor) and output (receptor) tips on
the ordnance transfer lines which are
coupled to the Interrupter. Two transverse
apertures in the shaft are aligned with the
ports to provide propagation paths when the
rotor is in the Armed state. When Safe, the
apertures are maintained at 90 degrees to the
propagation paths. The apertures, which are
carefully configured slots rather than
cylindrical bores, are shown in Figure 8.
\0 20 30 46 SO 60
Figure 7:
Damper Effect on Rotor
(J 88)
4X FULL
Figure 8:
Propagation Apertures in Rotor Shaft
- 218 -
The dimensions and configuration of these
slots evolved during development testing, to
provide reliable detonation propagation
across in airgap of almost 1/2 inch. To put
this simple fact in perspective, the airgaps
between donor and receptor tips in ordnance
transfer lines are usually of the order of 40
to 60 thousandths of an inch.
As shown in Figure 9 a spur gear is
mounted on the outboard end of the rotor
shaft. This gear meshes with a floating
gear-rack, which is coupled, by means of a
pin projecting from its back-face, with a
spring-loaded push rod. Depressing the
push rod against its spring, by the insertion
of a Safing key, will thus activate the rack,
thereby causing the spur gear, and hence the
rotor shaft, to rotate. This is the mechanism
for manually driving the interrupter from the
Arm to the Safe state. A partially slotted
section in the push rod ensures that it can
only drive the rack in the Sating direction.
In other words, the unit cannot be manually
driven from the Safe to the Arm position.
The Safing Key that is used with this device
is a simple bayonet-type pin featuring a
radial button and integral blade at one end.
When the key is inserted into the housing,
its radial button engages a slot which guides
the blade on the key into engagement with a
clevis on the end of the push rod. As
insertion continues, the key depresses the
push rod, which is also guided by a pin-in-
slot feature, thereby safing the unit. After
the key is fully inserted, it is rotated 90
degrees, where it's button meets a stop.
From this position, the spring-loaded push
rod forces the key back, until it's button is
captured in a detent slot. At this point, with
the Safing Key detented while holding the
push rod in a depressed (and rotated) state,
the Interrupter is locked in the Safe
condition.
SATING -PIM
VJetJei or \>raitd irtU Hsg
RACK
Rotor -Co Ha r
Figure 9:
Manual Safing Mechanism
One simple feature on the push-rod permits
the Interrupter to satisfy a current test range
requirement which stipulates that, when
installed, SAD safing keys must not be
removable when an inadvertent attempt is
made to arm the device. A notch in the
push rod is aligned with the pin on the rack
when the detented Safing Key has rotated
the engaged push rod through 90 degrees.
This notch permits a small amount of rack
movement if an attempt is made to drive the
rotor from Safe to Arm. The amount of
rack travel, which corresponds to approxi-
mately 10 degrees of rotor rotation, is
sufficient to drive the rack pin into the push-
rod notch. When trapped in the notch, the
pin prevents rotation of the push-rod, which,
in turn, prevents rotation of the Safing Key,
and hence it's removal from the unit.
As well as providing the detonation transfer
barrier and an important part of the manual
safing mechanism, the rotor shaft serves one
more purpose, namely that of a flag bearer.
A two-color disc is mounted on the end of
the shaft, and viewed through an offset
window in the housing, for visual status
monitoring. When the shaft is in the Safe
position, only the green side of the "Flag"
disc is observable, when in the Armed
- 219 -
position, only the red side is seen.
DEVELOPMENT
A pair of passive electrical circuits are
incorporated in the Interrupter, for remote
interrogation and monitoring of the unit's
Safe/ Arm status. These circuits, which are
shown schematically in Figure 10, are
alternately closed by sub-miniature snap-
action electrical switches, actuated by the
rotor. This design approach was selected
primarily because of its simplicity, hence
potential reliability and cost effectiveness,
compared with the PCB/brush-contact type
of rotary switches commonly used in SADs.
The approach was rendered viable by the
fact that no EED firing circuits require
switching within the Interrupter.
ji
PT02E-8-4P
J2
PTD2E-S-3P
SAFE INPUT
SAFE RETURN
ARM INPUT
ARM RETURN
SAFE MOMTDR
MONITOR RETURN
ARM MONITOR
Figure 10:
Interrupter Electrical Schematic
A comprehensive development test program
was undertaken, directed towards the design
characterization and refinement of the
barrier, relative to its effectiveness, both as
a block, and as a propagation path in the
ordnance transfer line. The blocking tests
were conducted using special fixtures
capable of precision settings of a range of
angular misalignments. Short lengths of
CDF line, with standard detonation end-tips,
were used to accurately represent the
transfer lines in these tests. Effective and
reliable blocking was found with the barrier
apertures less than 40 degrees out of
alignment with the output ports. In the Safe
position, the apertures are misaligned a full
90 degrees.
During the transfer tests, several changes
were made to the barrier aperture
configuration before reliable propagation
across the 1 12 inch airgap could be
achieved. When the optimum aperture size
and shape appeared to have been derived, it
was proven by means of a Bruceton series
of tests.
A commercially available linear solenoid
was selected as the drive-train prime mover,
because of its compact size and advertised
high pull-in force. During development
testing, the solenoid proved to be marginal
in performance at the specified lowest input
voltage level. This was partly because the
switch actuator drag forces, on the rotor,
were higher than expected. Changes were
made to the switch actuators, and eventually
the switches themselves were changed,
resulting in a solution to the problem. In a
recent design refinement of the Interrupter,
the solenoids were increased in size to
substantially enhance the pull-in force
margin.
- 220 -
EXPLOSIYE GAP PROPAGATION
: Tests per DOD-
-E-83578
VIBRATION:
Frequency
20 Hz
20 to 70 Hz
70 to 800 Hz
800 to 20000 Hz
2000 Hz
Overall
X and Y Axis
.026 G 2 /Hz
4-6 dB per Octave
0.3 2 GVKz
-6 dB per Octave
.051 GVHz
19.8 GRMS
Z Axis
.041 G 2 /HZ
+6 dB oer Octave
0.50 G 2 /Hz
-6 dB per Octave
.08 G 2 /Hz
25.0 GRMS
SHOCK:
Frecruencv
100
100 to 1500
1500
3000
Peak Acceleration
45
+5 dB per Octave
4100
4100
BENCH TEST 25 cycle
test at vacuum (
26.8V input)
TEMPERATURE CYCLING: 8
cycles -8 5°F and
+ 180°F
CYCLE LIFE TEST: 1000
cycles
STALL TEST: 32V inDUt
for 5 minutes and for 1 hour
Figure 11: The Qualification Test Program
One area of concern, going into the
development program, was the possibility of
the linear drive trains dislodging and
displacing the detented rotor, when
subjected to the full range of shock and
vibration environments specified by the
customer. No such problems were
experienced when the units were subjected
to the dynamic tests, thus indicating the
effectiveness of the pneumatic dampers.
QUALIFICATION
In September of 1993, a group of
Interrupters successfully completed a
qualification test program, as defined by the
customer. Figure 11 shows the tests that
were conducted, which included temperature
cycling and a 1,000 cycle life test, as well
as the dynamic environments. This program
has qualified the Interrupter for flight at the
Wallops Island Test Range.
FUTURE REFINEMENTS
The Interrupter is a new product, and as
such, we would be very naive to think that
it cannot be improved. As already noted,
the solenoids in the first units were smaller
than optimum, and the next larger standard
frame size solenoid is planned for future
units.
Already, studies have been made on a cost
effective installation of a rotary switch, as
shown in Figure 12. This will reduce
frictional drag on the rotor, as well as
provide for the switching of additional
circuitry. In a current new application for
the Interrupter, EEDs will replace the input
transfer lines. The firing circuits for these
EEDs will be routed from the power input
connector to the rotary switch, and back
outside the housing through an additional
connector. The EEDs would be cabled to
the additional connector, which will be
- 221 -
mounted on the aft face of the housing.
Another possible design refinement would
be full integration of the pneumatic dampers
within the main housing, rather than in the
tubular extensions. This would have the
advantage of reducing the overall length of
the unit, although it might make the
assembly of the device slightly more
difficult, therefore, more expensive.
CONCLUSION
The Interrupter described in this paper is a
"patent pending" device which offers a
significantly lower cost alternative to
conventional Safe and Arm devices, for
some applications. The original design was
limited to applications involving ordnance
transfer lines interconnecting system
initiators with independent output devices.
A recent refinement to the Interrupter, in
which a rotary switch replaces the original
microswitches and an additional connector is
added , permits electrically initiated
detonators to be installed in the unit's input
ports. This would allow the Interrupter to
be used in many more SAD applications.
The refinements will not eliminate the basic
advantage that prompted the generation of
the Interrupter concept in the first place.
That is, the Interrupter will remain a
completely passive device, with no internal
ordnance components, hence it will be
completely safe to handle.
ARM SOLENOID
SAFE MONITOR #1
L SAFE MONITOR #2
SAFE CONDITION
-OET # 1
SAFE SOLENOID
ARM MONITOR
ARMED CONDITION
Figure 12:
The Rotary Switch Refinement
- 222 -
Sii-22
6m
10
A VERY LOW SHOCK ALTERNATIVE TO CONVENTIONAL. PYROT ECHNICALLY
OPERATED RELEASE DEVICES
Mr. Steven P. Robinson
Senior Mechanical Design Engineer - Research & Technology
Boeing Defense & Space Group
Seattle, Washington
ABSTRACT
NiTiNOL is best known for its ability to remember a
preset shape, even after being "plastically" deformed.
This is accomplished by heating the material to an
elevated temperature up to 120 degrees C. However,
NiTiNOL has other material and mechanical
properties that provide a novel method of structural
release. This combination of properties allows
NiTiNOL to be used as a mechanical fuse between
structural components. When electrical power is
applied to the NiTiNOL fuse(s), the material is
annealed reducing the mechanical strength to a small
fraction of the as-wrought material. The preload then
fractures the weakened NiTiNOL fuse(s) and releases
the structure.
This paper describes the mechanical characteristics of
the NiTiNOL alloy used in this invention, structural
separation design concepts using the NiTiNOL
material, and initial test data. Elimination of the
safety hazard, high shock levels, and non-reusability
inherent with pyrotechnic separation devices allows
NiTiNOL actuated release devices to become a viable
alternative for aerospace components and systems.
PSTCOPUCTION
Explosive bolts and separation nuts have been
successfully applied for structural release operations
for over 40 years. These devices were simple, cost
effective and very reliable. However, the increased
sophistication, and susceptability, of electrical and
electronic systems in aircraft, missiles and spacecraft
has increased the effect of pyrotechnically actuated
release devices from being a mere nuisance to a
critical path situation that must be accounted for in
assuring successful system performance. This has
elevated the status of structural separation testing, via
explosive bolts, to a very time consuming and costly
endeavour.
Within the last five years, emphasis has been placed
on finding alternatives to explosive bolts and
separation nuts. The reason for this change of
direction is based primarily with the explosive nature
of these devices. The safety issues, when dealing with
explosives, add additional costs to assembly, testing
and storage of aerospace components. The shock
generated by these devices is becoming a critical
design consideration because of the sophisticated
electronics being implemented to lower cost and
improve system performance. EMI susceptability,
potential contamination from explosive byproducts
and limited shelf life are other factors that demonstrate
explosive structural separation is no longer as cost
effective and simple to use as in the past
Historically, non-explosive structural separation
involved electro-magnetic solenoids or wax actuators
pulling pins to release the structural elements. These
are capable of performing the release functions but
operate at a distinct disadvantage because of the
slower actuation speed and greater volume and weight
compared to pyrotechnic devices.
Since 1986, Boeing Defense & Space Group has been
actively researching a class of materials known as
Shape Memory Effect (SME) alloys to provide a
simple actuation mechanism that will combine the
best features of both non-pyrotechnic and pyrotechnic
release technologies. Through this work, Boeing has
developed proof-of-concept structural release concepts
based on the shape memory effect characteristic of
NiTiNOL. These early concepts demonstrated that
NiTiNOL is capable of achieving most of the design
goals of eliminating explosives, providing reliable
performance, and demonstrating multiple operation
capability. However, these devices were volume
- 22'5 -
inefficient and slow compared to existing pyrotechnic
equivalents.
To improve the performance of our release design
concepts, a review of the basic characteristics of
NiTiNOL was initiated to determine if any properties
were overlooked that would help reduce the size and/or
increase speed of operation. This review uncovered the
fact that "as-wrought" NiTiNOL, prior to annealing,
is very strong. The ultimate tensile strength can be as
high as 270 KSL When the NiTiNOL is annealed,
restoring the crystalline phase structure necessary for
shape recovery, the ultimate tensile strength is
reduced by a factor of 2 or more. This fact along with
other characteristics such as high electrical resistance,
excellent corrosion and fatigue capabilities led us to
believe that a simple, effective, and fast NiTiNOL
mechanical "fuse" separation concept is feasible.
Using NiTiNOL as a mechanical "fuse" appeared to
be a simple structural separation concept with few of
the problems associated with pyrotechnic devices.
INITIAL CONCEPT DEVELOPMENT
The first test to demonstrate the NiTiNOL mechanical
fuse concept was relatively simple. This is shown in
Figure 1. One end of a NiTiNOL wire was mounted
NiTiNOL
wire
terminal strip
power
supply
weight
Figure 1 NiTiNOL Structural "Fuse" Test Set-up
to a terminal strip. This was also the positive
terminal of a power supply. A weight was suspended
from the wire. The other end of the NiTiNOL wire
was tied to the negative terminal of the power supply.
When power is applied, the NiTiNOL is heated well
into its annealing temperature zone. The strength of
the NiTiNOL falls to near zero allowing the dead
weight to fracture the wire releasing the weight.
This demonstrated that using NiTiNOL as a
mechanical fuse as a means of holding and releasing a
given preload was feasible. However, any structural
alloy should be capable of accomplishing the same
task. A comparison chart showing the requirements of
a mechanical fuse compared to the characteristics of
NiTiNOL, nichrome, beryllium-copper, and steel is
given in Figure 2. As shown , NiTiNOL has the best
combination of properties necessary for a mechanical
fuse release concept
The most significant factor is the dramatic change in
strength capability at elevated temperature. This
reduction in the tensile strength of NiTiNOL is
crucial to the preload breaking the structural tie and
releasing the load. None of the other materials show
as large a strength reduction at elevated temperature.
The demonstration of fusing a single NiTiNOL
element does not automatically demonstrate the idea
can be scaled up to practical sizes and applications.
Since conventional separation nuts are capable of
loads up to 25,000 lbf, the NiTiNOL separation idea
would also have to be capable of achieving these load
levels. In order to accomplish this, a relatively large
number of NiTiNOL fuses would have to be
incorporated in parallel fashion to increase the load
carrying capability to levels equivalent to explosive
bolts and nuts. Multiple NiTiNOL fuse element
arrangements appear to be the only way to maintain
large load carrying capability and still have the
resistance of the elements high enough for efficient
electrical heating
However, the large number of elements, if they were
all heated at the same time, would require a
prohibitive amount of electrical power. This is not
possible with existing power system ratings on
today's aerospace systems. A NiTiNOL fusible
element requires a low voltage, high current electrical
pulse to efficiently heat the element in the shortest
amount of time.
A review of separation time requirements showed a
large percentage of release operations do not require
separation times less than 10 milliseconds as is
typical of pyrotechnically operated separation nuts and
bolts. The near instantaneous release time is just a
consequence of utilizing explosives in the separation
device. This fact allows us to reduce the number of
elements being heated at any one time to a minimum
because separation time is not always critical.
By applying this fact to the NiTiNOL fuse concept,
we can reduce the instantaneous power requirement to
manageable levels. This is shown in figure 3. The 5
element group is mechanically attached in parallel to
- 224 -
distribute the load and increase the overall load
carrying capability. The element lengths are all
Material Property Comparison Chart
Properties
fuse
ream'ts
NiTiNOL
Steel
304
Steel
Beryllium Nichrome
Cooper Ni70.Ci2S.Mher!
electrical
resistivity
(microhm-cm)
High
100
100
72
20
134
tensile strength
(KSI)
(room temp.)
High
250
210
110
115
150
tensile strength
(KSI)
(1000 deg F)
Low
>25
150
50
85
100
corrosion
resistance
High
High
High
High
Med.
High
fatigue
resistance
High
High
High
Med.
High
-
thermal
conductivity
(BTU/hr-ft-F)
Low
10.4
10.4
«
120
,4
Comparison of NiTiNOL to other structural alloys
Figure 2
stationary structure
NiTiNOL fusible
f MYli ir
\ y element (5 pi)
Rl
B
* 1
R3
1 rs
R
■71 „
.5
Jp
Pa
ft
^1 power
1 supply
released
structure
R1>R2>R
3>R4>R5
NiTiNOL Element Sequential Separation Concept
Figure 3
different to produce a uniformly increasing resistance
value range. The elements are wired in parallel. When
current flows through the elements, the shortest
NiTiNOL fuse draws the most current, heats the
fastest and fractures first. Now the load is carried
among fewer elements. This increases the stress
levels in each element. The power is also shared
among fewer elements causing the elements to heat
even faster. This cascading effect fractures each higher
resistance element until the last one in the group
separates. Figure 4 shows an idealized trace of the
cascading separation effect. The increasing resistance
of each successive element causes a distinctive
zipping effect
To further increase the load carrying capability,
multiple groups of these subsets of NiTiNOL fusible
elements can be arranged to be released in series. As
soon as the last element in the first group separates,
power is transfered to the next group of elements,
thereby continuing the separation sequence.
NiTiNOL Fusible Element Release Sequence
Figure 4
The number of element groups can be increased to
accomodate a wide range of loading conditions. The
time-to-separate requirement must be addressed to
assure there is no impact to the overall separation
operation.
However, the increase in the separation time may not
be critical if a two step separation approach is taken.
An "arming" operation could take place which would
release the majority of NiTiNOL fuse elements. This
would leave a minimum number of elements to
maintain the structural attachment. When actual
separation occurs, the power required and separation
time will be kept to a minimum due to the minimum
number of elements left to fuse open. This concept
allows a large number of structural elements to be
maintained across the joint satisfying a wide range of
available power, time-to-separate, and structural load
cases.
This concept is postulated for large separation joints
such as payload fairings and other large linear
structural interfaces. In fact, the majority of this work
was performed in anticipation of the next generation
heavy lift launch vehicles (HLLVs).
As a result of this initial work, a patent (#5,046,426)
has been awarded to The Boeing Company.
NASA/JSC SEQUENTIAL SEPARATION TEST
Using the concept described in the previous section,
Boeing Defense & Space Group was contracted by
- 225 -
NASA/JSC to perform a feasibility experiment
demonstrating that a NiTiNOL sequential structural
separation system is capable of loads in the range
needed for commercial applications. Since this was a
small experiment, a candidate separation load was
assumed to be 5000 lbf. This would provide a
reasonable loading condition without imposing extra
costs.
The basic design concept is shown in figure 5. To
expedite the experimental hardware fabrication, we
utilized NiTiNOL strip, 1.4" w x 0.004" t, that was
available in-house, as part of our ongoing IR&D
effort. Although the dimensions of the strip was not
optimized for this experiment, we felt valuable
information on laser cutting of NiTiNOL and
operation of this patented NiTiNOL non-pyrotechnic
release concept could be achieved.
The structural members were fabricated from 4.0" dia.
molybdenum disulfide impregnated nylon. This
provided an inexpensive, electrically isolating
material capable of handling the 5000 lbf projected
load. Mounting studs were attached to the center of
the nylon parts to provide sufficient grip length for
installation onto an Instron tensile test machine. The
NiTiNOL fusible element strip was installed across
the interface between nylon members. The NiTiNOL
fusible element member was attached by two(2) rows
of 32 each 6-32 fasteners. These were installed into
tapped holes in the nylon parts. The load across each
fastener was 125 lbf max. The one concern was
whether the attachment holes, in the NiTiNOL strip,
were strong enough to react the tensile load without
tearing out.
The cutout pattern and slots, defined the five (5)
NiTiNOL fusing elements per each of the eight (8)
groups. The cutouts were produced by a high powered
laser cutting system located in the Boeing Materials
Technology Laboratory located in Renton, Wa.
Utilizing computer controlled laser cutting provided
several benefits. Unique patterns can be cut into the
strip with great accuracy. This also provides a high
degree of dimesional repeatability, critical for some
operations. Laser cutting also provides a way to
minimize the area of the heat affected zone which
would compromise the large differential strength
characteristic of NiTiNOL from its unnannealed state
to its annealed state.
The structural separation operation uses an electrical
circuit that applies battery power to opposite pairs of
fusing elements. This assures a symmetrical release
of the load minimizing any off-axis unloading
situations resulting in excessive tip-off rates. As the
last elements of the first two groups are fused opened,
battery power is switched to the next pair of fusing
element groups. This continues until all fusing pairs
of element groups have been severed. The circuit
diagram is shown in figure 6. To expedite the circuit
design, automobile starter solenoids were utilized in
the circuit design to transfer battery power between
NiTiNOL fusing element groups.
When switch SI is engaged, 28 V is applied to the
first starter solenoid closing the circuit and applying
12 V battery power across opposite groups of
NiTiNOL elements. The 4 ohm resistor prevents the
second solenoid from engaging until the last
NiTiNOL element, from the first 2 groups, has fused
open. Battery power is then switched to engage the
second solenoid, which in turn applies battery power
to the next pair of opposite NiTiNOL element
groups. This continues until the last NiTiNOL
elements are fractured releasing the structural load.
EXPERIMENTAL TEST RESULTS
Using 0.004" thick foil for this test generated concern
that the foil might fail in the attachment holes at the
required load of 5000 lbf. A load test was performed
to determine the maximum load capability. As
predicted, the failure occured in the mounting holes at
approximately 3200 lbf. It was obvious that a goal of
5000 lb was not possible with the current material.
However, no alternative was available to support
testing. Therefore, it was recommended that the test
load be reduced to 2000 lbf. This would still
demonstrate the feasibility of this technology with
the current experimental hardware at a realistic load
value.
One test was performed to demonstrate feasibility.
The test article was mounted on an Instron tensile test
machine with full scale readout of 5000 lbf. The load
was uniformly increased to 2000 lb indicated. As the
load reached the test level, switch SI was closed
applying power to the first solenoid. The first pair of
NiTiNOL element groups fused opened in 156
milliseconds, the second pair in 182 msec, the third
pair in 164 msec, and the last pair in 194 msec. The
total time to release was 0.838 seconds. The trace of
the release operation is shown in figure 7. As the
oscilloscope trace shows there was some bounce of
the solenoid contacts generating some delay of power
to the NiTiNOL elements, increasing the apparent
separation time.
The circuit performed as designed. Once the switch
was engaged, the application of battery power was
autonomous and continuous. This resulted in a very
simple circuit capable of transferring high current
pulses as many times as needed.
- 226 -
NITINOL RELEASE TEST F I X TURE ( FULL Y ASSEMBLED
NITINOL FUSIBLE ELEMENT STRIP
eeee -
«rH$^
1HREAOED STUO
STRUCTURE CNYLON )
8 9 e e HG/fl*
$ $ $ f 4H
NITINOL FUSIBLE
ELEMENT GROUP (I QF 8)
STRUCTURAL ATTACHMENT
HOLES
Figure 5 NASA/JSC Sequential Structural Separation Demonstration Experiment
released structure
))))))))
starter 1
solenoid)
(1 of 4^
stationary
structure
4 ohms
(typ)
+
12 V battery
asi
Til ■
si
s~
power supply
Figure 6 NASA/JSC NiTiNOL Fusing Element Electrical Circuit
SUMMARY
Boeing Defense & Space Group believes this
technology could provide a viable alternative to
explosive separation systems utilizing linear shaped
charges to weaken and fracture a structural joint, such
as those on large payload shrouds. Further research
into the possibility of gradually releasing the preload,
prior to full separation, offers design possibilities that
could reduce the shock of separation, power usage,
and separation time even further.
- 227 -
Although this type of release concept may require a
unique electrical system, such as dedicated on-board
batteries, the changes appear to be minimal and
simple to implement.
Time-to-Release Separation Test - Oscilloscope
Traces (2000 lbf preload)
Figure 7
If an existing electrical system, capable of operating
pyrotechnic devices with 5A DC max. current output
is the only source of power, work was accomplished,
under contract with the Naval Research Laboratory, to
develop such a release device, for spacecraft use, based
on this invention. This work is described in the
following section.
NiTiNOL FUSIBLE LINK RELEASE DEVICE
(NAVAL RESEARCH LABORATORY)
The Naval Research Laboratory contracted with
Boeing to develop a NiTiNOL based mechanism to be
included as part of the Advanced Release Technologies
(ARTs) program. The requirement of being able to
interface with an existing 28V/5A spacecraft power
bus system needed a different design approach than the
NASA/JSC concept. In order to accompliash
separation of a 2000 lbf preload within 0.250 second
using a limited power budget, we used a single
NiTiNOL fusible element, in conjunction with a
large mechanical advantage, as the active member to
accomodate a 2000 lbf preload. The basic concept is
shown in figure 8.
The overall size of the device is 3.50" x 3.50" x 1.5".
Although larger than conventional separation nut
designs, the size envelope is small enough to be
useful in many separation operations. Future design
iterations can conceivably reduce the size even further.
The most significant change between the NASA/JSC
concept and this concept is the use of a 9:1 step-down
transformer. The transformer, along with the DC/AC
converter electronics, allows the device to operate
with an existing 28V/5A max electrical power bus
system. This system is typical of current spacecraft
designs. The electronics converts 28V DC to 28V AC
at 100 KHz. The step-down transformer converts the
chopped 28 V/5A AC to approx. 3.1 V/45 A AC
power. The high frequency of the chopper electronics
allows us to use the smallest transformer possible.
The total power usage has not changed. However, it
has been converted to a more useable form for
efficient heating of the NiTiNOL fusible element.
The design concept provides a mechanical advantage
of approximately 24:1. This enables a NiTiNOL
fusible link, sized for 150 lbf, to be able to withstand
a 2000 lbf preload. In fact, the fusible link is sized for
3600 lbf. This corresponds to a positive margin of
safety of approximately +1.75. The NiTiNOL fusible
link design is also shown in figure 8. In order to
minimize the transformer lead lengths, the design of
the fusible link is a U-shape configuration allowing
both transformer leads to be on the same side of the
release device. This also provided the added benefit of
- 228 -
STOWE
RELEASED
TENSION LINK
HOUSING
TORSION SPRING
(1 OF 2)
Figure 8
TRANSFORHER-
NiTiNOL Fusible Link Release Device (NRL)
doubling the strength of the NiTiNOL mechanical
fuse without increasing the overall size of the release
device.
The release device configuration is straightforward.
Two (2) spring loaded jaws are closed to capture the
tension link. The NiTiNOL fusible link is installed
on two phenolic blocks at the ends of the jaws. The
jaws have a step at the bottom where the tension link
engages the jaws. When the preload is applied
through the tension link, the step creates a 0.10"
moment arm. The NiTiNOL fusible link has a
moment arm of 2.4 ". This creates a 24:1 mechanical
advantage. The allows a relatively small fusible link
to be employed against a substantial preload. Figure 9
describes the geometry in greater detail.
In order to keep the device weight and volume to a
minimum, the transformer, designed to operate at a
frequency of 100 KHz, was used. The transformer size
NiTiNOL Fusible Link Reaction Force Geometry
tension link
20q01b NiTiNOL
fusible link
2.40"
lb preload
applied
0.10"
pivot pt
(2000x0.10")= 2.40" x F
F = 851b
Figure 9
- 229 -
was 1.3" L x 1.0" W x 0.25" t. Mounting the
transformer to one of the jaws kept wire lengths to a
minimum. This prevented inductance from becoming
a problem. Too much inductance would reduce the
amount of power through the NiTiNOL fusible link
compromising the heating of the NiTiNOL and the
performance of the device.
The preload is applied by threading a bolt into the top
of the tension link assembly. As the bolt was
torqued, the tension link would be pulled up and
engage the jaws. The moment generated by the
tension link against the jaw tries to force the jaws
apart. The NiTiNOL fusible element reacts this torque
until the NiTiNOL is electrically heated. When this
occurs, the link becomes structurally weak and
fractures, allowing the jaws to spring out and the
tension link to be extracted.
The DC to AC chopping circuit is on a separate board
and can be installed in any convenient place. It can
also be installed on the release device housing itself.
TEST RESULTS
The release device was proofloaded to 2000 lbf
without separation. When power was applied, the
release device demonstrated release time less than 200
msec. Several tests were also conducted at lower
preloads. The effect of the preload variation on release
time was apparent. It showed that lower preload
values yielded higher release times. At no preload, the
release time was approximately 50% greater. This
required the NiTiNOL to be heated to near the melting
temperature. Under actual conditions, this zero preload
situation would be very remote.
A longterm loading effects test was also performed on
a NiTiNOL fusible element. This was to determine if
any stress relaxation or creep phenomenon was
present using NiTiNOL. The link was mounted in a
fixture with a simulated preload. This was stored for
approximately six (6) months. Measurements were
taken on a daily basis. No significant increase in
length was observed for the entire 6 month period.
Separation tests confirmed the ability of a NiTiNOL
fusible link release device to maintain and release a
2000 lbf preload reliably. Testing at NRL is ongoing.
Initial testing shows separation times are consistently
within 50 msec. However, this is dependent on the
same power and preload being applied during each
separation test.
SUMMARY
This non-pyrotechnic release concept demonstrated
that a single NiTiNOL fusible element can reliably
hold and release a given preload using a typical 28V,
5A electrical bus system. Even with the apparent
dependency of release time to preload, this can be
attributed to the limited power available. The effect
can be minimized by proper sizing of the NiTiNOL
fusible link and optimizing the heating to the power
availability. In addition, the shock of separation was
insignificant. There is no contamination or safety
issues associated with this device.
The release device is completely reusable except for
the NiTiNOL fusible link. This feature allows the
same device to be operated many times during ground
testing, and still be available as the flight unit. The
benefits of this device are shown in figure 10.
Benefits
1) Non-pyrotechnic
2) Fly-as-tested capability
3) Little or no separation shock
4) No shelf life limitations
5) No safety hazards
6) No EMI susceptability
7) Fast separation time
8) No contamination potential
Figure 10
NiTiNOL Beneffits Chart
These features can provide a very cost effective
product especially if extensive ground testing is
contemplated. The cost of the NiTiNOL material does
not appear to be a limiting factor because commercial
usage continues to increase as more applications are
realized. As usage increases, the material price will
decline accordingly.
CONCLUSION
Load capability and separation times demonstrated by
these concepts show that NiTiNOL fusible element
based devices, using this Boeing patent, have the
potential to achieve the same performance as
pyrotechnic devices. This can be accomplished
without the detrimental effects attributed to the use of
explosives,
Boeing Defense & Space Group feels this technology
will provide a much needed reduction in safety related
and shock environment issues involving aerospace
vehicles. Reducing shock environmental requirements
imposed on vehicle sub-systems and components will
play a major role in reducing vehicle development
costs. The costs associated with handling, storage and
- 230 -
assembly of pyrotechnic devices can be practically
eliminated if this technology can be developed to its
fullest capability.
Both of the concepts, described previously, offer both
ends of the design spectrum that is possibile using
this simple technology. Many design alternatives can
be created if the drawbacks, associated with
pyrotechnic devices, can be eliminated. We understand
this and are continuing to improve the basic concepts
described here.
One of the most intriguing design possibilities is the
two-step arming/separation function described
previously. This idea offers unique advantages and
design flexibility that provides the designer with
options not possible with conventional pyrotechnic
systems. This ability to slowly release large preloads
all but eliminates the heavy shock environment
imposed on the surrounding structure. This can be
accomplished without jeopardizing the actual release
function.
The future of non-pyrotechnic structural separation,
based on this patent, will be expanding. The
capabilities offer so many advantages that this
technology will become a major part of structural
separation for the next generation of aerospace
vehicles.
- 231 -
INVESTIGATION OF FAILURE TO SEPARATE AN INCONEL 718 FRANGIBLE NUT
<, lit- h
70O0
William C. Hoffman, III
Carl Hohmann
NASA Lyndon B. Johnson Space Center, Houston, TX
Abstract
The 2.5-inch frangible nut is used in two places to
attach the Space Shuttle Orbiter to the External Tank. It
must be capable of sustaining structural loads and must
also separate into two pieces upon command. Structural
load capability is verified by proof loading each flight nut,
while ability to separate is verified on a sample of a
production lot. Production lots of frangible nuts
beginning in 1987 experienced an inability to reliably
separate using one of two redundant explosive boosters.
The problems were identified in lot acceptance tests, and
the cause of failure has been attributed to differences in
the response of the Inconel 718. Subsequent tests
performed on the frangible nuts resulted in design
modifications to the nuts along with redesign of the
explosive booster to reliably separate the frangible nut.
The problem history along with the design modifications
to both the explosive booster and frangible nut are
discussed in this paper. Implications of this failure
experience impact any pyrotechnic separation system
involving fracture of materials with respect to design
margin control and lot acceptance testing.
Introduction
The 2.5-inch frangible nut is used in the Space
Shuttle Program to attach the Orbiter to the External Tank
at two aft attach points as shown in figure 1. Structural
loads illustrated in table 1 are carried by each frangible
nut. Upon completion of Space Shuttle Main Engine
cutoff, at approximately 8 minutes, 31 seconds after
Shuttle launch, the Orbiter is separated from the External
Tank by initiation of pyrotechnics at the forward and aft
attach points. Aft structural separation is accomplished
by fracturing each of four webs on the two frangible nuts,
as illustrated on figure 2. Separation is accomplished by
initiating one or both of the -401 configuration booster
cartridges shown in figure 3. The Orbiter frangible nuts
are safety critical devices which are required to reliably
operate for Shuttle crew safety. Production lots beginning
in 1987 experienced an inability to operate reliably with
the performance margins demonstrated in the original
qualification. An intensive failure investigation followed
which has identified the Inconel 718 used in the frangible
nuts as the cause of the failures. The manufacturer of
Inconel 718 forgings used in the qualification and initial
lots of frangible nuts for the Shuttle Program went out of
business, and NASA was forced to solicit new sources for
the frangible nuts. The change in Inconel 718 suppliers
and the differences in the characteristics of the material
led to a performance degradation.
The first section of this paper discusses the original
qualification program and the original Inconel 718
material and chemical properties. The second section of
the paper discusses the failure analysis performed by
NASA and the resultant design solution arrived at through
iterative testing.
Design and Qualification History of
2t?-inch Frangifrte Nut
The 2.5-inch frangible nut is designed with two
primary requirements. The first requirement is that the
nut have the capability to carry structural loads with
specified margins against material yield and rupture. The
second requirement is that the frangible nut reliably
separate into two pieces when either one or both booster
cartridges are initiated. Inconel 718 was selected for the
frangible nut due to the combined high material strengths,
and to its resistance to creep and corrosion. The
qualification matrix shown in table 2 illustrates the type
and number of tests performed to demonstrate reliable
operation in the presence of flight and ground
environmental conditions. The performance margin was
demonstrated using nominal booster cartridges in
frangible nuts whose web thicknesses were increased
above the maximum allowable by 20% as shown on the
-101 margin nut in figure 4. Shuttle Program
requirements dictate a margin demonstration of 15%, but
the additional 5% margin was chosen to gain confidence
in the frangible nut design. All margin tests were
successful. Design, development, and test of the 2.5-inch
frangible nut were conducted under NASA contract
NAS 9-14000 and results of the qualification were
reported in document CAR 01-45-1 14-0018-0007B 1 .
Material Configuration of the Original Manufacturer's
2.5-inch Frangible Nut
The supplier of the qualification nuts and boosters
procured Inconel 718 which was manufactured to meet
AMS 5662 2 . A compilation of chemical data, material
properties, and typical microstructure grain size for a
representative Inconel 718 heat lot used in the original
- 233 -
PAGL
E £it,
^^;ViXNALLY BL
- A ■'■?'/
manufacturer's frangible nuts is shown in table 3. No
additional restrictions were placed on the Inconel 718
other than requiring compliance with AMS 5662 .
Figure 5 is a representative micrograph of the original
manufacturer's Inconel 718 shown at a magnification of
100X.
Based upon the successful qualification program, the
design was considered complete and production contracts
were issued to support Shuttle flights.
Frangible Nut Production Failures
NASA solicited new manufacturers of the 2.5-inch
frangible nut in 1987 in order to develop additional
sources of supply for the Shuttle Program. Two
qualification contracts were issued with the intent of
demonstrating the new manufacturer's processes. The
second manufacturer was awarded NASA contract
NAS 9-17496 and the third manufacturer was awarded
NASA contract NAS 9-17674. During qualification
testing performed under NAS 9-17496 3 , in accordance
with table 4, failures were encountered during frangible
nut margin tests. The frangible nut failed to sever the
outer web, web number 4 as shown in figure 6, when fired
using a single booster cartridge. Further testing resulted
in a successful separation using a margin nut with webs
15% over the maximum allowable thickness. In an effort
to establish performance margin for the frangible nuts and
booster cartridges, the weight of RDX in the booster
cartridges used in margin tests was reduced by 15%, and
nominal frangible nuts were used instead of nuts with
120% webs. Three margin tests successfully separated
using 85% charge weight booster cartridges and nominal
frangible nuts as shown in table 4.
Material properties, chemical data, and micro-
structure grain size for the Inconel 718 are shown in table
3. The Inconel 718 heat lot number for the NAS 9-17496
qualification lot is 9-11446. Figure 7 illustrates a 100 X
micrograph taken for heat lot 9-11446. There is a
dramatic difference in the precipitate distribution for heat
lot 9-11446 as compared with the original manufacturer's
Inconel 718 micrograph shown in figure 5.
The second manufacturer was authorized to produce
additional frangible nuts based upon successful
completion of the qualification program. The second lot
of frangible nuts, Inconel 718 heat lot 9-10298,
experienced an inability to separate under zero preload
using a single booster cartridge. The gap developed from
the single booster cartridge firing, illustrated in figure 6,
was measured to be less than 0.100" for the failed unit.
Web numbers 1 and 2 were fractured while web numbers
3 and 4 did not experience any cracking. Table 5 shows
the chronology of tests performed to understand the
failure cause and develop a means of overcoming the
problem. A design solution was arrived at through the
test series which consisted of modifications to both the
frangible nut and booster cartridge.
NASA's first response to the failure was to redesign
the booster cartridge to provide additional charge to
overcome the resistance to separate. Booster cartridge
internal cross sectional area was increased in increments
of 5% until successful separation was achieved. In the
course of performing the above tests, the nut was
observed to "clamshell" open until the outer ledge gap,
shown in figure 6, was reduced to 0.00". The frangible
nut outer ledge was machined to provide additional
rotational motion for web number 4 (the outer web) and
the modification to the frangible nut is illustrated in figure
8. The modified frangible nut was identified as a -302
configuration. An additional change was made by
loading the nominal charge weight into the bore of a
booster cartridge body which had been increased in cross
sectional area by 20%. An example of this booster
cartridge is shown by the -402 configuration in figure 3.
By combining the two modifications, the frangible nut,
which was unable to separate under zero preload using a
single booster cartridge with 1950 mg of RDX,
successfully separated with no increase in the explosive
weight of RDX or no reduction in the web thickness 4 .
Material properties, chemical data, and
microstructure grain size for Inconel 718 heat lot 9-10298
are shown in table 3. A 100X micrograph for heat lot
9-10298 is shown in figure 9. Heat lot 9-10298 is
markedly more resistant to separation than the
qualification heat lot 9-11446.
The third manufacturer of 2.5-inch frangible nuts
operating under NAS 9-17674 used Inconel 718 from heat
lot 9-11446 in its qualification test program. Heat lot
9-11446 is common to the heat lot used in the
qualification program performed by the second
manufacturer under NAS 9-17496. The third
manufacturer began qualification testing in accordance
with the test matrix shown in table 6. Testing began with
a margin nut which, at NASA's request, had a web
thicknesses 20% over the maximum allowable thickness.
The 120% margin nut is represented in figure 4 by the
-101 configuration. The 120% margin nut failed to
separate. The margin test was selected due to experience
with failures in margin tests during the second
manufacturer's qualification test program.
The failure to separate the frangible nuts using single
booster cartridges under zero preload or to demonstrate
margin using frangible nuts with overthick webs raised
concern at NASA over the new manufacturers* booster
cartridge performance. Potential causes in degradation of
the RDX detonation output were investigated by chemical
and physical analysis of each lot of RDX used by each
manufacturer. No evidence of degradation was found.
NASA then initiated a test program to inves'igate whether
the original manufacturer's booster cartridges performed
differently from new production lots. The first test
consisted of firing a frangible nut from the original
manufacturer under zero preload conditions using a
booster cartridge from recent production. The second test
involved firing a frangible nut from the second
manufacturer under zero preload conditions using a
booster cartridge from the original supplier. The original
supplier's frangible nut separated using a new
manufacturer's booster cartridge, and the new
manufacturer's frangible nut did not separate using the
original supplier's booster cartridge. These tests indicated
- 234 -
that the booster cartridge was not the cause of the
frangible nut failure to separate.
Further qualification testing under NAS 9-17674,
illustrated in table 6, resulted in failures to separate under
zero preload conditions even though three frangible nut
margin tests were conducted under preload conditions
using booster cartridges loaded with 85% of the nominal
charge weight. The failure of the zero preload, single
booster cartridge frangible nut test resulted in the
frangible nut opening until the outer ledges contacted and
the outer ledge gap, illustrated in figure 6, was reduced to
0.00". All of the third manufacturer's nuts were modified
to remove the outer ledges, illustrated in figure 8, thus
providing more rotational freedom for the outer web
during a single booster cartridge firing. The third
manufacturer resumed the sequence of tests described in
table 6 without failure following the frangible nut
modification 5 . The modifications to the frangible nut
were a result of tests performed during the failure
investigation matrix shown in table 5. Material
properties, chemical data, and microstrucure grain size
data for the Inconel 718 used in the third manufacturer's
qualification lot are shown in table 3, and the 100X
micrograph of the material heat lot is shown in figure 10.
Discussion
In each of the above qualification and production
heat lots, the Inconel 718 was produced in accordance
with AMS 5662. The material properties, yield strength,
tensile strength, elongation and reduction in area are
illustrated in table 3. Although a significant difference is
exhibited in Charpy impact strength 6 between recent
production lots and the original Inconel 718, reference
table 3, no correlation between Charpy impact strength
and frangible nut performance has been made. A NASA
test 7 using material having impact strength of 15 and
ultimate tensile strength 191.1 ksi, 0.2% offset yield
strength of 168.2 ksi, elongation of 16.0%, and reduction
of area of 27.0% resulted in failure when fired using a
single booster cartridge and under zero preload. The
exact combination of chemical, microstructural, and
physical data required to assure successful separation of a
heat lot of Inconel 718 under zero preload conditions
using a single booster cartridge has not been defined.
Additional test programs are underway at NASA to
further understand the cause of failures for the frangible
nuts produced under NAS 9-17496 and NAS 9-17674 and
to define what characteristics in the Inconel 718 are
critical for successful operation of the frangible nuts. The
investigations focus on material property variations in
Inconel 718 and on efficiency of coupling explosive
potential energy into the fracture of the four webs.
Future production of frangible nuts will be assessed
using additional destructive lot acceptance tests to assure
reliable operation of the flight hardware. At this time, no
quantitative test exists to differentiate Inconel 718 as
acceptable or unacceptable for use in flight nuts short of a
full scale destructive performance test. If failure occurs at
that point in production, the products are in final delivery
status and no rework is possible.
Conclusions
The most significant conclusions from the failure
investigations which NASA has performed on the 2.5-
inch frangible nuts are as follows:
A. Specification of Inconel 718 per AMS 5662 is not
adequate to guarantee successful separation of the
frangible nut using the original design booster cartridge.
B. No single chemical or material property currently
measured is an adequate gage of whether the Inconel 718
used in a frangible nut will result in failure or success
during perfomance tests.
C. The critical nature of the 2.5-inch frangible nut
mandates extensive testing be performed on each
production lot to demonstrate operational response and
performance margin.
References
1. Contract NAS 9-14000, Document Number CAR
01-45-114-0018-0007B, "Qualification Test Report for
Frangible Nut, 2-1/2 Inch and Booster Cartridge,"
Released May 29, 1980.
2. AMS 5662 Revision F, "Alloy Bars, Forgings, and
Rings, Corrosion and Heat Resistant, 52.2Ni - 19
Cr - 3.0Mo - 5.1(Cb + Ta) - 0.90Ti - 0.50A1 - 18Fe,
Consumable Electrode or Vacuum Induction Melted
1775°F (968°C) Solution Heat Treated," Issued
September 1, 1965, Revised January 1, 1989.
3. Contract NAS 9-17496, Document Number 3936-10-
301-401, Revision A, " Qualification Test Report for
2.5-inch Frangible Nut, NASA PN SKD26100099-301
and Booster Cartridge, NASA PN SKD26100099-401,"
January 15, 1991.
4. Contract NAS 9-17496, Document Number
RA-468T-B, "Acceptance Data Package for 2.5-inch
Frangible Nut, NASA PN SKD26100099-302,"
June 5, 1992.
5. Contract NAS 9-17674, Document Number
0718(03)QTR, "Qualification Test Report 2.5-inch
Frangible Nut with Booster Cartridge, Used on the
Space Shuttle Aft Separation System," June 19, 1992.
6. American Society for Testing and Materials Standard
E23-88, "Standard Methods for Notched Bar Impact
Testing of Metallic Materials, Type A Specimen."
7. NASA Test Report 2P333, "Frangible Nut Test
Program."
Acknowledgements
The authors wish to acknowledge the work of
Ms. Julie Henkener, materials engineer for Lockheed
Engineering and Sciences Company, Houston, Texas, in
preparing, reviewing, and interpreting the Inconel 718
metallurgical data throughout the frangible nut failure
investigation.
- 235 -
TABLE 1
2.5 INCH FRANGIBLE NUT STRUCTURAL LOAD REQUIREMENTS
Limit Load
Ultimate Load
Proof Load
Axial Load
415,270
581,400
456,800
(Lbs)
Moment
53,275
75,215
59,097
(in-Lbs)
TABLE 2
ORIGINAL MANUFACTURER QUALIFICATION TEST MATRIX FOR
2.5 INCH FRANGIBLE NUT AND BOOSTER CARTRIDGE
Test
Nut
Group
NO
Functional
Temp
<-F)
Preload Booster
Tension Mount
(lbs) (in-lb)
Cartridges
Dual/Single
Functional
(pass/fail)
Room Temp.
A
70-F
240,000
Single
Passed
Firing
A
70-F
240,000
Single
Passed
A
70-F
240,000
Single
Passed
A
70-F
240,000
Dual
Passed
High Temp.
B
200-F
240,000
Single
Passed
Firing
B
200-F
240,000
Single
Passed
B
200-F
240,000
Single
Passed
B
200-F
240,000
Dual
Passed
Low Temp.
C
-65-F
240,000
Single
Passed
Firing
C
-65-F
240,000
Single
Passed
C
-65-F
240,000
Single
Passed
C
-65-F
240,000
Dual
Passed
Low Temp.
Firing with
Limit Axial Load
Room Temp.
Firing with
Zero Preload
Margin Demo.
Firing
E
E
E
E
-65-F
-65-F
-65-F
-65-F
378,000
378,000
378,000
378,000
65,200
65,200
65,200
65,200
Single
Single
Single
Dual
F
70-F
Single
F
70-F
Single
F
70-F
Single
G*
G*
G*
70-F
70-F
70-F
240,000
240,000
240,000
Single
Single
Single
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Group G nuts had web thicknesses 120% the nominal maximum allowable
- 236 -
TABLE 3
MATERIAL PROPERTIES, CHEMICAL DATA, AND MICROSTRUCTURE GRAIN SIZE FOR INCONEL 718 USED
IN FRANGIBLE NUTS BY MANUFACTURERS
ORIGINAL
NAS9-17496
NAS9-17674
NAS9-17496
MANUFACTURER
QUALIFICATION
QUALIFICATION
PRODUCTION
HEAT LOT
HEAT LOT
HEAT LOT
HEAT LOT
9-11446
9-11446
9-10298
0.2% Yield
Avg (ksi)
148.4
165.8
160.3
152.6
Std. Dev. (ksi)
6.5
0.2
2.3
0.6
Ultimate Tensile
Avg (ksi)
188.5
194.2
192.0
190.7
Std. Dev. (ksi)
4.1
1.2
2.4
0.8
Elongation
Avg. (%)
18.6
18.7
20.2
13.0
Std. Dev.
1.6
0.5
0.6
Reduction of Area
Avg. (%)
28.2
30.3
33.2
38.0
Std. Dev.
2.5
1.2
1.5
Charpy Impact Strength:
Avg. (Ft-Lbs)
19.8
28.8
29.3
39.7
Std. Dev.
2.3
1.0
0.8
2.9
Grain Size (ASTM)
5-8
5-8
6-8
Chemical Data: C
0.034
0.027
Ti
0.98
0.98
S
0.001
0.002
B
<.0001
<.001
Fe
17.672
17.78
Al
.5
0.510
Cu
.1
0.06
Ni
53.5
53.75
Co
0.18
0.34
B
0.003
0.003
P
0.01
0.013
Si
0.14
0.13
Mn
.1
0.08
Mo
2.99
2.98
Cr
18.4
18.0
Se
<.0003
<.O0O3
Pb
<.0001
<.0001
Cb+Ta
5.29
5.34
0.027
0.023
0.98
0.910
0.002
0.002
<.001
<0.00001
17.78
18.55
0.51
0.52
0.06
0.050
53.75
53.05
0.34
0.41
0.003
0.003
0.013
0.010
0.13
0.100
0.08
0.120
2.98
2.940
18.0
17.950
<.0003
<0.0003
<.0001
<0.0001
5.34
5.360
- 237 -
TABLE 4
NAS 9-17496 FRANGIBLE NUT AND BOOSTER CARTRIDGE
QUALIFICATION TEST MATRIX
Test
Room Temp.
Firing
Nut
Group
NO
V
I
Functional
Temp
(-F)
70-F
70-F
Preload
Tension Mount
(lbs) (in-lb)
350,000
270,000
Booster
Cartridges
Dual/Single
Single
Single
Functiona
(pass/fail)
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Passed
Failed
Failed
Passed
Passed
Passed
I
High Temp.
Firing
II
II
+200-F
+200-F
270,000
270,000
Single
Dual
Low Temp.
Firing
III
III
III
-65-F
-65-F
-65-F
270,000
270,000
270,000
Single
Single
Dual
Low Temp.
Firing with
limit Axial Load
V
I
V
-65-F
-65-F
-65-F
415,270
415,270
415,270
53,725
53,725
53,725
Single
Dual
Dual
Room Temp.
Firing with
Zero Preload
VI
70-F
No Load
Single
Margin Demo.
Firings
Vll
Vll
Vll
70-F
70-F
70-F
270,000
270,000
270,000
Single
Single
Single
(115% Web)
(126% Web)
(120% Web)
85% Booster
Cartridge
Margin Demo.
Firing
IV
IV
Vlll
70-F
70-F
70-F
270,000
270,000
270,000
Single
Single
Single
- 238 -
TABLE 5
FAILURE INVESTIGATION TEST MATRIX
Test
Preload
Nut Web
Chamfered
Booster
Booster
Results
Thicknesses
Outer Ledge
Load
Bore Area
(Klbs)
(%)
(Y/N)
(%)
(%)
(Pass/Fail)
1
100
N
110
110
Fail
2
100
N
115
115
Fail
3
100
N
120
120
Pass
4
80
N
100
100
Fail
5
100
Y
110
110
Pass
6
270
100
Y
100
100
Fail
7
100
N
100
120
Fail
8
100
Y
100
120
Pass
9
100
Y
105
105
Fail
10
270
115
Y
100
120
Pass
TABLE 6
NAS 9-17674 FRANGIBLE NUT AND BOOSTER CARTRIDGE QUALIFICATION TEST MATRIX
Test
Nut
Group
NO
Functional
Temp
(-F)
Pre-Load
tension Mount
(lbs) (in-lb)
Booster
Cartridges
Dual/Single
85% Booster G 70-F 270,000 Single
Cartridge G 70-F 270,000 Single
Margin Demo. G 70-F 270,000 Single
Firing
* -302 Nut represents nominal web thickness and chamfered outer ledges.
** -102 Nut represents 115% nominal web thickness with chamfered outer ledges.
Functional
(pass/fail)
Low Temp.
C
-65-F
270,000
Single
Passed
Firing
Low Temp.
E
-65-F
415,270
53,725
Single
Passed
Firing with
E
-65-F
415,270
53,725
Single
Passed
Limit Axial Load
E
-65-F
415,270
53,725
Dual
Passed
Room Temp.
D
70-F
No Load
Single
Failed
Firing with
D
70-F
No Load
Single
Failed
Zero Preload
D
70-F
No Load
Single
Passed
(-302 Nut)*
D
70-F
No Load
Single
Passed
(-302 Nut)*
D
70-F
No Load
Single
Passed
(-302 Nut)*
Margin Demo.
G
70-F
270,000
Single
Failed
(120% Web)
Firings
G
70-F
270,000
Single
Passed
(-102 Nut)**
G
70-F
270,000
Single
Passed
(-102 Nut)**
Passed
Passed
Passed
- 239 -
Figure 1. Illustration of orbiter/external tank aft attach
interface and cross section of 2.5 inch frangible
nut installation.
ISOMICA
DISKS
1920 mg .
RDX —I
ISOMICA
DISKS
HOUSING
1920 mg
RDX
HOUSING
-401 CONFIGURATION
-402 CONFIGURATION
Figure 3. Illustration of 2.5-inch booster cartridge
-401 configuration and modified design,
-402 configuration.
FRANGIBLE WEBS
BOOSTER
PORTS
TOP VIEW OF 2.5-INCH
FRANGIBLE NUT
SECTION A-A
FRANGIBLE NUT
SEPARATION PLANE
Figure 2. 2.5-inch frangible nut separation plane and
frangible webs.
-301 FRANGIBLE NUT WEBS
115% (0.149")
120% (0.156")
L
-1 01 , -1 02 MARGIN NUT WEBS
Figure 4. 2.5-inch frangible nut nominal web thickness,
(-301 configuration), 120% nominal web thickness,
(-101 configuration) and 115% nominal web thickness
(-102 configuration).
- 240 -
■■' ■ i r r-r- — r~^s^r * > 3 # g * W
Figure 5. 100 X micrograph of original frangible nut
supplier's Inconel 718.
^ * ■ ... ■
Figure 7. 100X micrograph of Inconel 718 used
inqualification test program under NASA contract
NAS 9-17496.
FRACTURED
WEBS
JL OUTER LEDGE
GAP
GAP DEVELOPED
FROM SINGLE BOOSTER
CARTRIDGE FIRING
Figure 6. Illustration of clamshell motion experienced by
2.5-inch frangible nut during single booster
cartridge firing.
TOP VIEW OF FRANGIBLE NUT
SECTION A
Figure 8. Illustration of material removal from outer
ledge of 2.5-inch frangible nut.
- 241 -
Figure 9. 100X Micrograph of Inconel 718 Used in
Production Lot under NASA Contract
NAS 9-17496.
Figure 10. 100X Micrograph of Inconel 718 Used in
Qualification Lot under NASA Contract
NAS 9-17674.
- 242 -
BOLT CUTTER FUNCTIONAL EVALUATION
S. Goldstein, T. E. Wong, S. W. Frost, J. V. Gageby, and R. B. Pan
The Aerospace Corporation
2350 E. El Segundo Blvd., El Segundo CA 90245
/
fi.
t
ABSTRACT
The Aerospace Corporation has been implementing finite difference and finite
element codes for the analysis of a variety of explosive ordnance devices. Both
MESA-2D and DYNA3D have been used to evaluate the role of several design
parameters on the performance of a satellite separation system bolt cutter.
Due to a lack of high strain rate response data for the materials involved, the
properties for the bolt cutter and the bolt were selected to achieve agreement
between computer simulation and observed characteristics of the recovered
test hardware. The calculations provided insight into design parameters such
as the cutter blade kinetic energy, the preload on the bolt, the relative position
of the anvil, and the anvil shape. Modeling of the cutting process clarifies
metallographic observation of both cut and uncut bolts obtained from several
tests. Understanding the physical processes involved in bolt cutter operation
may suggest certain design modifications that could improve performance
margin without increasing environmental shock response levels.
BACKGROUND
The Aerospace Corporation Explosive Ordnance
Office (EOO) was given hardware from a series
of satellite separation system ground tests
wherein several bolt cutters successfully
severed the interfacing bolts and others did
not. EOO also obtained a severed bolt from a
lot acceptance test of the cutter. The EOO
was asked to assess causes of the anomalous
performance and to determine corrective
actions. A multi-disciplinary team was
assembled and a review initiated.
The bolt cutter used in this application was
developed in 1 972 by Quantic (a.k.a. Whittaker
or Holex) for McDonnell Douglas, Huntington
Beach. A family of cutters known by part
number R13200 has since evolved. The
Quantic outline drawing for R 13200 states that
its severance capacity is a 5/1 6 inch diameter-
A286 CRES bolt having a tensile strength from
180 to 210 ksi and tensioned between zero
and 6000 lbs. A photograph of the hardware
is shown in Figure 1.
A finite element model, to be discussed further
in a later section, is shown in Figure 2 and
illustrates the configuration of the installed bolt
and cutter before functioning. The bolt cutter
consists of an explosive initiator, a chisel
shaped cutter blade, a blade positioning shear
pin, and an anvil in a cylindrical housing. The
bolt to be cut fits through a clearance hole in
the housing that places it against the anvil.
When the initiator is functioned, the blade is
accelerated and impacts the bolt. In both
system separation and lot acceptance testing
of the bolt cutter, it is seen that the cutter
blade penetrates only part way through the bolt
diameter. The cutting process is completed by
fracture of the bolt.
The initial finding of the team was that the
ductility of the bolt used in the anomalous
system separation tests was not compatible
with the specification in the bolt cutter outline
drawing. That is, a more ductile bolt than the
R13200 bolt cutter requires had been used.
The bolts used in the tests were solution
annealed and aged to AMS 5737. This
specification only requires a minimum ultimate
tensile strength (UTS) of 140 ksi.
Presented to the Second NASA/DOD/DOE Pyrotechnic Workshop, February 8-9, 1 994
- 243 -
To obtain the 180-210 ksi UTS, the A286
material requires cold working per AMS 5731 .
The bolts used in the system separation tests
had not been cold worked. It was found that
the Quantic target bolts, part number F12496,
used in bolt cutter lot acceptance tests are cold
worked. The F12496 drawing states that the
target bolt material comply with AMS 5731
and be cold worked to obtain 1 80-21 ksi UTS
following heat treat per Mil-H-6875. Since
1972, a large number of bolt cutters from
many production lots have successfully severed
the F12496 target bolts. No data base was
found to assess cutter performance with A286
bolts which had not been cold worked.
METALLURGICAL ASSESSMENT OF A286
BOLTS
Metallurgical analyses were performed to infer
the role of each parameter in the cutting
process. The analyses were performed on
fractured segments of a short bolt obtained
from a Quantic lot acceptance test and on both
fractured and unfractured long bolts from the
system separation tests. The analyses included
a microscopic examination of the fracture
surfaces, metallurgical studies of the regions of
deformation and fragmentation at the beginning
of the cutting process, and measurements of
material hardness and microstructure.
The team also found that the mass of the bolts
used in the system separation tests was at
least six times greater than the Quantic test
target bolt. The greater mass is due to greater
length and end diameter, which is required for
installation. The concern then was the lack of
information on the effect of bolt inertia on bolt
cutter performance.
The team directed efforts toward analyzing the
cut and uncut test bolts and in attempting to
duplicate the cutter performance analytically.
A F12496 target bolt, used in a bolt cutter lot
acceptance test, was obtained from Quantic
and also analyzed. In addition to assessing bolt
inertia effects, the team attempted to
determine the effect of bolt tension on the bolt
cutter performance. The parameters assumed
to affect the ability of the bolt cutter to sever
the bolts are:
• bolt configuration
• ductility of the bolt material
• preload in the bolt
Other parameters such as gapping between the
bolt and anvil and the anvil configuration were
also considered.
The following are the results of the material*
analysis from metallographic evaluation of the
test bolts, descriptions of the analytic modeling
techniques, a comparison of model attributes
and the team conclusions.
These studies, and an examination of the
photographs in Figures 3 through 9 lead to the
following observations:
• Grain size and hardness differences
exist between the long and short bolts.
The short bolt had a fine grain size and
high hardness (Re 42), and was
consistently severed. The long bolt
was larger grained and softer (Re 35),
and was not consistently severed. See
Figures 10a and 10b.
• The long and short bolts which had
been successfully severed exhibited
adiabatic shear bands in the deformed
material regions adjacent to both the
cutter blade and the anvil. Adiabatic
shear bands are regions of highly
localized plastic deformation resulting
from the high material temperatures
that are caused by high strain rate
loading.
• No evidence of adiabatic shear bands
were seen in the deformed material
regions adjacent to the anvil on the
long bolt which had failed to separate.
MODELING WITH MESA-2D
MESA- 2D is a finite difference code that was
used to analyze the behavior of the bolt cutter
and bolt during the early time portion of its
functioning. MESA is a reactive hydrodynamic
- 244 -
code that assumes, to a first approximation,
that material behavior can be described by fluid
dynamics when strong shocks are present.
The equations of motion to be solved are then
the time dependent nonlinear equations of
motion for compressible fluids.
Throughout a calculation, MESA-2D computes
and records all relevant dynamic and
thermodynamic properties for each cell (mass
element) in the model. These variables could
include position, velocity, pressure, internal
energy, temperature, density, intrinsic sound
speed, elastic and plastic work, plastic strain,
strain rate, and deviator stress. All of these
quantities output in graphical form or in tabular
form for further analysis. By integrating over
very small time steps, typically less than 1
nanosec, the MESA calculation can handle
impulsive loading of materials and allows their
dynamics to be resolved with sufficient
accuracy to elucidate the physical processes
involved [1J.
The numerical integrations required by the
calculations were performed with coordinate
meshes of between 40,000 and 60,000 cells.
This gives better than 0.1 mm resolution,
which is required to understand small systems
such as the bolt cutter.
Finite Difference Models
Figure 11 shows the cutter blade, the anvil,
and the bolt to be cut that were included in the
MESA finite difference model. It also shows
the particle velocity distribution after 20/ssec.
An alternative configuration was also
developed in which the massive ends of the
flight bolt were eliminated. The models were
analyzed using slab geometry and transmissive
boundary conditions for the hydrodynamic
equations. Bolt preload was not included.
In the computer simulations, the available
material properties of 304 stainless steel were-
used as the basis for the properties of all
metallic components. The yield strength and
shear modulus were adjusted by using 4340
steel for the blade and A286 for the bolt.
Strain rate effects were accounted for by
allowing these constants to vary [2, 3, 4).
The simulations were assumed to start when
the cutter blade begins to move, and neglects
the functioning of the initiator and the transfer
of energy to the cutter blade.
The initiator consists of 70% by weight
ammonium perchlorate <AP), 27%
polybutadiene acrylic acid (PBAA), and 3%
combined zirconium barium peroxide (ZBP),
ferrix oxide (FO), and epoxy resin. The ZBP
and FO as oxidizers will enhance the
performance of the main constituent, AP. The
remaining materials are inert binders. The
material properties of all these materials are not
known. An upper and lower bound estimate of
kinetic energy output was made from the
available chemical energy of the AP assuming
instantaneous energy release via detonation.
Since the exact energy partition is unknown,
trial computer models were run using several
candidate velocities within these limits. The
cutter velocity was determined by trial and
error, matching the resulting penetration into
the bolt to the experimental data. This velocity
was 332 m/sec.
Computational Results
The calculations began at time zero with the
bolt cutter blade poised to impact the surface
of the bolt and with the initial constant velocity
of 332 m/sec. The proper penetration of the
cutter blade into the material to agree with the
test data from Figures 5, 6 and 7 is achieved in
approximately 20 //sec. The material interfaces
show that both light and heavy bolts have
responded identically to this point. The time
elapsed to this point in the cutting process is
one order of magnitude smaller than the time it
had previously been assumed by the
community for bolt cutter function.
Compression and tension waves propagating
through the bolt show that there is no net
motion of the bolt ends since the particle
velocities of the end cells go to zero. The
velocity of the cutter blade also changes
direction several times after it penetrates the
bolt. This is evidence of an oscillation that is
set up which will cause the blade to bounce
back.
- 245 -
The model shows, as does the test hardware,
that all material deformation occurs within a 1
cm radius of the impact point of the cutter
blade. No rigid body motion of the bolt is
required for penetration, and indeed the
coordinates of the bolt ends do not change
throughout the cutting process in the
calculation.
Shear deformation can be discerned from
inflections in the particle velocity distributions
as early as 10 //sec. These patterns are
apparent in Figure 11. This result agrees with
the evidence of the same behavior in the
photomicrographs of the cut surfaces. Ejection
of particles from the top surface of the bolt can
be seen. There is also a small crack that
appears near the tip of the cutter blade. All of
these features were seen in the hardware,
especially Figures 5 and 6. The indentation
from the anvil on the underside of the bolt can
also be seen beginning to form although it is
not obvious until some time later.
The material deformation is due almost entirely
to plastic work. The elastic contribution is
between two and three orders of magnitude
smaller than the plastic, and the penetration
process is completed before the effects of any
elastic waves can be seen. Therefore, the ends
of the bolt, and whether or not they are
massive, may have no effect on cutter
performance.
Blunting of the cutter blade edge occurs as
well. Figures 12 and 13 show this in the
hardware. The assumption had been that this
blunting resulted from the impact of the blade
against the anvil after the bolt had separated.
While there is undoubtedly some effect from
this, the blade edge is also blunted by erosion
during the bolt penetration process.
As configured, the MESA calculations do not
show that the cutter completely severs the
bolt. This may be partly attributed to-
insufficient brittleness in the material
description. However, the highest shear
locations match those in the photomicrographs
of the test bolt that failed to cut. The shear
deformation regions that originate at the anvil
side of the bolt are not as clear with the
resolution available in the calculation.
Additional calculations were performed using
both smaller and larger velocities for the cutter
blade. When the velocity is 133 m/sec, the
blade does not penetrate far enough to match
the data. When it is increased to 431 m/sec,
it is possible to separate the bolt by penetration
alone, independent of the formation of a shear
fracture. These calculations indicated that
depth of penetration of the blade into the bolt
is dependent on this variable alone. This is
consistent with the results of various empirical
penetration analyses for projectiles [5], which
show that penetration depth is a function of
the velocity of the penetrator and the ratio of
densities of the materials of penetrator and
target. Since both blade and bolt have the
same density, the only other determining factor
is penetrator velocity.
MODELING WITH DYNA3D
Due to analytical considerations of nonlinear
dynamics and stress wave propagation effects
in bolt cutter structural response, transient
dynamic analyses were performed using the
DYNA3D code. The DYNA3D code is an
explicit, nonlinear, finite element analysis code
developed by Lawrence Livermore National
Laboratory [8]. It has a sophisticated
simulation capability for handling frictional and
sliding interactions between independent
bodies.
A built-in feature in the DYNA3D code was
selected for modeling the sliding surface failure
behavior. A failure criterion based on the total
cumulative effective plastic strain is defined for
the elements adjacent to the contact surface.
When the rate-dependent plastic strain value
within an element satisfies this failure criteria,
the element is removed from further calculation
and a new sliding surface boundary is defined.
Parameters compared in this study include the
approaching speed of the cutter blade, the
applied bolt preload, the gap clearance between
the bolt and the anvil, and the contact surface
area of the anvil. TABLE I lists the four
parameters and their variations considered in
- 246 -
the finite element analysis matrix. In this table,
the 3,270 lbs bolt preload and a maximum gap
allowable of 0.065 inch between the bolt and
anvil were based on drawing specifications.
The loss of preload and a 50% reduction in
anvil's contact area were chosen to study their
impact in cutter performance.
The speed for the blade was determined using
system separation test data. In these tests, six
A286 bolts were preloaded to 3,270 lbs. Two
of the bolts had a cutting depth of 40% of the
bolt diameter and did not fracture. The other
four bolts had a slightly deeper blade
penetration, were totally severed and the cutter
blades also indented the anvil. The transient
dynamic analysis duplicated these conditions
by using a 6,000 in/sec (152 m/sec) speed.
Finite Element Analysis Matrix
The Taguchi experimental design technique [6,
7] was then adopted for establishing the
analysis matrix. This technique was also used
to analyze the finite element calculation results
to identify the optimum bolt cutter
configuration, especially in relation to preload
or applied tension on the bolt.
A Taguchi analysis matrix with 8 study cases
(a L 8 orthogonal array [6, 7]), shown in TABLE
II, was established to evaluate the criticality of
the four chosen parameters mentioned above.
Interaction effects between these parameters
were assumed to be negligible. Based on the
analysis matrix and the chosen parameter listed
in TABLE II, 8 different finite element models
were constructed. A baseline finite element
model of the bolt cutter configuration (case 1
in TABLE II) as shown in Figure 2. Due to
symmetry of the bolt cutter geometry, only one
half of the bolt cutter configuration was
modeled. This model consists of 618 solid
elements and 1027 nodes to simulate the 60
degree cutter blade, the 5/16 inch diameter
bolt, and the anvil.
Transient D ynamic Analysis
TABLE III lists the mechanical properties used
in the analysis. The values chosen for S7 tool
steel and A286 stainless steel were obtained
from references [9] and 110], respectively.
In the finite element analysis model,
nonreflecting boundaries were assumed at the
two ends of the bolt and the anvil to prevent
artificial stress wave reflections re-entering the
model and contaminating the results. A fixed
end boundary condition was assumed at the
lower end of the anvil. The bolt preload was
first generated by applying pressure loading on
the bolt with a built in dynamic relaxation
option. The cutter blade with the appropriate
approaching speed was then applied. A
transient dynamic analysis was performed to
estimate the damage in the bolt. The analysis
results for the eight study cases are listed in
the last column of TABLE II. The 0's and 1's
are corresponding to a partial or a complete
cutting of the bolt, respectively. Figure 14
shows the simulation results at 0.4 ms for the
baseline model in TABLE II. In Figure 15, with
a finer mesh model, it can be seen that the bolt
is completely severed by the cutter. It can be
seen that the failure configuration matches
fairly well with the test data in Figure 3,
Bolt-Cutter Performance Assessment
From finite element analysis results listed in the
last column of TABLE II, the bolt cutter
performance, based on variation levels for each
parameter, can be summarized. For example,
the cutter performed well with a bolt preload
(parameter A) of 3,270 lbs (level 1 ). It resulted
in three successful cuts and one failure. The
cutter performed poorly with parameter A at
level 2 (zero preload), with only one success
and three failures. Therefore, the analysis
results of level sum A, and A 2 are:
A,= 1
A 2 = 1
+ 1+1+0 = 3 cuts
+ + + = 1 failure
Total
= 4 cases
Other parameter sums are similarly calculated
and summarized in TABLE IV. These results are
also plotted in Figure 16 in bar chart format in
terms of the percentage of success. It can be
seen that the bolt cutter performance can be
improved with the design parameter setting of
A„ B 1# C 1# D 2 . That is, it is desirable to
- 247 -
improve the cutter performance by applying a
bolt preload of 3,270 lb, providing sufficient
energy for the cutter blade to reach a speed of
6,000 in/sec, ensuring that no gap exists
between the bolt and the anvil before firing,
and by reducing the anvil and the bolt contact
surface area by half.
Omeaa Transformation
In order to verify the assumption that
interaction effects between these four
parameters are negligible and to estimate the
response of the optimum condition of the bolt
cutter system, the omega transformation
technique [7] can be used. The omega
transformation is defined as follows:
Q(P) - -10log(1/P-1)dB
where P is the percentage of success. For the
cases of cutter failure (0%) and cutter success
(100%), they are treated as follows:
0% case - Consider this as 1 /(number of cases)
and perform the omega transformation. For the
current study, the number of cases is 8; thus,
(1/8)x100 = 12.5% orQ<12.5%)=-8.45 dB.
100% case - Consider this as (number of cases
- 1 )/(number of cases) and perform the omega
transformation. For the current study,
K8-1)/8]x100 = 87.5% orQ<87.5%} = 8.45 dB.
Based on the approach as shown in [7], the
optimum response, m, can be estimated by an
additive model.
mtA^^Dj) = T A1 + T B1 + T C1 + T 02 - 3 x T
= Q(75%) + Q(75%) + Q(75%)
+ 0(75%) - 3 x Q(50%)
= 4.77 + 4.77 + 4.77 + 4.77-
3x0
= 19.08 dB ( > 8.45 dB)
= 98.8% ( > 87.5% ).
Here T is the overall mean percentage of
success for all cases analyzed in Table IV and
T Xy is the average for parameter X at level y.
Thus, under the optimum conditions, the bolt
could be totally severed by the design of
A 1 B 1 C 1 D 2 . This was later confirmed by the
finite element analysis prediction. This result
indicates that the additive model is adequate
for describing the dependence of the structural
response on various parameters, and also
confirms that the assumption of negligible
interaction effects between various governing
parameters was valid.
CONCLUSIONS
The evidence obtained from the metallurgical
examination of test hardware suggests that
bolt severance from the impact of the bolt
cutter blade occurs as a result of a combination
of processes. These include:
reduction of the bolt diameter
penetration of the blade;
by
reduction of the bolt diameter by
penetration of the anvil;
wedge opening forces generated by the
cutter blade as it penetrates;
applied preload on the bolt; and
adiabatic shear band formation under
the combined effects of shock heating
and the applied stresses on the bolt.
The two analysis techniques that were
employed proved to be complementary to each
other in that they each were able to elucidate
different features of the ductile bolt behavior
and of the governing design parameters of the
system. In addition to the above conclusions,
which they confirm, are the following.
The MESA-2D analysis indicates:
• The bolt cutting process is completed
in less than 60 //sec.
• Neither the length nor mass of the bolt
has any effect on the ability of the
cutter blade to penetrate the bolt.
• The depth of penetration of the cutter
blade into the bolt is a function of the
cutter blade velocity.
- 248 -
• The bolt fractures due to shear in the
second part of the separation process.
The DYNA3D analysis also indicates:
• With the available explosive energy, a
preload in the bolt is necessary for the
fracture to occur and complete the bolt
separation.
• For effective severing, there should be
contact between the bottom surface of
the bolt and the anvil.
REFERENCES
[1] S. T. Bennion and S. P. Clancy,
"MESA-2D (Version 4)", Los Alamos
National Laboratory, LANL Report LA-
CP-91-173, 1991.
[2] E. L. Lee, H. C. Hornig, and J. W. Kury,
"Adiabatic Expansion of High Explosive
Detonation Products", Lawrence
Livermore National Laboratory, LLNL
Report UCRL-50422, 1 968.
• The bolt cutter is more effective if the
surface area of the anvil in contact
with the bolt is decreased.
This last conclusion presents a possible design
modification that is an alternative to increasing
the kinetic energy of the cutter blade with
additional explosive. Increasing the amount of
explosive could increase the shock from
functioning the device, whereas a change in
anvil configuration would not.
Further work is still needed on the bolt cutter
system to analyze the performance under
conditions where the cutter blade has a
non-parallel impact to the cross section of the
bolt.
ACKNOWLEDGMENTS
The authors would like to thank the following
individuals for their contributions to this work:
G. Wade of Quantic Industries, for providing
drawings, hardware, and other information on
the design and materials in the 13200 bolt
cutter; A. M. Boyajian, The Aerospace
Corporation program office, for his support of
this work; R. W. Postma, L. Gurevich, G. T.
Ikeda and R. M. Macheske, The Aerospace
Corporation, and J . Yokum of Defense-
Systems, Inc. for their interest and participation
in many valuable technical discussions.
[3] D. J. Steinberg, S. G. Cochran, and M.
W. Guinan, "A Constitutive Model for
Metals Applicable to High Strain Rate",
J. AppL Phys. 51 (3), 1498 (1980).
[4] G. R. Johnson and W. H. Cook,
" Fracture Characteristics of Three
Metals Subjected to Various Strains,
Strain Rates, Temperatures and
Pressures", Eng. Frac. Mech. 21 (1),
31 (1985).
[5] Joint Technical Coordinating Group for
Munitions Effectiveness (Anti-Air),
Aerial Target Vulnerability Subgroup,
Penetration Equations Handbook for
Kinetic Energy Penetrators (U), 61
JTCG/ME-77-1 6 Rev. 1,15 Oct. 1 985.
[6] Phadke, M. S., Quality Engineering
Using Robust Design . Prentice Hall,
Englewood Cliffs, NJ, 1989.
[7] Mori, T., The New Experimental
Design , ASI Press, 1990.
[8] Whirley, R. G. and Hallquist, J. 0.,
"DYNA3D Users Manual," Lawrence
Livermore Laboratory, Rept. UCRL-MA-
107254, May 1991.
[9] American Society for Metals, Metals
Handbook , Vol. 3, 9th Edition, 1980.
[10] Frost, S. W., "Metallurgical Evaluation
of Separation Bolt, " Aerospace
Corporation Interoffice
Correspondence, 9 Nov. 1992.
- 249 -
Table I. Parameters for Bolt Cutter Study
Parameter
Description
Variation Level
1
2
A
Bolt Preload, lbs.
3270
B
Cutler Blade Speed in./sec.
6000
5000
C
Gap between bolt and Anvil,
in.
0.065
D
Anvil Surface Reduction, %
50
Table II. Finite Element Analysis Matrix
(Taguchi Lg Orthogonal Array)
Analysis Run
Parameters
Results *
A
B
C
D
1
1
1
1
1
1
2
1
1
2
2
1
3
1
2
1
2
1
4
1
2
2
1
5
2
1
1
2
1
6
2
1
2
1
7
2
2
1
1
8
2
2
2
2
* 1 represents bolt totally fractured, represents bolt partially fractured
- 250 -
Table III. Mechanical Properties Used for DYNA3D Analysis
Structure
Material
Type
Poisson's
Ratio
Yield
Strength
(ksi)
Tensile
Strength
(ksi)
Elongation
(%)
Cutter
Blade
S7 Tool
Steel
0.31
210
315
7
Bolt
A286
Stainless
Steel
0.31
139
172
20
Anvil
A286
Stainless
Steel
0.31
139
172
20
Table IV. Cutting Efficiency
Parameter
Variation Level
1
2
A
3(75)
1 (25)
B
3(75)
1 (25)
C
3(75)
1 (25) ...
D
1 (25)
3(75)
Numbers in parentheses are percentage (%).
- 251 -
(iMlji|!|Hi|||l
liiliilll
Figure 1 : Top photo is the configuration of the long bolt used in system separation
tests. One bolt is fully separated, the other is not. Bottom photo shows the
bolt cutter with the internal blade visible through the hole at the anvil end
of the cutter.
- 252 -
l£&&i
I
i
Figure 2: Bolt cutter and bolt finite element model showing 1/2 the configuration
before functioning.
Figure 3:
Top photo shows separation
area on the short bolt. Bottom
photo is an SEM micrograph
providing a face-on view of the
fracture on the top right. Note
secondary cracks on the blade
cut area and complex fracture
surface in lower quadrants.
- 254 -
■ ; Kk
Pill: ^?^IS;
Figure 4:
Top photo shows separation
area on the long bolt. Bottom
photo is an oblique view of the
fracture seen on the top left.
Note the limited extent of the
blade cut surface remaining on
this segment.
- 255 -
Figure 5: Top photo shows impact area of the long bolt which failed to separate.
Bottom photo shows impact area after polishing away 1/4 of the bolt
diameter from the side of the bolt. Note the small 45° crack at the tip of the
notch produced by the blade impact.
- 256 -
Figure 6: Top photo shows impact area of the long bolt after polishing away 1/3
of the bolt diameter. Bottom photo shows same area after etching (with
dilute hydrochloric and nitric acid mixture). Note in this section there is
no crack at the tip of the notch. Adiabatic shear bands of localized
deformation are seen on both sides of the notch.
- 257 -
Figure 7: Top photo shows impact area of the long bolt after polishing away 1/2
of the bolt diameter. Bottom photo shows same area after etching.
Adiabatic shear bands emerge from the sides of the notch. There is no
evidence of similar bands adjacent to the anvil.
- 258 -
Figure 8: Top photo shows separation area of the short bolt. Bottom photo is a view
of the midplane of the bolt segment shown on the top left. Note that a band
of localized deformation (adiabatic shear band) has formed in the deformed
material above the anvil (see arrow).
- 259 -
Figure 9:
Top photo shows polished and
etched section through the
deformed area above the anvil
on the short bolt. Bottom
photo shows polished and
etched section through the
deformed area above the anvil
on the fractured long bolt.
Adiabatic shear bands of
localized deformation are
emerging in the area of the bolt
near the corner of the anvil.
50x
200x
260 -
'\
/->
;«**%.
X
\ --^P*
r\.
\
V
^
^
- : s»:
ViiJk.
\3
1000X
Figure 10a: Optical micrographs showing typical microstructure in the center of a
transverse section through the long bolt (etched with Glyceregia).
Microhardness measurements indicate Rockwell "C" of 35-36. This
corresponds to a tensile strength of 160 ksi.
■• TS-v"« ?■*':*<. --?-'-
><2& ; - ^ v . ^ V v*s*nJ^a *> -*
1000X
Figure 10b: Optical micrographs showing typical microstructure in the center of a
transverse section through the short bolt (etched with Glyceregia).
Microhardness measurements indicate Rockwell M C H of 41-43. This
corresponds to a tensile strength of 192 ksi.
- 261 -
VECTOR VELOCITIES
TIME
20.0084
LOCAL MAX 2.857E-02
^
GLOBAL MAX 2 . 857E-02
SCALED VEC 2.857E-02
i
CD
I
O
DC
12.0 _
10.0 _
8.0 _
6.0 _
4.0 -
2.0
0.0
-
r -■■■ ^
~
[ t 1
l t i I
t I I
i i i \
1 f 1
1 1 I
mm
MM
—
I 1 1
MM
t t I
ml
—
t 1 I
i i i i
1 I t
l M I
1 t I
I 1 I
till
I I I \
\l I
III/
k i\ i i i i i A 77
>v\ l l K l>&7
- .
- I
Z »-«.>*»»•«. — ZIZ %
,p^~~ + * + + + *<
1^-** + + + + + *
, /L _ — «• ^ >» *• * * »
#» ^ - ^ + * + * * -
{*
^\
"*?
1|
. !
—
I i I i I
,: : :
} 1 1 I.I 1
-6.5 -5.5
-4.5 -3.5
-2.5 -1.5 -.5 .5
Z (CM)
1.5 2.5 3.5 4.5
5.5
6.5
Figure 1 1 . MESA-2D model of cutter blade and bolt 20 ixsec after impact.
Figure 12: Top photo shows the cutting edge of the blade used in separating the long
bolt. Bottom photo shows damage to the anvil resulting from impact of the
blade after bolt separation.
- 263 -
Figure 1 3: Comparison of damage to the cutter blades used in separating the long and
short bolts. Blade used for the short bolt is missing more material (bottom
of each photo).
- 264 -
Figure 14: Bolt during impact of cutter blade at 0.4 msec in DYNA3D.
- 265 -
L.
Figure 15: Fractured bolt configuration for finite element analysis.
- 266 -
100
3270
Bolt Preload (lb)
6000 5000
Cutter Blade Speed (in. /sec.)
i
CD
i
0.065
Gap between Bolt & Anvil (in.)
50
Anvil Surface Reduction (%)
Figure 16: Parameter effects in bolt fracture study.
Choked Flow Effects in the NSI Driven Pin Puller*
Keith A. GonthierWd Joseph M. Powers*
Department of Aerospace and Mechanical Engineering
University of Notre Dame
Notre Dame, Indiana 46556-5637
Abstract
This paper presents an analysis for pyrotechnic combustion and pin motion in the NASA
Standard Initiator (NSI) actuated pin puller. The conservation principles and constitutive
relations for a multi-phase system are posed and reduced to a set of eight ordinary differential
equations which are solved to predict the system performance. The model tracks the inter-
actions of the unreacted, incompressible solid pyrotechnic, incompressible condensed phase
combustion products, and gas phase combustion products. The model accounts for multi-
ple pyrotechnic grains, variable burn surface area, and combustion product mass flow rates
through an orifice located within the device. Pressure-time predictions compare favorably
with experimental data. Results showing model sensitivity to changes in the cross- sectional
area of the orifice are presented.
Introduction
Pyrotechnically actuated devices are widely used for aerospace applications. Examples
of such devices are pin pullers, exploding bolts, and cable cutters. Full-scale modeling efforts
of pyrotechnically driven systems are hindered by many complexities: three dimensional-
ity, time-dependency, complex reaction kinetics, etc. Consequently, simple models have
been the preferred choice of many researchers. x » 2 ' 3 ' 4 These models require that a number
of assumptions be made; typically, a well stirred reactor is simulated; also, the combustion
product composition is typically predicted using principles of equilibrium thermochemistry,
and the combustion rate is modeled by a simple empirical expression.
Recently, Gonthier and Powers 5 described a methodology for modeling pyrotechnic com-
bustion driven systems which is based upon principles of mixture theory. Though this ap-
proach still requires that simplifying assumptions be made, it offers a rational framework for
1) accounting for systems in which unreacted solids and condensed phase products form a
large fraction of the mass and volume of the total system, and 2) accounting for the transfer
of mass, momentum, and energy both within and between phases. The methodology was
illustrated by applying it to a device which is well characterized by experiments: the NSI
driven pin puller.
'Presented at the Second NASA Aerospace Pyrotechnic Systems Workshop, February 8-9, 1994, Sandia
National Laboratories, Albuquerque, New Mexico. This study is supported by the NASA Lewis Research
Center under Contract Number NAG-1335. Dr. Robert M. Stubbs is the contract monitor.
* Graduate Research Assistant.
* Assistant Professor, corresponding author.
2 2-2%
?G02
/(o
_ 2 6 9 . 1page134Lintem
it? r-.M -v r
The focus of this paper is on using the methodology presented in Ref. 5 to formulate a
pin puller model which additionally accounts for the flow of combustion products through
an orifice located within the device; the model is then used to determine the influence of
product mass flow rates on the performance of the device. The present model also accounts
for multiple pyrotechnic grains and variable burn surface area. The model presented in this
paper is an extension of the model presented in Ref. 5 which did not account for product
flow through the orifice, multiple grains, or variable burn surface area.
Figure 1 depicts a cross-section of the NSI driven pin puller in its unretracted state. 6
The primary pin, which will be referred to as the pin for the remainder of the paper, is
driven by gases generated by the combustion of a pyrotechnic which is contained within the
NSI assembly. Two NSFs are tightly threaded into the device's main body. Only one NSI
need operate for the proper functioning of the pin puller; the second is a safety precaution in
the event of failure of the first. The pyrotechnic consists of a 114 rag mixture of zirconium
fuel (54.7 mg Zr) and potassium perchlorate oxidizer (59.3 mg KC10 A ). Initially a thin
diaphragm tightly encloses the pyrotechnic. Combustion is initiated by the transfer of heat
from an electric bridgewire to the pyrotechnic. Upon ignition, the pyrotechnic undergoes
rapid chemical reaction producing both condensed phase and gas phase products. The
high pressure products accelerate the combustion rate, burst the confining diaphragm, vent
through the NSI port (labeled "port" in Fig. 1), and enter into the gas expansion chamber.
Once in the chamber, the high pressure gas first causes a set of shear pins to fail, then pushes
the pin. After the pin is stopped by crushing an energy absorbing cup, the operation of the
device is complete. Peak pressures within the expansion chamber are typically around 50.0
MPa; completion of the stroke requires approximately 0.5 ms. 6
For sufficiently high NSI assembly/gas expansion chamber pressure ratios (~ 2.0), and
for a fixed cross-sectional area of the NSI port, there exists a maximum flow rate of combus-
tion product mass through the port. The occurrence of this maximum flow rate is referred
to as a choked flow condition. Such a condition results in the maximum flux of energy
into the expansion chamber; the energy contained within the chamber can then be used to
perform work in moving the pin and can be lost to the surroundings in the form of heat.
However, if the time scales associated with the flux of energy into the expansion chamber
and the rate of heat lost from the products within the chamber to the surroundings are of
the same magnitude, there may be insufficient energy available to move the pin; functional
failure of the device would result. Therefore, it is possible that variations in the flow rate
of product mass through the port may significantly affect the performance of the device.
Included in this report are 1) a description of the model including both the formula-
tion of the model in terms of the mass, momentum, and energy principles supplemented
by geometrical and constitutive relations and the mathematical reductions used to refine
the model into a form suitable for numerical computations, 2) model predictions and com-
parisons with experimental results, and 3) results showing the sensitivity of the model to
changes in the cross-sectional area of the NSI port.
Model Description
Assumptions for the model are as follows. As depicted in Fig. 2, the total system
is taken to consist of three subsystems: incompressible solid pyrotechnic reactants (s),
incompressible condensed phase products (cp), and gas phase products (p). The solid
pyrotechnic is assumed to consist of N spherical grains having uniform instantaneous radii.
The surroundings are taken to consist of the walls of the NSI assembly, the NSI port, and
- 270 -
1/4"
stroke
9/16"
ZrKC10 4
pyrotechnic
expansion pon^
chamber.
NASA Standard
Initiator (NSI)
assembly
energy
absorbing
cup
Figure 1: Cross-sectional view of the NSI driven pin puller.
NSI port-
Gas Expansion Chamber (2) — ^
combustion
products
^^s!H^^^
NSI Assembly (1)
gas phase products (g)
condensed phase products (cp)
shear pin
system boundary
Figure 2: Schematic of the two component system for modeling choked flow effects.
the gas expansion chamber. Both the NSI assembly and the gas expansion chamber are
modeled as isothermal cylindrical vessels. The gas expansion chamber is bounded at one
end by a movable, frictionless, adiabatic pin while the volume of the NSI assembly remains
constant for all time. The NSI port is assumed to have zero volume and is characterized by
its cross- sectional area.
Mass and heat exchange between subsystems is allowed such that 1) mass can be trans-
ferred from the solid pyrotechnic to both the condensed phase and gas phase products,
and 2) heat can be transferred from the condensed phase to the gas phase products. The
condensed phase - gas phase heat transfer rate is assumed to be sufficiently large such that
thermal equilibrium between the product subsystems exists. There is no mass exchange
between the system and the surroundings. Both product subsystems are allowed to interact
across the system boundary in the form of heat exchanges. The gas phase products are al-
lowed to do expansion work on the surroundings. No work exchange between subsystems is
- 271 -
allowed. Spatial variations within subsystems are neglected; consequently, all variables are
only time-dependent and the total system is modeled as a well-stirred reactor. The kinetic
energy of the subsystems is ignored, while an accounting is made of the kinetic energy of
the bounding pin. Body forces are neglected.
The rate of mass exchange from the reactant subsystem to the product subsystems is
taken to be related to the gas phase pressure within the NSI assembly, namely dr/dt —
—bP gi , where r is the instantaneous radii of the pyrotechnic grains, t is time, P gi is the
gas phase pressure within the NSI assembly, and b and n are experimentally determined
constants. All combustion is restricted to the burn surface of the pyrotechnic grains. In
the absence of burn rate data for Zr/KClO^ we have chosen values for b and n so that
pressure-time predictions of our model agree with experimental data. The equilibrium ther-
mochemistry code CET89 7 calculated for the constant volume complete combustion of the
Zrj KCIO4 mixture is used to predict the product composition; the initial total volume
of the pin puller (0.95 cm 3 ) was used in this calculation since a significant portion of the
system mass is contained within the gas expansion chamber at the time of complete com-
bustion. The component gases are taken to be ideal with temperature-dependent specific
heats. The specific heats are in the form of fourth-order polynomial curve fits given by the
CET89 code and are not repeated here.
The rate of gas phase product mass flowing from the NSI assembly, through the NSI port,
and into the gas expansion chamber is modeled using standard principles of gas dynamics.
The flow of condensed phase product mass through the port is assumed to be proportional
to the gas phase mass flow rate. The only energy interaction between the NSI assembly and
the gas expansion chamber is due to the energy flux associated with the exchange of mass
between these two components.
Using principles of mixture theory, a set of mass and energy evolution equations can be
written for each subsystem contained within the NSI assembly and gas expansion chamber.
These equations, coupled with an equation of motion for the pin, form a set of ordinary
differential equations (ODE's) given by the following:
fo(p»iV*i) = -PsxMn, (1)
-77 (Pc Pl V cpi ) = ricpp^Abn - ro cp , (2)
J t (Pgi v 9i) = C 1 - Vcp)ps 1 A b r b - ro„ (3)
ft(P*i V *i e »i) " ~P*i e *i A b r b, ( 4 )
-77 (pc P iVc Pl e cpi ) = r] cp p Sl € 3l A h r b - h cpi m cp - Q cPi9l + Qc Pl , (5)
J t (Pgi v 9i e 9i) = C 1 " nc P )ps l e 5l A b r b - h gi m g + Q cp , 9l + Q gi , (6)
fa(pC P2 V C P2 ) = ™>CJ>, (7)
J t (P82 V 9%) = ™S> ( 8 )
"77 \Pcj>2 *c P 2 e c P 2 ) == "cpi^cp — Qc P} g2 * *4cp2i \y)
- 272 -
^ (pg 3 V g2 e g2 ) = h gi m g + Q cp , g2 + Q g2 - W out2 , (10)
™ P ^(z P ) = F P - (11)
In these equations, the notation subscript "1" and subscript "2" are used to label quantities
associated with the NSI and the gas expansion chamber, respectively. Subscripts "s", "cp",
and u g" are used to label quantities associated with the solid pyrotechnic, condensed phase
products, and gas phase products, respectively. The independent variable in Eqs. (1-11) is
time t. Dependent variables are as follows: the density p 9i (here, and for the remainder of
this report, the index i = 1,2 will be used to denote quantities associated with the NSI and
the gas expansion chamber, respectively); the volumes V Sl , F cPt , V gi ; the specific internal
energies e Bl , e cp ., e gi ; the specific enthalpies h cpi , h gi ; the pin position z v \ the pyrotechnic
burn rate r&; the area of the burn surface Ab\ the rates of product mass flowing through the
NSI port m cp , rh g ; the rates of heat transfer from the surroundings to the gas phase products
Qim J the rates of heat transfer from the condensed phase products to the gas phase products
Q C p,9i\ the rate of work done by product gases contained within the expansion chamber in
moving the pin W ou t 2 ; an( i the net force on the pin F p .
Constant parameters contained in Eqs. (1-11) are the mass of the pin m p , the density of
the unreacted solid pyrotechnic p 5l , the density of the condensed phase products p cpi and
/> cp2 , and the mass fraction of the products which are in the condensed phase r) cp . As it is
understood that the pyrotechnic is contained entirely within the NSI, the notation subscript
"1" will be dropped when referring to quantities associated with the solid pyrotechnic. Also,
since p cpi = p cp2 = constant, these two quantities will be referred to as p cp .
Equations (1-3) govern the evolution of mass and Eqs. (4-6) govern the evolution of
energy for the solid pyrotechnic, the condensed phase products, and the gas phase products
contained within the NSI, respectively. Equations (7) and (8) govern the evolution of mass
and Eqs. (9) and (10) govern the evolution of energy for the condensed phase products and
gas phase products contained within the gas expansion chamber, respectively. Equation
(11) is Newton's Second Law which governs the motion of the pin.
Geometric and constitutive relations used to close Eqs. (1-11) are as follows:
V 1 = V, + V cpi +V gi , (12)
(13)
(14)
(15)
(16)
(17)
(18)
(19)
- 273 -
v 2 =
'■ Vcp 7 + Vg 2 i
Z
v 2
p ~ A '
r[V s }--
/3V,\ 1/3
A b [V 3 ] =
(367TATV; 2 ) 173 ,
P 9i
= PgiRT gi ,
n[P gi ]
= -- = bP n
dt 91 '
e,[T,]--
= f>/ei[T,],
N cp
€ cpi [T C pi] = /_j *cp e cp [Tcpi\ y
i=i
N g
e gi [T 9i ] = Y,Y 9 3 ei[T gi ],
i=i
^[r 5 ] = ^y/^r(ei[r 5 ]),
Nep d
Cvcpi [T C pi] = 2^ <V~<JT \ e °P *■ C P*V '
i=i
*c
"-cpi L^cpiJ — 2-*t OP cp L^cpiJ i
N
^[^]^^[TJ,
i=i
Nc,
c pcpi 1-^cpiJ = 2-f c p~JFt \ c p t c pi J / '
j-! ajt cpi
Vcp,pi 1-^cpij^iiJ = hcp&Acpi {lepi ~ -tgi) i
Qcpi = Qcpi [J-cpil ?
ifP ff2 A p <F cr<t
W ou t 2 — i^ 2 , ,
-i
\
l(ft)""((ft)^-») »(%)<(*)*
T£±I
„(%)>(*>),-.,
JTcp
1 -*7cp,
m fl
(20)
(21)
(22)
(23)
(24)
(25)
(26)
(27)
(28)
(29)
(30)
(31)
(32)
(33)
(34)
(35)
Here, and throughout the paper, braces [ ] are used to denote a functional dependence on
the enclosed variable. Equations (12-14) are geometrical constraints; in Eq. (14), A p is
the cross-sectional area of the pin. Equation (15) is an expression for the radius r of each
- 27^ -
spherical pyrotechnic grain; N is the total number of pyrotechnic grains. The area of the
burn surface is given by Eq. (16); it is assumed here that the area of the burning surface is
the total surface area of the N pyrotechnic grains. Equation (17) is a thermal equation of
state for the gas phase products. Occurring in this expression are the gas phase pressure
P 9i , the gas phase temperature T 5 -, and the ideal gas constant for the gas phase products R
(the quotient of the universal gas constant and the mean molecular weight of the product
gases). The pyrotechnic burn rate r& is given by Eq. (18).
Equations (19-21) are caloric equations of state for the solid pyrotechnic, condensed
phase products, and gas phase products, respectively. Here, T s is the temperature of the
solid pyrotechnic, and T cpi is the temperature of the condensed phase products. Also, Y/,
Yj p . , Yj. , N s , N cp , and N g are the constant mass fractions and number of component species
of solid pyrotechnic, condensed phase product, and gas phase product species, respectively.
Here, and throughout the paper, the notation superscript "j" is used to label quantities
associated with individual chemical species. Since for both ideal gases and condensed phase
species, the internal energy is only a function of temperature, the specific heat at constant
volume for the solid pyrotechnic, c V5 , the condensed phase products, c vcpi} and the gas
phase products, c vgi , can be obtained by differentiation of Eqs. (19-21) with respect to their
temperature. Expressions for the specific heats at constant volume are given by Eqs. (22-
24). The specific enthalpies for the condensed phase products and the gas phase products
contained within the NSI assembly are given by Eqs. (25) and (26), respectively. These
expressions can be differentiated with respect to their temperature to obtain the specific
heats at constant pressure c pcpi and c P5l , Eqs. (27) and (28).
Equation (29) gives an expression for the rate of heat transfer from the condensed
phase products to the gas phase products. In this expression, h cPi3 is a constant heat
transfer parameter, and A cpi is the surface area of the condensed phase products. The term
h CPi9 A cpi is assumed large for this study. The functional dependencies of the heat transfer
rates between the surroundings and the product subsystems are given by Eqs. (30) and
(31). The functional form of these models will be given below.
Equation (32) models pressure-volume work done by the gas contained within the ex-
pansion chamber in moving the pin. Equation (33) models the force on the pin due to the
gas phase pressure and a restraining force due to the shear pins which are used to initially
hold the pin in place. Here, F cr i t is the critical force necessary to cause shear pin failure.
The work associated with shearing the pin is not considered.
The flow rate of gas phase product mass through the NSI port is given by Eq. (34). 8
Occurring in this expression are the cross-sectional area of the port, A e , and the specific
heat ratio for the product gases contained within the NSI assembly, 7 (= c P5l /c V5l ). This
expression accounts for mass choking at elevated NSI assembly /gas expansion chamber
pressure ratios. The condensed phase product mass flow rate through the port is given by
Eq. (35).
With the assumption of large heat transfer rates between the condensed phase and gas
phase product subsystems (i.e., hcp^A^ — ► 00), the product subsystems remain in thermal
equilibrium for all time. Therefore, we take T Pl = T cpi = T 9l and T P2 = T cp2 = T 52 , with T Pl
defined as the temperature of the combined product subsystem contained within the NSI
assembly and T P2 the temperature of the combined product subsystem contained within the
gas expansion chamber. With this assumption, one can define the net heat transfer rates
Q Vl and Q P2 governing the transfer of heat from the surroundings to the combined product
- 275 -
subsystems:
Q Pl [T Pl ] = Qcp, + Q gi = hA Wl (T w - T Pl ) + *A Wl (aT* - eT^) , (36)
Q n [TpJ = Q cp2 + Q g2 = hA W2 [V.] (T w - T P2 ) + aA W2 [V 2 ] (aT* - eT p 4 2 ) , (37)
where
^"^A/ 1 ' ""* " e ' ^ 2L " J "1A P
Equations (38) are expressions for the surface area of the NSI assembly and the gas expan-
sion chamber, respectively, through which heat transfer with the surroundings can occur;
the parameter A\ in the first of these relations is the constant cross-sectional area of the
NSI assembly.
Mathematical Reductions
In this section, intermediate operations are described that reduce the governing equa-
tions to a final autonomous system of first order ODE's which can be numerically solved to
predict the pin puller performance. To this end, it is necessary to define a new variable V 2
representing the time derivative of the gas expansion chamber volume:
*.**. (39)
The final system consists of eight first order ODE's of the form
£ = f(«). (40)
where u = (V 2 ,V 8y V cpi , p gi ,T PlJ V cp2 ,T P2 ,V2) T is a vector of dependent variables and f is a
non-linear vector function. These eight dependent variables will be referred to as primary
variables. It will now be shown how to express all remaining variables as functions of the
primary variables.
Quantities already expressed in terms of the primary variables are the gas phase pressure
inside the NSI P 9l [p gi ,T pi ], the heat transfer rates Q Pl [T Pl ] and Q P2 [V 2l T P2 ] y the specific
internal energies e cpi [T Pi ] and e gi [T Pi ], the specific heats at constant volume c vcpi [T Pi ] and
c vgi [T Pi ], the specific enthalpies /icpJTpi] and h 9l [T Pl ], and the specific heats at constant
pressure c pcpi [T Pl ] and c pgi [T Pl ]. Also, with a knowledge of P gi , Eq. (18) can be used to
express r& as functions of p gi and T Pl :
rb[p gi ,T Pl ] = bP? 1 [p gi ,T Pl ]. (41)
Addition of Eqs. (1), (2), (3), (7), and (8) results in a homogeneous differential equation
expressing the conservation of the total system's mass:
j f {psV, + PoVcn + p gi V gi + PcVcn + p gi V g2 ) = 0. (42)
Integrating this expression, applying initial conditions, denoted by the subscript "o", using
Eq. (12) to eliminate V gi in favor of Vi, V„ and V cpi , using Eq. (13) to eliminate V 92 in
favor of V2 and V cp2 , and solving for p g2 results in the following:
rT/ ,r T/ T/ , m - p a V, - p cp Vc Pl - p gi (Vi -V.-Vcpi)- PcpVcp 2 ( .„,
Pg, [^2, V„ Vcpi , p gi , V CP2 \ V 2 -V ' ^ '
- 276 -
dV 3 _
dt
-Mn,
dV cpi
_ VcpPi
*Mn -
rh cp
dt
Pep
dVcp 2 .
_ rn C p
where
Wo = Ps^So "I" PcpVcpio + Pjio Vffio + PcpVcp 2 o + Pg2oVg20*
Here, rn represents the initial mass of the system. Substituting Eq. (43) into Eq. (17)
determines P 92 as a function of the primary variables:
P 92 [V2> V„ V cpi , p gi , V CP2 , T P2 ] = p 92 [V 2 , K, V CP1 , p 5l , K P2 ] i?T P2 . (44)
With a knowledge of P 32 , Eqs. (32), (33), (34), and (35) can be expressed in the following
forms, respectively:
w out2 = ^,V.,K w ,P ft ,V w r ft ,Vi], (45)
F p = Fp^,^,^,^,^,^], (46)
m g = mp^^^V^^p^^Tp^Fcp^TpJ, (47)
"*cp = ™ cp [V2 , V*> Vc Pl » P51 ? Tpi > v cp 2 >T P2 \. (48)
We next simplify the remaining mass evolution equations. Since both p 3 and p^ are
constant, Eqs. (1), (2), and (7) can be rewritten as
(49)
(50)
Hi ~ n ■ (51)
at Pep
To simplify Eq. (3), we use Eq. (12) to replace V gi in favor of V a and Vcpj, use Eqs. (49)
and (50) to eliminate the resulting volume derivatives, and solve for the time derivative of
d Pgi _ (*-» -(*-£) *»)/».*■- *»-&*■»
The energy evolution equations will now be simplified. We first multiply Eq. (1) by e s
and subtract the result from Eq. (4) to obtain
de.
-3f-°-
Thus, in accordance with our assumption of no heat transfer to the solid pyrotechnic, its
specific internal energy remains constant for all time. Integrating this result, we obtain
e a = e so . (53)
Addition of Eqs. (5) and (6), and addition of Eqs. (9) and (10) result in expressions governing
the evolution of energy for the combined product subsystems contained within the NSI
assembly and gas expansion chamber, respectively:
^ [pcpVcp^cpx + PgxVgitgi] = Pt^aMn - h cpi m cp - h 9l m g + Q Pl , (54)
- 277 -
-j t [pcpV cp2 e cp2 + pg 2 V g2 € g2 ] = h cpi m cp + h gi m g + Q P2 - W out2 . (55)
The net heat transfer rates given by Eqs. (36) and (37) have been incorporated into these
expressions. Multiplying Eq. (2) by e cpi , multiplying Eq. (3) by e gi> subtracting these
results from Eq. (54), using Eqs. (20) and (21) to re-express the derivatives in terms of T Pl ,
and solving for the derivative of T Pl yields:
dT Pl _ p s (e s - r] cp e cpi - (1 - Tfe,) e gi ) A b r b - (/i cpi - e^ ) m cp - (h gi - e gi ) rh g + Q Pl ^
at pep ^cpi c vcpi + Pg\ Vg\ c vg\
(56)
Similarly, multiplying Eq. (7) by e cp2 , multiplying Eq. (8) by e 52 , subtracting these results
from Eq. (55), using Eqs. (20) and (21) to re-express the derivatives in terms of T P2 , and
solving for the derivative of T P2 yields:
dT P2 _ (h cpi - e cp2 )rh cp + (h gi - e S2 ) ra g + Q P2 - W oui2 ^ .^
dt PcpVcp2 € Cp2 C VCp2 » P92^92 C Vg2
Lastly, Eq. (11) can be split into two first order ODE's. The first of these equations is
given by the definition presented in Eq. (39). The second equation, obtained by using Eq.
(39) and the geometrical relation given by Eq. (14), is expressed by the following:
^ = Vi. (58)
dt m p
Equation (39), (49), (50), (52), (56), (51), (57), and (58) for a coupled set of eight
non-linear first order ODE's in eight unknowns. Initial conditions for these equations are
V 2 (t = 0) = V 2oy V s (t = 0) = V JO , V cpi (t = 0) = Vcp,*,
p gi (t = o) = p, l0 , T Pl (t = 0) = T OJ V^t = 0) = V CP20 , (59)
T P2 [t = 0) = T 0i V 2 (t = 0) = 0.
All other quantities of interest can be obtained once these equations are solved.
Results
Numerical solutions were obtained for the simulated firing of an NSI into the pin puller
device. The numerical algorithm used to perform the integrations was a stiff ODE solver
given in the standard code LSODE. The combustion process predicted by the CET89 chem-
ical equilibrium code followed the chemical equation given in Table 1. Parameters used in
the simulations are given in Table 2.
Predictions for the pressure history inside the NSI and the gas expansion chamber are
shown in Fig. 3. Also shown in this figure are experimental values obtained by pressure
transducers located inside the gas expansion chamber. 9 A rapid increase in pressure is
predicted within the NSI assembly immediately following combustion initiation (t =
ms); the pressure continually rises to a maximum value near 195 MPa occurring near the
time of complete combustion (t = 0.023 ms). The pressure within the expansion chamber
increases more slowly due to mass choking at the NSI port. Following completion of the
combustion process, the pressure within the NSI assembly decreases to 53.9 MPa occurring
near t = 0.06 ms; during this same time, the pressure within the gas expansion chamber
uniformly increases to a maximum value of 53.4 MPa. There is a subsequent decrease in
- 278 -
both pressures" to values near 22.5 MPa at completion of the pin's stroke (t st = 0.466 ms).
These decreases in pressure result from work done by the product gases in moving the pin
and heat transfer from the combined product subsystems to the surroundings.
Figure 4 shows the predicted temperature history for the combustion products contained
within the NSI assembly and the gas expansion chamber. Since the only energy exchange
between subsystems contained withih these two components is due to the flux of product
mass through the NSI port, the resulting temperatures of the combined product subsystems
do not thermally equilibrate. Figure 5 shows the predicted density history for the gas phase
products inside the NSI and the gas expansion chamber. As a consequence of the product
temperature difference, a significant difference in gas phase density is also predicted.
The predicted velocity history of the combustion products flowing through the NSI port
is given in Fig. 6. Here, a rapid rise in velocity to a maximum value near 928 m/s is predicted
immediately following combustion initiation; during this time, the flow through the port
becomes choked. The flow remains choked as the velocity slowly decreases to 830.3 rajs.
Subsequently, there is a rapid decrease in velocity to a minimum value of approximately
7 m/s ocurring at t = 0.63 ms. This rapid decrease in velocity occurs as the pressures
within the NSI assembly and the gas expansion chamber equilibrate following completion
of the combustion process. As the pin retracts, gases within the expansion chamber expand
creating a slight pressure imbalance across the NSI port; consequently, the velocity of the
flow begins to slowly increase to a value of 23 m/s at completion of the stroke.
Figure 7 shows the time history of the predicted pin kinetic energy. A continual increase
in kinetic energy to a maximum value of approximately 31.4 J at completion of the stroke
is predicted. This value compares to an experimentally measured value of approximately
22.6 J. The larger value for the predicted kinetic energy is consistent with the fact that
frictional effects, which would tend to retard the motion of the pin, have not been accounted
for in the model.
Figure 8 gives results showing the sensitivity of the model to changes in the NSI port
cross-sectional area, A e . For this study, we use the predicted pin puller solution as the
baseline solution (baseline parameters given in Table 2). The sensitivity of the model is
determined by solving the pin puller problem and finding the parametric dependency of
three predicted quantities: the pin kinetic energy at completion of the stroke, the stroke
time, and the maximum pressure attained within the NSI assembly. Quantities presented
in this figure have been scaled by values obtained from the pin puller simulation presented
above. For decreasing values of A e , pin kinetic energy decreases while both the stroke time
and maximum pressure within the NSI increase. These results are primarily due to smaller
mass flow rates through the port resulting from decreasing port cross-sectional areas. For
slightly larger values of A e , both the stroke time and the pin kinetic energy approach a
nearly constant value while the peak pressure within the NSI decreases.
Conclusions
The model presented in this paper is successful in predicting the dynamic events asso-
ciated with the operation of an NSI driven pin puller. In addition to tracking the interac-
tions between the reactant and product subsystems, the model also accounts for multiple
pyrotechnic grains, variable burn surface area, and combustion product mass flow rates
through the NSI port. Results of a sensitivity analysis reveal that variations in the cross-
sectional area of the port may significantly effect the performance of the device. Specifically,
significant decreases in the pin kinetic energy result from decreases in port cross-sectional
- 279 -
area. In the presence of friction, the Smaller kinetic energy of the pin may be insufficient to
overcome frictional effects resulting in functional failure. Decreases in cross-sectional area
may arise from the partial blockage of the NSI port by foreign matter or by the accumula-
tion of condensed phase combustion products. Moreover, it is possible that the very high
predicted pressures within the NSI assembly resulting from decreasing port cross-sectional
areas may be sufficient to cause structural failure of the NSI's webbing, thereby jamming
the pin and preventing it from retracting. Such structural failures have been reported in
the past. 6
References
1 Razani, A., Shahinpoor, M., and Hingorani-Norenberg, S. L., "A Semi-Analytical Model
for the Pressure-Time History of Granular Pyrotechnic Materials in a Closed System,"
Proceedings of the Fifteenth International Pyrotechnics Seminar, Chicago, IL, 1990, pp.
799-813.
2 Farren, R. E., Shortridge, R. G., and Webster, H. A., Ill, "Use of Chemical Equilibrium
Calculations to Simulate the Combustion of Various Pyrotechnic Compositions," Proceed-
ings of the Eleventh International Pyrotechnics Seminar, Vail, CO, 1986, pp. 13-40.
3 Butler, P. B., Kang, J., and Krier, H., "Modeling of Pyrotechnic Combustion in an Automo-
tive Airbag Inflator," Proceedings - Europyro 93, 5 e Congres International de Pyrotechnic
du Groupe de Travaile de Pyrotechnic, Strasbourg, France, 1993, pp. 61-70.
4 Kuo, J. H., and Goldstein, S., "Dynamic Analysis of NASA Standard Initiator Driven Pin
Puller," AIAA 93-2066, June 1993.
5 Gonthier, K. A., and Powers, J. M., "Formulation, Predictions, and Sensitivity Analysis of
a Pyrotechnically Actuated Pin Puller Model," Journal of Propulsion and Power, accepted
for publication, 1993.
6 Bement, L. J., Multhaup, H. A., and Schimmel, M. L., "HALOE Gimbal Pyrotechnic Pin
Puller Failure Investigation, Redesign, and Qualification," NASA Langley Research Center,
Report, Hampton, VA, 1991.
7 Gordon, S., and McBride, B. J., "Computer Program for Calculation of Complex Chem-
ical Equilibrium Compositions, Rocket Performance, Incident and Reflected Shocks, and
Chapman-Jouguet Detonations," NASA Lewis Research Center, SP-273, Cleveland, OH,
1976.
8 Fox, R. W., and McDonald, A. T., Fundamentals of Heat and Mass Transfer, 3 rd ed. John
Wiley and Sons, Inc. 1985, pp. 599-617.
9 Bement, L. J., private communication, NASA Langley Research Center, Hampton, VA,
1992.
- 280 -
Table 1: Stoichiometric equation used in pin puller simulations.
4.0908Zr(s) + 2.9178KCl0 4 (s)
2J198Zr0 2 (cp) + 2A786KCl(g) + l.ZUOO(g)
+1.2305ZrO 2 (g) + 1.0136O 2 (ff) + 0.6472C/(<7)
+0.mOK(g) + 0.2434iirO(</) + O.UOZZrO(g)
+0M88ClO(g) + 0.0285K 2 Cl 2 (g) + 0.0040tf 2 (<7)
+0.003lCf a (y) + 0.0002Zr(g) + O.OOO10 3 (5)-
Table 2: Parameters used in pin puller simulation.
parameter
value
Vcp
0.43
N
100
A e
0.100 cm 2
A p
0.634 cm 2
Ax
0.634 cm 2
Vi
0.125 cm 3
Ps
3.57 g/cm 3
Pep
5.89 g/cm 3
T 3
288.0 K
T w
288.0 K
h
1.25X10 6 g/s 3 /K
e
0.60
a
0.60
Fcrit
3.56 Xl0 7 dyne
b
0.003 (dyne/cm 2 )- - 60 ™/ s
n
0.60
v 2o
0.824 cm 3
v,
0.038 cm 3
Vcp\o
7.425 Xl0 -8 cm 3
P910
6.202 xl0~ 6 g/cm 3
T
288.0 K
*CP2<>
6.576X10" 7 cm 3
v 2
0.0 cm 3 js
- 281 -
200 I '' '''■■' ' I ' ' I I ' ' ' ' ' r i i i | i i i i i i i
150
^ 100
50
-0.10
predicted result
^— experimental result
0.50
Figure 3: Predicted and experimental pressure histories for the pin puller simulation.
6000
4000
2000
I i i i i | i i i i i i i i i | i ■ ' I
i r ■ i I i
-0.10
0.00
0.10
0.20
t(ms)
0.30
0,40
0.50
Figure 4: Predicted temperature histories for the pin puller simulation.
- 282 -
0.30
r t t ? i i r r-r i i i i i i i i i i i i i t i i i i i i i i l r m r t ~ r-\
Figure 5: Predicted temperature histories for the pin puller simulation.
i
1000
1 1 1 rV'l I 1 1 1 I I 1 T I "1 IT 1 1 I T ITTH IIIIIITItlfl
T' ] "T I'T 1 ! I 1 1 1 1 1 I T I ! T T T T"T -
800
-
^
-
600
s
1
1
-
-
•
r
400
~
200
-
.1 1 I..JL 1 1 1 1 1
-0.10 0.00 0.10 0.20 0.30 0.40 0.50
t(ms)
Figure 6: Predicted velocity of the flow through the NSI port for the pin puller simulation.
- 283 -
^Q I I I I I I i i t I | I I i I i i i I I | I I I > t i i > i i i i I r t I I I I | i i i | t
30
tq 20
10
r< i i i i i i i i |_
I I 1 I I 1 1 I ■ I 1 I I > I I I I 1 I I I t I I
-0.10 0.00
0.10
0.20
t(ms)
0.30
0.40
0.50
Figure 7: Predicted kinetic energy of the pin for the pin puller simulation.
2
3
8
1 -
-
I 1 1 —
—\ 1 1 1 — 1—| 1 1 1 1 1 T" "T 1 |
^
4
-
Wt
^^-^^^ \
- ^^
Jl 1 1
t • > ...... i
0.01
0.10
MK
1.00
Figure 8: Sensitivity of the model to changes in the NSI port cross-sectional area. The
values presented in this figure have been scaled by the gaseline values A* = 0.10 cm 2 ,
KE* = 31.4 J, t* = 0.466 ms y and P^ = 195.2 MPa.
- 28^ -
FINITE ELEMENT ANALYSIS OF THE SPACE SHUTTLE
2. 5 -INCH FRANGIBLE NUT
J2V/5
I 1
/I
Darin N. McKinnis
NASA Lyndon B. Johnson Space Center, Houston, TX
Abstract
Finite element analysis of the Space
Shuttle 2.5-inch frangible nut was
conducted to improve understanding
of the current design and proposed
design changes to this explosively-
actuated nut. The 2.5-inch frangible
nut is used in two places to attach
the aft end of the Space Shuttle
Orbiter to the External Tank. Both
2.5-inch frangible nuts must
function to complete safe
separation. The 2 . 5 -inch frangible
nut contains two explosive boosters
containing RDX explosive each
capable of splitting the nut in
half, on command from the Orbiter
computers. To ensure separation, the
boosters are designed to be
redundant. The detonation of one
booster is sufficient to split the
nut in half. However, beginning in
1987 some production lots of 2.5-
inch frangible nuts have
demonstrated an inability to
separate using only a single
booster. The cause of the failure
has been attributed to differences
in the material properties and
response of the Inconel 718 from
which the 2.5-inch frangible nut is
manufactured. Subsequent tests have
resulted in design modifications of
the boosters and frangible nut.
Model development and initial
analysis was conducted by Sandia
National Laboratories (SNL) under
funding from NASA Lyndon B. Johnson
Space Center (NASA-JSC) starting in
1992 . Modeling codes previously
developed by SNL were transferred to
NASA-JSC for further analysis on
this and other devices. An explosive
bolt with NASA Standard Detonator
(NSD) charge, a 3/4-inch frangible
nut, and the Super*Zip linear
separation system are being modeled
by NASA-JSC.
Introduction,
The 2.5-inch frangible nut is used
in two places to attach the aft end
of the Space Shuttle Orbiter to the
External Tank, as shown in figure 1.
Each 2.5-inch frangible nut must
function to complete safe separation
of the Orbiter from the External
Tank. Separation of each nut
requires fracturing of four webs as
shown in figure 2 . The 2 . 5-inch
frangible nut contains two explosive
boosters containing 100% RDX each
capable of splitting the nut in
half. To ensure separation, the
boosters are designed to be
redundant. The detonation of one
-401 configuration booster, figure
3 , is sufficient to split the nut in
half. However, beginning in 1987
some production lots of 2.5-inch
frangible nuts demonstrated an
inability to separate using only a
single -401 booster. The cause of
the failure has been attributed to
differences in the material
properties and response of the
Inconel 718 from which the 2.5-inch
frangible nut is manufactured.
Details of the failure investigation
were reported by Hoffman and
Hohmann 1 . Subsequent tests have
resulted in design modifications of
the boosters and frangible nut.
Finite element analysis of the Space
Shuttle 2.5-inch frangible nut was
conducted in cooperation with Sandia
National Laboratories (SNL) ,
Albuquerque, New Mexico using two
finite element analysis computer
programs developed at SNL: JAC and
PRONTO. JAC is a quasistatic finite
element solver. JAC was used to
simulate tensile pulls of Inconel
718 in order to generate material
characterizations of the Inconel
718. The output of JAC can be used
to qualitatively determine the
advantage of one sample of Inconel
718 over the other. JAC ' s output
however can also be provided as
input to PRONTO to improve the
accuracy of booster and nut
simulations. PRONTO is a dynamic,
large deformation, finite element
solver. PRONTO was used to conduct
simulations of booster detonation
and the response of the nut. These
codes were primarily run at SNL, on
a Cray Y-MP supercomputer. At NASA-
JSC the codes were installed and run
on a Sun workstation.
- 285 -
The first part of this paper
discusses the material
characterization process necessary
for an accurate analysis. The second
part of this paper discusses the
structural analysis and design
changes to the nut which were
analyzed with comparison to test
results. The third part of this
paper briefly describes other
devices which are being analyzed
with this process.
Inconel Material Characterization
Process
To conduct a structural analysis of
the 2 . 5-frangible nut, material
characterization of Inconel 718 is
necessary. Material characterization
requires a tensile test and a
tensile test simulation using the
JAC2D program. The procedure used
is :
1) Perform a tensile test. The
tensile test must be carried out
through failure, if at all possible,
or at a minimum into necking. This
is because reduction in area is a
significant factor in the
characterization process.
2) Convert the tensile test
engineering stress/strain data to
true stress/strain over the range
from yield to necking. Conversion of
the data to true stress/strain is
straight forward but necessary as
the finite element programs use true
stress/strain. True stress is found
from engineering data according to
the equation:
true eng v eng
True strain can be calculated
according to the following equation.
''true
= ln(£ eng+ D
Both equations are valid until
necking begins, when the cross
sectional area is no longer
constant .
3) Curve fit the true stress/strain
data to a power- law hardening
relationship, of the form
C = G ys + A<£ p -e L >n
to determine the hardening constant,
A, and hardening exponent, n. O is
the effective stress, C is the
yield strength, £ p is the equivalent
plastic strain, and £ L is the Luders
strain. Inconel displays no Luders
strain so this term can be
considered zero. £ p should be
evaluated according the Heavyside
function, designated by the
brackets, i.e. zero if its value is
negative.
4) Conduct a simulation of the
tensile test using the JAC2D
program. The finite element mesh for
this simulation is shown in figure
4. The left hand side is the initial
mesh. The right hand side is the
mesh near failure. Note that only
the upper quadrant of the test is
simulated due to two symmetry
planes. A 2 mil reduction in
diameter, which was measured from
the test samples , and included in
the mesh geometry assures
localization at the symmetry plane
on Z=0.
5) Convert and review the results of
the JAC2D analysis to obtain the
tearing parameter. The results of
the JAC2D analysis are converted in
post-processing to the selected form
of the tearing parameter, in this
analysis it is
TP
£f
"J:
<2Gt)
3(Gt-Om)
-de
where Ot 1S tne maximum principal
stress, <J m is the mean stress, and
£ is the equivalent plastic strain.
This is evaluated from zero to £f r
the strain at fracture. Knowledge of
the final reduction in area from the
tensile test is used here. The time
step, tf f in the simulation is noted
when the radius of the Z=0 symmetry
plane equals the radius of the
failed test sample.
The tearing parameter can then be
plotted versus time for the node at
the center of the sample, where the
tearing parameter is at a maximum in
this model. The tearing parameter is
then the value of the curve at tf.
Using this method, tearing parameter
sensitivity to time and/or reduction
in area is displayed.
- 286 -
The yield stress and elastic modulus
from the tensile test, and the
calculated values of tearing
parameter, hardening constant (A)
and hardening exponent (n) are
necessary to define Inconel 718 for
the structural analysis to follow.
The only other data required is the
Poisson's ratio and density. These
are all the parameters required by
PRONTO' s constitutive model for this
analysis.
To confirm the results of the curve
fit and JAC2D analysis, the JAC2D
results can be plotted against the
original tensile test data. If
necessary, adjustments in A and n
can then be made and another JAC2D
analysis can be run until the
analysis and tensile test agree. The
tearing parameter can then be
reevaluated. When the analysis and
test agree, the material
characterization process is complete
and the structural analysis can be
conducted on the 2.5-inch nut with
the PRONTO program.
Selection of the Tearing Parameter
Fail nre Definition
Chapter 16 of Numerically Modelling
of Material Deformation Processes 2
describes some of the prominent
models that have been developed for
ductile failure. However, in finite
element analysis, most empirical
models share the common approach of
conducting an experiment or test on
the material in question to
determine the critical value, or
tearing parameter, of the material.
For example, the original model used
a tensile test on a notched specimen
to determine a tearing parameter.
There are then different theories
for which stress and strain
components should contribute to the
accumulation of the tearing
parameter and in what empirical
formulation. Apparently the correct
formulation is strongly dependent on
the material, geometry, and other
factors for a specific problem, as
well as the experience of the
analyst .
Using JAC, the calculation for
tearing parameter is done in post-
processing, providing complete
flexibility to change the
formulation of the tearing parameter
calculation. The tensile test
simulation does not even have to be
rerun. New post processing commands
are all that is required. PRONTO' s
designers also anticipated the need
for alternative constitutive models
and tearing parameter formulations
to meet the needs of the specific
problem. And PRONTO supports post
processing to permit reformulation
of the tearing parameter if desired.
However, NASA-JSC sought the ability
to visualize in real-time the death,
or failure, of material based on the
tearing parameter. PRONTO supported
adaptive or real-time death for
energy, Vonmises stress, pressure,
and other variables but not the
tearing parameter. Therefore, the
tearing parameter selected to
describe failure of the Inconel 718
in the 2.5-inch frangible nut was
added to the elastic/plastic power
law hardening material model of
PRONTO specifically for this
application. This new constitutive
model, the power law hardening
strength model, was based on the
elastic/plastic power law hardening
material model. The elastic/plastic
power law hardening material model
used by PRONTO was documented by
Stone, Wellman, and Krieg^ .
RDX Material Characterization
Using PRONTO, explosives are modeled
using Jones-Wilkins-Lee (JWL)
parameters which were obtained from
the Lawrence Livermore National
Laboratories (LLNL) Explosives
Handbook Properties of Chemical
Explosives and Explosive Simulants 4 .
The LLNL handbook also describes the
formulation of the JWL parameters
and their use to predict the
"pressure-volume-energy behaviour of
the detonation products of
explosives in applications involving
metal acceleration" . However, JWL
parameters were not available from
the handbook for 100% RDX, the
explosive used by the booster. JWL
parameters for 95% HMX were used
instead. HMX is known to be slightly
more energetic than RDX.
structural Analysis - Phase I
Nut and Booster Geometry -
Initial structural analysis of the
2.5-inch nut began in the spring of
1992. At that time, tensile test
data from yield through necking was
not available for the Inconel 718.
However, structural analysis was
conducted to evaluate the
- 287 -
sensitivity of the nut to various
geometrical factors. The finite
element mesh currently being used is
shown in figure 5. The slight
differences between this mesh and
the mesh used in phase I of the
analysis are described later in this
paper. Figure 6 shows in detail the
side of the nut with a booster
included where detonation will be
modeled. The following changes in
the nut geometry were analyzed to
determine the effect on nut
separation: radial gap between the
booster cartridge material and the
nut, outer notch depth of the nut,
as shown in figure 7 , and the
booster aspect ratio. The results
were reported by K. E. Metzinger 5 .
Radial gap between the booster and
the nut is limited to 7 mil maximum
by the tolerances on the nut and
booster. The analysis and tests
agree that minimizing the gap as
much as possible, including the use
of grease, is beneficial. Analysis
shows the benefit is greatest in
reducing gap from 7 mil to 4 mil, 5
times greater than from 4 mil to 2
mil. The advantage of reducing gap
from 4 mil to 2 mil is the same as
from 2 mil to . 5 mil. This suggests
that tightening tolerances on the
part to reduce gap probably would
not be cost effective beyond 4 mil.
Reduction of gap from 2 mil to . 5
mil through the addition of grease,
epoxy, or other agents would
probably not justify the added
complexity and cost of such a
change .
The outer notch depth of the nut has
also been shown to be a factor in
nut separation. The original flight
configuration of the 2.5-inch
frangible nut had an outer notch
depth of 0.303 inches. Reducing the
depth from 0.303 to 0.018 allows the
nut halves to rotate further about
the fourth web, from approximately
25 degrees to over 60 degrees.
Without a reduction, the corners of
the nut at the outer notch pinch
together, resulting in energy lost
to compressive plastic strain. *
Rotation of the halves places the
elements of the fourth web, the last
web to fail, under increasing
tension. Increased tension means
increased tearing values in those
elements and improved likelihood of
failure. This change was first
demonstrated in test and repeated by
the analysis. The outer notch depth
was reduced to 0.075 in the -302
configuration of the nut which is
the current flight configuration.
Although testing preceded analysis,
the analysis showed two
disadvantages to decreasing the
outer notch depth: reduction in
delivered energy to the nut from the
booster and increased time until
separation. Reducing the outer notch
depth the nut causes web 1, the
first web to fail, to fail earlier
in time, before all the energy of
the booster can be imparted to the
nut. The analysis showed this loss
to be small but significant if the
outer notch depth is not properly
sized. An outer notch depth of 0.153
inches was actually shown to be less
likely to separate than either a
larger notch, 0.303 inches, or a
smaller notch, 0.018 inches. The nut
has not yet been designed to the
optimum notch size. Further analysis
will be required to determine the
optimum size of the outer notch
depth to ensure separation.
Furthermore, the increased rotation
permitted by the smaller notch depth
causes the nut to fail later in
time, in general. Although this is
not a concern in the current design,
this factor may be important in
applications with smaller tolerances
in separation time.
Booster aspect ratio is defined as
the diameter of the charge over the
length of the charge. It was
proposed that increasing the aspect
ratio would increase the effect
impulse delivered by the booster to
the nut, with no additional RDX.
Considerable energy was being lost
or underutilized because it was
located at or below the bottom of
the webs of the nut and the
separation was thought to be
progressing in zipper fashion, from
the top of the web toward the
bottom. The advantage of increased
aspect ratio was demonstrated in
tests and analysis. As a result,
NASA-JSC has modified the booster
from the -401 configuration to the
-402 configuration as shown in
figure 3 for all future production
of the booster.
- 288 -
Structural Analysis - Phase II
A Copper Booster
A second phase of analysis was
conducted in September 1992 to study
the effect of changing the booster
cartridge material from stainless
steel to copper. This study is
briefly documented by K. E.
Metzinger in a memo to D. S.
Preece^. This study showed that a
copper booster would absorb less
energy in expanding within the
booster port of the nut, making more
energy available for nut separation.
A nut would thus be more likely to
fracture with a copper booster than
with a stainless steel booster, as
shown in figure 8 .
The analysis also showed that the
NASA Standard Detonator (NSD) , the
initiating charge of the booster, is
capable of blowing the top of the
booster off and allowing the booster
pressures to vent. This is confirmed
by tests in which the booster top
consistently separates from the
assembly. Analysis showed that a
copper booster would vent earlier
than a stainless steel booster and
the existing design does not permit
strengthening in the area of
fracture to prevent venting.
However, venting is not considered
to be a major concern as the
analysis showed that the impulse
delivered from the booster to the
nut precedes the loss of the booster
top.
Unfortunately, copper has known
compatibility problems with RDX. So
a copper booster is not feasible.
Testing has confirmed the analysis
results by using modified stainless
steel boosters, outer diameters
machined down and copper sleeves
inserted over the stainless steel,
shown in figure 9. These boosters
were successful in every test.
Although these modified boosters
have not been accepted for use in
flight at this time, they have an
advantage over a pure copper booster
in that they would not increase the
generation of shrapnel or increase
venting because the top of the
booster is unchanged from the flight
boosters, solid stainless steel.
Structural Analysis - Phase III
pgfinina th e Model
In 1993 the goal of the analysis was
to improve the accuracy of the model
so that design changes or
variability between production lots
of Inconel 718 could be compared
quantitatively. Qualitative accuracy
had already been demonstrated in the
earlier analyses. To provide
quantitative accuracy in the
analysis it would be necessary to
perform material characterization,
as previously described, for
different lots of Inconel 718 and
correlate test performance with the
analysis .
The selected lots were HSX and HBT.
It had been shown in earlier actual
tests that these two lots of Inconel
718 had significantly different
characteristics based on their
performance. No HBT nut has ever
separated completely using the -401
booster, while no HSX nut has ever
failed to separate with a -401
booster. The analysis had to show
that HBT would not separate and HSX
would not .
The first step was to conduct a
material characterization of HSX and
HBT, then a structural analysis with
the calculated material properties.
The tensile test data for HSX and
HBT is shown on figure 10.
The model accurately predicted that
HSX nuts would be much easier to
fracture than HBT nuts.
Significantly different tearing
parameters, 0.345 for HSX and 0.675
for HBT, indicated this trend.
However, structural analysis
conducted on HSX nuts failed to
simulate a nut which completely
separated. Clearly the model was not
yet quantitatively accurate. Since
the material characterization
process with JAC analysis appeared
sound, geometry and other
characteristics were evaluated to
increase the accuracy of the model
and simulate a separating HSX nut.
Three factors were found to increase
accuracy of the model: the addition
of a simulated bolt, increasing the
granularity of the mesh in the webs,
and increasing the number of points
used to initiate detonation of the
explosive.
One of the refinements was that the
number of elements in the webs was
increased slightly. This is done by
remeshing the nut's geometry. This
reduces the size of the average
289 -
element in the web area of the nut.
In PRONTO, the tearing parameter
must be exceeded for the entire
element for failure of that element
to occur. A smaller element is thus
more likely to fail due to localized
increases in tearing parameter.
Reducing average element size
increases the number of elements
which increases output file sizes
and run times. Smaller elements also
require smaller time steps, further
slowing model processing. Thus this
step, while increasing accuracy,
increases run times, a common
problem in finite element analysis.
To increase accuracy of the model,
the explosive material was provided
with more initial detonation points.
The original model had a single
detonation point at time = 0. From
this point the detonation wave was
calculated to spread throughout the
RDX. Ten detonation points were
added to the model, each simulating
detonation at time=0 . Thus the
detonation of all the RDX occurs in
a more even distribution and shorter
time period. This produces slightly
more output from the explosive and
simulates a mature detonation wave
as opposed to an initiating charge.
This change did not require
remeshing and was very easy to
implement .
A bolt was inserted into the hole of
the nut. The addition of the bolt is
significant to the separation of the
nut, critical in some borderline
cases, according to the analysis.
Figure 11 shows the nut opening for
2.5 mil radial gap and 4.5 mil
radial gap HSX nuts. The 4.5 mil nut
is opening similarly to the 2.5 mil
nut until about 2 milliseconds. At
that point opening has stopped and
the nut is beginning to close down.
However, at 3 . 5 milliseconds the nut
which is moving to the left impacts
the stationary bolt. The impact
provided the necessary energy to
complete the failure of web 4 and
separation. At this time there is no
experimental data to confirm this
effect. However, testing is
typically conducted with a bolt and
no pre-load and should be included
in the analysis. The effect of
threads is not considered in the
analysis. This change requires
remeshing, the addition of a new
material elastic Inconel 718, and
the addition of contact surfaces.
The number of elements added was
kept to a minimum by treating the
bolt as a perfectly elastic pipe.
The simulation of an HSX nut with
these changes resulted in a
separating nut, failure of all four
webs. Even with the changes which
resulted in more energy to the nut
and easier fracture, HBT nuts did
not separate, still in agreement
with tests. This study was
documented in an SNL report^ .
Future Studies of the 2.5-inch Nut
A tearing parameter is used to
determine when the Inconel 718
material would fail. It has been
proposed that the stainless steel of
the booster should also be allowed
to fail using a tearing parameter
calculated by a JAC analysis. Even
if the stainless steel is not
permitted to fail, performing a JAC
analysis, including a tensile test,
should enhance the model's accuracy.
Modeling conducted to date has not
included material characterization
of stainless steel as was done for
the Inconel 718. NASA-JSC is
currently conducting tensile testing
of stainless steel samples from
booster lots to perform this
analysis .
One geometrical design consideration
which has not been modeled is the
application of a backing plate or
washer to the nut. During testing
this was shown to have significant
effect on the separation of the nut,
overshadowing most other variables.
Nuts without the backing plate, were
not as likely to separate. However,
to include the backing plate the
model must be converted into three
dimensions. NASA-JSC plans to
conduct these analyses in 1994.
NASA-JSC will probably run this
analysis on their Cray to handle the
significant increase in the number
of elements necessary to conduct
this analysis.
Structural Analysis and Material
Characterisation Conclusions
The most significant conclusions
from the analysis performed on the
2.5-inch frangible nuts are as
follows:
A. Radial gap between the booster
and the frangible nut is an
- 290 -
important dimension. This gap should
be minimized if complete separation
is desired.
B. The energy absorbed by the
stainless steel booster is
significant. Switching from an all
stainless steel cartridge to a
cartridge of reduced diameter and
the addition of a copper sleeve
should increase the impulse
delivered to a nut. An all copper
booster housing is not recommended
due to compatibility issues between
copper and RDX. However, a hybrid
booster made of stainless steel with
a copper sleeve has been shown in
test to be effective.
C. Reduction in area obtained from a
tensile test of an Inconel 718
sample is significant . Reduction in
area is a significant factor of the
tearing parameter. Inconel with a
relatively small reduction in area
will be easier to break.
Other Applications
NASA-JSC is currently pursuing
analysis models of the Space Shuttle
3/4-inch frangible nut, the
Super*Zip linear separation system,
and a JSC-designed explosive bolt
utilizing the NASA Standard
Detonator (NSD) as the actuating
charge. These models can use the
same process as was used for the
2.5-inch frangible nut with slight
variations.
The mesh for the explosive bolt
model is shown in figure 12. Six
prototype explosive bolts have been
fired to date. Agreement with the
analysis has been excellent. The
analysis has provided design
modifications which will be used to
slightly change the separation plane
and ensure positive retention of the
bolt in its confining washer.
The mesh for the Super* Zip linear
separation system model is shown in
figure 13.
Conclusions
The test and finite element analysis
methodology developed by SNL and
NASA-JSC has been successfully
demonstrated. This methodology
requires the use of SNL developed
software which has been successfully
transferred, with substantial
assistance from SNL, to NASA-JSC.
Training in the use of these codes
has been provided. This methodology
can now be used by NASA-JSC in
several ways .
Analysis can be conducted on new
production lots of Inconel 718.
Inconel 718 lots which possess
material properties and tearing
parameters outside of acceptable
limits can be rejected before
expensive machining and acceptance
testing is conducted.
Analysis can be conducted on sample
lots of Inconel 718 to determine the
effect of various heat treatment
procedures on the microstructure.
This approach will suggest measures
to further control the forging
process .
Analysis can be conducted to
quantify the effects of proposed
design changes before manufacturing
and testing is initiated. Analysis
could also be used to establish the
design margin of the current
configuration or select a more
meaningful design margin criteria.
Currently design margin is
determined by increasing the web
thickness to 120% of the maximum
allowable, as shown in figure 14.
This choice for margin demonstration
is not ideal. It is unlikely that
the web thickness will be
incorrectly manufactured and that
this error will be overlooked in
acceptance inspections . Furthermore ,
no additional information beyond
separation versus failure to
separate is obtained. It has been
suggested that velocity of the nut
halves as the nut separates would be
a better demonstration of margin
where failure to separate provides a
velocity of zero. At this point,
test methods including breakwires
and high-speed photography are being
used to determine the velocity of
nut halves for comparison with the
analysis.
The test and analysis methodology is
general enough that it can be
successfully applied to other
mechanical devices and design
problems. NASA-JSC is currently
pursuing analysis models of the 3/4-
inch frangible nut, the Super*Zip
linear separation system, and a
NASA-JSC designed explosive bolt
- 291 -
utilizing the NSD as the actuating
charge .
References
1. Investigation of Failure to
Separate an Inconel 718
Frangible Nut, William C.
Hoffman, III, and Carl Hohmann,
NASA Lyndon B. Johnson Space
Center , Houston , TX .
2. Numerical Modelling of Material
Deformation Processes, Edited by-
Peter Hartley, Ian Pillinger,
and Clive Sturgess, Springer-
Verlag, Germany, 1992 .
3. A Vectorized Elastic/Plastic
Power Law Hardening Material
Model Including Luders Strain,
Charles M. Stone, Gerald W.
Wellman, Raymond D. Krieg,
Sandia National Laboratories,
Albuquerque, New Mexico, SAND90-
0153, March 1990.
4. LLNL Explosives Handbook
Properties of Chemical
Explosives and Explosive
Simulants, B. M. Dobrantz and P.
C. Crawford, UCRL-52997.
Lawrence Livermore National
Laboratory, Livermore,
California, January 1985.
5. NASA Frangible Nut Preliminary
Findings, Memo from K. E.
Metzinger to D.S. Preece, Sandia
National Laboratories,
Albuquerque, New Mexico, August
25, 1992.
6. NASA Booster Cartridge Material,
Memo from K. E. Metzinger to
D.S. Preece, Sandia National
Laboratories, Albuquerque, New
Mexico, October 5, 1992.
7. Structural Analysis of a
Frangible Nut Used on the NASA
Space Shuttle, Kurt E.
Metzinger, Sandia National
Laboratories, SAND93-1720,
November 1993 .
modeling. The author also wishes to
thank Carl Hohmann, NASA-JSC, who
recommended many of the design
modifications and variables which
were studied and supported the
interpretation of the analysis.
Acknowledgments
The author wishes to acknowledge the
work of D.S. Preece and Kurt E.
Metzinger, Sandia National
Laboratories, Albuquerque, New
Mexico, in model generation, initial
modeling and analysis, and in
technical support for NASA-JSC
- 292 -
ORBITEFVEXTERNAL TANK
AFT ATTACH INTERFACE
Enforced /-direction
Displacement
S
p //\\
•j "TrtTi
si ~t T i n '
o IJlj j lflijlJ Qf
z H l UI-l iit i ll t l
No /-direction
Displacement
--'0 -0 -10 .20 -.10 .00 .10 .20
"jjTfYP
IIHIIIUMIIMfl
ItltMlllldllfifl
Figure 1. Location of the 2.5-inch
frangible nut between the Space Shuttle
Orbiter and External Tank.
Figure 4. Tensile test mesh for
simulation by JAC2D.
TOP VIEW OF 2.5-INCH
FRANGIBLE NUT
FRANGIBLE WEBS
SECTION A-A
FRANGIBLE NUT
SEPARATION PLANE
-3.0 2.0 i. a
1.0 2. a 3.0
Figure 2 . Top view and side view of the
2.5-inch frangible nut.
ISOMICA
DISKS
1920 mg ,
RDX — I
HOUSING
1920 mg
RDX
HOUSING
-401 CONFIGURATION
-402 CONFIGURATION
Figure 3. Side view of the
2.5-inch frangible nutbooster,
-401 and -402 configurations.
Figure 5. 2.5-inch frangible nut mesh.
Y'-!v'T.ui;f : T : f..V;;:.:o - • .'
t* ttt t
Poinl A |
Web 1
*— £jq»losive
Cartridge
_ _„.1_. .1 L. .-..A J. J
00 1.25 ISO 1.75 2.00 2.25 2. SO 2.75 3.00
Figure 6. 2.5-inch frangible nut mesh,
detailed view.
- 293 -
TOP VIEW OF FRANGIBLE NOT
SECTION A
Figure 7. Outer notch depth of the nut.
0.60
T "" i
— ■ 1 .- T ~
0.50
S^"
0.40
Copper
304L
a
£ 0.30
9
■
1
0.20
■
0.10
/>'"
i _i
0.000
0.002 0.003
Time (sec)
0.00£
Figure 8 . Nut opening as a function of
booster material, copper versus
stainless steel.
~Uh\
J qr_rvw\
1 Copper sleeve
Figure 9 . Stainless steel booster and
stainless steel booster with copper
sleeve.
250x10 -I
200-
150-
CO
•
?
•
■c
CD
01
100-
c
•
?
•
LU
■
50-
1
0.00
Typical Tensile Test Data for Inconel 718 Lots HBT and HSX
(.005/rnin strain rate)
^HSX
— HBT
i I i i i i | i i
0.05 0.10
Engineering Strain (inches/inch)
1 I ' '
0.15
i j i i i i | i — i i i |
0.20 0.25 0.30
Figure 10. Tensile test data for Inconel 718 lots HBT and HSX.
- 294 -
I
2.0 30
Time (ms)
Figure 11. Nut opening as a function of
gap.
Explosive bolt body
Confining washers
ration plane
explosive charge
ZZZZZZZZ3\ ai . 25 "
zzzzzzza :
T
-301 FRANGIBLE NUT WEBS
ZZZZZZZ3
115% (0.1 49")
120% (0.156")
Z22ZZZZ3I
-1 01 , -1 02 MARGIN NUT WEBS
Figure 14. Web dimensions for
2.5-inch frangible nuts, -301
flight configuration, and -101 and
-102 margin configurations.
Figure 12 . Finite element mesh for the
explosive bolt with NSD charge.
Aluminum doublers
Lead sheath confinement
HMX explosive cords, end on
Figure 13. Super*Zip linear separation
system finite element mesh.
- 295 -
ANALYSIS OF A SIMPLIFIED FRANGIBLE JOINT SYSTEM
514- IS
~Joo4-
Steven L. Renfro
The Ensign-Bickford Company
Simsbury, CT
James E. Fritz
The Ensign-Bickford Company
Simsbury, CT
Abstract
A frangible joint for clean spacecraft, fairing, and stage
separation has been developed, qualified and flown
successfully. This unique system uses a one piece
aluminum extrusion driven by an expanding stainless steel
tube. A simple parametric model of this system is desired to
efficiently make design modifications required for possible
future applications. Margin of joint severance, debris control
of the system, and correlation of the model have been
successfully demonstrated.
To enhance the understanding of the function of the joint, a
dynamic model has been developed. This model uses a
controlled burn rate equation to produce a gas pressure wave
in order to drive a finite element structural model. The
relationship of the core load of HNS-IIA MDF as well as
structural characteristics of the joint are demonstrated
analytically. The data produced by the unique modeling
combination is compared to margin testing data acquired
during the development and qualification of the joint for the
Pegasus* vehicle.
Introduction
Frangible joints have been demonstrated
as robust and contamination free
separation systems for various spacecraft
and launch vehicle stage and fairing
separation. Typical frangible joint
systems are initiated using mild
detonating fuse (MDF) detonation
products to expand an elastomeric
bladder which then compresses
dynamically against a formed stainless
steel tube. The high pressure developed
at the tube forces it to a more round
shape in order to fracture an aluminum
plate along a stress concentration
groove. This fracture provides
separation without fragmentation or
contamination because the products are
contained within the steel tube. A typical
joint cross section is depicted in Figure 1.
Integrating this technology into new
systems, with more challenging
environmental conditions, could benefit
from analytical modeling to properly
configure each system. Understanding
the mechanism required to sever the
aluminum extrusion is crucial to meet
new system requirements with full
confidence.
The purpose of this report is to
document The Ensign-Bickford
Company's efforts to develop a simple
analytical tool using widely available
hydrodynamic and finite element
computer codes.
Background
The ANSYS 5.0 # finite element software
allows for transient input to structures in
the frequencies expected during a small
damped detonation event. The frangible
joint geometry is believed suitable for this
type of analysis. To generate transient
pulses for input into the finite element
® Pegasus is a Registered Trademark of Orbital Sciences Corporation
• ANSYS is a Registered Trademark of Swanson Anaysis Systems, Inc.
- 297 -
J-fy
model, simple one-dimensional
hydrodynamic analysis is used.
For a one-dimensional Lagrangian model,
a cylindrical geometry was assumed.
The SIN 1 hydrodynamic code was used
to solve conservation equations of
momentum, mass, and energy. In
order to use this information as input for
the finite element model, individual or
groups of cells were monitored to
develop input equations for the finite
element calculations.
Since the hydrodynamic analysis is one
dimensional, it limits the amount of
understanding developed regarding the
specific stress state existing in the
aluminum. Peak stress locations and
probable points of secondary failure
cannot be determined, and assumptions
must be made for the stiffness and
response characteristics. A two
dimensional hydrodynamic analysis
would assist in understanding these
effects, but such analysis is time
consuming, and requires access to
sufficient hardware and software
resources. Also, the hydrodynamic
model is unable to account for a wide
range of thermal loads and structural
preloads in the parts, and cannot be
used to evaluate stresses in the part due
to events other than the explosive
loading (i.e., flight loads, thermal
response, assembly loading).
To understand the dynamic response of
the frangible joint, an ANSYS 5.0 finite
element model was created for use in a
non-linear transient analysis. This
analysis was used to determine the
dynamic response of the aluminum when
subject to transient loads driving the
material above its yield strength. This
methodology had been successfully used
by The Ensign-Bickford Company to
solve problems involving explosively and
pryotechnically loaded structures. This
paper represents the first time this
technique used input developed by a one
dimensional hydrodynamic analysis code.
Model Development
Using the SIN analysis, the critical areas
were determined for input into the
ANSYS 5.0 model. The timing and
reaction of the shock waves incident and
reflected from the interior steel wall result
in two distinct types of relationships, both
of which are decaying sinusoidal
functions.
The area of the stress riser has extremely
high initial amplitude which rapidly
decays. This is consistant with the
geometry present at this location. A thin
layer of elastomeric material and a thin
aluminum section bounding the steel do
not support reflected pressure waves as
well as the thicker off axis areas.
Basically, the initial detonation front
experiences a rapid ring down within the
wall of the steel tube. The inside surface
of the steel responds approximately as
illustrated in Figure 2.
The second input function used is from a
cross section at 45° from the stress
riser. This relationship was similar in
frequency to Figure 2 with a much lower
initial amplitude. Figure 3 shows this
relationship.
A logical choice for a third function is 90 °
to the separation plane. Most frangible
joint designs use air gaps combined with
thin silastic sections to control position of
the MDF and to allow easy installation. If
no air gaps are assumed, the resulting
function resembles the data in Figure 3
- 298 -
with lower amplitude. Introducing the air
gaps increases the difficulty of the
hydrodynamic analysis without any real
benefit. This third function was therefore
not used for this simplified approach.
The source explosive used for this
particular design is HNS-IIA. The
equation of state for HNS is not currently
available as part of the SIN database.
Alternate explosive materials were used
to bracket the response of HNS. The
density, chemistry, detonation velocity,
and Chapman-Jouget pressure were
matched as closely as possible with
candidate materials from the SIN
database. Table 1 lists the explosives
used and their properties compared to
HNS.
To simplify the ANSYS model geometry,
symmetric constraints are used along the
notch edge and one half of the joint
mounting flange. The length of the
flange was shortened to reduce the
number of degrees of freedom which
needed to be incorporated into the
model. This model is shown in Figure 4.
The transient loads are applied as
pressure pulses along the interior of the
aluminum. These loads have the same
time profile as that predicted by the one
dimensional hydrodynamic analysis,
however input pressure amplitudes are
reduced to achieve numerical stability.
Unfortunately, this assumption is
required, although it is expected that the
results still allow development of an
understanding of the aluminum response.
The aluminum material (6061 -T6) was
assumed to act in an elastic-perfectly
plastic manner. That is, once the yield
strength of the material is exceeded, no
additional load can be supported by that
material. Plastic convergence is
achieved using the Modified Newton-
Raphson method, based on a Von-Mises
yield criterion. For the transient portion
of the analysis, the Newmark time
integration scheme is utilized, using
Rayleigh damping with only mass matrix
contributions (Beta damping). This
applied damping is necessary in order to
provide stability of the solution.
However, a Beta term is chosen which
ensures a low level of damping (0.05% or
less) above 10,000 Hz.
For the initial time steps, the symmetry
constraints are applied to both the top
notch and the flange edges of the model.
When sufficient stress levels are
determined in the notch to induce section
failure, this symmetry constraint on the
notch is removed and the leg of the
section is allowed to bend up and away
from its initial position. This is done to
simulate proper function of the joint
during the explosive event.
Results of Finite Element Model
As part of the preliminary work
performed using this model, simple static
stress analysis (linear and non-linear) as
well as modal analysis were performed to
verify model integrity and to learn about
the basic structural characteristics of the
model. Some important data was
gleaned from these runs, including the
presence of a potential plastic hinge near
the flange region of the aluminum
structure. Additionally, the modal runs
showed that the aluminum had its
second, third, and fourth normal modes
between 50 and 200 kHz. This was
important information, since it showed
that the aluminum is capable of dynamic
elastic structural response near the input
frequency of the shock pulse. The 2 nd ,
3"*, and 4 th , mode shapes are shown in
- 299
Figure 5.
Once the simpler analysis had been run
and verified with hand calculations, the
more complex non-linear transient
analysis was run. The input pulse was
characterized as a shock pulse with a 1 .5
/xsec rise and a 1.5 /xsec decay at the
notch location. The magnitude of this
pressure pulse was chosen to remain
slightly below the yield point of the
material (approximately 36 ksi) to avoid
model stability problems. As noted
above, this assumption needed to be
made, however; much information about
the dynamic response of the structure
was still learned.
The final results are illustrated in Figure
6. During the rise time of the initial
pressure pulse, the structure cannot
significantly respond to the high
frequency input. The structure simply
transmits the shock wave through the
material thickness. By the time the pulse
is damped, the structure begins to
significantly respond, and peak stresses
in the notch exceed the allowable
material strength. A plastic condition
through the wall is reached. It is at this
time that separation occurs, and the
symmetric boundary condition along the
notch edge is removed. After this time,
the load is no longer applied and the
inertial loads of the aluminum leg are all
that is left driving the deflection.
Obviously, the loading assumption is
somewhat non-realistic; the shock wave
applied to the aluminum will continue
along the inner wall even after separation
has occurred.
After this, the frangible joint is behaving
as a cantilever beam with a fixed edge
along the mounting flange. A plastic
zone develops along much of the length
of the flange wall. It is interesting to note
that a plastic hinge develops in the bend
region of the aluminum leg. This hinge
location corresponds well to explosive
over tests where a section of the
aluminum became a flyer.
Finally, at 24 /xsec, the leg has plastically
deformed over its entire length, a plastic
hinge occurs near the top of the
extrusion, and model convergence is no
longer possible using the elastic-perfectly
plastic static strength allowable. The
predicted deflection at this time is 0.103
inches. For the actual hardware, it would
be expected that energy would be
expended by bending at the plastic hinge
until the impulse had been dissipated.
Discussion
The aluminum is capable of responding
to the input shock pulse in the 2 to 3
Msec regime, suggested by the modal
analysis and supported by the transient
analysis. At approximately 3 /xsec after
the shock pulse has arrived at the interior
of the aluminum stress riser, failure at the
groove is expected to occur. There
remains sufficient energy to severely
deform the legs once the failure at the
stress riser has occurred. A secondary
plastic hinge forms at the bend joint near
the mounting flange for this particular
design.
The aluminum cross section is very
efficiently dissipating the applied impulse
once the stress riser failure occurs. In
other words, plastic stresses do not
localize and exist over much of the inner
and outer surfaces of the aluminum.
All of these discussion items show good
agreement with test specimen articles.
No failures of this particular joint have
- 300 -
occurred which would disagree with the
conclusions of this analysis.
The hydrodynamic analysis would
provide much better resolution if a two
dimensional model were used. Digital
resolution of individual cell results could
be used as forcing function for the finite
element techniques.
Although not specifically addressed by
this paper, the one dimensional
hydrodynamic analysis combined with
the two dimensional ANSYS analysis
shows good promise for evaluation of the
effects of thermally induced strains and
launch load induced stresses. A two
dimensional hydrodynamic input would
further enhance the ability of this
technique to simulate flight functional
conditions.
References:
1)
2)
Charles L Mader: Numerical Modeling of
Detonations : University of California
Press; 1979; pp. 310 -332.
B.M. Dobratz; LLNL Explosives
Handbook; UCRL-52997,
301 -
Figure 1 Frangible Joint Before and After Function
- 302 -
-I r
5 10
Time From Detonation of MDF (usee)
Figure 2 Pressure Time History at Interior of Steel Tube at Stress Riser
- 303 -
0.02'
to
-Q
~ 0.015-
o
2
- 0.01-
4>
8
« 0.005-
u
o
.c
CO
0-
4>
i -0.005-I
Q.
E
<
-0.01
10 20 30
Time From Detonation of MDF (usee)
40
Figure 3 Pressure Time History at 45" From Stress Riser
- 304 -
m
P;
****?&
1*:
. If !
Y
Ml
k_nK
NX
Figure 4 ANSYS Finite Element Model
- 305 -
MODE 2
52.827 HZ
MODE3
102.348 HZ
MODE 4
154.759 HZ
Figure 5 ANSYS Finite Element Model Elastic Normal Modes
- 306 -
FEB 7, 94
6:08:03
NODAL SOLUTION
STEP«3
SUB «56
TIME=.140E-04
SEQV ( AVG)
DHX «. 103667
SUN =606.504
SKX =37224
A -0
B =3660
C =7300
D =10950
E =14600
F =18250
6 =21900
H =25550
=32650
=36500
*.':**»:*k&^''>:
m . : - . :■. " i " "*"* • '" " ^J ' ' • ' -• ' 1 ! ^3 • ' -- ' ■ ' ■"* ' - ' • ' ■' 1 - l -£ ■ ■ ■ ■xz^2Qs<^ ~ Lx/ - ; ' Jk ' ^ii»L-^iJiA ^
Figure 6 Results of Hydrodynamic and FEA Combined Model
- 307 -
Table 1. Explosive Properties Used to Bracket HNS Performance 2
Material
Chemical
Formula
Density
(9/cm 3 )
Detonation
Pressure
(kbar)
Detonation
Velocity
(mm/Msec)
HNS
C 14 H 8 N 6 12
1.60
200
6.80
TATB
C e H 6 N 6 6
1.88
291
7.76
TNT
C 7 H 5 N 3 O e
1.63
210
6.93
- 308 -
UNLIMITED DISTRIBUTION
PORTABLE, SOLID STATE, FIBER OPTIC COUPLED
DOPPLER INTERFEROMETER SYSTEM FOR DETONATION AND SHOCK
DIAGNOSTICS
K. J. Fleming, O.B. Crump
Sandia National Laboratories
Albuquerque, New Mexico, 87123
i
VISAR (Velocity Interferometer System for Any Reflector) is a specialized Doppler
interferometer system that is gaining world-wide acceptance as the standard for
shock phenomena analysis. The VISAR's large power and cooling requirements, and
the sensitive and complex nature of the interferometer cavity have restricted the
traditional system to the laboratory. This paper describes the new portable VISAR,
its peripheral sensors, and the role it played in optically measuring ground shock of
an underground nuclear detonation. The Solid State VISAR uses a prototype diode
pumped Nd:YAG laser and solid state detectors that provide a suitcase-size system
with low power requirements. A special window and sensors were developed for
fiber optic coupling (1 kilometer long) to the VISAR. The system has proven itself
as a reliable, easy to use instrument that is capable of field test use and rapid data
reduction using only a notebook personal computer (PC).
INTRODUCTION
Detailed analysis and accurate models of shock
phenomena and high speed motion require an
instrument that is capable of measuring the high
acceleration of surfaces accurately and non-
intrusively. Dent blocks and stress gauges can only
infer the final velocity of detonations while critical
information pertaining to the acceleration is
unknown. A versatile instrument that optically
measures acceleration, displacement and velocity is
VISAR. VISAR (Velocity Interferometer System
for Any Reflector) uses coherent, single frequency
laser light to illuminate a target that has some
reflectivity. The reflected light is collected and
routed through a modified, unequal leg, Michelson
interferometer. As the target moves, the resulting
Doppler information is detected and electronically
analyzed, then the data are converted to velocity and
displacement time histories using software operating
on a personal computer (PC). The sensitivity,
accuracy, and high bandwidth of VISAR is
attributed to the optical method of measurement and
its 400 MHz bandwidth is primarily limited only by
the electronics in the system.
Although the VISAR technique is excellent for
measuring shock phenomena, there are some
limitations with the conventional VISAR, such as;
inherent sensitivity to adverse environments found
outside the laboratory, hazardous unenclosed laser
beam, high current, voltage and cooling
requirements, and an inability to measure devices not
in the "line of sight" of the laser beam, e.g. through
smoke, tunnels and inside chambers. In an attempt
to improve on the versatility of VISAR, a solid state
system with fiber optic coupling and rugged
components has been developed and rigorously
tested in harsh environments. The fiber optic
coupled sensor used to send and collect the light at
- 309 -
the target is unique from previous techniques and, in
recent tests, has performed flawlessly even after four
months encapsulation in curing concrete. The solid
state VISAR described in this paper was used to
measure ground shock generated by a nuclear
detonation at the Nevada Test Site (NTS).
BACKGROUND
The VISAR was developed by Barker and
Hollenbach 1 primarily for measuring free surface
velocities of materials in gas gun experiments. An
improved version of VISAR, developed by
Hemsing^, electronically inverts and adds the 180°
out-of-phase optical signals that were previously
wasted, which effectively cancels target self-light
and doubles the signal intensity. During fast shock
jumps, the system may miss Doppler information
which can cause discrepancies in measured velocity.
For this reason, Kennedy and Crump 3 developed the
double-delay-leg system. The double-delay- VISAR
takes the return light, splits the optical signal and
routes it through two interferometer cavities with
different sensitivities. The data can then be more
accurately reduced by comparing the results of the
two systems. The conventional VISAR has many
sensitive components mounted on an optical table.
The Fixed-Cavity VISAR, developed by Stanton,
Crump and Sweatt 4 , simplifies the interferometer
cavity by cementing the movable components
together. The result is a rugged, small, easy to use
system with a minimal amount of adjustment.
A low cost, portable VISAR using a diode laser and
a fiber optic coupled sensor has been developed by
Fleming, and Crump 5 with successful velocity
measurements taken on electrically initiated slappers.
The diode's invisible laser light makes alignment to
the target difficult and the aberrated, high
divergence beam profile of the laser is difficult to
propagate through space for any extended length.
Both problems are solved by the development of an
imaging fiber optic coupled sensor^ that has intra-
optic video capabilities. The sensor allows for
remote target measurements and verification of the
correct area of target illumination, (figure 1).
IMAGING FIBER OPTIC COUPLED
INPUT FIBER OPTIC FROM TARGE
RETURN FIBER
OPTIC TO
VISAR
figure 7. Drawing of imaging optical feedback
sensor for VISAR.
THEORY OF OPERATION
In a typical experiment, a laser beam is focused to a
small spot onto a target of interest. The reflected
light is collected and routed to the interferometer
cavity (figure 2). A dichroic mirror is inserted into
the light collecting assembly to transmit the laser
light and reflect the other wavelengths (This
technique is valuable for viewing the target, allowing
for precise alignment of the laser beam.). _
FOCUSINCMX)LLECTING LENS
| TARGET y ^ ^TURNING MIRROR
^/THRUHOLE
t ^06N-16NLASKk )
§|||f^ICHROIC MIRROR
'flllf • — FOCUSING LENS
fVISAR
CAVITY
j
FIBEROPTIC
figure 2. Conventional method for collecting
Doppler information from target
- 310 -
The return light, containing equally distributed S and
P polarization components, is collimated and sent
through the interferometer cavity (figure 3). A
50/50 beamsplitter separates the light so that one
beam travels through the glass "delay bar" and the
other travels through air and an 1/8 wave retarder
before recombining and producing an interference
(fringe) pattern .
tfSLATOR
"INPUT LIGHT
FROM TARGET
MIRROR
MV50 BEAMSPLITTER
rLASS "DELAY BAR"
figure 3. Fixed cavity VISAR schematic showing
beam paths and piezo angular translator (PZAT).
"Data" figures are photodetectors.
In order to obtain quality fringe patterns, the image
distances in both legs of the interferometer must be
equal to within a few thousandths of a inch. If both
legs of the interferometer are air, the measured
distance would be equal. However, the refractive
properties of glass make the image distance in the
glass delay leg farther away than the image distance
in the air reference leg. This relationship is defined
by:
x=h(l-l/n)
where h is the delay leg length and n is the index of
refraction. The distance the light has to travel in the
delay leg is farther than the reference leg and the
velocity of light is slower in glass than in air. Using
the relationship from equation (1), the delay time x is
given by:
x=(2h/c)(n-l/n)
where c is the speed of light in a vacuum. Using
these relationships, the fringe count F(t) relates to
target velocity u(t-t/2) as 7:
XF(t) 1
u(t- r/2) = — .
in which A, is the wavelength of the laser light, Av/v
is an index of refraction correction factor if a
window is used, 6 is a correction factor with respect
to wavelength for dispersion in the delay bar.
Equation (3) may be manipulated to obtain the
velocity-per-fringe (VPF)* constant for the
interferometer. The VPF equation is:
VPF i .-L
2<l + Au/u) l + £
With these relationships, VISAR cavities with
different sensitivities can be designed for optimal
performance with regard to anticipated velocity
versus Doppler resolution parameters. In any
experiment, it is helpful to know that everything is
operating correctly. Active feedback from the
measuring instrument is a good method of assuring
proper operation. The piezoelectric angular
translator (PZAT) performs one such function by
electrically moving a mirror in the cavity, effectively
changing the cavity dimensions. When the cavity
dimension changes by A/2, a 180° phase change
occurs which effectively simulates the fringe record
for a velocity change equivalent to one-half the VPF
value. The return interference signal is monitored
and the experimenter is now able to verify that the
system is functioning correctly.
* The VPF is a numerical constant unique to an
interferometer cavity, typically given as mm/us or km/s. For
instance, a cavity with a VPF of 1 would have an interference
pattern of a 360° sine wave for a target accelerating to 1
mm/us.
- 311 -
In figure 3 t one component of light passes through
the 1/8 wave retarder twice, which makes it 90° out
of phase with the other component. The polarizing-
beam splitting cubes then separate the S from the P
light and each beam is sent to a photo detector
coupled to a digitizer. Recording two 90° out of
phase signals produces an interference pattern that is
a sinusoidal plot. Phase resolution of the signal is
poor when the intensity of the sine wave is at a
maxima or mimima. Making the two sinusoidal
traces 90° out of phase insures that at any point in
time one of the signals will be in a region of good
resolution. Also, target acceleration or deceleration
can be discriminated. During target acceleration,
one signal pattern will lead the other by 90° and a
deceleration will cause the opposite to occur.
SOLID STATE VIS AR DEVELOPMENT
The original intent for the development of the Solid
State VISAR was for a portable "in house" tool that
could be shared by several experimenters and used in
the laboratory or in the field. At the same time the
Defense Nuclear Agency (DNA) was interested in
optical based instrumentation for use at (NTS). One
particular experiment required an "up close"
measurement of ground shock generated by the
detonation. Since the nuclear event yields radiation
and electro-magnetic fields, optical sensors are
preferred because of their relative insensitivity to
these phenomenon. Also, the sensors require no
electricity which adds a greater margin of safety to
personnel. The following are some of the
requirements for the system to function:
• Doppler measurement over kilometer-length
fiber optics
• Rugged system, operating on 120 VAC
• Must run several days with no adjustments
• Sensors must withstand mechanical and chemical
abuse
• Window and sensors must survive concrete
encapsulation and measure ground shock a few
meters from the detonation
• Data acquisition bandwidth limited to 20 MHz
EXPERIMENT DESCRIPTION
Measurement of ground shock produced by the
detonation is important because it contains valuable
information used for analysis and modeling of the
test. This ground shock measurement method uses a
window, with sensors coupled by fiber optics to a
VISAR cavity. The window is oriented towards the
device and the entire area is filled with concrete.
When the device detonates, a shock wave is
transmitted through the concrete and into the
window where the shock wave imparts a particle
velocity in the window. The Doppler shift, which
corresponds to the particle velocity in the window,
is transmitted through the fiber optic to the VISAR
cavity. The fringe data are converted to electronic
signals and stored on digitizing oscilloscopes
(digitizers). The mechanism for triggering the
digitizers is a time of arrival (TOA) gauge. The
TOA gauge is simply a fiber optic loop protruding in
front of the window with a laser connected to one
end and a photodetector attached to the other.
When the shock wave breaks the fiber optic, laser
light no longer enters the detector, it's output
voltage drops, triggering the digitizers in VISAR.
The characteristics of the window and the material
transmitting the shock wave into the window must
be known for accurate particle velocity
measurements. The simplest way to use a window is
to choose a material that has already been
characterized. Unfortunately, the unusual laser
wavelength and the large window thickness required
for adequate recording time (40|as) did not allow
previously characterized windows to be used. The
material chosen for the window used in this
experiment is Schott BK-7 glass, which has good
broadband optical transmittance and is available in
the 8" thick x 14" diameter required for the test.
Several specimens of BK-7 as well as cored samples
of the concrete were analyzed for their shock
properties by impacting them into other known
window materials, then into themselves using a gas
gun as the target accelerator. The results from the
analysis, commonly called a Shock Hugoniot,
- 312 -
determine whether the material is suitable for the
shock pressure predicted for the event. The data
also correlate the impedance mismatch at the
grout/glass interface. The anticipated shock
pressure for the NTS test, a few meters from the
device, is « 70 IcBar in the grout. Figure 4 is a
display of the type of plots for the shock pressure
tests obtained using BK-7 as the impacted material.
The BK-7 behaves like fused silica up to 90 kBar.
Although BK-7 does not turn opaque at pressures
above 90 kBar as fused silica does, the non-linear
"shock-up" makes particle velocity correlations
more difficult.
1™
-^"•tei
K**r}
J
s~~lS
K^
1
at
£***•
ft
%M Tmm mm
m LM LM ■.«• i.m MM
TIME <US>
figure 4. Data plot of BK-7 particle velocity versus
time.
The VISAR designed for the underground test
contains a diode pumped Nd: YAG laser operating at
1319 t|m wavelength, with a CW output of 160
mW, and a 5 kHz, single frequency linewidth. This
laser is a good choice for this system because it is
stable, has low sensitivity to optical feedback, and
the wavelength exhibits very low attenuation and
high bandwidth in silica fiber optics. This high
performance is due, in part, to the self cancellation
of different wavelength-dependent dispersion effects
that occur in fiber. The photodetectors in the
system are comprised of indium-gallium-arsenide
(InGaAs) photodiodes coupled to low noise/high
gain operational amplifier circuitry. The peak
sensitivity for these detectors happens to be at 1320
rim wavelength, which not only affords greater
sensitivity, but also increases the signal to noise
ratio. The linear response range for the
detector/amplifiers is DC to 125MHz with a linear
response better than 3% and an output voltage of
40mV/nW of light at 1320 rim wavelength (The flat
linear response is critical for accurate data
collection).
One of the most critical parts of the system design
was the fiber optic coupled sensors. Laser radiation
is injected into a 50 micron graded index, multimode
fiber optic connected to sensors which image the
fiber optic onto the rear surface of the window. The
return light reflected from the window's rear surface
is collected and injected into a 100 |im step index,
multimode fiber optic connected to the VISAR
cavity. A redundant sensor is linked to the VISAR
cavity in the event of damage to one of the sensors
(figure 5). Correctly designing the optical train is
paramount to attaining good signal strength that
won't degrade under harsh environmental conditions
(Obviously, after the sensors are encapsulated in 100
foot thick concrete, re-aligning is impossible.).
There was some concern about stress induced
polarization after observing wildly fluctuating S and
P ratios when the fiber optic was bent. These
fluctuations in polarization will change the sine-
cosine relationship critical to accurate data analysis.
In most cases, this polarization problem occurs
when highly polarized laser beams are injected in
short lengths of fibers. The root cause is the mode
structure is not fully mixed in the fiber optic and
stressing the fiber optic redistributes these modes
causing a change in the polarization (The laser
output is single mode-single frequency and should
not be confused with fiber optic propagation
modes.). Since there is no room for error on the
real test, three solutions are incorporated to remedy
the problem: installing a mode scrambler that
pinches the fiber optic into a serpentine shape, using
a long fiber optic to mix the modes, installing a
rotatable linear polarizer at the entry into the
- 313 -
TIME (microseconds)
figure 6. Three of several TOA gauges
interferometer cavity. The new modifications solved
the problem.
The sensors perform three functions; collimating and
1
0.5
| -0.5
-1
-1.5
•2
0.I
figure 7.
90°out<
, r ^~-
h
/
j
/
■ )
i^
l
955.06 •*
►54. Wm
m
i.i.i
95 0.95 0.95 0.96 0.96
Tlme(ms)
Raw, unreduced data. Notice the
f -phase signals.
focusing the laser radiation onto the rear surface of
the window, collecting the return light, and injecting
the light into the return fiber optic. The sensor
configuration is similar to figure 1 except that the
camera is omitted, since there is no need to see the
rear window surface.
TOA GAUG ES
I =
FIBER OPTIC LOOP
SHOCK
WAyE ■
CKUP SENSOR ^N,
ER OPTIC SENSOR
8"x 14" BK7 GLASS
MIRRORED COATING
FOCUSING
OPTICS
SOLID STATE LASE
50 um fibe r
;>ptic cable
iobi
100 um fiber
optic cable
DETE 7TOR
- VIS AR CAVITY
figure 5. Diagrammatic layout of the window,
sensors, time of arrival (TOA) gauges, VISAR
cavity, and laser.
Although the primary function of the TOA gauge is
to trigger the digitizers, utilizing a TOA array
provided additional shock data. Several gauges
were placed around the window with the tips of the
TOAs staggered to intercept the shock wave front
at different points in time (figure 6). As the shock
front breaks the TOAs, the digitizers record the
time-of-break that is then correlated to shocks
arrival time and velocity.
EXPERIMENTAL RESULTS
The VISAR and TOA gauges performed with
strong, clean signals recorded on all instrumentation
channels. The Doppler information, in unreduced
form, is shown in figure 7. The signal strength is
lVolt peak to peak which is well above the noise
floor that has, in the past, caused difficulty in
accurate data reduction. The 90° phase relationship
between the two traces indicates the stress induced
polarization problem has been cured.
Figure 8 shows the reduced data. There is an
impedance mismatch between the BK-7 and the
grout but the shock Hugoniot for these materials is
- 314 -
known and was used in calculating the final particle
velocity. The peak recorded particle velocity was on
the order of 0.6 mm/us, which corresponds to a
pressure at the interface of 85 kBar.
figure 8. Reduced data showing particle velocity
versus time
The results indicate that the yield of the device was
greater than expected (60 kBar). The choice of
BK-7 was fortunate because if fused silica was
available and used, the data would have been lost.
(Fused silica is known to become opaque at
pressures above * 82 kBar.) The BK-7 is apparently
able to withstand slightly greater shock pressures
before going opaque and at 1/3 the cost, it is
significantly less expensive.
ACKNOWLEDGMENTS
This work was performed at Sandia National
Laboratories, Albuquerque, NM for the United
States Department of Energy under Contract DE-
AC04-76DP0089. This project was truly a team
effort and the authors gratefully thank the following
people for their participation:
Leonard Duda- financial and technical design
support, John Matthews and Richard Wickstrom-
software support, Larry Weirick, Mike Navarro,
Heidi Anderson- BK-7 characterization & gas gun
support, Bill Brigham, Theresa Broyles, Dan
Sanchez- Electronic design & fabrication, Dan Dow-
mechanical fabrication, Terry Steinfort, Robert
Vasquez- mechanical design & installation, and
William TarbelU shock analysis. A special thanks to
Lloyd Bonzon for supporting the concept in its
infancy.
REFERENCES
1. L.M. Barker and R. E. Hollenbach, Laser
Interferometer for Measuring High Velocities of
Any Reflecting Surface. Journal of Applied
Physics 43:11 (Nov 1972)
2. W.F. Hemsing, Velocity Sensing Interferometer
(VISAR) Modification. "Review of Scientific
Instruments 50:1 (Jan 1979).
3. IE. Kennedy, Org 7130, private communication.
4. KJ. Fleming, O.B. Crump Jr., Portable. Solid
State VISAR . SAND92-J36L April, 1992
5. O.B. Crump Jr., PL. Stanton, W.C. Sweatt, The
Fixed Cavity VISAR. SAND92-0162 (March
1 992). Sandia National Laboratories,
Albuquerque, NM.
6. K.J. Fleming, Fiber Optic Coupled Probe for
Versatile Interferometry . Department of Energy
Patent Disclosure SD-5034, S-74-181
7. L.M. Barker and K.W. Schuler, Velocity
Interferometry System . Journal of Applied
Physics. 45,3692(1974).
- 315 -
DEVELOPMENT AND QUALIFICATION TESTING OF A
LASER-IGNITED, ALL-SECONDARY (DDT) DETONATOR
Mr. Thomas J. Blachowski Mr. Darrin Z. Krivitsky
CAD R&D/PIP Branch CAD Weapons/Aircraft Systems Branch
Indian Head Division Indian Head Division
Naval Surface Warfare Center Naval Surface Warfare Center
Indian Head, MD 20640 Indian Head, MD 20640
Mr. Stephen Tipton
B-1B Systems Engineering Branch
Oklahoma City
Air Logistics Center
Tinker AFB, OK 73145
Abstract;
The Indian Head Division, Naval Surface Warfare Center (IHDIV, NSWC) is
conducting a qualification program for a laser-ignited, all-secondary (DDT)
explosive detonator. This detonator was developed jointly by IHDIV, NSWC and
the Department of Energy's EG&G Mound Applied Technologies facility in
Miamisburg, Ohio to accept a laser initiation signal and produce a fully
developed shock wave output. The detonator performance requirements were
established by the on-going IHDIV, NSWC Laser Initiated Transfer Energy
Subsystem (LITES) advanced development program. Qualification of the
detonator as a component utilizing existing military specifications is the
selected approach for this program. The detonator is a deflagration-to-
detonator transfer (DDT) device using a secondary explosive, HMX, to generate
the required shock wave output. The prototype development and initial system
integration tests for the LITES and for the detonator were reported at the
1992 International Pyrotechnics Society Symposium and at the 1992 Survival and
Flight Equipment National Symposium. Recent results are presented for the
all-fire sensitivity and qualification tests conducted at two different laser
initiation pulses.
- 317 -
Introduction:
The INDIV, NSWC
Devices (CADs), and Ai
The CAD Engineering Di
development and engine
sources , energy transm
CADs, and their asscci
three services. The C
policy and conducts se
power signal transmiss
stores /weapons deliver
In addition, administr
Improvement Programs (
for CADs is performed
for cartridges, CADs,
authority.
s the lead service for cartridges, Cartridge Actuated
rcrew Escape Propulsion Systems (AEPS) for all services.
vision at IHDIV, NSWC manages and implements the
ering functions ir. the fields of ballistic power
ission systems, and control devices such as cartridges,
ated signal or energy transmission subsystems for the
AD Engineering Division also recommends and establishes
rvice qualification for cartridges, CADs, and related
ion systems for aircrew escape and survival and
y and deployment for the Department of Defense (DoD) .
at ion of research, design, development, and Product
PIP) for ignition devices and -electro-explosive devices
by the Division. Development of design specifications
and related ballistic systems is maintained under this
Background t
The IHDIV, NSWC has pursued development of LITES for these applications.
LITES utilizes chemical f lashlamps to generate light which is amplified by a
laser rod, focused into fiber optic transfer lines, and delivered to optically
initiated pyrotechnic output devices. Proof-of-Principle tests and the
exploratory development program (13th International Pyrotechnics Society
Proceedings - 1988) were completed. An advanced development program was
conducted to miniaturize the laser housing while maintaining the proven
neodymium doped phosphate glass rod and commercially available flashlamp
concept. The miniaturized laser (Figure 1) is a mechanically actuated device
which generates sufficient energy, when delivered through a bundle of fiber
optic lines, to initiate an optical output device. The LITES advanced
development program has designed optical output devices which produce
ballistic pressure or a shock wave output (detonator) as required for a
specific aircrew escape system application (18th International Pyrotechnics
Society Symposium - 1992). FLashlam-s
f-m — -**'*^'
| ussa ROO
PUCSHATS GLASS
1.15 INCnSS
INITIATION m£C*AVSm
F:S=K CrTC LINs
Figure 1: LITES Mechanically Actuated Laser Assembly
- 318 -
As part cf th
Mound AppL ied Techr.
(Table l") for the I
to-de to nation trans
wavelength input ar.
commercially aval la
requirements , alone
a Shielded Mild Det
independent cf the
specifically for us
detonator to be use
line configuration
technology required
design goal through
Pyrotechnics Societ
v Svmc
:t~:s :::;:
art , t r.
rough
a. set!
es cf discussions with EG&G
^^95 ^ 1 r.Z Z
V N S **
C est
s c 1 l s h e
d the following requirements
r— igr. i «s -
deccr.a
tor.
Soecif
icaily, this deflagration-
(DO? j cev
ice ( F
igure
2 ) wou
id accept a 1.06 pm laser
culd cr.lv
cental
r. set
tndary
explosives that are
from save
ral sc
urces
in the
United States. These
th the win
— '-j w a . .
c gen
e rat ion
of an output equivalent to
ting Core:
(SHDGj
tip,
allows
the optical detonator to be
er attic s
ignal
tission
system. Although developed
ith LUES,
e f f c r
t s we
re take
n to permit this optical
%- a variet
v cf e
r.ercv
culse
duration and fiber optic
er ignitic
n s v s t
ems .
x n a ^ >-i
ition, transition of the
manuf accu
re the
detc
r.ator t
o industrv was held as a
this deve
Icemen
t pro
g r am (1
3th International
vT.tosiu" -
1992 )
Detonator Requirements
•
All secondary explosive device
•
Flat window configuration
•
Shielded Mild Detonating Cord (SMDC) tip output
•
Hermetic all v sealed
•
Structurally sound, all Reactants contained
•
No proprietary components
•
Transition government developed technology to
industry for competitive procurement
Table 1: Laser-Ignited Detonator Design Requirements
Figure 2: Laser-Ignited, All Secondary (DDT) Detonator
- 319 -
Test Program Preparation:
Definitions:
Prior to establishing the qualification test matrix and performance
requirements for the laser-ignited detonator itself, it was necessary to
define the components and the parameters involved in the overall aircrew
escape system. For this paper, an Ordnance Initiation System is defined as a
"^system consisting of three distinct components: (1) a signal generator and
controller which is capable of establishing an initiation pulse of sufficient
intensity at the required time interval, (2 ) a signal transmission system
capable of transferring the pulse to all output devices within the envelope of
the application, and (3) output devices (initiators or detonators) which
either perform the required work function directly or initiate a second in-"
line device which performs the function. As previously described, these
output devices include items such as initiators, squibs, gas generators,
electro-explosive devices, thermal batteries, cutters, and detonators. An
example of an aircrew escape system ordnance initiation system is shown in
Figure 3 .
>
Figure 3: Generic Aircrew Escape System
During the evaluation of an ordnance initiation system, the parameters
of the output devices must be clearly identified. Several existing government
specifications clearly define the "all fire" energy of an output device and
the "no fire" energy of an output device. The "all fire" energy level of an
output device is defined as the minimum amount of energy or power required to
initiate that output device in its final configuration with a reliability of
0.99 at a 0.95 confidence level. The "all fire" energy level will be
determined by any suitable test method consisting of a sample size of not less
than 20 output devices. This quantity is not defined in the existing
specifications; however, a statistically significant sample size must be
tested to verify the stated energy levels.
Threshold energy levels, a 50% initiation energy level, or a reliability
of 0.9999 at a 0.98 confidence level are technically very useful values and
may be required for a specific application. Any of these values; however,
cannot be identified as the "all fire" energy level of an output device.
Conversely, the "no fire" energy level of an output device is the
maximum amount of energy or power which does not initiate the output device in
its final configuration within five minutes of application. At this
initiation level, less than 1.0 per cent of all output devices at a level of
confidence of 0.95 can actuate. Again, the "no fire" energy level will be
determined by any suitable test method consisting of a sample size of not less
than 20 output devices.
- 320 -
Current Specifications:
d general specifications in place to specifically address
ultimately implementation of laser initiation system
There are no
qualification and ultimately implc
technology in the U. S. Department of Defense, the Department of Energy, and
the National Aeronautics and Space Agency (NASA). Much discussion has taken
place over the past years as to which existing specification or series of
specifications are most applicable to this new technology. A partial list has
"been compiled of the specifications most often mentioned in these discussions
(Table 2) .
•--^-Specification \ | -y^-:. Title
MIL-STD-1316
• Safety Criteria for Fuze Design
MIL-STD-1512
• Design Requirements and Test Methods for
Electrically Initiated Electroexplosive
Subsystems
MIL-STD-1576
• Safety Requirements amd Test Methods for
Space Systems Electroexplosive Subsystems
MIL-E-83578
• General Specification for Explosive Ordnance
for Space Vehicles
MIL-C-83125
• General Design Specification for Cartridges
and Cartridge Actuated/Propellent Actuated
Devices
MIL-C-83124
• General Design Specification for Cartridge
Actuated Devices/Propellent Actuated Devices
MIL-D-81980
• General Design Specification for Design and
Evaluation of Signal Transmission Subsytems
HIL-I-23659
• General Design Specification for Electric
Initiators
MIL-D-21625
• Design and Evaluation of Cartridges for
Cartridge Actuated Devices
MIL-D-23615
• Design and Evaluation of Cartridge Actuated
Devices
Table 2: Current Specifications for Laser Technology Implementation
Specification Selection Process:
To successfully conduct and complete development and qualification
testing on the laser-ignited detonator and to ultimately implement this device
and other laser initiation system technology into next generation aircrew
escape systems, three different approaches have been identified (Table 3, next
page).
- 321 -
APPROACH ! ADVANTAGES
DISADVANTAGES
NEW
SPECIFICATION
• GENERAL FORMAT
• TECHNOLOGY SPECIFIC
• LENGTHY APPROVAL PROCESS
• NEW REQUIREMENTS
• TECHNOLOGY NOT MATURE
SYSTEM
SPECIFIC
DOCUMENT
• SPECIFIC REQUIREMENTS MET
• WRITTEN TO SCHEDULE
• ?JZ/?SQ DOCUMENTS PREPARED
• NOT GENERAL
• VERY DETAILED
EXISTING
SPECIFICATION
• GENERAL FORMAT
• NO NEW REQUIREMENTS
•- PRECEDENCE
• DATED REQUIREMENTS
• MUST 3E AMENDED
Table 3: Specification Approach Advantages/Disadvantages
The first approach is to generate a new specification for laser
initiation sysiem components . The general format of this type of
specification will allow implementation of the technology on a wide variety of
platforms. The technology definitions included in this specification will
allow Program Managers and design engineers the ability to better compare
alternatives during the preparation of Trade Studies, program plans, etc. The
required testing and reporting will better establish this technology baseline
that will serve all users.
The disadvantages of this approach are severe. Laser initiation
technology is rapidly advancing to new levels. What was thought to be a
technical barrier a few years ago has changed. As these continued
advancements occur, there has not been sufficient time for the "off-the-shelf
components to mature. The baseline has been moving. Writing a specification
without fully identifying this baseline is very difficult. Once an agency has
officially undertaken the specification writing task, there is a well defined
and lengthy approval process through any Department of the Government. With
the constantly changing baseline of the technology and the lengthy approval
process, this approach is unattractive.
The second approach is to allow Program Managers to
specifications for a single system. The advantages of th
numerous. The Program Managers have a "hands on" feel of
their platform. Specialized needs, power requirements, s
performance among other parameters would be contained in
Potential suppliers then have a defined goal to design an
technology alternative as a solution and all the pre-sele
reporting needs are highlighted. Competing solutions, tr
overall program technical risk are clearly outlined to th
This overall approach will be conducted for every system;
of assets allocated (management time, engineering assets)
prepare
is approach are
the requirements for
afety margins, output
this single document.
individual
ction testing and
ade studies, and the
e Program Managers.
however, the amount
is great.
This leads directly into the disadvantages of this
detailed system specific document requires an investment
time and resources. The amount of technical detail in t
depend on the individual program office or on the contra
their preparation. Issues such as competitive procureme
technology or sole sourcing the procurement to a particu
life of the platform must be addressed at this step. If
document becomes too detailed, sole source procurement o
very likely. Upon completion of these documents, they rr.
to other platforms. Some requirements may transition to
well; however, most will not.
approach. The very
of Program Management
hese documents will
ctor assigned with
nt of the selected
lar vendor for the
the system specific
r its variations, are
ay not be applicable
a general system very
- 322 -
The third approach is to utilise existing specifications to implement
laser initiation technology into current and planned platforms. There are
several advantages to this approach. Existing specifications are written to a
general format thus allowing all alternative technologies to design
engineering solutions. The previous test requirements for each platform are
well defined and established. Potential vendors for a specific platform have
a defined baseline of past knowledge to build upon. Precedence has been
"established by the Program Managers utilizing these specifications. There are
no new technical limitations for implementing laser initiation technology onto
any platforms.
The disadvantages of this approach include the time dated nature of all
the listed specifications (Table 1), and they must be amended somewhat to
address new technical concerns. The listed specifications were written to
address the general design issues of that time and, even including amendments
and re-issuances, do net address some of the attributes of laser initiation
technology. Minor modifications to these specifications to address these
special attributes allow these documents to govern implementation of a new
technology onto current and future DoD platforms.
Existing Specifications Selected:
Following this process, the third approach of selecting existing
specifications was chosen to allow for implementation of laser initiation
system technology into DoD applications. The specifications selected by
IHDXV, NSWC are as follows:
(1) the signal generator and controller (Laser Assembly) will be
governed by MIL-C-83124,
(2) the signal transmission system (STS) will be governed by
MIL-D-81980, and
(3) the optical output devices (Initiators and detonators) will be
governed by MIL-C-83125.
These documents were selected because MIL-C-83124 and MIL-C-83125 apply
to energy sources and ballistic devices (cartridges and CADs) for all three
services. This tri-service approval is very attractive in making the
specification requirements as general as possible while still meeting a DoD
baseline. For the STS, MIL-D-81980 was selected. This document is a
Department of the Navy specification but has precedence in testing energy
transfer systems for the other services.
The laser-ignited detonator is an optical output device and the
Qualification Test Procedure (QTP) to allow for qualification and
implementation of this device was written against the requirements specified
in MIL-C-83125.
Qualification Test Procedure:
A QTP was prepared by IHDIV, NSWC to detail all environmental test
conditions and output performance requirements for the laser-ignited
detonator. As previously described, this procedure governs only the laser-
ignited detonator; the laser signal generator (Laser Assembly) and the fiber
optic signal transmission system will not be subjected to these environmental
tests. All of the environmental tests and required number of detonators are
shown in Table 4 (next page). The test matrix requires 161 detonators to
successfully demonstrate this technical concept.
- 323 -
Environment*] Tcsi /
Quantity
4 J «
6
9 9
i
9
9
12
12
6
9
30
10
30
Visual Inspection
4
6
6
9
9
9
9
12
12
6
9
30
10
30
X-Riy <fc n-Rjy Inspection
4
6
6
9
9
9
9
12
12
6
9
30
10
30
Dry Gas Leakage
4
6
6
9
9
9
9
12
12
6
9
30
10
30
Noa-Electric Initiation
(-90° F)
4
40* Drop Test
6
6* Drop Test (70° F) *
6
• Shock
9
9
9
9
• TSH&A
9
9
9
• Low Temp. Conditioning
9
9
• VTb ration
9
Cook-Off
12
Hifh Temp. Exposure (70* F)
12
Salt Fog (70* F)
6
Hi$h Temp. Storage (200 # F)
9
Functional Low Temp.
(-65* F)
30
Functional Ambient Temp.
(70* F)
10
Functional Hi^h Temp.
(225* F)
30
Table 4: Qualification Test Matrix for Laser-Ignited Detonator
Table 4 Notes:
(1) TSH&A is defined as Temperature, Shock, Humidity, and
Altitude Cycling.
(2) The temperature in parentheses is the functional firing
temperature of the detonators,
(3) The "•" denotes SEQUENTIAL TESTING which means the nine
vibration detonators were subjected to all four
environments and functionally tested; three detonators
at -65° F, three detonators at 70° F, and three
detonators at 200°F. The Low Temp. Conditioned
detonatorB were also subjected to TSH&A cycling and
Shock prior to functional tests as described above.
(4) For the 40' Drop and Cook-Off Tests, no functional
test firings are required. The detonators must survive
these environments and be safe to handle and discard.
- 324 -
Successful completion of this QT? demonstrates the laser-ignited
detonator concept. Additional testing will be required prior to release of
this device to service use. The application specific locking connectors (both
from the fiber optic transmission system to the detonator and from the
detonator to its work performing device) must be demonstrated through a
similar environmental test series prior to aircrew escape system
implementation.
Short Pulse Qualif ication Test Results:
Defining the specific laser energy pulse, its duration, and the
configuration of the energy delivery system was performed at this time.
Driven by a specific aircrew escape system application, the viability of a
microsecond(s) long pulse duration was considered. Based on the
recommendations from EGSG Mound and by this Activity's research, the laser-
ignited detonator was capable of being successfully initiated with a pulse of
this duration. A 150-microsecond pulse duration delivered through a hard clad
silica (numerical aperture of 0.37) fiber optic line was established as the
initiation condition. A 20 unit Neyer threshold test* was conducted to
determine the all-fire energy of the laser-ignited detonator. Based on these
test results, the 0.99 reliable at a 0.95 confidence interval energy value was
determined to be 131.3 milli joules in this configuration. The diagnostic
equipment was verified for this conf icuration (Figure 4). To further insure
initiation of the detonator in this configuration, the following values were
used to begin the qualification testing:
• 150 millijoules of laser energy
• 150 microsecond pulse duration
• 200 micron fiber (NA « 0.37)
Nd:YAG Laser Pulse
0.10
0.08
« 0.06
o
M
0.04
>
J5
0.C2
GC
0.00
•0.C2
•50 50 100
Time - microseconds
150
200
Figure 4: 150 Milli joule Laser Energy Pulse from Quanta ray DCR-2A Laser
Ten detonators were selected from the Functional Ambient Temperature
group of the QT? to begin the testing (Table 5, next page). The first six
detonators successfully initiated and met all the performance requirements.
The seventh detonator did not initiate. After a series of discussions, IHDIV,
NSWC and EG&G Mound representatives agreed to continue the testing. The
eighth and ninth detonators functioned as designed. The tenth detonator did
not initiate. At this point, the qualification testing was halted.
1 - "More Efficient Sensitivity Testing"
Applied Technologies - October 20, 1989.
Barry T. Neyer, MLM-3609 EG&G Mound
- 325
Tcrt
10
Function
Temp* ram re
70* F
70* F
70° F
70° F
70* F
70° F
70° F
70° F
70° F
70' F
Pre-Shc* Tent*
(ml)
151.9 ± 1.3
151.2 ± 0.4
149.5 ± 0.3
150.3 ± 0.6
149.7 ± 2.2
149.7 ± 1.7
149.6 ± 1.4
152.3 ± 0.4
148.7 ± 0.6
150.9 ± 2.6
Function?
YES
YES
YES
YES
YES
YES
NO
YES
YES
NO
Pulae DuT*Lk>n
150
150
Function Time
(pscc}
55.5
77.5
150
58.0
153
50.5
150
63.5
153
71.5
150
150
60.0
149
73.0
156
Indent
Cm.)
0.058
0.052
0.051
0.055
0.055
0.053
0.051
0.051
Table 5: Short Pulse Laser-Ignited Detonator Test Results
Short Pulse Failure Investigation:
A complete failure investigation was undertaken to determine the cause
of the non-initiation of these detonators and to establish engineering
solutions to eliminate these non-initiation causes from the design concept.
This was a wide ranging investigation which included a re-assessment of the
window design and status during the testing, the energetic material post-test
condition, and the diagnostic test equipment itself.
The fiber optic line delivering the required energy pulse was examined.
A standard SMA-905 connector was used to link the line to the detonator. This
connector centers the fiber optic line in a stainless steel sleeve with epoxy
filling the surrounding gap. One potential failure cause was that if this
epoxy slightly covered the face of the fiber or at the tip of the fiber, the
epoxy was vaporized as the energy pulse exits the fiber. This phenomena would
block the laser energy from the window and result in a greatly decreased
amount reaching the energetic material, inducing non-initiation of the
detonator.
A second cause involving damage to the window was also investigated.
During detonator manufacture, optical transmission of the window was tested
prior to loading of the energetic material. This detonator design requires a
contact between the fiber optic line and the window. Due to this design and
the optical transmission testing, surface damage occurred to the window.
These damage patterns were identified for all detonators and these patterns
were grouped into eight categories: . flawless windows, small pits in the
center of the window, small pits in the center and damage outside the center
of the window, very light scratches and small dots on the window, deep
scratches, film coating on the window, a deep inclusion in the window, and
small center dots in the window with extra debris. Either or both of these
investigated causes could result in non-initiation of the detonator.
- 326 -
Based on this completed- failure investigation and the assets available
to continue this development and qualification program, the overall system
initiation conf igura tier, was re-addressed. A question was posed to the
aircrew escape system and aircraft system designers, "Could a system be
designed, within existing aircraft parameters, to generate and support a laser
pulse duration of 12 milliseconds?" The response from these designers was
that a 12 millisecond long pulse could be implemented to resolve the
demonstrated failure pattern.
Long Pulse Qualification Test Results :
Re-establishing the detonator conceptual design initiation pulse
duration was the primary solution to the non-initiation experienced during the
short pulse qualification testing. This longer duration lowers the power
density of the pulse and greatly lessens the potential for laser induced
damage in the window and/or the fiber optic line. In addition, lowering this
power density and increasing the pulse duration renders slight imperfections
in the window less critical to successful initiation of the detonator. This
pulse duration allows the laboratory designed and developed detonator to be
demonstrated as rugged enough for field applications* No enhancements, such
as re-polishing the windows to reduce surface damage, were performed on any of
the environmentally stressed detonators.
As for the transmission system itself and the diagnostic test equipment,
to further reduce the possibility of inducing a non-initiation, a glass/glass
fiber optic line was selected (with a numerical aperture of 0.22). The SMA-
905 end connector was assembled into this line utilizing a minimum of epoxy
that was held away from the fiber tip itself* A 20 unit Neyer threshold test
was conducted in this configuration to determine the 0.99 reliable at a 0.95
confidence interval all fire energy of the detonator. Based on this test
series, the following values were used for the long pulse qualification
testing:
• 132.8 millijoules of laser energy
• 12 millisecond pulse duration
• 200 micron fiber (NA « 0.22)
The 132.8 millijoule, 12 millisecond laser energy pulse was confirmed
through the diagnostic test equipment as before. The Function Time (defined
as the time from laser pulse initiation to the output shock wave impacting a
detector at the back of the test fixture) of the detonators was recorded and a
minimum of 0.040 inch indent was established as the detonator output
requirement. A total of 131 detonators were functionally tested using the
initiation configuration and the results are grouped by environmental test
condition (Table 6, next page). An additional 18 detonators successfully
completed the QT? requirements without undergoing functional testing (the 40'
Foot Drop Test and the Cook-off detonators). Also, 12 detonators that had
undergone environmental conditioning were functionally tested for information
only (Table 7, second page). Using the long pulse configuration, the laser-
ignited detonator did not achieve all of its design goals for this QTP.
- 327 -
■■"■■ Environmental
Function
Temp. (*F)
I Required
/ Successful
Function
Tune (msec.)
Indent
Other
Results
NON-ELECTRIC
INmATION
-90* F
4
4
3.59 ± 0.89
0.053 ± 0.003
NONE
6 FOOT DROP
70" F
6
6
4.54 ± 2.23
0.053 ± 0.002
NONE
SHOCK
-65* F
70' F
200* F
3
3
3
3
3
3
5.55 ± 0.68
3.21 ±0.77
6.33 ± 0.42
0.054 ± 0.002
0.054 ± 0.001
0.050 ± 0.002
NONE
NONE
NONE
SHOCK, TSH&A
-65° F
70* F
200* F
3
3
3
2
2
2
7.57 ± 1.42
6.36 ± 0.23
6.99 ± 1.18
0.048 ± 0.001
0.O48 ± 0.004
0.O43 ± 0.002
(0.027)
(0.025)
(0.026) {0.041}
SHOCK, TSH&A,
LOW TEMP.
-65* F
70*F
200* F
3
3
3
3
1
2
6.16 ± 0.21
6.85 ± 0.84
6.41 ± 0.48
0.050 ± 0.0W
0.046
0.045 ± 0.001
NONE
(0.016) (0.031)
(0.025)
SHOCK, TSH&A,
LOW TEMP.,
VIBRATION
-65* F
70* F
200* F
3
3
3
1
2
3
6.18 ± 1.00
3.30 ± 1.02
7.59 ± 1.23
0.042
0.055 ± 0.000
0.O4S ± 0.004
(0.031) (0.033)
1
NONE
SALT FOG
70' F
6
6
3.65 ± 1.06
0.051 ± 0.004
NONE
HIGH TEMP.
STORAGE
200* F
9
8
6.60 ± 1.78
0.050 ± 0.003
(0.031)
LOW
TEMPERATURE
-65 # F
30
30
3.62 ± 1.12
0.051 ±0.003
NONE
AMBIENT
TEMPERATURE
70* F
10
10
2.83 ± 0.43
0.053 ± 0.002
NONE
HIGH
TEMPERATURE
225* F
30
25
7.71 ± 1 JO
0.051 ± 0.003
(0.025) (0.025)
(0.033) (0.025)
(0.024) {0.042}
Table 6: Long Pulse Laser Ignited Detonator QTP Results
Table 6 Notes:
(1) The Other Results indicated in " ( ) M are
unacceptable indents. They are below the QTP mandated
0.040 inch indent.
(2) The Other Results indicated in "{ } M are marginal
indents. These very closely achieve the 0.040 inch
indent .
(3) The n l n indicates an initiation failure.
- 328 -
[ Environmental
Temp. CD
# Rtqurrcd
# Successful
Function
Time (msec.)
I~dcn!
Go.)
Other
Resuhs
COOK-OFF
SURVIVORS
375 °F / 70* F
400* F / 73* F
3
1
2
11.85 ± 3.21
5.36
0.049 ± 0.001
(0.016)
(0.011)
HIGH TEMP.
EXPOSURE
325° F/70° F
300° F / 70° F
n 75* F ■ "0* F
3
2
3
12.32 ± 2.66
8.76 ± 1.36
13.18 ± 0.54
ALL £ (0.015)
(0.025) (0.022)
(0.021) (0.023)
Table 7: Long Pulse Laser Ignited Detonator Non-QTP Results
Table 7 Notes:
(1) The Other Results indicated in " ( ) " are
unacceptable indents- They are below the QT? mandated
. 040 inch indent .
(2) The "2 M indicates an initiation failure.
Long Pulse Failure Investigation:
At this writing, the long pulse failure investigations are underway.
There are two separate investigations being conducted by IHDIV, NSWC and EG&G
Mound personnel: the first is to determine the cause of the two non-
initiations, and the second is to determine the apparent temperature and/or^
temperature cycling effect on the detonator and its not consistently achieving
the minimum 0.040 inch indent into an aluminum dent block.
Determining the cause of the non-initiations is the first priority. Of
the 143 functional detonator tests completed, there were 2 non-initiations.
Both of these detonators had been subjected to elevated temperature
environments (one during the TSH&A cycling had seen 160° F and the other
during High Temperature Exposure had seen 275° F for a period of 12 hours).
The detonators that had passed the indent requirement exhibited longer
function times after being subjected to elevated temperatures. Some of the
detonators in the non-QTP test series had even functioned after the 12
millisecond laser pulse was completed. For the detonators subjected to cold
environments, the function times are somewhat faster and all of these indents
are acceptable. The diagnostic test set-up and operator handling procedures
are also under review as part of this failure investigation. All of this
information is being evaluated to determine the cause of these two non-
initiations.
The second investigation to determine the lack of sufficient indent into
the dent block is also of great importance. Obtaining the 0.040 inch indent
demonstrates this HKX, laser-ignited detonator is a one-fcr-one replacement
candidate for the widely used SMDC lines and output tips which use HNS
(Hexanitostilbene) as their energetic material. Demonstrating an identical
indent for this laser-ignited detonator will greatly reduce the number of
future tests required to assure this one-for-one replacement in all fielded
applications. To begin this investigation, a record of the post-test
detonator column condition is being compiled. For tests that achieved the
0.040 inch indent, the column had fragmented or blossomed outward. In some
cases, this expansion had not fragmented the metal column, just widened it
slightly. And, in some other cases, the output column of the detonator
remained the same size. Several theories are being explored to explain these
test results. Once these theories are proven through additional testing,
engineering solutions can be implemented to the detonator design concept to
eliminate the potential of low indents.
- 329 -
Conclusions :
This paper has presented a new laser-ignited detonator concept developed
jointly by IHDIV, NSWC and EG&G Mound. Development and qualification methods
for this new technology and new device have been presented using existing
military specifications to establish the acceptance requirements. Diagnostic
test equipment development, set-up, and specialized operating procedures were
designed to demonstrate the performance of the detonator. Two Neyer
"sensitivity test series were conducted to establish the "all fire- energy
level. Two different initiation systems (different pulse durations, all fire
energy levels, and connector interfaces) were investigated during this
program. The laser-ignited detonator design was demonstrated as feasible
within the system constraints. The concept^ is not completed. The reasons for
non-initiation and the low indent results must be identified and resolved
before this device is subjected to further system tests. Through the on-going
failure investigations, solutions to these shortfalls are seemingly
attainable. Upon implementation of these solutions, this detonator will be
subjected to a final test series. Successful completion cf this delta
qualification test series will allow the detonator to be released for field
applications including aircrew escape systems.
Biography;
Mr. Thomas J. Blachowski has held his present position as an Aerospace
Engineer in the CAD Research and Development/Product Improvement Program*
Branch at IHDIV, NSWC for the past 8 years. Ke has been directly involved in
LITES, laser initiation, and laser detonator development efforts since 1988.
In addition, he has managed the Cartridge Actuated Device (CAD) Exploratory
Development and Advanced Development programs since 1989. Mr. Blachowski
received his Bachelor of Science degree from The Ohio State University in
1985.
- 330 -
EXCELLENCE
BY DESIGN
ENGINEERING DIRECTORATE
NA
Lewis Research Center
Pyrotechnically Actuated Systems
Database and Catalog
Second NASA Aerospace Pyrotechnic Systems Workshop
February 8-9, 1994
Sandia National Laboratories
Albuquerque, NM
NASA Lewis Research Center
Cleveland, OH
Prepared by:
Analex Corporation
e bvSn e engineering directorate
Presentation Agenda
Purpose of Database/Catalog
Database Ground Rules
Format for Database
Schedule
Database/Catalog availability
NASA
Lewis Research Center
L EXCELLENCE __ ^^
,bv desk* ENGINEERING DIRECTORATE
Lewis Research Center
Purpose of Database/Catalog
Pyrotechnically Actuated System s Database
The purpose of the Database is to store all pertinent design, test and certification data for all
existing aerospace pyro devices into a standardized Database accessible to all NASA/DOD/
DOE agencies.
A pplications Catalog
The purpose of the Applications Catalog is to identify and provide a quick reference for the
pyrotechnic devices available, including basic performance and environmental parameters.
I
- 332 -
EXCELLENCE
Da " M ENGINEERING DIRECTORATE
NASA
Lewt» R— ewch Center
Database and Catalog Ground Rules
Develop database on the Macintosh computer system using OMNIS 7 software.
Include current and past (non-obsolete) pyro devices used on launch vehicles, spacecraft,
and support systems. Compile information from all NASA/DOD/DOE Centers.
Include pertinent design and specification data.
Include sketches for each device and system.
Provide cross reference indexes in Catalog.
Catalog to be extracted from the database.
Provide for updating capability.
Format
Example I TITLE: Detonator - NASA Standard
AGENCY/CENTER: NASA Johnson Space Center (JSC)
PHYSICAL DATA:
-—♦810 HEX
N5D BODY
.5B6 - .596
,995 -1.000
.39Z - .403
-LEAD A2I0C
-RDX
1
— 0.277 - .2BO
T
-DISCS
-9/16 - 1BUNF-3A
.793 - .808
NASA STANDARD DETONATOR (NSD) SCHEMATIC
CONTRACTOR: n/a
SUBCONTRACTOR : HI Shear Tech. Corp., Explosive Technology Co., and
Universal Propulsion Co.
DEVICE IDENTIFICATION NUMBER: NASA SEB26100094
PURPOSE : To provide a high leveled detonating Shockwave for
initiating an explosive train or separating frangible devices.
- 333 -
Format (Cont.)
^jiEfrTHp]l ^ t PREVIOUS USAGE: Apollo, Skylab, Apollo-Soyuz, and Space Shuttle.
OPKRATIONAL DESCRIPTION i The NSD id the standard detonator for the
Space Shuttle and is provided as GFE to all shuttle users by the
Johnson Space Center. The NSD consists of the NASA Standard
Initiator {NSD threaded into an A-286 stainless steel body
containing a column of Lead Azide progressing into a column of RDX.
When the NSI is fired with the Pyrotechnic Initiator Controller
(PIC) 38 vcs capacitor (6B0 microfarads) discharge, the NSD produces
a . 040 inch minimum dent into a mild steel block at ambient
temperature.
ENERGY SOURCE t
TYPE OF INITIATION: NSI.
CHARGE MATERIAL: Dextrinated Lead Azide (376 mg) and RDX (400 mg) .
ELECTRICAL CHARACTERISTICS: n/a.
OPERATING TEMPERATURE/PRESSURE:
TEMPERATURE RANGE: Low -420°F, High +200°F.
PRESSURE: n/a.
DYNAMICS :
SHOCK: 30g, 11 msec sawtooth.
VIBRATION: Random <-65°F to +200°F) at 2000cps.
QUALIFICATION:
DOCUMENTATION: SKD-26100097 Design & Performance Spec, Qualification
Documentation provided by each contractor and on file at JSC.
SERVICE LIFE:
SHELF: 4 years minimum from Lot Acceptance test date, 10 years
maximum based upon successful passing Age Life Testing per
NSTS 08060.
OPERATIONAL: See Shelf Life above.
ADDITIONAL REFERENCES: n/a.
ADDITIONAL COMM TCNT' I ? « DOT Class-C explosive.
SPECIAL FEATURES: n/a.
Schedule for Pyrotechnically
Actuated Svstems
Database
and Reference
Cataloa
Activity Name
1993
1994
1995
J ! A
s
O
N
D
J
F j M | A | M | J
j
A
S J O ! N | D ' J
F | M | A j M | J
j
A
s
o
Identify all devices
i ' j
1
i '
" f r '
__;_.
'"i~-
-..
Collect all data
I
i |
j
! i ' \
Compile data into catalog
^^^^^_
! ■ i I
i I I
' \ ■
Distribute first draft of
catalog
I
I
! i
i i
i
i
i I : ;
!
Edit and revise catalog
!
i
r t
I ! ; I i
1 . ! 1
_L .
Steering Committee approval
of Catalog
i I i
A! i ! ;
I : i i
— ■
! ; i
Publish 1994 issue of
NASA/DOD/DOE Catalog
I
!
! i I :
_....:_ ; _._.
i
■--
I ! i
__t__^__;_ ,___
Enter information into
database
J
I ! ! I
^^^
! l i I
I : s
Distribute first draft of
database
I i j I
i i
t i
| !
Edit and revise database
|
mmm
*-':-]
i
(
i i
Steering Committee approval
of Database
--
—
1
A
I !
i
Publish 1995 issue of
NASA/DOD/DOE Database
|
' i
J • i
r ;
i
■
i ; I
Maintain database and catalog
thru 1995
i
._j —
i
i
_ r " , _
I ! I
1
;
.-._
i
Steering Committee Meetings
and status report
A
i
a;
i
A
1
i
A
! i
I : i
A
;
: I -
t
ri
__
—
!
....
— .
—
—
i
\ i
J. __
...j..., —
—
i
■
Steering Committee approval milestone
i
rev. 1/26/94
i
i
i
i
j
- 33H -
EXCELLENCE
vam ENGINEERING DIRECTORATE
NASA
Uwfc R—eareh Center
Database and Catalog Availability
♦ Database and Catalog will be released as government issue.
♦ Catalog will be available in October 1994.
♦ Database will be available in October 1995.
- 335 -
Page intentionally left blank
FIRE, AS I HAVE SEEN IT
Dick Stresau
Stresau Laboratory, Inc.
Spooner, WE 54801
ABSTRACT
Fire (and much else) is described as I have seen it (in the sense that "to see" is "to understand") from a
succession of perspectives (which seems, like that of most moderns, to parallel the sequence of
perspectives had been assumed by scholars in the past) since childhood. Origin and originators of some
of these perspectives (e.g., that of the "Bohr atom" and the Chapman-Jouguet theory of detonation) are
mentioned in passing. For the most part, I believe my views to be quite similar to those of others who
have concerned themselves with fire in its various forms. However, data, which may not have considered
by others, have led me to see explosion and the shock to detonation transition from apparently new
perspectives, which are discussed.
INTRODUCTION
Like, I suppose, most people I first saw fire from an
"on scene, eyewitness" perspective, Explanations, by
adults, of fire and other things we sensed (saw, heard,
felt, tasted, or smelled) helped me to see things in the
sense that "to see" is "to understand", from a
"common sense" perspective. The explanations,
however, were in words which may not have been
understood as they were intended. As punsters often
remind us, each of many words and phrases of
English, and other living languages, has a number of
meanings. For example, the 1967 edition of the
"Random House Dictionary of the English Language"
(1) gives fifty-four definitions of "fire".
PYROTECHNICS
"Pyrotechnics" the subject of this workshop, is given
as a synonym of "pyrotechny" - "The science of the
management of fire and its application to various
operations" (2). So defined, it is among the oldest of
technologies (2V£). The survival of the human race
(adapted as it was and is, to the climate of equatorial
Africa) in the "temperate" zones, during the "ice ages"
depended upon the establishment of (indoor)
environments similar to that to which it is adapted, for
which pyrotechny, "The management of fire" is
essential. Its most prevalent application is still to this
purpose. More fires are used to heat buildings than for
any other purpose. It is an essential part of such other
prehistoric technologies as pottery, glass making,
metal smelting, casting and forging, as well as the arts
of cooking, baking, etc. Remains of fireplaces are
accepted by archaeologists, as evidence of the presence
of early man at a site. It could be said that
pyrotechnics, as defined above, played an essential
role in "the ascent of the mind" (3) and the rise of
civilization. Pyrotechny or pyrotechnics (also referred
to, by some who practice it, as "combustion engineer-
ing") is also part of modern practices of these ancient
technologies and arts and of currently practiced
technologies and arts including those of "firemen"
(members of both fire departments and steam locomo-
tive crews), heat-power, automotive, and jet aircraft
engineers, (torch) welders, and heating contractors.
As defined in most dictionaries and to most people
who use the term, "pyrotechnics" are "fireworks",
especially those used in public parks on Fourth of July
evenings, Of these, the most spectacular are the
skyrockets, which explode at their apogees in luminous
"sprays". Such displays were made, in China, several
hundred years B.C.(4).
"The rockets' red glare,-" of our national anthem was
that of military rockets, used by the British in the 1814
bombardment of Fort McHenry, which, by the way,
utilized and verified the capability of rockets of
carrying substantial payloads.
In the late 1920s and early 1930s, science fiction often
about outer space travel, was popular (notably, with
preteen and teen aged boys, which included me at that
337
time). We read that this interest had been shared, since
their boyhood, be some scientists, including Goddard,
in U.S.A., and Ley and von Braun, in Germany, all of
whom made and tested rockets.
During World War II, when most combatants
developed rocket propelled weapons (including the
U.S. "bazooka" ammunition), von Braun led the group
at Peenemunde, where the German ballistic missiles,
including the V-2, were developed. After the war,
many of the group were recruited by D.O.D. agencies.
Von Braun came to Redstone Arsenal to participate in
the U. S. Army's guided missile program, and, when
interest in "outer space" was intensified by the success
of the Russian "Sputnik" he realized part of his
boyhood dream as the leader of the group that put
"Explorer I" into orbit (5).
The events mentioned, parts of the sequence which led
to the establishment of NASA, have led me to
speculate as to whether von Braun or any of his
associates or their successors in the space effort
thought of the design and development of space vehicle
propulsion systems as applications of "pyrotechny" or
"pyrotechnics". They do refer to explosives and
propellants (which Picatinny Arsenal and the American
Defense Preparedness Association include among
"energetic materials") as "pyrotechnics".
LANGUAGES AND PERSPECTIVES
As the years passed , having participated in
conversations, committee meetings, workshops,
seminars, symposia, etc., I have come to recognize
that each art, profession, specialty, and often working
group or family, communicates in its own language,
each, in U.K., Canada, U.S., etc, a variant of
English, using many of the same words often with
different meanings. In recognition of the possibility of
having been misunderstood, explanations are apt to
conclude with, "See what I mean?, and include efforts
to illustrate the meanings of the words by means of
metaphors and models, such as working and scale
models, sketches, "layout" and "detail" drawings,
graphs, chemical formulas and equations, mathematical
equations and sets of them, and, in recent years,
computer manipulated numerical models, each of
which shows the subject, from a different perspective.
"Model" as used here indicates "a description or
analogy used to help visualize something (as an atom)
which cannot" (literally) "be seen" (2). It can serve
this purpose if the analogy is to something which can
be seen (literally or in the sense that "to see" is "to
understand"). What some refer to as "models" are
referred to as "theories" by others.
Each of us sees things from a constantly changing
perspective. In each encounter, and when we are
reading, or writing, we try to consider each subject
from the perspective of the speaker, writer, listener, or
reader. Pursuant to this effort, each of us has assumed
a succession of perspectives, those of parents,
playmates, teachers, professors, lecturers, bosses,
commentators, the authors of books and articles we
have read and those of the people whose views are
conveyed. Thus we have viewed our vicinities, the
world, the universe, and much within them from a
variety of perspectives, including those which can be
categorized as "eyewitness", "common sense",
"reasonable", "intuitive" , "practical" , "rational" ,
"theoretical" , references to those credited with
proposing them, as "Aristotelian" , "Newtonian" ,
"Cartesian", etc., and those of several trades, sports,
sciences, etc.
Consideration of any subject begins with the choice of
a perspective from which details which we wish to
consider are visible and. others are obscured. Such
choices are called "simplifying assumptions (or
approximations)", in which numbers which seem too
small to consider are dropped as "infinitesimals of the
second order" and numbers too large to think about
are equated to infinity (6). Sometimes such
simplifying assumptions (or approximations) must be
reassessed on the basis of more recent experience or
data, which result in the consideration of a subject
from another perspective. Such changes of perspective
have been essential to the advance of science, and to
the education of each individual.
To reiterate, the perspective from which each of us
sees things is and has been constantly changing. The
"steam" from a teakettle and the melting of ice showed
us that water exists in more than one state. (Other
observations and experiences showed us that other
substances also freeze, melt, boil and condense.).
Steam emerging from the teakettle spout was invisible
as air, (or, at least transparent), forming a visible
cloud a few inches from the end of the spout.
Someone may have explained that steam is a gas, like
air (and thus, invisible) which, mixing with the cooler
air, condensed to liquid water, in droplets too small to
settle out, which we saw as a cloud. If they thought
we could understand, they may have gone on to say
that such suspensions of droplets of liquids or particles
of solids, which are too small to settle out of fluids
(liquids or gases) in which they are insoluble, are
338
called "colloidal suspensions" and that, when the fluid
is air, they are called "aerosols" and are the "stuff" of
clouds, fog, and mist, and (of other compositions) of
smoke and smog
FIRE, FROM "KID'S" PERSPECTIVES
The earliest impressions of fire, which I can
remember, were the sights of the yellow flames of
candles on a birthday cake and of trash and wood
fires. Fire had been the source of most artificial light
until a bit over a century ago. As we (including the
earliest human observers) saw the flames spread over
the surface of the fuel, it was apparent that the light,
which seemed to be the essential property of fire, is
"catching", like a cold or the flu. This impression is
perpetuated in the usage of "light" for "ignite" and
"catch fire" for what the fuel does when lit.
Our perspective changed with the passage of time and
the accumulation of experience, and we came to see
fire, from a more "practical" perspective, as a source
of heat, and it became clear that firelight is a mani-
festation of the heat of combustion. Some of us had
noted that "firelight" is similar, in color to the light
emitted by glowing coals or metal or ceramic which
was a bit hotter than "red hot". With a little thought,
it became apparent that black smoke, is air borne soot
which, when hot enough, emits black body radiation,
so the yellow flames of candles, oil lamps, and wood
and trash fires can be seen as "yellow hot black
smoke". Flames of other colors are effects of atomic
and molecular emission (whereby elements and
compounds are identified in spectroscopic analysis)
which occur at elevated temperatures. Although the
usage of "light" for ignite persisted in our
conversation, we came to recognize that ignition
occurred when a fuel element was "hot enough". By
this time we had learned to think of heat in the
quantitative terms of temperature and it became
generally accepted that the temperature at which each
fuel started and continued to burn was its "kindling
point" or "ignition temperature". The propagation of
fire (combustion) is seen by many as the progressive
heating of unburned fuel to its "kindling point" by the
heat of combustion of the burning fuel. (The title
"Fahrenheit 451" (614) of the novel by Ray Bradbury,
and the movie made from it, is derived from the
supposition that 451°F is the "kindling point" of
paper). However, the episode described below has left
me skeptical of this view.
When five or six years old, at a friend's invitation, I
joined him in watching his father paint their dining
room wall. He (the father) having painted the wall a
light beige, let it dry, was applying a darker brown
paint, a few square feet at a time, and, while each
patch was "fresh", "blotting" it with crumpled news-
paper to expose the lighter paint in a "stippled" pattern.
He tossed the paint soaked clumps of paper into a
bushel basket. After about an hour, the pile of paint
soaked paper in the basket began to smoke and the
man grabbed the basket and ran out in the yard before
it burst into flame. He managed to drop it so quickly
that the only damage to him was some slightly singed
hair. A few years later, when a fireman, visiting our
school to talk about fire and its prevention, warned of
the danger of "spontaneous combustion", I knew, from
on scene, eyewitness observation, what he was talking
about, from the "practical" perspective of the fire
fighter, but didn't see why "spontaneous combustion"
could happen if the "ignition temperature" of the paper
was as high as it seemed to be.
At the time of the above episode, our family lived in
a suburb of Milwaukee. Sunday drives (in the "Model
T") often carried us to deserted stretches of Lake
Michigan beach, on which there were, often
"fireplaces", made by arranging rocks in a circle. My
Dad often built fires of driftwood , which was usually
available. If suitable vegetation grew nearby, he'd
sharpen "green" branches or "shoots" to make "spits"
for toasting marshmallows or broiling hot dogs. As we
sat around the fire I saw it as the focal point of the
family's togetherness".
A few years later, I went with my parents on an
automobile trip around Lake Michigan. Most
memories of the trip, particularly that of the ferry boat
crossing of the Straits of Mackinac, are pleasant, but
one, less pleasant but more vivid, is that of mile after
mile of "burnt over country" left by the "Peshtigo
fire", which, fifty years earlier (on the date, Oct. 20,
1871, of the more notorious though less disastrous
Chicago fire.) had devastated 1 ,280,000 acres,
including three-quarters of the shores of Green Bay
(7). Even after fifty years, the effects of the fire were
quite apparent. I suppose that my parents thought that
I had been sufficiently persuaded of the importance of
keeping fire under control to trust me, as they did,
with the responsibility of burning trash (in a woven
wire trash burner) and leaves (in the gutter, as was the
practice in our oak shaded neighborhood).
My household duties, as subteen, besides trash
burning, raking and burning leaves, and lawn mowing,
included tending the coal furnace, which involved
shaking out ashes, adjusting the damper when neces-
339
sary, and shoveling coal, in the course of which I had
plenty of opportunity to observe the fire, which was
mostly glowing coals, with a few flickering flames.
When the fuel was coke, there were no flames nor
smoke.
After a few years, as a Boy Scout, I became involved
in a discussion of the concept of "kindling points" or
"ignition points". In the course of the discussion, I
recalled die "spontaneous combustion" episode I'd
seen. By that time, of course, I'd forgotten, if I ever
knew, the temperature on the day when I'd witnessed
spontaneous combustion but guessed that it must have
been between 60°F and 90°F and wondered, out loud,
whether paint soaked newspaper had a kindling point
in that range. The answer was that it didn't but that
"self heating" had raised the temperature of the stuff
in the bushel basket to its kindling point. It would be
more years before I could sort out the distinctions
between "self heating", "burning", "fire", and
"combustion". (Perhaps I haven't yet, but con-
sideration from various perspectives has helped me to
understand those who use these words.).
Based on our earliest impressions of such matters, the
aphorism that, "Where there's smoke, there's fire.",
seemed to be a "matter of common sense". However,
when we saw smoke, but no flames, coming from an
overloaded extension cord or from toasting bread or
frying bacon that was getting black and said to be
"burning", with no flame evident, and that, as fire
spread across burning wood, smoke often appeared
ahead of the flame, we pondered the questions as to
what was meant by such words as "smoke" and "fire"
and, specifically, what is the composition of smoke
(including, the liquid "hickory smoke" and "mesquite
smoke" in bottles on grocery store shelves). We'd find
answers in considering these questions from an
"intermolecular" perspective of fire and fuels.
We may have noticed that, if metal ceramic or
anything else that can stand the heat, is heated
sufficiently, it gets "red hot" and, if heated more, the
red brightens to orange, yellow, and, with further
heating, the object becomes "white hot". Although I
don't remember hearing (he phrase, "yellow hot", it
seems an appropriate designation of a condition
between "red hot" and "white hot". We may have
heard or read that such glow is called "black body
radiation", although a red hot poker doesn't look
black.
Some of us noticed that, the flames of candles and
kerosene or alcohol lamps are yellow, those of a gas
stove are blue (if the burner is "properly" adjusted,
but yellow if the air intake is restricted to make a
"rich" mixture.
We learned, when quite young, that, although candles
and matches could be "blown out", fire, in general,
was energized by blowing or "fanning" ("red hot"
glowing coals brightened and became "yellow hot"),
controlled by "damping the draft" and "smothered" by
depriving it of air. It is apparent that the foregoing
was known by prehistoric humans. Smelters,
foundries, and forges in archeological sites had flues,
dampers, and other means of forcing and limiting the
supply of air to fires.
Those of us who are old enough to have had spending
money in the 1920s (before the passage of "safe and
sane Fourth" ordinances) celebrated the Fourth of July
with firecrackers and other fireworks (some,
apparently, still do), in the course of which, we
learned that gunpowder and other pyrotechnics burn
without air (and, in fact, burn faster when confined -
"smothered"), which had been known by some
alchemists as long ago as the ninth century (4).
"Educational toys" included chemistry sets, which
provided amusement, seeing the color changes and
foaming resulting from chemical reactions, and,
perhaps, the beginning of a "chemical" perspective.
While, since "playing with fire" was discouraged, in-
gredients of gunpowder and similar mixtures were not
included in chemistry sets, some of us learned (by
reading) what they were and found ways to get some,
and set out to make our own fireworks. I joined a
fourth grade classmate in the "Universal Research
Laboratories" as he called his basement in the
preparation of some black gunpowder which we loaded
into a home made skyrocket (which flew straight up to
about six feet from the ground before it lost stability
and tumbled). In the course of these efforts, we
viewed chemistry from the "practical" perspective
from which it seemed that what had worked for others
should work for us (a perspective shared with the
Middle Ages alchemists who had practiced pyrotechny
since antiquity).
A "CHEMICAL" PERSPECTIVE
When, in high school, we were shown a "chemical"
perspective, we saw that (as Lavoisier had shown in
1779 (5)) the fire we had seen (from an "eyewitness"
perspective) was "oxidation" (combining with the
oxygen of air) and that gunpowder and other pyro-
technics burn without air because they are mixtures of
340
fuels with nitrates, chlorates, or other compounds
which decompose when heated releasing oxygen which
reacts with the fuels. All of which is expressed in
stoichiometric equations, such as:
2H 2 +0 2 -»2H 2 (1)
for the reaction of hydrogen and oxygen, and:
2KN0 3 +C + S-» C0 2 +S0 2 +2KO (2)
for the burning of black powder of stoichiometric
composition.
In stoichiometric equations, as equations (1) and (2),
the symbols (H, O, C, K, N, and S) stand for
elements (hydrogen, oxygen, carbon, potassium,
nitrogen, and sulfur) and the formulas, which are
essentially inventories of the proportions of the
elements of which each compound (water (H 2 0),
carbon dioxide (CO^, potassium nitrate (KN0 3 )) are
referred to as "empirical" formulas, since they are
based on empirical (experimental) data as are valences
(upon which predictions are made, of formulas of
compounds which have yet to be made) assigned each
element. The small integers, which express these
proportions, suggested to Proust (in 1799) and
corroborate the "law of definite proportions", which
suggested (in turn, in 1801, to Dalton) the basis of
modern atomic and molecular theories. Atomic
theories were proposed, some hundreds of years
B.C., by Pythagoras, Democritus, and Lucretius (5,8).
The modern theories are based on and supported by
empirical data. Some see atoms as portrayed by
models. The structural formulas, which are used to
represent organic compounds are models (diagrams) of
their molecules. Some organic chemists, before trying
to make a compound, try to build a scale model of its
molecule, in which the atoms are represented by
plastic spheres of various sizes and colors. As I
understand it, the colors are only for identification of
the elements represented but the sizes are scaled
(typically 2 or 3 centimeters per angstrom) from the
effective sizes of the atoms represented. Similar
models (typically, styrofoam balls, joined by tooth-
picks (Figure 1) are used for educational purposes.
Figure 1. Educational Models of Molecules (enlaced,
from Edmund Scientific Co. catalog)
The perspective induced by such models can be
referred to as an "intermolecular" perspective. Fire
can be seen from this perspective, in the sense that "to
see" is "to understand", only with reference to other
perspectives, views from some of which have been
mentioned in the foregoing discussion. Consideration
from "practical" , "empirical" , "scholarly" , and
"theoretical" (including laws of gravity, magnetism,
fluid mechanics, thermodynamics, heat transfer, and
reaction kinetics is necessary to "see" fire clearly.
"PRACTICAL" PERSPECTIVES
Based on some of our earliest experiences, such as
falling down and dropping things, and observations,
such as those of falling objects and the flight of balls,
led us to accept the aphorism that "what goes up, mist
come- down.", which I've heard cited (on television)
as "the law of gravity". Rubber band (referred to, by
some, as "elastic bands" showed us that some things
are elastic, that is,when deformed, they tended to
recover their pervious shape. These and similar ex-
periences and observations gave us,when we were very
young, a practical, through rudimentary perspective of
gravity and mechanics.
Most of us played with magnets, usually horseshoe
shaped steel items, painted red, except at the ends,
which picked up nails, pins, etc, to which they came
close. If we had two magnets, we found, after a few
tries, that they attracted or repelled one another,
depending upon which end of one was close to which
end of the other. Someone older, probably told us that
the ends were called "poles", one "north" and the
other "south" and that opposite poles attract, and like
poles repel one another. They may have gone on to
say that the earth is a giant magnet and the needle of
a compass a tiny one, which aligns itself with the
earth's magnetic field.
Our earliest impressions of electricity were related to
its practical applications. Lights could be turned off
and on from across a room or upstairs from downstairs
or vice versa, by "closing" or "opening" a switch.
Vacuum cleaners, electric fans, and washing machines
ran if "plugged in" and "turned on". When we first
learned of such possibilities, electricity .seemed akin
to magic. Play, with electric trains, the small motors
which came with Erector sets, and the lighting fixtures
associated with them improved our "practical"
perspective of electricity. The electricity involved in
such play came from transformers, which were "plug-
ged in". We learned, quite early that a direct connec-
tion of the - terminals of a transformer made it hum
341
quite loudly and get warm. We were told to "break"
the "short circuit" before it "burned out" the trans-
former.
Some of us learned that batteries could be used instead
of transformers to run electric trains, etc. We all
became aware of batteries as parts of flashlights and/or
battery operated toys. We found that batteries differed
from transformers in three ways;
1. They have "positive" and "negative" terminals,
marked " + " and"-".
2. They discharge as they are used and in a short
time, when "shorted".
3. They don't hum, even when "shorted" (but do
warm).
We were told that the reason for these differences was
that the "electrical current" from a battery is "direct
current" - "D.C.", which flows, without variation, in
the same single direction, while the current from a
transformer, and "house current" are "alternating
current" - "A.C." which flows, alternately, in opposite
directions. Since the direction changes and changes
back again sixty times per second, it is called "sixty
cycle", or, in recent years, "sixty hertz", current. The
reason most "house current" is A.C. is that its voltage
can be changed by means of transformers. Most of us
had learned, when quite young, that one could get a
"shock" from 110 volt "house current", but not from
the 5 to 10 volt output of a transformer. Later we
learned that the compelling motive for the use of A.C.
by utilities was the greater efficiency of transmission
at thousands of volts, which would be unsafe as "house
current", so the high voltage of the transmission lines
is transformed to 1 10 volts by a transformer near each
point of use.
With the passage of time, we acquired some
"practical" perspectives of household and automotive
electrical systems and the magneto powered ignition
systems of outboard motors, chain saws, and lawn-
mowers, all of which are powered by "internal
combustion engines" in which a fuel-air mixture is
ignited by "spark plugs" which emit sparks when
actuated by electrical pulses from their "ignition
systems". To many "spark" became synonymous with
"ignition" (a matter to be discussed when we get to
"ignition").
In the late 1920s, as a result of the interaction of
advancing technology, patent law, and business
competition the best radios were home made, so lots
of people made their own (which were battery
powered). By the early *s, the "art" had advanced and
"store bought", "plug in" radios replaced the home
made battery sets the parts of which became available
to teenagers for basement experimentation, from which
we gained "practical" perspectives of electronics. One
misconception, which was corrected, by the view from
the "electronic" perspective was that electrical current
flows from positive to negative. We became aware
that electrical current is the movement of negatively
charged electrons, from negative to positive. We had
previously learned, from demonstrations of
electrostatic effects (with combs and bits of paper),
that like charges (as like magnetic poles) repel one
another, and opposite charges attract. We were to
learn, later, that these principles apply to chemical
reactions, including fire as well as electrolysis.
"Practical" perspectives are acquired, along with
"know how", skills, or "arts", by imitation,
instruction, and experience. Experience is gained by
"trial and error" (referred to, by old time machinists
as "cut and try" and, by those who would dignify it,
as "Edisonian research"), followed by practice of
techniques which were found to be successful.
"Practical" perspectives are those from which we
(including everyone who has ever lived) consider the
application of things and materials to immediate or
anticipated purposes. The "practical" motorist is
aware that the high compression engine of a
"Corvette" will run best on "high octane" gas (which
may cause a "Model T" to overheat) but may not have
considered, from a "scientific" perspective, the reasons
for a high compression engine, nor why "high octane"
gasoline does what it does. My impressions of such
matters go back to the late twenties, when "Ethyl" and
"Benzol" pumps began to appear at gasoline stations
and we heard that it was needed for the newer cars
(like the recently introduced Chrysler) with "high
compression" engines (7 to 1 was considered "high")
which would "knock" on "regular" gas". I saw and
heard it tried and the "knocks sounded as if something
was trying, with a hammer, to beat its way out of the
engine. I was told that knock was the result of the
"regular" "burning too fast" at high pressures and that
the burning could be slowed by adding tetraethyl lead
or benzine to make "Ethyls" or "Benzol". Still later,
I learned that gasoline was rated for its resistance to
"knocking" by means of the "Research Method",
which involves the use of an internal combustion
engine of adjustable compression ratio, which has been
calibrated using mixtures of isooctane (100 octane) and
normal heptane (zero octane) (10), I have never had
occasion for further consideration of such tests. I
have, somehow, gained the impression that "knocking"
342
of an internal combustion engine has been ascribed to
"detonation" of the fuel-air mixture. In this respect,
I don't know don't know which of the several
meanings of "detonation" was intended, but would
guess the definition of Chapman(12) and Jouguet(13),
which is reviewed in the later section hereof headed -
EXPLOSION AND DETONATION.
Also, in the late 1920s (I was in my early 'teens), I
was on a seagull banding expedition (for the National
Bird Survey) in northern Lake Michigan aboard a
Diesel powered Coast Guard tug (similar to the fishing
tugs which were common in the upper lakes at that
time). The Diesel engine, as I recall, was about six
feet high and ten feet long. Preparatory to starting it,
the engineer lit a blow torch over each of the four
cylinders. When they were hot enough, he ran the
engine as a compressed air motor to "crank it", after
which he quickly reset hand operated valves and the
engine ran as a Diesel engine. I was told that, in a
Diesel engine, the fuel (kerosene - or "coal oil", as
some called it then) was ignited by "compression
ignition" rather than a spark". My dad and the
organizer of the expedition (to whom bird banding was
a combination hobby and public service activity) were
engineers by profession. One of them explained the
"Diesel cycle" to me, about (as remembered after six-
ty-some years) as follows;
Air, which had been drawn into the cylinder
in the intake stroke, is compressed "adia-
batically" (my introduction to this word, and
to the subject of thermodynamics) which
raises its temperature above the ignition
temperature of the fuel, which burns as it is
injected, (the engine can't "knock" because
the fuel can't burn any faster than it is
injected into the hot air). The heat of
combustion of the fuel raises the temperature
and hence the pressure of the air and product
gases, which expand adiabatically, imparting
more mechanical energy to the system than
was used in the compression stroke.
The above explanation, in combination with the
rationale that Diesel engines, which have higher
compression ratios than gasoline engines, should be
more powerful and efficient, besides which, they used
cheaper fuel. All of which persuaded me that auto-
mobiles should have Diesel engines. Based on this
conviction, I enrolled, a few years later (in 1934),- at
M.I.T. in Course IXB, "General Engineering" (in
which each student could choose courses appropriate
for his intended specialty) to specialize in automotive
Diesel engines. After a year or so. recognizing that I
was taking the same courses as those in Course II
"Mechanical Engineering" whose schedules had been
prearranged, so I switched course to avoid the hassle
of trying to arrange my own, while others in my
classes were doing the same, These moves were
motivated by the recognition that practical objectives
are most attained by those who understand the prin-
ciples involved.
This transition, of my perspective, from "practical" to
the "scholarly" is one of many I, and, seemingly many
others, have made since humans became human.
"SCHOLARLY" PERSPECTIVES
As the word implies, a "scholarly" perspective was
gained in school. That acquired in the lower grades is
scholarly" in the sense that, like that of the Medieval
"Scholastics", it presented the perspective from which
the world was seen a few millennia ago, when the
classics, which, often, explained phenomena with
reference to such models as anthropomorphic animals
(e.g. the tortoise and the hare) and objects (the
mountain which talked with the squirrel), supernatural
entities such as, fairies, brownies, trolls, gods, and the
heroes of Greek, Norse, etc. mythology, were written.
From a modern perspective, it is, sometimes, hard to
tell where the line was drawn between the
metaphorical and the literal. Even in modern
discourse, the location of this line is sometimes
indefinite. As we progressed in school, the,
"scholarly" perspective melded into "classical",
"historical", "mathematical" and "scientific"
perspectives, which were narrowed to those of specific
n subjects" or, "academic disciplines", such arithmetic,
science, algebra, geometry, chemistry, and physics,
and further, to trigonometry, calculus, organic and
physical chemistry, applied mechanics,
thermodynamics, electrostatics, and vector analysis. As
a result we saw fire and other phenomena and things
from a succession of perspectives, between which we
shifted, often after a few seconds.
"Classical" perspectives included those mentioned
above based on mythology and those of Greek
philosophers, including Plato, Euclid, Pythagoras, and
Aristotle. Euclid's geometry in which the subject is
considered from a "logical" perspective, is, in English,
still taught. Aristotle viewed physical science from a
"logical" perspective in which phenomena are
explained in terms of relationships derived from "first
principles", which, like the axioms of geometry were
considered (on the basis of what some modern
343
scientists view as "intuition" when they refer to a
phenomenon as "counter-intuitive") to be "self evident
truths". While the axioms of geometry have stood the
test of time, some of Aristotle's "first principles", such
as that "heavy objects fall more rapidly than light
ones" were discredited by empirical data.
Consideration of phenomena from the "empirical"
perspective, followed by views from "graphical",
" analytical " , and " theoretical " perspectives has
advanced science since the renaissance. Empirical
data are quantitative data, the product of measurements
of physical quantities, including time, dimensions,
position, force, mass, etc, and functions thereof, such
as velocity, acceleration, pressure, energy, and power.
Some such measurements (for example, those of
astronomers, microscopists, etc.) are made, using
instruments, of natural phenomena which are beyond
the control of the observers. Others are made in the
course of experiments, including the establishment of
preconditions and determination of results. By
"plotting" such data a "graphical" perspective is
gained, the view from which may suggest
relationships, which can be expressed in algebraic
equations, manipulation of which can yield an "analyt-
ical" perspective. Consideration of an object, material,
system, or phenomenon from "empirical", "graphical"
and/or "analytical" perspectives may lead to the
conception of a model or theory, usually, at first
"heuristic" but, for purposes of discussion and
analytical verification, represented by a diagram,
mathematical or chemical formula, equation or set of
equations, graph or scale model, which provides
another perspective, which can serve as the basis for
verification, or at least support, of the theory by
prediction of observed or experimental data. Such a
sequence has resulted in the advance of each science.
However, since the sciences differ with respect to the
phenomena and quantities with which they are
concerned, each has evolved an unique perspective
(each of which is the result of such a sequence).
From "hydraulic" perspectives, water and other liquids
are seen as "incompressible fluids" which behave in
accordance with Pascal's law, that "Pressure (force per
unit area) exerted at any point on confined liquid is
transmitted, undiminished, in all directions" (10). The
"hydrostatics" perspective is that from which systems
in which the effect of flow upon pressure is negligible,
so that Pascal's law can be applied without reserva-
tion.
Systems and phenomena in which the effect of
movement upon pressure is significant are considered
from the "hydrodynamic" perspective, from which this
effect is seen to be determined by Bernoulli's principle
(which is the law of the conservation of energy stated
in terms of pressure, density, and velocity (5,11).
Although, for liquids, the assumption of
incompressibility is a reasonable approximation (in
fact, when the empirical data, upon which the
principles of hydraulics and hydrodynamics were
based, were obtained, the available instruments were
sufficiently precise to determine the compressibility of
liquids, the compressibility of gases was apparent to
Hero in the first century (5) and must be taken into
account in considering their behavior. The behavior of
gases is considered from a "thermodynamic" per-
spective in terms of the "gas laws", which relate
pressure, specific volume, and temperature.
Liquids and gases are seen, from "hydraulic",
"hydrodynamic", and "thermodynamic" perspectives
(as they are from "eyewitness", "common sense",
"intuitive" "practical" and "empirical" perspectives) as
continuous media (thus legitimizing the application of
algebra, calculus, and differential equations in the
generation of theory from empirical data. In contrast,
from the "intermolecular" perspective, which is
mentioned a few pages back, a gas is seen as a
"swarm" of atoms and molecules, moving in random
directions at random velocities, and bouncing,
elastically, from one another ("like tiny billiard balls"
as Mach, scornfully, put it) when they collided, as
envisioned by Maxwell and Boltzmann, who
considered this motion in terms of statistical
mechanics, assuming what has become known as the
"Boltzmann factor", exp(-E/RT), for the statistical
distribution of kinetic energy, E, among the molecules
and atoms of a volume of gas, at absolute temperature,
T, where R is the "gas constant" for the mechanical
equivalent of heat. The result of their consideration (in
1 87 1) from this "intermolecular perspective has
become known as "The Maxwell-Boltzmann kinetic
theory of gases", that heat is molecular motion and
pressure is the aggregate effect of impacts of many (if
the order of Avogadro's number (6.026X10 23 ) times the
"Boltzmann factor") molecules on a surface. That the
"gas laws", which had been established in the previous
century, on the basis of experimental data, by Boyle
and Charles, can be derived from the kinetic theory of
gases has validated the theory.
As Mach's remark, alluded to in the preceding
paragraph, implies, heat is viewed from more than one
perspective. Some, apparently including Mach, view
it as a fluid (as it seem to be from casual observation
as well as carefully controlled "heat flow" experi-
344
ments). Even today, though heat is generally seen as
"molecular motion", the phrase "heat flow" is
common. Although the Maxwell-Boltzmann kinetic
theory of gases, when generally accepted, established
the view that heat is molecular motion, I'm not sure
that Maxwell or Boltzmann considered the motion to
include rotation and/or vibration.
Watt's invention of the steam engine (in 1769) and its
widespread application motivated the development of
the thermodynamics of steam, in the course of which
it became evident that, although the "gas laws" apply
to "superheated steam", they don't to "wet steam", so
that "steam tables" and "Mollier charts" were needed
for quantitative prediction of operating characteristics
of steam engines. Van der Waals considering such
"two phase" systems from the "intermolecular"
perspective of Maxwell and Boltzmann, assuming
finite sizes of (and attractions between) molecules
derived the "equation of state" ,which is known by his
name, in 1873.
Chemistry, considered from the "empirical"
perspective, had suggested and corroborated the "law
of definite proportions" which, in turn, suggested the
atomic and molecular theories. Faraday, viewing
electrolysis from an "empirical" perspective,
established his "laws of electrolysis", which introduced
the concepts of "equivalent weight" and valence, in
1832 (5). (He also favored the proposition that electric
current is composed of particles (something that
Franklin had suggested nearly a century earlier
(incorrectly assuming the particles to have what he
designated, and is still referred to as a "positive"
charge) and would be verified, in the 1890s, by
Arrhenius and Thomson, who corrected Franklin's
error) (5).
" Equivalent weights " as measured by Faraday ' s
methods, are ratios of atomic weights or valences. By
1860, the lack of consensus regarding the means of
separating atomic weight from valence had chemistry
in a state of controversy and confusion which moti-
vated the convening of the First International Chemical
Congress, ins which these matters were resolved. By
the late 1860s, atomic weights and valences of all
elements known at the time had been determined.
When Mendeleev tabulated the elements in order of
atomic weights, and entered valences in the table, he
noted a periodicity of the valences, and in 1871, he
published the, now ubiquitous, Periodic Table of the
Elements.
As pointed out and illustrated herein, perhaps too
often, each of us sees things, substances, systems, and
phenomena from a sequence of constantly changing
perspectives, and the sequences are individual. In my
case, the perspectives alluded to in the foregoing were
gained by observation, experience, study in school,
and recreational reading. I don't remember the exact
sequence, but it seems that before I acquired an
"intermolecular" perspective (in fact, before the
styrofoam used to make the models shown in Figure
(1) was invented) I had read a book (9) which induced
an "intra-atomic" perspective, from which I saw an
atom as a "nucleus" of closely packed protons and
neutrons, surrounded (as the sun is by planets) by elec-
trons.
AN "INTRA-ATOMIC" PERSPECTIVE
Each electrostatically positive proton attracts an
electrostatically negative electron, so the electrons,
which don't fall into the nucleus (as the planets don't
fall into the sun) because they are moving too fast.
Thus, the electrons orbit about the nucleus as the
planets do about the sun. The analogy of an atom to
the solar system is flawed by the difference between
gravity, which attracts all heavenly bodies to one
another and the electrostatic forces, which attract
electrons to protons but repel them from one another.
The orbital patterns of electrons are determined by the
interaction of these forces and the laws of motion
established by Newton's demonstration that they can
be invoked as the basis of the derivation of Kepler's
(empirical) laws of planetary motion (as well as the
principles of relativity, and wave and quantum
mechanics postulated, formulated and demonstrated in
the early 20th century, by Einstein, Planck, Bohr,
Pauli, Heisenberg, and others (8)), of which my
understanding was (and still is) too vague to include in
the model upon which my "intra-atomic" perspective
was based). In this model, the equilibrium positions of
the electrons, as determined by their attraction to the
nucleus and their repulsion of each other is attained
when they are spaced in an orbit where the attraction
of the electrons to the nucleus is balanced by their
repulsion of each other (plus the centrifugal force due
to their motion in that spherical surface). Two
electrons can occupy such an orbit, from which
additional electrons are excluded in accordance with
the Pauli exclusion principle, (that only two electrons
(with opposite "spins") can occupy any given
"quantum state") (8). It seemed that, in the language
of atomic physics, the term "orbit" meant the spherical
surface (referred to, by some (5)(8) as a "shell")
where these forces are in equilibrium such that the
345
attraction of the electrons to the nucleus balanced their
repulsion of one another plus the centrifugal force due
to their motion in this spherical surface and the effect
of the Pauli exclusion principle etc. Electrons which
are excluded from this inner orbit locate in
surrounding orbits, which are larger because the net
attractive force of the nucleus has been diminished by
the repulsive force of the electrons in the inner orbit,
so there is room for eight electrons to attain
equilibrium positions in compliance with the Pauli
exclusion principle. A third orbit has room for eight
electrons, while the fourth and fifth orbits contain
eighteen electrons each and the sixth has room for
thirty-two. A seventh orbit, presumably could contain
thirty-two, if and when elements that heavy are dis-
covered.
The foregoing is a description of the heuristic model
of an atom, which I remember, after sixty years as the
basis of the intra-atomic H perspective got from reading
"Inside the Atom", by Langdon-Davies (9), as well as
high school courses I had completed in chemistry,
physics, and solid geometry. In my reconstruction of
the model, I was helped by the copy of the book (9),
which I got for Christmas in 1933 and still have, as
well as more recent publications, including periodicals
and references (5), (8), and (10), by university courses
in chemistry, physics, mechanics, thermodynamics,
physical chemistry, fluid mechanics, etc and from
conversations with and lectures by scientists, including
Gamow, Eyring, and Kistiakowski, all of which may
have "edited" my memory of some details. It is
apparent, from "browsing" through references (5) and
(8) , that the model described above is an
approximation of that which is sometimes referred to
as "the Bohr Atom", which is the result of the work,
guided by Niels Bohr at the Bohr Institute, by an
international group of physicists, including Heisenberg,
Pauli, Gamow, Fermi, and Oppenheimer who
considered their work in progress, from perspectives
of earlier contributors to science, including
Pythagoras, Dalton, Avogadro, Mendeleev, Thomson,
Maxwell, Boltzmann, Van der Waals, Rutherford,
Planck, and Einstein, to mention a few (8). As a high
school senior, I saw the model, as one sees a ship on
a foggy night (only by its running lights), befogged as
it is by relativity (which equates matter to energy) and
wave and quantum mechanics (which consider light
and electrons, seemingly alternately, as waves,
particles, vibrations, and/or orbits(8)) and my present
view is still quite misty. The model described above,
however, has clarified, somewhat, my view of
chemistry, electronics, and thermodynamics.
AN "INTERATOMIC" PERSPECTIVE
The electrostatically negative field of a "saturated"
(filled) electron orbit or "shell", in combination with
the Pauli principle, results in a repulsion of electrons
or other electron "shells" which increases with
proximity so abruptly that (for atoms of so called
"monatomic", "noble", or "inert" gases (helium, neon,
argon, krypton, xenon, and radon) all of whose
electron orbits are saturated), Mach's reference to the
molecules (which include atoms of monatomic gases)
in accordance with the Maxwell- Boltzmann kinetic
theory of gases as that of "tiny billiard balls" can be
considered an accurate analogy.
Of the hundred plus known elements, only the six inert
gases mentioned above have saturated" outer electron
orbits. Atoms with unsaturated outer orbits join in
groups in which the electrons of the unsaturated outer
shells (orbits) are shared. The most familiar grouping
(from a "chemicals' perspective) is in molecules,
where atoms with relatively few electrons in their
outer shells (metals, such as sodium, which has one)
combine with those with nearly saturated outer orbits
(nonmetals, like halogens, including chlorine, whose
outer orbits lack one electron each of saturation, in
which all orbits are saturated, such as that of sodium
chloride (NaCl table salt).
The electrons of the unsaturated outer electron orbits
are referred to as "valence electrons" because their
numbers correspond with the valences of the elements
to which they apply.
As mentioned a few pages back, Faraday had
introduced the concept of valence in 1832, and
Mendeleev had published his Periodic Table in 18771.
The "Bohr atomic model", roughly described above,
was conceived, in part, as an explanation of the
empirical evidence of the periodicity indicated in
Mendeleev's table.
The "valence electrons" of two or more atoms are
drawn into saturated orbits by some of the forces
whose equilibrium determines the numbers of electrons
in the saturated orbits (or " shells " ) while the
electrostatic equilibrium between the protons and
electrons of each atom hold it together. Thus
molecules are formed in which atoms are so grouped
that they can share electrons to saturate all orbits while
the electrostatic equilibrium of each atom is
maintained. Such combinations of forces, which hold
molecules together, are called molecular bonds. Figure
1 shows models of such molecules, of which the
346
"billiard balls" are a less accurate analogy than they
are of the on atomic molecules of "inert" gases in that
they are assemblies of spheres rather than separate
balls, so that their movement, involving significant
fractions of their kinetic energy ("heat") includes that
of rotation and vibration. While models, such as those
shown in Figure 1, are usually scale models they
cannot be viewed as "working" models, because the
"atoms" are rigidly joined, while the real atoms of real
molecules assume equilibrium relative positions
(determined electrostatic, electromagnetic, and other
forces involved in the for saturation of atomic electron
orbits) about which they vibrate or orbit (orbiting is,
essentially, vibration in two or three dimensions.)
Consideration of heat as molecular motion, from this
perspective has led to the distinction between
"rotational", "vibrational", and "translational" heat,
which accounts for the differences between gases with
respect to ratios (k=C p /C v ) of specific heat at constant
pressure (C p ) to that at constant volume (C v ).
Molecules are groups of atoms held together by the
combination of the quantum mechanical forces which
establish conditions for saturation of atomic electron
orbits end the electrostatic equilibrium which results in
the equality, in each atom, between the number of
positive protons in the nucleus and the total number of
electrons which orbit about it. The repulsion of
"saturated" orbits for additional electrons (including
those in other "saturated" orbits) increases so sharply
with proximity that the comparison to "tiny billiard
balls (or golf, tennis, ping-pong, or basket balls) is an
accurate analogy of the bounce of colliding molecules,
atoms, or groups of atoms, including "ions" (atoms or
groups of atoms of which all electron orbits are
saturated). The forces which hold the electrons in
orbit, and thus maintain saturation, combine with the
electrostatic force which maintains the equality
between the nuclear protons and orbiting electrons of
each atom to result in attraction which, like gravity, is
relatively constant close in and, varies inversely as a
function of greater separation so that that which is
referred to as "vibrational heat" is alternate collision
and separation of atoms and groups of atoms,
including "ions" (atoms with outer orbits saturated by
the transfer of electrons, which leaves each ion with
an electrical charge). Those with more electrons in
orbit than protons in their nuclei have negative charges
and those with less have positive charges. The
attraction between the atoms and groups of atoms
(including ions) of a molecule (in the gaseous state),
like the gravitational field of a planet, varies so little
"close in" that it can be viewed as constant and varies
as an inverse function of greater distances, while their
repulsion of one another increases with proximity, as
sharply as that of elastic solid objects. Thus, the
motion of those components of molecules associated
with "vibrational heat" is more analogous to that of
bouncing balls than to that of vibrating piano strings.
AN "INTERMOLECULAR" PERSPECTIVE
The specific heat of a gas is the quantity of energy
associated with a one degree increase in the
temperature, of a unit quantity of the gas. Considered
from the Maxwell-Boltzmann intermolecular
perspective, heat is the kinetic energy of molecular
motion. At constant volume, the energy required to
heat a given quantity of gas one degree is only the sum
of the corresponding "translational", "vibrational", and
"rotational" motion of the molecules, while, at
constant pressure, the energy involved in the expansion
is added. Since only translational heat is involved in
expansion, where vibrational and rotational heat are
significant fractions of specific heat, ratios of specific
heat at constant pressure to specific heat at constant
volume are reduced.
From the perspective of the Maxwell-Boltzmann
kinetic theory of gases, only the mutual repulsion of
molecules, atoms, and ions (at very close proximity),
(which result in effectively elastic rebound from
collisions, like those of "tiny billiard balls") are dis-
cernible. As mentioned, the empirically established
gas laws of Boyle and Charles can be derived from the
theory. However, from the "interatomic" perspective
discussed in the previous section hereof, molecules,
except for those of inert gases, are more complex than
balls . A more accurate analogy would be an
assemblages of balls as represented by the models
shown in Figure 1, except that they are not rigidly
connected, but vibrate about equilibrium relative posi-
tions, since molecules, atoms, and ions are attracted to
and repelled from one another by forces (mostly
electrostatic and magnetic) which vary with their
degrees of proximity, relative positions, and
orientations. From this perspective, it is apparent that
the kinetic theory of gases, including the "Boltzmann
factor", applies to "vibrational" and "rotational" as
well as "translational" heat.
NOTES ON THERMODYNAMICS
Carnot "founded" (5) the science of thermodynamics
with his book, a partial title of which is "On the
Motive Power of Fire", in which he cited empirical
data showing that, in expansion of a gas, heat is
transformed into "work" and conversely, in
347
compression, "work" is transformed into heat, a half
century before Maxwell and Boltzmann presented their
kinetic theory of gases (which includes the postulate
that that which is sensed and measured as pressure of
a gas is the integrated effect of impact of molecules
upon the surface). If, as implied by the "tiny billiard
ball" analogy, the molecular motion, which the kinetic
theory of gases equates to heat, was only translational,
thermodynamics would be much simpler since the
interchange between heat and work would be complete
and direct in all adiabatic processes.
Carnot "founded" the science of thermodynamics to
provide a rational approach to the design of steam
engines for maximum efficiency (conversion of as
much of available heat as possible into work). He and
such successors as Rankine and Joule developed and
verified thermodynamic theory which is still in use,
with reference to empirical data, and included the "gas
laws" of Boyle and Charles, which were also based on
empirical data, before Maxwell and Boltzmann
proposed the kinetic theory of gases and, of course,
before that theory had been elaborated to include
consideration of vibration and rotation of molecules.
"STATES" OF MATTER (THE VAN DER WAALS'
EQUATION OF STATE)
Thermodynamics, as noted above, is concerned, from
a practical perspective, with transitions of "heat" to
"work" and vice versa. In its rudimentary form, such
consideration involves the "gas laws", which, though
originally based on empirical data, can be derived
from the "kinetic theory of gases". However, as each
of us has "always known", the gaseous state is only
one of several in which matter exists. The first
application of thermodynamics was to steam, which is
the gaseous phase of water, which, when cold enough,
freezes into ice.
The "gas laws" of Boyle and Charles, for purposes of
"engineering thermodynamics" are usually combined
in the "ideal gas equation":
PV = nRT (3)
where:
P is pressure,
V is specific volume,
n is the quantity (gram moles) of gas,
R is the "gas constant", and
T is the absolute temperature.
Although "live" or "dry" steam behaves as an "ideal
gas", at lower temperatures and higher pressures,
steam condenses to liquid water and the "gas laws"
cease to apply.
Van der Waals accounted for this changed behavior
with the change from the gaseous to the liquid state in
terms of the Maxwell-Boltzmann "kinetic theory of
gases" by assuming an attraction (a) between, and a
finite volume (b) of molecules, to derive (in 1873 (5))
his "equation of state":
(P+a/V 3 )(V-b) = nRT
as given in Ref. (11).
(4)
Considered from the intermolecular perspective, the
van der Waals equation of state implies that, as two
molecules approach one another they are mutually
attracted by a force which varies inversely with their
separation until they collide and bounce apart "like
tiny billiard balls". After bouncing apart, each
molecule flies until it bounces off another. If the
temperature T, is above the "boiling point", the
molecules behave in accordance with Maxwell-
Boltzmann "kinetic theory of gases" and, of course, as
an "ideal gas" in accordance with the "gas laws". At
lower temperatures, their kinetic energy is insufficient
for each molecule to escape the attraction of its
neighbors before it is bounced back by collision with
a molecule of the gas. This effect, at liquid gas
interfaces, is known as "surface tension".
As it seems from casual observation and all but the
most precise empirical data, water (as well as other
liquids) is considered in hydraulics and hydrodynamics
to be of constant density. Although more precise data
have shown water and other liquids to have finite
compressibilities and thermal expansion coefficients,
the fact that they are considered to be negligible in
most practical applications is evidence that the
amplitude of the molecular motion, apparent as "heat",
is small compared with the gross linear dimensions of
the molecules, so that it can be considered "vibrational
heat" like that of the relative movement of atoms,
ions, and other groups of atoms within molecules as
discussed above.
Considered from a closer perspective, the analogy of
molecules to "billiard balls" is seen to be a simplifying
approximation which applies to gases and liquids at
temperatures high enough that the amplitudes of the
vibrations of "vibrational heat" are large compared
with the deviations from spherical symmetry of the
molecules. At lower temperatures, the weaker
vibrations (which are still random) result in repeated
348
"trials" (reorientations) until adjacent molecules "fit
together" and move closer, with a resulting increase in
their mutual attraction (the "van der Waals force"),
which, along with their asymmetry, maintains their
relative positions and orientations. This is the process
we observe as "freezing", "solidification", or
"crystallization".
Each of us has been aware since early childhood that
water boils and freezes, and as our vocabularies
increased we learned that "water", "ice", and "steam"
are three "phases" or "states" of the same substance.
With the passage of time, we found out that most other
substances also can exist in "gaseous", "liquid" and
"solid" states.
Our earliest memories (not quite earliest for those in
my age group) include the sight of "neon signs"
glowing on store fronts, billboards, etc. Later, we
heard or read that the neon lights were tubes filled
with rarified gases, (neon, in the originals, which glow
red). Other gases glow in other colors, but they are
all called "neon signs" which glowed when "ionized"
by the flow through them of electric current. In this
context, we learned, as we became more sophisticated,
that "ionization" meant the separation of electrons
from atoms (or the ions of molecules from one
another), after which, in an electrical field, the
electrons (and negative ions) are attracted to the
"anode" (positive electrode), and the positive ions
(atoms or groups of atoms with electrons missing) are
propelled toward the cathode (negative electrode). If
the electrical field is sufficiently strong, and the free
paths are long enough, the ionization is maintained by
collisions, which "knock" more electrons free as
others enter atomic orbits with resulting luminosity.
Gases are also ionized by temperatures high enough
that the "vibrational heat" is sufficient to overcome the
attraction between their ions and collisions between
molecules "knock them apart". Ionized gas is referred
to as "plasma", and as a "fourth state of matter"(9).
Plasma glows. Its light emission be can seen, from
the "intra-atomic" perspective, to result from the
falling of electrons into orbit. The color, wave length,
or spectral characteristics of the light are unique for
each element, and are used in spectroscopic analysis,
to identify them The familiar blue flame of a gas stove
results from such luminosity of plasma of which
carbon and oxygen are principal constituents, and the
red light of a railroad "fiizee" is the spectral emission
of strontium,
Van der Waals (in 1873) considered the relationship
between temperature, pressure, and specific volume of
substances close to their "boiling points" from the
perspective of the recently (1871) presented
Maxwell-Boltzmann "kinetic theory of gases" ,
assuming a finite size of each molecule and an
attraction between similar atoms and molecules which
became known as the "van der Waals force". A half
century or more later, from the intra-atomic
perspective of the "Bohr atom", the "van der Waals
force" was seen to be "caused by a temporary change
in dipole moment arising from a brief shift of orbital
electrons from one side to another of adjacent atoms or
molecules" (16).
The van der Waals equation of state was derived as a
basis for thermodynamic analysis of systems involving
"wet steam" in which water is present in both gaseous
and liquid states. The "van der Waals force" is also,
as discussed a few paragraphs back a factor in
crystallization, the transition from the liquid to the
solid state. However although it plays a role, the "van
der Waals force" is not all that holds crystals together.
Other forces, visible from the "interatomic" and
similarly close perspectives, contribute. Thus though,
as would be expected (based on the description of
crystallization a page back, in which the "van der
Waals force" was invoked), most substances "shrink"
when they solidify, water does not. My impressions,
from "intra-atomic", "inter-atomic" and
"intermolecular" perspectives are too "fuzzy" to
include as a logically cohesive part of this paper, but
a few seem sufficiently relevant to mention. Some
molecules, particularly those of a number of "organic"
compounds, are so large and/or complex that they
exist only in the solid state. They "decompose" (break
into smaller molecules) at rates dependent on
temperature and the "reaction kinetic" properties of the
substance. Conversely some compounds which are
liquid at "room temperature", "polymerize" (their
molecules join to form larger ones, which exist only in
the solid state) when heated or "catalyzed" and they
solidify.
Crystalline and chemical bonds are similar in that they
are effects of and governed by forces and principles
discernible from "intra-atomic", "inter-atomic", and
"inter-molecular" view-points and that, from the
empirical perspective, they are "exothermal" (evolve
heat) (because solidification prevents translational and
rotational movement of atoms and molecules so that all
thermal energy becomes "vibrational heat", which is
"sensible").
349
Purity is a relative term. The word "pure" is often (in
some contexts, usually) preceded by a percentage.
"100% pure" is not quite credible. So, all substances
are mixtures. Each solid and liquid has a finite vapor
pressure (or gaseous decomposition product) and thus
an odor, which may not be apparent to most humans,
but is to many animals and can be detected by means
of spectroscopy. Similarly, gases and solids are soluble
in liquids and gases and liquids are absorbed or
adsorbed by solids. The distinction between the states
of matter is, thus, based on practical and empirical
considerations.
Many familiar substances, including wood, whipped
cream, mud, smoke, mashed potatoes, glue, wet-
cement, and shaving cream are composed of matter in
more than one state and owe their characteristic
properties to interactions of their components in two or
more states. The properties of such mixtures depend,
to some extent, upon the "state of aggregation" (the
size, shape (often fibrous), hardness, frictional
properties, and distribution of solid components, and
the sizes and distribution of droplets, bubbles, and
pores, and, where such mixtures seem solid, from the
"empirical" perspective, upon the structure of the
substance, including the bonds (molecular, crystalline,
and other) between the components, as well as their
distribution.
Matter, in its various states, has been viewed from
"practical" and "empirical" perspectives. With a view
to prediction of the behavior of systems, empirical data
are plotted, and the indicated relationships are
expressed in algebraic equations, which, when used in
analysis with calculus or differential equations, are
assumed to apply to infinitesimal intervals, an
assumption whose validity, is questionable when
considered from the "intermolecular" or other
theoretical perspectives which have been discussed
herein, but have been essential to the advance in the
states of the arts to which they apply, and, where the
principles of logic and mathematics have been applied
to the satisfaction of the scientific community, have
come to be accepted as "rigorous theory".
Although the van der Waals equation of state (equation
(4)) relates pressure (P), specific volume (V), and
absolute temperature (T) for substances under
conditions where both gaseous and liquid states exist,
the phrase "equation of state" seems to have acquired
the more general meaning of any equation relating
specific volume to pressure, such as that for adiabatic
compression or expansion of an gas";
PV 7 = a constant (5)
which has been referred to as the "gamma (y) law
equation of state" , which is considered to be one of the
"ideal gas laws" derived from the empirically
established laws of Boyle and Charles, which can be
derived from the Maxwell-Boltzmann "kinetic theory
of gases"(17) The "wet steam", to which the van der
Waals equation of state was first applied, is a
"colloidal suspension" of liquid water in gaseous
steam. As has been mentioned, "colloidal
suspensions" consist of droplets or particles of liquids
or solids which are too tiny to settle out from the fluid
in which they are suspended. Qualitatively, their
failure to settle out can be ascribed to their
bombardment from all directions by molecules close to
their size and (in the case of "wet steam") of a similar
density. A quantitative explanation is beyond the scope
of this paper. However, the observation, in 1827, by
Brown, of what came to be known as "Brownian
motion" of colloidally suspended cells and particles,
was explained on these bases (in 1871) by the
Maxwell-Boltzmann "kinetic theory of gases" and
elucidated by the concept of "Maxwell 1 s demons" (5).
It is my impression that the phrase "equation of state"
was first used to identify the relations between
pressure (P), temperature (T), and specific volume (V)
of "wet steam", a colloidal suspension of liquid water
in gaseous steam. In the "gamma equation of state" in
its original application, to "ideal gases", the effect of
temperature is taken into account by the use of
"gamma" the ratio of specific heat at constant pressure
to that at constant volume (= C p /C v ).
For hydrodynamic consideration of the behavior of
substances in other states or "states of aggregation",
experimentally determined relationships of specific
volume (V) to pressure (P), referred to as "equations
of state" (often "gamma law" equations of state" with
empirically determined values of gamma) are used.
From the practical perspective of the designer of
hydraulic systems, water and other liquids are seen as
incompressible fluids. However, in consideration of
large or sudden changes of pressure (particularly,
those of detonation and the strong shock waves it
induces), their compressibility must be taken into
account (11).
To some, the mention of detonation in the above
paragraph may seem to be a change of subject from
that of "fire" indicated in the title hereof. It's not,
because detonation is a form of combustion as will be
pointed out in the section hereof headed -
EXPLOSION AND DETONATION. However, it may
350
be somewhat premature at this point, so farther
discussion is postponed until we get to it there.
The subject of detonation came up at this point because
consideration of detonation from a theoretical
perspective involves relationships between pressure
and specific volume which, as mentioned above, have
come to be known as "equations of state", even for
porous solids, where materials in more than one state
are present. For such materials, a more appropriate
term for the pressure/volume relationship might be
"equation of state of aggregation" (which doesn't "roll
off the tongue like "equation of state")
Fire, usually, involves changes of state. Yellow flames
of candles and wood and trash fires are glowing black
smoke (a colloidal suspension of carbon particles
(soot), the result of evaporation and condensation of
the fuel or volatile components or decomposition
products thereof and the subsequent decomposition of
this colloidally suspended condensate to carbon and
gaseous products whose oxidation provides the heat
which sustains the process. Such fires involve
transitions from solid to liquid to gaseous states,
followed by reversals to the liquid state (in a colloidal
state of aggregation), and finally back to the gaseous
state before the oxidation takes place.. The familiar
blue flame light of a gas stove flame is spectral
emission of the plasma to which the gaseous products
of combustion have changed. Glowing coals glow due
to the oxidation of solid carbon to gaseous carbon
dioxide.
That changes of state occur at specific temperatures
was common knowledge long before quantitative scales
of temperature were proposed. Both Fahrenheit and
Celsius established their "degrees" as fractions (1/1 80th
by Fahrenheit, and l/100th by Celsius) of the difference
between the freezing and boiling points of water. The
scales having been established, and instruments for
measuring temperature having become available,
determinations were made of freezing and melting
points of other substances. Since it was known that
fuels started to burn when heated sufficiently, it
seemed reasonable to determine the "ignition point" or
"kindling point" (the lowest temperature at which a
substance will continue to burn without addition of
external heat (16)) of each of various substances. For
most fuels, which require air, oxygen, or some other
oxidant for combustion, such determinations present
experimental difficulties. Pressure had been found to
affect freezing and boiling points and, it was
suspected, might affect kindling points. Where the fuel
was solid and the oxidant gaseous, the temperature and
fiber stress of the fuel and the temperature and
pressure of the oxidant could interact to affect ignition.
These experimental difficulties seem to have resulted
in such skepticism on the part of their editors
regarding "ignition points" that none of the standard
handbooks (10,11,17) at hand as I write this, includes
such data. These difficulties are alleviated for
substances or mixtures which contain or include
oxygen or another oxidant or which react
"exothermally", (with the evolution of heat). Thus the
Smithsonian Physical Tables (18) include tables of
ignition temperatures of gaseous and dust mixtures
with atmospheric air of several fuels and several
publications (4, 19, 20, 21) include "ignition points"
or "explosion temperatures" of pyrotechnics and
explosives.
Although my doubts regarding the concept of an
"ignition point" as a physical property of each fuel
dated from my childhood observation of "spontaneous
combustion", the general concept by those with whom
I discussed such matters, (and apparently others (6V£))
combined with my practical experience with "lighting"
fires persuaded me of its general validity. I visualized,
the propagation of fire as the progressive heating of
the fuel, by the heat of combustion, to its "ignition
point" .
"Fire", the subject of this paper, has been defined (2)
as "The visible heat and light emanating from any
body during the process of its combustion or burning. "
As has been pointed out, or at least implied, in the
foregoing, heat and light are forms of energy, of
which my changing perspectives are discussed in the
following.
CHANGING PERSPECTIVES OF ENERGY
As mentioned before, herein, each of us sees things
from a constantly changing series of perspectives. The
following account of the succession of my perspectives
of energy is included in the belief that it roughly
parallels that of most who may read this, as well as
those who have considered such matters in the past and
whose views have been alluded to.
My earliest impression of energy was that of a busy
person who could stay busy all day. This perspective,
which seems to be that of the fitness program
participant who reported "having more energy" as a
result of a low calory diet and an exercise program
(which seems contradictory from perspectives I have
gained more recently.)
351
As seen from this earliest perspective, play required
energy. The experiences which came with play,
coasting down hill, bouncing balls, etc., lent reality to
views of energy from perspectives to be gained in
school and elsewhere.
Work, like lawn mowing, also took energy, and after
such work, I had less energy left for other activities.
After school work, on the other hand, I had more
energy for play.
In ninth grade "General Science", I began to acquire
"physical "perspectives of energy. "Work" was
defined as a form of energy equal to force times
distance, which was transformed to other forms of
energy as it was accomplished. For example, the
work of lifting a pound weight a foot was transformed
to one "foot-pound" of "potential energy". If the
weight is dropped, the potential energy is transformed
to "kinetic energy".
My science teach, aware that we were also taking
algebra, taught us equations for work (W):
W = Fx
where F is force and x is distance,
potential energy (PE):
PE = mhg = wh (6)
where m is mass, w = mg is weight, h is
height, and g is the acceleration of gravity,
and kinetic energy (KE):
KE = mv 2
where v is velocity.
(7)
Since we were familiar with the English system of
units, he told us that work (w) was measured in foot-
pounds, force (F) in pounds, distance (x) in feet, mass
(m) in "slugs" (a mass of one slug weighs 32 pounds)
and velocity (v) in feet per second. Thus, I began to
see things, including energy, from "analytical" and
"mechanical" perspectives.
He told us that, as a weight falls, the sum of its
potential energy and kinetic energy remains constant in
accordance with the "law of the conservation of
energy". He demonstrated the conservation of energy
with a pendulum, which continued to swing,
alternately transforming potential energy to kinetic
energy and kinetic energy to potential energy. He
explained the reduction of the swing as the result of
friction, which, he said, transformed the kinetic energy
to heat, which, he said, is another form of energy.
As its name implies, "General Science" includes many
subjects, including those mentioned above and heat,
chemistry, electricity, waves, (gravity (on water
surfaces), elastic (including sound), and
electromagnetic - radio, light, etc.), radiation (usually
electromagnetic waves, but sometimes streams of such
particles as electrons, protons, etc.). Each of these
subjects deals with one or another form of energy
and/or transformations of one form of energy to
another. The conservation of energy was shown (from
perspectives assumed to be familiar to ninth graders)
to apply to all transformations from one form to
another.
Play, experience, conversation, observation, and
recreational reading extended the range of my
perspectives, some of which have been discussed
herein before. Some early impressions, like that (from
an Aristotelian perspective) that heavy objects fall
faster than light ones, were corrected in the above
mentioned "General Science" course. It was explained
that air friction slows light objects more than it does
heavy ones. Similarly a sled, coaster wagon, or
bicycle is slowed less by friction on a steep hill than
on a gentle slope, so it goes faster. If it weren't for
friction, the speed, after a given change in elevation
would be unaffected by the slope, since all of the
potential energy would have been transformed to
kinetic energy.
As I advanced through high school, geometry (both
plane and solid), trigonometry, and advanced algebra
provided "graphical" and "analytical" perspectives,
and chemistry and physics provided "scientific"
perspectives, from which I could reexamine
impressions gained, since early childhood, from such
previously mentioned perspectives as "eyewitness",
"common sense", "intuitive", and "practical".
The combination and interaction of experience,
observation, and education persuaded me that work,
heat, light, and sound are forms of energy and such
forces as those of gravity, and magnetic and
electrostatic "attractions of opposites" are factors of
energy, as are time and distance, and that, in any
isolated system, the total energy remains constant
(which is "the law of the conservation of energy")
The freshman physics course, which was required for
all M.I.T. students, in which the notation of calculus
(also required) was used to express Newton's laws of
352
motion and gravity, and to derive from them equations
of motion of falling bodies, basic principles of
ballistics, and the equations of orbital motion of the
planets, as Newton had nearly 300 years before,
showing that Kepler's Laws, which were
generalizations of Brahe's observations, were empirical
verification of his laws of motion and gravity.
The lecturer of the course Nathaniel H. Frank, who
was also the author of the textbook "Introduction to
Mechanics and Heat" (22), used in the course, which
included consideration of the language of physics and
unit systems (metric and English), kinematics (both
linear and plane - introducing the concept of vectors),
kinetics, and statics of mass points and particles
(including Newton's laws of motion and gravity -
planetary motion is considered from Copernicus' and
Kepler's extra orbital perspective, from which the
planets are seen as mass points), linear and plane
dynamics, work and energy, potential energy,
hydrostatics, elasticity, acoustics, heat conduction,
thermodynamics, the first law of which is the
conservation of energy, which it shows to be
applicable in gases to adiabatic systems (from which
no heat is lost), as well as to reversible mechanical
processes (as distinguished from irreversible processes
such as frictional heating).The text discusses "entropy"
(S), a term coined by Clausius (5) for the ratio
(S = Q/T) of the heat content (Q) of a system to its
absolute temperature (T), which was shown to be a
measure of the unavailability of the heat for
transformation to work, and quotes Clausius statement
of the first and second laws of thermodynamics in
closing, - "The energy of the universe remains
constant. The entropy is always increasing. "
Recently, in retrospect, I have wondered how I
reconciled this statement with my impression, from the
"cosmic" perspective gained in recreational reading,
that the sun and other stars had been radiating energy
for billions of years. Perhaps Frank had cited
Einstein's "Special Theory of Relativity", which holds
that mass (M) is a form of energy (E) which is
expressed in:
E = Mc 2
where c is the speed of light.
(8)
I do remember having read, a few years earlier, that
the energy radiated by stars was the product of
reactions of atomic nuclei and that there was enough
energy in a glass of water to propel an ocean liner
across the Atlantic, which had led me to envision a
device capable of transforming nuclear energy into
work, which would fit into the rear hub of a bicycle
(like a coaster brake). I had no idea as to how this
might be accomplished, but thought it would be nice
to have one installed in my bike. My freshman year
was 1934-'35. A decade later, the conversion of
nuclear to other forms of energy (on a much larger
scale) was an important factor in the conclusion of
World War II. I still have no idea as to how it might
be applied to bicycle (or even automobile) propulsion,
but it is now used to propel submarines and generate
electric power, some of which has been used to charge
the batteries of electrically propelled cars. However,
in the 1930s, nuclear energy was considered to be the
"stuff of science fiction" (like space travel) and
engineering courses were concerned with more
"practical" matters.
Another freshman course was Synthetic Inorganic
Chemistry.
Sophomore courses included physics (optics,
electrostatics, electrodynamics, and magnetism)
differential equations, machine drawing, physical
chemistry , graphic analysis , and industrial
stoichiometry.
As a mechanical engineering major, I took courses in
applied mechanics (including stress analysis,
kinematics, and kinetics), metallurgy, fluid
mechanics, materials testing, manufacturing and
construction processes, as well as such "general"
subjects as English, history, descriptive astronomy,
and economics.
Each course considered its subject from a unique
perspective, each of which was somewhat familiar to
me from earlier education, experience, and reading,
and some of which have been mentioned herein. From
one perspective it is apparent that each form of energy
is either potential or kinetic energy or a combination
thereof, and that other forms of energy, such as heat,
sound, electromagnetic radiation (including light), etc.
are manifestations of these. Each classification is the
result of the perspectives from which it has been
considered. From the "inter molecular" perspective of
the Maxwell-Boltzmann kinetic theory of gasses, for
example, heat is seen as kinetic energy of molecules,
ions, and atoms. From the "interatomic" perspective,
which has been discussed, it becomes apparent that,
while this view is applicable to "translational" heat,
"rotational" and "vibrational" heat are combinations of
kinetic and potential energy as are sound and vibration
as well as gravity waves on water surfaces. An
electrical charge is potential energy while "direct
current" is kinetic energy of electrons and "alternating
353
current" alternates between kinetic and potential
energy. The "heat of combustion" of fuels, in general,
is the potential energy of the attraction of the atoms
and ions of the carbon, hydrogen, and other elements
with positive valences, which they may contain, to
those of oxygen.
Consideration from the several perspectives discussed
herein has left me with the conviction that physical and
chemical phenomena and processes are, in general,
transformations of energy between forms, often
involving changes of state of the matter involved.
Although views from several perspectives, which have
led me to this conviction, have been discussed
previously herein, the following account of my
progress toward it (as recalled decades later) may tend
to substantiate the conviction in the minds of readers:
My earliest quantitative impressions related to energy
were in terms of power (which, I was to learn, means,
in general, the rate at which energy is transformed
from one form to another). Light bulbs were (and are)
graded in watts, a unit of power. Then, as now,
illumination of a room or other space was quantified,
by many, in terms of "watts of light". I'm still not
sure that those who refer to light in these terms are
aware that the watt is a unit of power and I doubt that
many recognize (as I have come to with the passage of
years) that the rating of a light bulb in watts is a
statement of the rate at which it is expected to
transform electrical energy, by "ohmic heating" into
heat, which is, in turn transformed, as "black body
radiation" into electromagnetic radiation, mainly in the
visible range of the spectrum. My earliest impressions
of the relative power of automobiles and outboard
motors came from advertisements of their
"horsepower". I heard (or read) that James Watt had
coined the term "horsepower" for use in
advertisements of the steam engine he had invented in
terms which, he hoped, would appeal to his intended
customers. In 1783, based on experiments with a
strong horse, he established the value of a horsepower
as 550 foot pounds per second. By 1800, the metric
system, which included the watt, so named in honor of
Watt, who had defined "power" as a physical quantity
(a horsepower is 746 watts), had been accepted by an
international commission and has since been adopted
internationally by scientists. Although most ratings of
devices which are activated by electricity seemed to be
in terms of power, it was paid for by the "kilowatt
hour", a unit of energy. Of course, a kilowatt hour is
more than 2 x /i million foot-pounds (the foot pound was
the first quantitative unit of energy I learned about in
school).
A difficulty in the consideration of transformations of
energy in quantitative terms is the variety of units in
which physical quantities (including energy) are
expressed. The above discussion of transformation of
energy between mechanical forms is a repetition of the
explanations, (as I remember after sixty-some years)
by my science teacher, who used the English system,
with which we were familiar. It seemed reasonable
that it took a foot-pound of work to lift a pound a foot.
I learned, in ninth grade "General Science", that the
work of lifting an object weighing a pound a foot was
transformed into a foot-pound of potential energy and
that, if the object was dropped, the potential energy
would be transformed into kinetic energy. All of which
seemed to confirm my previous experience and the
aphorism that: "What goes up, must came down.",
which has been applied, with varying degrees of
pertinence, to prices, temperatures, unemployment,
voltages, and the popularity of entertainers. I had also
noticed that some things, when lifted and dropped on
to same surfaces, bounced, and/or made a noise when
they hit. With the passage of time, I learned to explain
the bounce as the result of the transformation of
kinetic energy to elastic potential energy followed by
its transformation back to kinetic energy, and the noise
as the result of the transformation of same of the
energy to sound (which is alternately kinetic and
potential energy). Nothing seems to bounce forever,
because, I learned, at each bounce, same of the kinetic
energy is transformed into sound and some is
transformed into heat. The foregoing seemed a
satisfactory qualitative explanation, but a
demonstration in quantitative terms was difficult, not
only because of the problems of measuring the
quantities of sound and heat evolved during a bounce,
but also because of the problems of conversion
between the units in which the results of such
measurements would be expected and those in which
kinetic energy is expressed. (Energy has been
expressed, by specialists in various fields, in
foot-pounds, inch-ounces, foot-tons, BTUs, ergs,
joules (watt-seconds), watt-hours, kilowatt-hours,
calories (cal.,(gm)), and Calories (cal.,(kg) or
kilocalories). Some scientists express the view that
confusion can be eliminated by the use of the
"universal" metric system, Perhaps, but a Ph. D.
chemist once told me of an instance when he and a
colleague allowed the ice cubes in their drinks to melt
in their mouths, assuming that this would absorb the
calories in the alcohol , forgetting that some
nutritionists refer to Calories as "calories" (so they'd
have had to melt two kilograms, rather than two grams
of ice to absorb the 150 nutritionists "calories" in each
354
drink). In view of these difficulties, I satisfied myself
with consideration of this matter in terms of the
"coefficient of restitution" the ratio (e=v 2 N x ) of the
(upward) velocity (v 2 ) of an object after it bounced to
its (downward) velocity (Vj ) before it hit.
The transformations of energy, mainly mechanical
forms (work, kinetic, and potential energy are
considered above, from "eyewitness" , "common
sense", and "empirical" perspectives). As a student of
mechanical engineering, I acquired a thermodynamic
perspective, from which transformations heat and work
are considered and that of applied mechanics (which
considers relationships of stress and strain, the integral
of which is elastic potential energy). Other courses,
which are mentioned a page or two back, presented
hydraulic, hydrodynamic, aerodynamic, graphical,
analytical, kinematic, dynamic,, and stoichiometric,
and other chemical (including organic) perspectives.
Recreational reading had, from early childhood,
provided a succession of perspectives, including those
of nursery rhymes, Bible stories, Aesop's fables, fairy
tales, Indian legends, Greek and Norse mythology,
history, geology (24), astronomy (22), cosmology
(23) , and atomic and intra-atomic physics (9) .
Considered from those perspectives which seemed
"scientific" to me, in about 1940, I saw (and still see,
with a few revisions based on what I've learned since
then) energy transformations in the universe and the
world about as follows:
Technical discussions should follow logical or
chronological sequences, preferably both. The
sequence of my perspectives, as remembered after fifty
years, is neither. If I have failed in the following
effort to put them in "proper" order, I hope that
readers will be tolerant.
In 1940, I was unaware of the "big bang" theory of
the origin of the universe, which had been proposed
(by Le Maitre (5)) in 1927. (I was to learn, from
Gamow, of the theory, a few years later.). However,
I had been aware and accepting of the
Chamberlin-Moulton theory that the planets, (including
the earth) of the solar system were the "drops" formed
in the "breaking" of a tidal wave raised from the
surface of the sun to a connecting arm by a passing
star, each of which was drawn together by gravity. In
the contraction, gravitational potential energy was
transformed into kinetic energy, which was, in turn,
transformed into work, and then, to heat, some of
which was radiated as black body radiation, cooling
the planets until solid surfaces were formed, the
surface temperature of each planet continued to drop
until equilibrium was reached between the radiant
energy received from the sun and that lost by radiation
from the planet. As each planet acquired an
atmosphere by diffusion and volcanic eruption from its
interior and by gravitational attraction of interplanetary
gases and "solar wind", the temperature, in each case,
was affected by absorption of radiation by atmospheric
gases (referred to, in recent years, by
"environmentalists", as the "greenhouse effect"), by
the point to point variation of the "albedo"
(reflectivity) of planetary surfaces, in combination with
the rotational and orbital movement of each planet
about non-parallel axes, has resulted in variations of
surface and atmospheric temperatures with time and
location, which result in the phenomena referred to as
"weather" and "climate". The water vapor which has
been a significant fraction of the earth's atmosphere
has contributed to the complexity of these phenomena
since the range of temperatures with include the mean
equilibrium temperature of the earth's surface and
atmosphere is conducive to the existence, of significant
fractions of this water in each of all three (gaseous,
liquid, and solid) states or phases, transitions between
which are accompanied by mutations between
translational, vibrational and rotational heat, which are
seen from the "empirical" and "thermodynamic"
perspective as "latent heats of fusion and
vaporization", and changes of specific volume in
which heat is transformed into work and consequent
convection which transforms work into the kinetic
energy of wind.
The liquid water, which covered most of the earth's
surface, dissolved some of the gases and solids with
which it came into contact to become a "primordial
soup" in which many chemical reactions were bound
to take place, producing a wide variety of chemical
compounds of varying complexity. It has been
postulated that, given "enough time", a molecule
would form which would be capable of reproduction
and have the other characteristics of a living cell, and
that such cells would further organize themselves and
adapt to their environments to evolve to the many
organisms which have existed on the earth. Statistical
calculations (in the 1950s), which are cited by
"creationists", indicate that there hasn't been "enough
time" . More recently, numerical models of
"coevolution", have reduced estimates of "enough
time" (26).
I have yet to acquire mathematical or computational
techniques or perspectives from which I can consider
with confidence the relative validity of the views of
355
"evolutionists" and "creationists", but, based on
paleontolological evidence, I am persuaded that living
organisms have existed on the earth for billions of
years, which implies the presence of liquid water, and
that the equilibrium between radiant energy received
(less than 0.05% of the sun's radiation) and lost during
this period, would require radiation by the sun of a
quantity of energy which is credible only on the basis
of the consideration that (as stipulated in Einstein's
"Special Theory of Relativity") that mass (M) is a
form of energy (E) as related by:
E = Mc 2 (8)
where c is the speed of light.
My view of energy transformations, past, present, and
anticipated, which seem relevant to the subject of this
paper, is outlined below:
Mass is transformed, in the interior of the sun and
other stars, by thermonuclear reaction, to heat, which
is transformed, at or near the surfaces of the sun and
stars to "black body (electromagnetic) radiation". A
fraction (referred to as the "albedo" of the planet) of
the electromagnetic radiation which is intercepted by
each planet is reflected. Most of the rest is
transformed into heat, and, eventually, reradiated as
"black body radiation" (maintaining its surface
temperature equilibrium) . Some of the radiation
intercepted by the earth, is transformed, by
photochemical reactions (including photosynthesis) into
(chemical) potential energy, which, for the organic
compounds synthesized in photosynthesis which are
used as fuels, is referred to as their "heat of
combustion", and when they are used as foods as their
(nutritionist's) "calory content". In animals (including
humans) the potential energy in foods referred to as
"nutritionist's calories" is transformed into work and
heat by movement and metabolic processes. Fire
transforms the "heat of combustion" of a fuel into the
kinetic energy of molecules referred to by some as
"sensible heat".
Although neither prehistoric man nor I (as a kid)
considered such matters from these perspectives.
Transformations of energy, by fire from chemical
potential energy ("heat of combustion") to heat, and
from heat to light, sound, work, and kinetic energy
have been applied to form the basis of most "know
how", trades, technologies, crafts, arts, and sciences,
and provided a series of perspectives, to and by
mankind through prehistory and history, and to (by)
me in the course of growing up, education,
recreational reading, and research, both literature and
experimental, of the world and everything in it, and of
all that has happened.
The word "efficient" seems to have originally, meant
"effective". With the development of systems for the
transformation of energy from one form to another,
when preceded by a percentage, it has come to mean
the percentage of available energy which has been
transformed as intended.
MY PRE-'41 PERSPECTIVES OF FIRE
As mentioned earlier in the section headed: "A KID'S
PERSPECTIVE OF FIRE", my earliest impression of
fire was that of a yellow flame, which I generalized to
the view that fire and light are aspects of the same
thing. Grown ups talked about "lighting" fires and
about "firelight", usages which I adopted.
Anyone who has tried will recognize the difficulties of
recalling how the world looked and what each word
meant in early childhood, without having one's
memories distorted by more recent learning and
experience. In view of these difficulties, I'm sure that
this account in not completely accurate (for example,
in the final paragraph of the previous section headed
"LANGUAGES AND PERSPECTIVES" I quoted,
adults, explaining that the visible "steam" from a
teakettle was not steam, but a suspension of droplets of
liquid water, I included the words "colloidal" and
"aerosol", neither of which are defined in terms
applicable to the explanation in a 1939 dictionary (2),
so they couldn't have been included in an explanation
to me in the 1920s), but it is the best that I can do.
I could see the light and feel the heat of a fire and of
the sun, and got the idea that light and heat are
related, but not the same. If the fire was in a stove, I
couldn't see its light, but could feel its heat and,
though I could see sunlight reflected from snowbank,
I didn't feel much heat.
In time, I began to see that heat is needed to start a
fire and that fire is a source of heat. The heating
elements of other sources of heat, like electric stoves,
toasters, and space heaters, glowed when they were
hot enough, and I began to recognize that the light of
a flame was an effect of its heat. After seventy some
years, I can't remember my introduction to the concept
of an "ignition" or "kindling point" as a property of
each fuel, but I do remember my observation (which
is described in that earlier section) of "spontaneous
combustion", which was the source of my reservations
regarding that concept. Practical experience induced
356
me to accept the concept, with the reservations alluded
to. Paper was easy to light with a match, apparently
because its thickness was small compared with the
dimensions of a match flame so that some of it could
heated to its 'kindling point". As a Boy Scout, learning
to build a fire without paper, as required to pass the
second class firemaking test, I was taught to use twigs
or shavings of dimensions similar to those of a match
stick to pick up the flame from the match. It took a
few seconds, apparently, to heat the twigs to their
kindling point. Once the twigs were burning, larger
pieces of wood were placed in the flame, The larger
sticks took longer to "catch fire", as I saw it, because
there was more wood to heat to its "kindling point". It
became apparent that the ignition and spread of fire
depends upon the heating of the fuel to its kindling
point by an external source of heat or the established
fire.
I was told, when building a fire, to place the new
sticks or logs, above those which were already
burning, because "Heat rises.". As I grew older, I
learned that the effective rise of "heat" was, more
accurately, stated as "Hot air rises. " due to
convection, which occurs because fluids, including air,
expand when heated, and become buoyant with respect
to fluids of similar composition (but cooler.) I learned
that other heat transfer mechanisms were conduction
and radiation.
Like, I suppose, most people, both living and dead
(some for long times), I had experienced heat transfer
by all three mechanisms since early childhood. My
early experiences with light and "radiant heat" (which,
I learned , after a few years , is called " infrared
radiation" in the language of physics), are recalled a
page back. We have all felt the heat conducted from
warm and hot objects. In the kitchen, heat is
conducted by a frying pan, from the burner to the
food, in toasting and broiling, heat is transferred by
radiation. Boiling and baking involve convection.
Convection is utilized in a hot air heating system, to
transfer the heat, from the furnace in the basement,
through a duct system to living quarters on the floors
above, and, for fireplaces, and coal and wood furnaces
and stoves to provide the "draft" of air needed to keep
the fire burning.
My memories of youthful impressions of heat transfer
and, more specifically, convection are outlined above.
In the course of the recall, it occurred to me to check
recent references regarding the current meanings of the
words. Dictionaries, both 1939 (2) and 1976 (16)
define "convection" essentially as described above,
The Random House Dictionary (1) defines it as "The
transfer of heat by the circulation of the heated parts
of a liquid or gas", with no mention of cause of the
circulation. The term seems to be sometimes used in
this latter sense.
I had been aware, since early childhood, that fire
required air. I'd watched while people "smothered"
fire, or blown or fanned fires to make them burn
faster or hotter, and had been shown how to regulate
a fire by adjusting a "damper". All of which prepared
me for the "chemical" perspective which is discussed
in the earlier section under that heading, and the
recognition that the fire with which I was familiar was
oxidation.
As my perspectives changed between the several which
have been mentioned in the foregoing, my views of
fire and the changes of state and composition of
matter, and transformations and transfers of energy
between forms and locations involved, changed as if I
was "channel surfing" on a television set with a
"zapper" (to use a metaphor which would have been
meaningless in the 1930s). On rainy days, I'd seen
water flow down hill, faster down steeper slopes.
When I acquired a graphical perspective, and saw it
applied to hydrodynamics, electricity, and heat
transfer, pressure, voltage, and temperature seemed,
almost always, to be plotted as vertical displacements
from the origins of graphical representations of the
spatial distribution of these quantities. By analogy to
water "seeking its level" I saw fluids, electricity, and
heat flowing downward, from points or regions of high
pressure, voltage or temperature at rates proportional
to (and in the direction of) the gradients (or "slopes")
of these quantities. I have recently learned that this
view of heat transfer (as seen from the "empirical"
perspective) led Lavoisier and, later Mach, to see heat
as a fluid (5).
As I remember at the time of this writing, the
perspectives I gained from play with a chemistry set
was more accurately characterized as an "alchemic"
than as a "chemical" perspective. Like the ancient and
medieval alchemists, I followed recipes and observed
reactions. The operations of the "Universal Research
Laboratories", which are also mentioned in that section
were, like Roger Bacon's thirteenth century
experiments with gunpowder (4), more alchemy than
chemistry.
Although I may have acquired a (somewhat indistinct)
chemical perspective from the activities mentioned
357
above and recreational reading, my high school
chemistry course clarified my chemical perspective and
presented a few glimpses from the "intermolecular"
perspective mentioned under that heading.
From the "intermolecular" perspective, it became
apparent that even so simple a reaction as that depicted
in equation (1):
2H 2 + 2
2H 2
(1)
is not the single step reaction implied by the
stoicheometic equation (1). Each oxygen molecule
must be dissociated to provide the single oxygen atom
for each water molecule. Based on models of water
molecules, such as those shown in Figure 1, in which
the hydrogen atoms are on opposite sides of the much
larger oxygen atoms, it seemed that the hydrogen
molecules also must be dissociated to be oxidized.
I don't remember how or when, but at some time
before I graduated from high school I became
convinced that heat is molecular motion, the nature of
which has been discussed herein. In the solid state,
where crystalline bonds hold the molecules in their
relative positions, only vibration about its equilibrium
position is possible for each molecule (or atom). With
increasing temperature, the amplitude of the vibration
is sufficient to move each molecule so far from its
equilibrium position that the crystalline bonding force
can no longer restore it, and the solid melts. In the
liquid state, molecules are free to move relative to one
another, but are drawn together by the "van der Waals
force", further increase in temperature results in
movement beyond the effective range of this force and
the liquid was said to "boil" or "vaporize". In the
vapor or gaseous state, molecules are separated
sufficiently that they move independently until they
collide, as can be seen from the perspective of the
Maxwell-Boltzmann kinetic theory of gases.
Considered from the perspectives outlined in the
foregoing paragraphs, I saw heat conduction to be the
result of essentially mechanical interactions of
molecules and atoms. In a solid, the vibration of each
molecule about its equilibrium position is
communicated to its neighbors by the same crystalline
binding forces that establish their equilibrium relative
positions. In a liquid, the molecular motion is
communicated mostly by the van der Waals
intermolecular attraction force and the intermolecular
repulsion which determines the effective volume of
each molecule and hence the specific volume of the
liquid. In a gas, viewed from the perspective of the
Maxwell-Boltzmann kinetic theory of gases, the
movement is communicated by effectively elastic
collisions between molecules,
Although the view of heat transfer as seen from the
"intermolecular" perspective, as described above, was
more consistent with the structure of matter in its
various states, as seen from this perspective,
quantitative consideration would involve too much
complex computation (since it would have to take into
account the variation with relative directions of the
intermolecular, interionic, and interatomic attraction
and repulsion forces) for practical purposes.
Like most students, I learned to consider heat transfer
from the empirical perspective (from which Lavoisier
and Mach had seen heat as a fluid), which is a more
practical approach to heat transfer calculations. Such
consideration, for engineering purposes (11), yields:
q = k A(T,-T 2 )/x
(9)
where: q is the rate of heat transfer through a panel
of area A and thickness, x, and T { and T 2 are
temperatures on either side of the panel,
while k is the thermal conductivity of the
substance of the panel.
The value of k can be determined experimentally by
measurements of q when values of other variables are
preestablished.
For purposes of theoretical consideration of systems in
which heat transfer is a factor, equation (9) can be
generalized as a partial differential equation:
q = -k A[dTIdx]
and in vector notation as:
q = -k A VT
(10)
(11)
I gained this perspective of heat transfer, by
conduction, several years after I had learned to build
fires as a Boy Scout. From this perspective, in
combination with the concept that each fuel has a
"kindling point** and heat capacity, I began to see why
the techniques I had learned as a Boy Scout were
effective and necessary.
A log or large piece of wood can't be "lit" with a
match because, although the temperature of the flame
is well above the "kindling point" of the wood, its
thermal conductivity is much lower so that the
temperature at the surface attains an equilibrium such
that the rate at which heat is conducted into the wood
is equal to that at which it is conducted from the
flame. Paper, twigs and shavings can be lit because the
358
heat transferred from the flame is conducted through
the fuel only a short distance until it reaches another
surface from which it is conducted by air, whose
thermal conductivity is equal to or less than that of the
flame, so the heat accumulates in the paper, twigs, or
shavings until the "ignition" or "kindling point" is
reached.
While the view of ignition, from the perspective of
thermal conduction, outlined above, explained some of
my experiences as a Boy Scout, they left some
observations unexplained. From the perspective of
"states" of matter, which are discussed earlier herein,
it is apparent that, although most of the fuels discussed
above are solid, the flames, like the visible "steam"
from a teakettle, the clouds in the sky and most of the
white "smoke" which rose from a burning pile of
damp leaves, seemed to be lighter than air. As
mentioned in the earlier section headed
"LANGUAGES AND PERSPECTIVES" I was told
that the visible "steam", white "smoke" and clouds, as
well as fog and mist, were droplets of liquid water too
small to settle out, and referred to as "colloidal
suspensions" as were similarly suspended droplets and
particles of other substances. Grey, brown and black
smoke are such suspensions of other substances as is
evidenced by their odor, while flames are suspensions
of carbon which is so hot it glows. The droplets and
particles are too widely scattered to have as much
effect on the density of the air as the heat (from the
fire?), so the "steam", "smoke" and clouds floated
upward. This upward movement of flames, often
referred to, by poets, novelists, and journalists, as
"leaping", and in technical discussion as "convection",
plays a role in the propagation of fire, as mentioned,
a page or so back, in the account of my recollections
of Boy Scout firemaking.
I don't remember when I first heard the aphorism,
"Where there's smoke there's fire.", but I'm sure that
it was before my twelfth birthday that I began to
question its (absolute) truth. I'd seen smoke coming
from overloaded extension cords, and stop after the
appliances which had overloaded them were
disconnected. I'd seem pictures of smoke (identified as
such) coming from volcanoes although I hadn't been
told of any underground source of the air which would
have been needed to sustain a fire. I wondered what
smoke was. The white smoke, from burning damp
leaves was obviously, like visible "steam", fog, mist,
and clouds, a colloidal suspension of liquid water, but
the grey, brown, and black smoke were something
else. I was a few years younger, when an aunt, who
lived in an in-town apartment, reached out of her
window and showed me a blackened finger tip. She
identified the black stuff on her finger as "soot"
which, she explained, had settled out from the black
smoke, which came from chimneys of building in
which, she said, "soft coal" was burned. It seemed to
me that grey smoke must be a mixture of black smoke
and white smoke, but, from its odor, I was sure that
all smoke contained something else.
Consideration of the observations, experiences and
hearsay mentioned in the foregoing paragraph from my
developing chemical perspective resulted in views of
fire and smoke which I found satisfying. Although I
questioned that "where there's smoke there's fire.",
it was apparent that, where there was smoke, fire
could be expected. If the overload which caused an
extension cord to overheat wasn't removed, the cord
would soon "burst into flame". By analogy to the
formation of the aerosol referred to as visible "steam"
beyond the spout of a teakettle, I reasoned that
something in the insulation of the extension cord (bare
wires, when heated by electric current, don't emit
smoke) must have evaporated and condensed, after
mixing with cooler air, to form the droplets of the
colloid referred to as "smoke". Reflecting on earlier
experiences and observations, some of which have
been mentioned hereinbefore, I recalled that, when
organic substances are heated, smoke often appears
before flame.
The word "organic", like many others, has a number
of meanings, the most general of which is "Arising
from an organism. "(2). Organic chemistry is
essentially the chemistry of carbon, which owes its
complexity to four "covalent" bonds whereby carbon
atoms bond with one another, and those of other
elements to form a wide variety of molecules (aver
15000 of which are listed in the Handbook of
Chemistry and Physics (10)). Because carbon atoms
combine in several ways,it is possible for different
molecules (of compounds with different properties) to
have the same composition in terms of the numbers of
atoms of carbon and other elements. For this reason,
organic compounds are usually identified by structural
formulas which are, essentially, diagrams or models of
their structure. It is quite apparent, from
consideration of such structural formulas, that many
organic molecules are too large and irregular in shape
to bounce around like "tiny billiard balls" (as Mach
characterized the picture presented by the
Maxwell-Boltzmann kinetic theory of gases) but are
more likely to break into smaller molecules. In other
words, some organic compounds tend to decompose
rather than evaporate when heated. (I became
359
somewhat dimly aware of such matters at an early age
because of my father's involvement in the development
and construction of "cracking stills" in which large
molecules of crude oil were "cracked" into the smaller
molecules needed in gasoline.)
The familiar fuels are organic materials (in the sense
of "Arising from an organism. "(2)). As such they are
composites of a number of substances (Mostly organic
compounds of carbon, hydrogen, and nitrogen, in
solid, liquid, and gaseous states. Wood, for example
is a mixture of cellulose, which is "made up of
long-chain molecules (fibers) in which the complex
unit QjHioOs is repeated as many as 2000 times" (17),
lignin (C 41 H 32 6 ) sugars, resin, acetic acid , water, air,
and other substances.
When a campfire had subsided to glowing coals and,
for one reason or another, a hotter fire was desired, a
few sticks of kindling were laid over the glowing
coals, In few minutes (particularly if the glow was
brightened by blowing or fanning the coals, the
"kindling 11 began to emit smoke, which, a minute or
two later, burst into flame. I had noticed that the
smoke appeared before the flame.
Consideration from perspectives hereinbefore
discussed, particularly the "chemical" perspective and
that form which "states" of matter are viewed, led me
to see the sequence of observable phenomena outlined
above as resulting from the following sequence of
chemical and physical events:
The "kindling" was heated by radiation and convection
from the glowing coals. When it reached temperatures
conducive to such processes, volatile components of
the "kindling" began to evaporate and nonvolatile
components decomposed to volatile compounds which
evaporated. The vapor, mixing with cooler air
condensed to form the droplets of the colloidal
suspension (or "aerosol") referred to as "smoke".
Further heating brought the smoke to its "ignition
point" so it "burst into flame" .
The above description satisfied me in 1940, and it still
does except for my continuing reservation regarding
the concept of "ignition points" and the colloquialism
of the phrase "burst into flame" and its implication of
an "eyewitness" rather than a "chemical" or "physical"
perspective.
These misgivings were alleviated by replacing the final
sentence (which included the dubious phrases) with the
following continuing description:
If and when the smoke was further heated, the gaseous
decomposition products of the wood, such as methane
(CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), carbon,
hydrogen, etc. oxidize, raising the temperature still
higher, decomposing and oxidizing the compounds
which had condensed to form the droplets of the
colloidal suspension referred to as "smoke".
Most decomposition products of the organic substances
commonly used as fuels are in gaseous or plasma
states at temperatures associated with combustion.
The most notable exception is carbon, which is solid
at much higher temperature. The charcoal, which is
the most familiar decomposition product of wood is
mostly carbon. The glowing coals which remain after
the flames have subsided are mostly carbon, which
continues to burn while oxygen is available. Enough
of the heat of combustion is transferred from the
carbon dioxide, which is the reaction product, to the
oxygen of ambient air and unburned carbon to
maintain the reaction and the glow, which is black
body radiation. Similarly, the organic substance of the
droplets of the colloidal suspension referred to as
smoke decompose to the gaseous products mentioned
above, and the small particles of carbon, referred to as
"soot", whose colloidal suspension in air is called
"flame", when it glows, and "black smoke" after it
cools enough to stop glowing.
As mentioned a few paragraphs above,the "smoke"
emitted by heated wood is a colloidal suspension of
volatile components of the wood. Their composition
varies from one species of wood to another. Many
have proven useful. Perhaps the best application of
wood smoke is to the preservation of food, such as
ham, bacon, and fish.
The flavor of smoked meat has been sufficiently
popular to inspire the invention of the "pit barbecue"
on which meat is smoked while it is broiled and
roasted, although preservation is not a consideration
because the food is eaten while it is still hot. Hickory
and mesquite smoke seem to be most popular for these
purpose, as well as (in condensate form) as flavoring
for barbecue sauce, etc.
Other volatile components of wood, which are
undoubtably seen as wood smoke but may not
condense to "smoke" before they are condensed to
liquids in stills, are turpentine, which is used as a paint
thinner and brush cleaner, and creosote, which is used
as a wood preservative and harsh disinfectant (17).
360
The last couple of pages contain descriptions of fires
with which I was most familiar before 1941, in which
wood or paper were the fuels, as I saw them from
several perspectives. I was also aware of combustion
of other fuels to which some parts of these descriptions
are not applicable.
I was aware that although most of the other fuels I had
seen burning were of organic origin, they tended to
have properties more similar to the intermediates of
wood burning than to the wood itself. Most were
gaseous, volatile, or colloidal suspensions, like
components of wood smoke, or mostly carbon and
ash (like charcoal), when visibly burning.
I had heard coal, petroleum, and natural gas referred
to as "fossil fuels", meaning that they were the
remains of prehistoric organisms which had
decomposed and been buried by such geological
processes as volcanic eruption and sedimentation. I
had seen the beginning of the formation of coal in the
peat bogs of the upper midwest, many acres of spongy
moss, where a misstep could result in a foot coated,
almost to the knee, with dark brown rotted moss,
referred to as "peat", which, in the United States, is
used as fertilizer and (dried) as thermal insulation,
packing, and "potting soil" for plants, but in countries
where other fuels are expensive, dried peat is used, in
large quantities, as fuel. The top layers in a peat bog
are of relatively low density, but, at greater depths the
older peat, which has been rotting longer and
consolidated by the combination of increasing pressure
and the upward diffusion of water and other low
density (compared with that of carbon [3.51]) liquids
and gases (most of which are products of the
continuing decomposition (rotting) of the peat). Gases
diffuse to the air above as "marsh gas" (which
sometimes catches fire and is referred to as "will o'
the wisp" or "ignis fatuus"). With the passage of
time, the growth of the moss continues, piling up more
peat, so that at the bottom continues to consolidate
while decomposing, and its density, carbon content,
and hardness increase with time and depth and the peat
is changed, progressively, to lignite, bituminous and,
finally, anthracite coal.
Petroleum, like coal, is a product of decomposition
(decay) of organic matter, in this case, marine animals
and plants, which, because of their much lower
oxygen/hydrogen ratio than the peat moss, which is
mainly cellulose (a carbohydrate (or hydrate of carbon,
which can decompose to carbon and water)) tends to
decay to hydrocarbons. As in the formation of coal,
the process includes the "piling up" of the matter for
long periods of time.
In the course of the millions of years during which
coal and petroleum have been forming, various
geological events and processes, including volcanic
eruptions, earthquakes, and continental drift, have
occurred, resulting in deformation of the earth's crust
and the formation of mountain ranges and
displacement of continents, in the course of which
some of the forming coal and petroleum were covered
by layers of rock, which sealed pockets of the gaseous
products of the decomposition of organic matter
whereby the coal and petroleum are formed. These
trapped gases are known as "natural gas".
Some fossil fuels are used as recovered. Coal is
burned in furnaces to heat buildings, and in boilers of
locomotives, ships, and power plants to generate
steam. Natural gas is distributed through pipes to
residences and other buildings where it is the fuel for
furnaces, space heaters, cook stoves, fireplaces, and
refrigerators.
Some coal, generally bituminous coal, is heated in
kilns, to continue the process of decomposition to
gaseous hydrocarbons (methane, ethane, etc.), which
are referred to as "manufactured gas" and distributed
through pipes in communities beyond the range of
natural gas distribution pipelines, and carbon and ash,
known as "coke", which is sold as household fuel, and
used in blast furnaces in which iron ore is reduced to
"pig iron", some of which is remelted and cast, to
make the wide variety of cast iron items with which
we are all familiar, but most of which is converted to
steel by oxidization of most of its carbon content in
Bessemer converters or open hearth furnaces. Much
of the gas from coke ovens of iron works is used as
the fuel of large (at the Engine and Condenser
Department of Allis-Chalmers, where I had a summer
job in 1937, there was an eight foot bore by twelve
foot stroke engine, for this purpose, on the drawing
boards) internal combustion engines, which drive the
blowers for the blast furnaces, etc.
Petroleum is a mixture of hydrocarbons, which are
separated, by distillation, into gases, including
methane, butane, propane, and pentane, liquids,
including naphtha, gasoline, kerosene, and fuel and
lubricating oils, waxes, and asphalt. Asphalt, wax,
and the "heavy" (viscous) oils owe their properties to
the large size and complexity of their molecules,
which, since the 1920s have been "cracked", at high
temperature and pressure (which can be reduced by
361
using catalysts) to the smaller molecules of the more
volatile compounds needed for internal combustion
engines.
Not long after I'd learned to read, I discovered "car
cards", - advertising posters mounted in a row over
the windows of a street car. One of these (advertising
"Carbona", a dry cleaner) included a picture of a
woman, with an article of clothing in one hand, flying
through clouds, with the caption, "You can go twenty
miles on a gallon of gasoline" as at least one
automobile maker claimed at that time. My mother
explained the point of the ad - that gasoline vapor
could form an "explosive mixture" with air, but
Carbona doesn't. That night, my father explained that
Carbona is carbon tetrachloride which, though volatile,
like gasoline (so it is useful for dry cleaning) but,
unlike gasoline, it was not enflammable (gasoline
forms explosive mixtures with air because it is highly
enflammable).
I accepted these explanations because they came from
my parents, but didn't fully understand them at that
age (between six and ten). The distinction between
"enflammable" and "volatile" was unclear (as it still
seems to be to some television news reporters). My
father, sensing my perplexity , pointed out that
"enflammable" meant "easily ignited to burst into
flame" while "volatile" meant "easily evaporated".
My view of the subject was obfuscated by the frequent
spelling of "enflammable" as "inflammable", and the
apparent interchangeability of the prefixes " in- " ,
"un-\ and "non-". (It would be fifteen years before
I saw less ambiguous word "flammable" on a tank
truck.) The meanings of such words as "explode",
"explosion" "explosive", "detonate", and "detonation"
and "detonable" were unclear to me then as they still
seem to be to many. I am often, still, unsure what
others mean by them, although I now think I know
what I mean.
Consideration of such matters from the various
perspectives, acquired in the course of education,
reading, conversations, and basement and backyard
activities, clarified my views of fire, while presenting
new perspectives, consideration from which led to
other pictures, some of which were somewhat "fuzzy",
leading to further research (literary, experimental, or
analytical), a sequence which continues to this day.
Following is an effort to summarize my picture of fire,
as I now remember seeing it, in 1940 (which was two
years after my graduation as a mechanical engineer):
Most of the fires which I'd seen consisted of flames,
which behaved as gases or colloidal suspensions (like
smoke), and/or glowing coals. Clearly, most solid and
liquid filets volatilize as part of the combustion process
which showed me that more than the single step,
implied by stoichiometric equations, such as Equations
(1) and (2), are involved in the process. In the
burning of gunpowder, expressed in equation (2):
2KN0 3 + C + S -► C0 2 + SO 2 +2KO + N 2
the potassium nitrate (KN0 3 ) molecules must
dissociate to provide the oxygen atoms to oxidize the
carbon and sulfur. Considered from the "interatomic"
perspective, which has been discussed herein before,
it seemed that the oxidation of hydrogen must follow
the dissociation of the oxygen molecules, and probably
those of hydrogen. I began to see fire, except where
elemental carbon, as coal, coke, or charcoal, or in a
similar form, is the fuel, is a multistage process. The
decomposition, melting or sublimation, and/or
evaporation, and condensation to the aerosol referred
to as "smoke", precedes its further decomposition,
dissociation, oxidation, and ionization, the effects of
which are seen as the flames of familiar fuels (except
carbon in its various forms).
By 1940, I had acquired enough of the vocabulary of
chemistry to understand that chemical processes and
changes of state were either "exothermal"
(characterized by the evolution of heat) or
"endothermal" (characterized by the absorption of
heat) and was aware that freezing, condensation, and
the formation of most molecules by joining atoms,
ions, or "free radicals" are exothermal, while melting,
sublimation, boiling and other evaporation or
vaporization, decomposition, ionization, and
dissociation are endothermal. I came to recognize that
"ignition" or "kindling", considered from the
perspective outlined above, from which fire is seen as
a multistage phenomenon, occurred only after
sufficient heat had been transferred to a fuel element
to result in the necessary succession of endothermal
processes (which is unique for each fuel), and maintain
the exothermal oxidation until the evolution of heat
from the latter is sufficient to heat the "soot" (the
particles of carbon which are products of the
decomposition of the colloidally suspended droplets of
hydrocarbons called "smoke") to the incandescence
visible as "flame". Fire, in general, stabilizes when
heat losses reach equilibrium with evolution of heat.
When losses exceed evolution of heat, a fire "dies
out". When the evolution of heat exceeds losses and
continues to do so, the fire is self accelerating. A few
362
years later, the course of "literature research at the
Naval Ordnance Laboratory, I was to read of such a
self accelerating fire referred to as a " thermal
explosion" (which will be discussed in more detail a
few pages hence), but, in 1940, "explosion still meant
to me, as it had since I learned the word, a "bang"
and a flash and an impulse which could throw things
around (As a kid, I had seen tin cans, propelled by
firecrackers, fly higher than a house.)* and some tines
broke them. Dictionaries (1,2) gave "detonation" as
a synonym of "explosion", and an encyclopedia (15)
stated that "detonation is a distinct phenomenon in
which the chemical transformation is induced in every
particle at (he same instant". Even then, I didn't
believe that. I already saw fire as the Multistage
phenomenon described above, of which each stage
takes time. I had heard the combustion of an internal
combustion engine referred to as "an explosion" (at the
beginning of each power stroke), and the anti-knock
property of Ethyl and other high octane gasoline
ascribed to the fact that it was "slower burning" than
regular. However, having considered the Otto cycle
(which is employed in most automobiles), I was aware
that even high octane gasoline burned fast enough that
the reaction was complete before the piston moved
enough that the volume change had to be considered in
thermodynamic calculations, but "regular" , in a high
compression engine, burned so fast that the resulting
rapid pressure increase is propagated through the
cylinder head to the air as a sound or "shock" wave.
Waves had been familiar to since early childhood,
when I saw them on water. My dad built a radio
before I was ten and I soon learned to estimate where
to set the dials from the wavelength of each station,
published in the paper. I heard that radio waves were
waves in "ether" but, before I found out what "ether"
was, I read about the Michelson-Morley experiment,
which showed that there was no such thing. As a
teenager, I had built audio equipment, including
amplifiers and recording equipment, in the course of
which I acquired practical, empirical, and graphical
perspectives of sound, which prepared me for
acoustical and analytical perspectives of sound I was to
learn in physics courses. In 1940, I was aware that
both "explosion" and "detonation" are derived from
Latin words describing sounds (those of clapping and
thunder respectively), and that both referred to sudden
fire (sudden enough that the pressure rise, due to the
heat evolved, was propagated as a sound wave, from
which I inferred that the reaction was completed) in a
small fraction of a second (the maximum period of a
sound wave), but my mental pictures of the processes
were rather indistinct until, as a participant, at the
Naval Ordnance Laboratory (N.O.L.), in the research
and development of systems of which pyrotechnics and
explosives are components.
Although, in 1940, my impressions of explosion and
detonation were not very clear, I could see, from a
heuristic perspective of the Maxwell-Boltzmann kinetic
theory of gases (as I understood it) that the combustion
of an "explosive mixture" of gaseous fuel and air is
the effect of random intermolecular collisions of
sufficient magnitude to break (dissociate) molecules in
into atoms, ions, free radicals. I saw that, in this
state, hydrogen and carbon atoms and/or ions can bond
to those of oxygen to form carbon dioxide and water,
processes which are exothermal (evolving heat) - the
kinetic energy of molecular motion) thus increasing the
frequency of collisions of sufficient magnitude to
initiate the sequence outlined above in the previously
unreacted fuel/air mixture. I saw that this sequence
should be expected to propagate at a velocity close to
the average of those of the molecules (which is about
that of sound).
Consideration of the heuristic model, described above
from a quantitative perspective, would have required
statistical analysis beyond my abilities. Perhaps I
could have clarified my view by consideration from
acoustical, hydrodynamic, and/or fluid mechanical
perspectives, to each of which I had been introduced,
but I didn't make such an effort until, at N.O.L., I
was engaged in explosive research, the course of
which I learned that others, including Rankine (whose
steam engine cycle I had learned of in thermodynamics
courses) had done so in the nineteenth century.
My earliest impressions of fire were effects of
observations of and experience with such familiar fuels
as paper wood, coal, charcoal, candle wax, and
gasoline. I had became convinced that air is essential
to fire. It didn't take long for experience with
fireworks (which available, in late June and the first
three days of July, in the 1920s, at grocery and drug
stores, to any kid with a dime), to cast doubt on this
conviction. My experience, at the "Universal
Research Laboratory" (as a fourth grade classmate
referred to his basement) in the preparation of black
gunpowder, which burned quite vigorously in a rocket
(which was lacking in aerodynamic stability and
tumbled a few feet off the ground). I can't say, at this
time (1995) whether, at that time (1926), I understood
why gunpowder could barn without air, although other
fuels couldn't. However, by 1940, I had learned that
the burning of familiar fuels is oxidation, requiring the
oxygen of air, but that gunpowder, as well as other
explosives and pyrotechnics, burned without air
363
because they contained oxygen as a component of
relatively unstable compounds, such as potassium
nitrate. Thus, I saw, the burning of gunpowder is a
multistage reaction (one stage of which is the
decomposition of the nitrate) which, in fuses, is too
slow to be called H an explosion".
In 1940, World War II had become the "Battle of
Britain", Japan was rearming the invading Asiatic
neighbors, and the U.S. armed services were engaged
in an effort to regain and surpass the preparedness lost
as the result of the pacifism and disarmament
following World War I. Pursuant to this effort, the
U.S. Naval Ordnance Laboratory (NOL) recruited
over 1700 scientists and engineers, of which I was
one.
FIRE, AS I SAW IT AT NOL (EAU)
Arriving at NOL, in early 1941, I was given new
perspectives, particularly of fire, too frequently to
retrace after fifty-odd years. My first assignment, at
NOL, was to the Propellant and Pyrotechnics Group of
the Experimental Ammunition Unit (EAU), where I
worked with an "ordnance man", directed by the
pyrotechnics specialist on the adaptation of display
fireworks for use as signals (such as "Submarine
Emergency Identification Signals"). My principal
assignment, in that group was design and drafting, but
I spent some time in the laboratory, where we did
some preparation, fabrication, and testing of
pyrotechnic mixtures, systems, subsystems,
components, etc. Our approach, in such adaptation,
was generally that of "trial and error" or, to dignify it,
"Edisonian research". Based on the view, from the
"practical" or "common sense" perspective, that
mixtures and practices which had been used, with
success, by others, were most likely to serve our
similar purposes, we usually followed recipes, some
dating back to those of medieval alchemists and
ancient Chinese artisans. On occasion, we tried to
improve mixtures by application of stoichiometry, but
experience tended to confirm the above mentioned
view, from the "practical" perspective. It was
apparent that more than stoichiometry was involved.
We noted that the behavior and properties of
pyrotechnic mixtures were affected by the granulation
of their ingredients as well as the densities to which
they were loaded. Of the properties so affected,
sensitivity, which includes their susceptibility to
initiation by the stimuli available for this purpose when
intended, as well as that to initiation by accidentally
applied stimuli (and resulting hazards), is of primary
concern to all involved in the manufacture and
application of pyrotechnics and explosives.
Although, from instruction, conversation, and "hands
on" experience, I had acquired some "eyewitness",
"common sense", "practical", and "empirical"
perspectives of such matters, I felt a lack of applicable
"chemical", and "scholarly" perspectives. The EAU
had no official library, but I had noticed a number of
books on ordnance, explosives, and pyrotechnics on
desks and shelves, which I borrowed and read. One,
which caught my eye was The Chemistry of Powder
and Explosives" (4), by Tenney L. Davis (who had
been the lecturer of my second semester freshman
chemistry course). The book was intended to be a
textbook for a graduate course on the subject, the
book includes ( in the 1941 edition) chapters on
PROPERTIES OF EXPLOSIVES, BLACK POWDER,
PYROTECHNICS, AND AROMATIC NITRO
COMPOUNDS. It starts by defining an "explosive as:
"a material, either a pure of single substance or a
mixture of substances which is capable of producing
an explosion by its own energy".
"It seems unnecessary to define an explosion, for
everyone knows what it is. ~ a loud noise and the
sudden going away of things from where they had
been --".
As I read it, I accepted it, but soon began to recognize
that, as with many words, although everyone knows
what "explosion" means, it doesn't necessarily mean
the same to everyone. Recently, a steam automobile
enthusiast told me that "Explosion is the most
inefficient form of combustion", implying, I support
that a steam automobile should be more efficient than
one with an internal combustion engine. Do those
who talk about "the population explosion" mean "a
loud noise - etc." or "the most inefficient form of
combustion"?
Davis, in the first chapter on PROPERTIES OF
EXPLOSIVES, points out that, although an explosive
can produce an explosion by its own energy, it can
liberate this energy without exploding (as black
powder does in a fuse). Here, he injected an
explanation of the difference between a "fuse" which
is a device for communicating fire" and a "fuze",
which is a device for initiating explosion (usually
"detonation") of the "bursting charges" of shells,
bombs, mines, grenades, etc.". A section of the first
chapter on PROPERTIES OF EXPLOSIVES headed,
Classification of explosives includes paragraphs
(condensed below) on:
364
I. Propellants, or "low explosives" which (in their
usual application) burn but do not explode, and
function by producing gas which produces an
explosion (by busting its container, such as the paper
tube of a Chinese firecracker or the metal case of a
bomb). Examples: black powder, smokeless powder.
II. Primary Explosives or "initiators" , which explode
or detonate when heated or subjected to shock.
Examples: mercury fulminate, lead azide, lead salts of
picric acid, etc.
III. High Explosives, which detonate under the
influence of the shock of the explosion of a suitable
primary. Examples: dynamite, TNT, tetryl, picric
acid, etc.
It is pointed out that these classes overlap because the
behavior of explosives is determined by the nature of
the stimuli to which they are subjected and by the
manner in which they are used. Nitrocellulose,
"colloided" such smokeless powder, is a propellant, as
compressed guncotton, is a powerful high explosive,
and, as lower density guncotton, has been used as the
"flash charge" of electric detonators, TNT,
nitroglycerine, and other high explosives have been
ingredients of smokeless powder. Mercury fulminate
can be "dead pressed" so that it loses its power to
detonate from flame.
A review of the foregoing two pages has led me to
recognize the need for an explanation. Although the
discussion FIRE AS I SAW IT AT NOL (EAU) is, as
implied based on my memories after fifty-some years,
the review of Davis's book (4), is a reflection of
current "browsing" through a copy at hand. The
quotations enclosed in quotation marks, including the
following, are direct copies.
"Propagation of Explosion"
"When black powder burns the first portion to receive
the fire undergoes a chemical reaction which results in
the production of hot gas. The gas, tending to expand
in all directions from the place where it was produced,
warms the next portion of black powder to the kindling
temperature. This then takes fire and burns with the
production of more hot gas which raises the
temperature of the next adjacent material. If the black
powder is confined, the pressure rises, and the heat,
since it cannot escape, is communicated more rapidly
through the mass. Further, the gas- and heat-
producing reaction, like any other chemical reaction,
doubles its rate for every 10° (approximate) rise of
temperature. In a confined space the combustion
becomes extremely rapid, but it is believed to be
combustion in the sense that it is a phenomenon
dependent upon the transmission of heat. "
"The explosion of a primary explosive or of a high
explosive, on the other hand, is believed to be a
phenomenon which is dependent upon the transmission
of pressure or, perhaps more properly, upon the
transmission of shock. Fire, friction or shock, acting
upon, say, fulminate, in the first instance cause it to
undergo a rapid chemical transformation which
produces hot gas and the transformation is so rapid
that the advancing front of the mass of hot gas
amounts to a wave of pressure capable of initiating by
its shock the explosion of the next portion of
fulminate, and so on, the explosion advancing through
the mass with incredible quickness. In a standard No.
6 blasting cap, the explosion proceeds with a velocity
of about 3500 meters per second. "
"If a sufficient quantity of fulminate is exploded in
contact with trinitrotoluene, the shock induces the
trinitrotoluene to explode, producing a shock adequate
to initiate the explosion of a further portion. The
explosive wave traverses the trinitrotoluene with a
velocity which is actually greater than the velocity of
the initiating wave in the fulminate. Because this sort
of thing happens, the application of the principle of the
booster is possible. If the quantity of fulminate is not
sufficient, the trinitrotoluene either does not detonate
at all or detonates incompletely and only part way into
its mass. For every high explosive there is a
minimum quantity of each primary explosive which is
needed to secure its certain and complete detonation.
The best initiator for one high explosive is not
necessarily best initiator for another. A high explosive
is generally its own best initiator unless it happens to
be used under conditions in which it is exploding with
its maximum "velocity of detonation".
The section of Davis's book quoted above presents
views of explosion and detonation from "common
sense" and "empirical" perspectives. I am sure Davis
was aware of "theoretical", "analytical"
"hydrodynamic", etc. views which had been expressed
in the previous century or more, but confined his
description to views from perspectives with which, he
felt confident, his students and other readers of his
book would be familiar. References to the "kindling
temperature" and the "doubling of reaction rate for
every 10° rise of temperature" are evidence of an
"empirical" perspective based on standardized tests
365
similar to those described a few pages on in the first
chapter of the book (4).
The section of Propagation of Explosion is followed
by a section on Detonating Cord which is also
referred to as "cordeau" (after the French "cordeau
detonant") and "Primacord" (a trademark of the
Ensign Bickford Company), a narrow tube filled with
high explosives whose principal use in blasting is the
simultaneous (or in close sequence) initiation of
detonation of two or more explosive charges. It can
also be used to fell small trees as had been
demonstrated in an ROTC class I had attended a few
years before.
The first chapter of "The Chemistry of Powder and
Explosives" (4), entitled PROPERTIES OF
EXPLOSIVES also includes descriptions of
experiments, which can be performed in a college
chemistry laboratory to demonstrate some of these
properties, as well as standardized tests for them, and
cites U.S. War Department Technical Manual TM
2900 "Military Explosives" (25) and a number of
Bulletins and Technical Papers of the U.S. Bureau of
Mines in which such standardized tests are described
in more detail. Properties for which tests are
described in this chapter include Velocity of
Detonation Sensitivity (including "explosion" ,
"ignition", or "kindling" temperature and impact
sensitivity) and Tests of Power and Brisance.
The section on Velocity of Detonation begins with a
paragraph in which the subject is considered from the
"empirical" perspective of the time (ca 1940), which
no longer seems relevant. It mentions detonation
velocity measurements by Berthelot and Vielle, who
used a "Boulenge* chronograph" which is not
described, except for the mention that its (lack of)
precision was such that they were obliged to employ
long columns of explosives". It goes on to say, "The
Mettegang recorder, now commonly used, is an
instrument of much greater precision and makes it
possible to work with much shorter charges". The
Mettegang recorder is described as an instrument
whereby time is determined as proportional to the
distance (measured with a micrometer microscope)
between marks made on a rapidly moving smoked
metal surface.
Also mentioned is the "Dautriche method" in which
the detonation velocity of an explosive being
investigated is compared with that of detonating cord,
which can be determined using relatively imprecise
timers with long lengths of the cord.
The use of high speed photography and cathode ray
oscillographs, in measurement of detonation velocity,
are mentioned as recent developments.
The section on Sensitivity Tests includes descriptions
of "impact" or "drop" tests in which (typically) the
height is determined which will result in the explosion
of a sample of the explosive being investigated
contained in a hole in a block of steel, when a two
kilogram weight is dropped on a plunger in contact
with the explosive sample.
Also described in a test of "temperature of ignition" or
"explosion temperature" in which a blasting cap cup
containing a sample of an explosive is thrust into
Woods metal which has been heated to a known
temperature. The procedure is repeated, with varying
temperatures, until the temperature is determined at
which the sample explodes or is ignited within five
seconds. In another test which is also described, the
blasting cap cup containing the explosive being tested
is dunked in Wood's metal at 100°C and the
temperature is raised at a steady rate until the sample
ignites or explodes. The temperature at which this
occurs is considered to be the "ignition" or "explosion
temperature". When the temperature is raised more
rapidly, the inflammation occurs at a higher
temperature". (As is illustrated in an accompanying
table).
In the section on Tests of Power and Brisance a
definition of neither "power" nor "brisance" is
included. It seems that, as with "explosion", Davis
assumed that it was unnecessary to define "power"
because everyone knew what it meant, while, in my
view, as with "explosion", although everyone knew
what "power" meant, it didn't mean the same to
everyone. (Dictionaries I've consulted (1,2,16)
include from eight to seventeen definitions) .
"Brisance" on the other hand, is not listed in a 1939
unabridged dictionary (2). More recent dictionaries
(1,16) define it as "The sudden release of energy by a
explosion", or something similar. Although "brisance"
wasn't defined in Davis (4) or the dictionaries I
consulted (2), it didn't take long for me to grasp its
meaning, whether from conversation, recognition
(having studied French in high school) that it was
derived from "briser"-to break, or from descriptions,
in Davis (4) and references cited therein, of tests of
power and brisance (each of which rated an explosive
in terms of the measurement of the deformation or
other change of a solid specimen which had been
exposed to its action.
366
The opening paragraph of the section on Tests of
Power and Brisance mentions a "manometric bomb"
as a means of measuring the energy liberated in an
explosion, but goes on to point out that the
effectiveness of an explosion depends upon the rate at
which the energy is liberated ("Power" as understood
by physicists and engineers). The high pressures
developed by explosions (which reflect this rate) were
first measured by the Rodman gauge, in which,
according to Davis (4), the pressure caused a hardened
steel knife to penetrate into a disc of soft copper. The
depth of the penetration was taken as a measure of this
pressure. Davis also mentions "crusher Gauges" in
which copper cylinders are crushed between steel
pistons, piezoelectric gauges, the "Trauzl lead block
test", in which the enlargement of a hole is taken as a
measure of "power" or "brisance", the "small lead
block test" of the Bureau of Mines, in which the
compression of the block is used a such a measure, the
"lead plate test of detonators" in which the diameter of
the hole punched through the plate by a detonator is a
measure of its output. Similar tests with aluminum
plates are also mentioned.
Explosive research was not, in 1941, among the
missions of the NOL, but tests similar to those of
PROPERTIES OF EXPLOSIVES mentioned and
described by Davis (4) in the chapter so titled, which
is reviewed above, were performed by ordnance men
assigned to those Fuze Group of the EAU (whose
laboratory, we of the Propellant and Pyrotechnics
Group shared, so I could watch now and then)
pursuant to the development of fuze explosive trains
(an activity in which I was to become engaged in a
few months, so that I acquired "hands on" experience
with such tests). Meanwhile, however, my job was to
help develop pyrotechnic signals as a member of the
Propellants and Pyrotechnics Group.
The adaptations of display fireworks, which were the
objects of our efforts, were, for the most part, charges
of mixtures of fuels such as charcoal, sulfur,
magnesium, sugar, aluminum, iron filings, and sodium
oxalate with oxidants, such as potassium, sodium,
barium, and strontium nitrates, and potassium chlorate,
and perchlorate, which were usually initiated by the
flames from fuses, such as Bickford safety fuse.
Sensitivity to such initiation was characterized in terms
of the maximum gap between the end of the fuse and
the surface of the pyrotechnic charge at which the
charge was ignited. It seemed to me that the
relationship between particle size, compaction, and
sensitivity was similar to the relationship between
analogous features of the twigs, shavings, or other
"tinder" and ignitability, which I had noted when
passing the Boy Scout second class fir building test in
1927. As I saw it then (in 1941) ignition required that
some of the fuel be raised to its "ignition
temperature", a concept in which I believed (with
some reservations) at that time. This seemed to be
more easily accomplished with small elements of fuel
in not too intimate contact with others.
We used black gunpowder for various purposes,
including augmentation of primer output to ignite flair
compositions.
In this connection, I learned that "cannon powder" was
the coarsest of those we used because black powder as
well as other propellants, burns at the surface of the
grains so that the coarser grains burn longer to
maintain the generation of gas over the longer time
that a cannon projectile spends in the barrel. I later
read (in Davis (4)) that the "grains" of smokeless
powder for large guns are perforated to provide an
increasing surface area as the burning progresses and
the holes enlarge so that the gas emission rate (which
is proportional to the area of the burning surface)
keeps pace with an accelerating projectile.
After a year or so with the Propellant and Pyrotechnic
Group, I was transferred to the Research Group of the
EAU, (supervised by Harry H. Moore) which, as I
remember, took on all tasks assigned to the EAU,
which were not obviously within the purview of the
Propellant and Pyrotechnic Group or the Fuze Group.
The Research Group also was responsible for the
design and development of some hydrostatic bomb
fuzes for antisubmarine warfare (probably because, at
some earlier date, the Fuze Group had been too busy
with other projects), an area in which I found myself
shortly after my transfer to the Research Group. My
attempt to design an improved hydrostatic fuze led to
the assignment of an attempt to establish fuze
explosive train design criteria. Before asking Mr.
Moore for fuze explosive train design criteria, I asked
members of the Fuze Group, who had designing fuzes
for several years. Their approach as I understood it,
was that of adapting a successful explosive train to a
new fuze, showing their proposed design to their boss,
Mr. Ray Graumann. If he approved, They'd have
some made and test them. Although I was to find out,
some years later, that this was a reasonably sound
approach (since Graumann was a nationally recognized
authority on fuze design), it didn't satisfy me, or Mr.
Moore, at the time, all of which led to the assignment
mentioned above. From the members of the Fuze
Group, I learned that the word "fuze" was derived
367
from "fuse", (I had read in Davis (4)) the distinction
between the terms, which is quoted hereinbefore and,
they said, "fuze" had been defined "by act of
Congress" (as has been quoted, from Davis (4)
herein).
About the only "fuze explosive train design criterion"
I learned from them was the requirement for "of-line
safety" to preclude the transmission of detonation from
a detonator to the bursting charge until after a fuze had
"armed".
Application if this criterion requires a definition or
standard of "detonation". The EAU Fuze Group used
the visible damage to the metal parts which had held
the explosive charge for this purpose, which, in turn,
requires a practiced eye. Members of the Fuze Group
could, at a glance, recognize evidence of detonation,
and even characterize the detonation as "high order"
or "low order". Some even identified certain damage
as evidence of "high intensity low order.
I was one of over 1700 engineers and scientists
recruited by NOL in 1939, '40, and '41 to meet the
increasing demands of the preparedness effort in
response to the rising hostilities in europe and the
perceived probability that the US would be involved.
The new employees, representing a wide range of
technical professions and coming from all over the
country, saw things from many perspectives, to which
we introduced on another. Few of us found ourselves
in a position to apply our previous (specific)
experience, but most could apply our general technical
backgrounds. Lunch time conversations covered a
wide range of subjects, mostly more or less technical.
Sometime, in 1 94 1 , I remember hearing that
"Detonation is a special kind of fire. " Somewhere else
I heard detonation referred to as a "chain reaction".
I felt the need for a more meaningful (to me
definition. It seemed to me that such a definition
should be more "scientific" than "a special kind of
fire", "a chain reaction", or "explosion", (as it is still
defined in dictionaries (1, 2, 13)). I didn't believe
that "detonation is a distinct phenomenon in which the
chemical transformation is induced in every particle of
the mass of explosive at the same instant" , as defined
in an encyclopedia (14). Davis' (4) description of
"Propagation of Explosion" which is quoted herein (a
few pages back) was more meaningful to me. Davis
(4) included a heuristic description of what he referred
to as the "propagation of explosion" in black powder
(which, now, seems applicable to other "energetic
materials" which have gaseous reaction products).
Based on impressions I'd gained, from conversations
with other EAU employees, that the burning rate of
black powder (and other propellants and explosives) is
proportional to pressure, I determined by a simple
integration that the pressure, and hence the burning
rate of a confined charge of black powder (or other
propellant or explosive) must increase exponentially
with the passage of time until its container, such as a
bomb case or the paper tube of a firecracker, bursts.
What Davis meant by "powder and explosives" is what
aerospace engineers seem to mean by "pyrotechnics"
and what others mean by "energetic materials."
Davis' (4) description provided a perspective of fire
(or combustion) including explosion and detonation,
which, as Davis pointed out in the paragraph quoted a
few pages back, are forms of combustion in that they
are dependent upon the transmission of heat. From
this explanation, combined with the thermodynamics I
had learned in engineering school, I began to see
detonation as "The rapid and violent form of
combustion in which energy transfer is by mass flow
in strong compression waves. " Although these words
are taken from the opening sentence of "Detonation"
by Weldon C. Ficket and William C. Davis (16),
(which was published in 1979) they express, more
adequately than any that come to mind in 1994, the
view I received in 1942 from the book (4) Tenney L.
Davis had published the previous year. This view is
quite similar to that held today by those who have
concerned themselves with detonation, but it is not
sufficiently quantitative to serve as a basis for fuze
explosive train design criteria. The need for further
research was quite apparent.
My assignments, in the Research Group of the EAU,
besides the attempt to establish fuze explosive train
design criteria, were various, including the adaptation
of a motion picture camera (designed for use in the
motion picture industry) for "slow motion" recording
(from aircraft) of surface effects of underwater
explosions, adjusting designs of coil springs, design of
loading presses, fuze test gear, blast gages, and mine
detonators (to replace those which were adaptations of
Nobel's original (1864) blasting cap, (and still in use
in the 1940s) with an adaptation of modern (as of the
1940s) commercial blasting caps. When NOL started
using "time sheets" to generate records of the
distribution of effort among projects, I found myself
trying to remember how many hours I had spent,
during each past week on each of 42 projects.
Research pursuant to the establishment of fuze
explosive train design criteria, at this stage, literature
368
research, was fit in between other, more urgent
efforts. I started with books on desks and shelves in
the EAU, including Davis (4), in which I reviewed the
parts which have been quoted hereinbefore, and
finished reading the 1941 edition, and when it turned
up, the 1943 edition. A couple of books on ordnance
and explosives, the titles and authors of which I have
forgotten, provided a historical perspective, but didn't
have much which seemed relevant to fuze design.
The chapters of Davis (4) on BLACK POWDER,
PYROTECHNICS, and AROMATIC NITRO
COMPOUNDS broadened and sharpened my historical
and chemical perspectives of fire (particularly in the
forms of explosion and detonation). The use of
"Greek fire", a mixture of saltpeter (potassium nitrate)
with combustible substance as an incendiary in naval
warfare is cited as a progenitor to the discovery that a
mixture of potassium nitrate, charcoal, and sulfur is
capable of doing useful mechanical work, and the
invention of the gun. The chapter traces the evolution
of black powder for blasting as well as use as a
propellant and includes tables of the proportions of
charcoal, sulfur, and saltpeter as described by Marcus
Graecus in the 8th century, Roger Bacon in the 13th
and others in the 14th, 16th, 17th, and 18th centuries,
as well as the stoichiometric equation (2):
2KN0 3 + C+S -► C0 2 +S0 2 +2KO
for the burning of black powder, and was aware that
black powder burns without air because the thermal
decomposition of the nitrate releases enough oxygen to
oxidize the charcoal, sulfur, and potassium, while the
nitrogen forms its own (N2) molecules.
Davis' (4) chapter on PYROTECHNICS, by which he
meant display and amusement fireworks (including
such noisemakers as firecrackers, flares, signals, etc.),
traces the development of such items from ancient
oriental origin to the fireworks we played with as kids
on the Fourth of July, and the signals and illuminating
flares used by the military, and warning flares used by
railroads and highway repair crews. This chapter had
been of specific interest to me as a member of the
Propellant and Pyrotechnics Group, providing
"chemical" and "historical" perspectives of materials
with which we were working. Included were tables of
compositions for colored lights, flares, fuzes, smokes,
marine signals, parade torches, whistles, lances,
rockets, Roman candles, stars, fountains, pinwheels,
mines, comets, meteors, torpedoes, flash cracker
compositions, sparklers, serpents, snakes, etc. (Many
of the foregoing terms were, apparently, used in the
sense which had been familiar to me as a kid,
shopping in late June and early July in preparation for
celebration of the Fourth, rather that in the senses, in
which they are used in connection with biology,
ordnance, astronomy, or defined in most dictionaries).
Consideration of these formulas led to recognition that
nitrates other than that of potassium, as well as
chlorates perchlorates, etc., have been used as solid
providers of oxygen, and increased my awareness that
firelight, other than the (black body radiation) of
familiar yellow flames, was spectral emission of some
elements (such as strontium, which emits red light) in
the plasma state and that colored smoke in a colloidal
suspension of dye in air.
Davis (4) chapter on AROMATIC NITRO
COMPOUNDS, after an introductory paragraph on
their usefulness, in which it is stated that they were
(when the book was published - in 1941) "the most
important class of military high explosives" warns of
their toxicity and the fact that they can be absorbed by
the skin. A paragraph on the chemistry of these
compounds was probably elementary to the graduate
students for which the book was written, but for a
mechanical engineer, such as I, it was a bit cryptic.
I'm not sure, in the 1990s, when I learned that
"aromatic compounds" include "benzene rings" "a
structural arrangement — marked by six carbon atoms
lined by alternate single and double bonds" (2a), and
that a "nitro group" (NO^ the oxygen atoms are
bonded to the nitrogen atom which in an aromatic nitro
compound is, in turn bonded to one of the carbon
atoms.
Considering the chemistry of aromatic nitro
compounds as discussed by Davis (4), and quoted
above, from the basic chemical perspective I had
acquired in chemistry courses, I saw that, like
gunpowder and other pyrotechnics, they contained
oxygen sufficient to oxidize at least some of the carbon
and hydrogen they contained, but that the oxygen
would be available only after decomposition of the
nitro groups (or, in the case of black powder, of the
potassium nitrate). I can't say, now, when I looked up
the heats of formation of the compounds involved, but,
when I did, I verified that the reactions were
exothermal. These relationships were, of course,
obvious to the graduate students in chemistry for
which Davis' book (4) was intended, as was the fact
that, at the anticipated temperatures of the reaction
products (carbon dioxide and water) they were in a
gaseous state, so that the product of their pressure and
volume was many times those of unreacted solid or
liquid unreacted explosives and propellants, as well as
369
those of gases or explosive mixtures of gases or
gases and sols (colloidal suspensions) This, their
combustion was considered to be an explosion or
detonation if it was fast enough - which, in turn, turns
on definitions of explosion and detonation .
EXPLOSION AND DETONATION
Explosion and detonation are among the many
words which, like fire and pyrotechnics have a
number of meanings. According to some dictionaries
(1,2), they are synonymous, although I doubt that any
participant in this workshop considers them to be.
Each of the words has a connotation of sudden
expansion , and each is derived from a Latin word
relating to the sound usually associated with it.
Detonation (some meanings of which will be
discussed below) is derived from the Latin for thunder
while explosion (like applause ) derives from the
Latin for clap , but it seems to be mostly commonly
used in the sense of bursting of a container such as
a boiler or a bomb, but it often means sudden burning
as in a dust explosion or that of another explosive
mixture of gaseous or finely divided fuel with air.
As observed by chemists and stated in the rule of
thumb which has been mentioned in the quotation of
Davis' (4) section on Propagation of Explosion that
any — chemical reaction, doubles its rate with each
10°C (approximate) rise of temperature, so that
exothermal reactions (in which heat is evolved) tend
to be self accelerating. If, as is usual, their reaction
products include one or more gases, the pressure rises,
if they are confined, until the container bursts. Since
surface or grain burning rates of propellants,
explosives and explosive mixtures increase with
increasing pressure (17), such burning is self
accelerating and the pressure and rate increase,
exponentially with time. Either the bursting of a
container or self accelerating process is an explosion
in one or another of the senses mentioned above.
(Self accelerating fire is referred to as thermal
explosion ). This association has led to the use of
explosion to mean any self accelerating process, such
as in population explosion (which seems sudden
only from such perspectives as historical or
geological ).
In lunchtime conversations, I had hear detonation
defined in several sets of terms. Dictionaries and
encyclopedias included definitions and descriptions
which didn't satisfy me. Davis' (4), discussion (which
has been quoted herein) gave me the clearest (though
still somewhat fuzzy) view of the process I had
acquired until my literature search in the areas of
explosives and detonation extended beyond the shelves
and desks of the EAU. Davis' (4), in the section on
Propagation of Explosion ,, which has been quoted
herein, made the transition to the discussion of
detonation with the statement that The explosion of a
primary explosive or of a high explosive is believed to
be a phenomenon which is dependent upon pressure
or, perhaps more properly, on transmission of shock
. The propagation of detonation mercury fulminate is
described as a reaction which produces hot gas and is
so rapid that the advancing front of the mass of hot
gas amounts to a pressure wave capable of initiating
by its shock the next portion of fulminate . The high
velocities of propagation of detonation (3500 meters
per second in the fulminate of a blasting cap and much
higher in TNT) are mentioned. Although Davis (4)
didn't consider shock or detonation waves from
physical, thermodynamic, or hydrodynamic
perspectives, his discussion left me with the impression
that consideration from such perspectives would be
appropriate, an impression which was to be verified
when I started reading OSRD reports.
As I recall, the other books on the desks and shelves
of the EAU, which included a couple of books on
ordnance, one, by a hobbyist, on fireworks, and the
Dupont Blasters Handbook , considered their subjects
from practical , empirical , and historical
perspectives, omitting discussion of chemical or
physical aspects of their subjects.
On the NOL library, I found the War Department
(which, after a decade or so, was to become the
Department of the Army) and Bureau of Mines
documents which had been cited by Davis (4) and
others from these sources and from Picatinny Arsenal,
Frankford Arsenal, the Ballistics Research Laboratory
(BRL) at Aberdeen, MD., the Naval Powder Factory
at Indian Head, Md., the Franklin Institute, the Bureau
of Standards, and the British Ministry of Supply and
Ordnance Board. I found these documents
informative, interesting, and (some of them) quite
pertinent to my objective of establishing fuze explosive
train design criteria, but none contained much to
clarify my views of explosion or detonation except for
a few OSRD reports.
370
REFERENCES
(1) Stein, Jess, (editor), The Random House
Dictionary of the English Language , Random House,
Inc. 1966-1967.
(2) Webster's Twentieth Century Dictionary of the
English Language (unabridged) . Publisher's Guild,
Inc., New York, N.Y., 1939.
(2V£) McCrone, John C, The Ape that Spoke .
William Morrow and Company, Inc., New York,
N.Y., 1991.
(3) Calvin, William H., The Ascent of the Mind. Ice
A ge Climates and the Evolution of Intelligence .
Bantam Books, New York, Toronto, London, Sydney,
Auckland, 1990.
(4) Davis, Tenney L., The Chemistry of Powder and
Explosives . John Wiley & Sons, Inc., New York,
1941, 1943.
(5) Asimov, Isaac, Asimov's Biographical
Encyclopedia of Science and Technology . Doubleday
& Company, Inc., Garden City, N.Y., 197.
(6) Gamow, George, One Two Three... Infinity . The
Viking Press, New York, 1947.
(6V4) Bradbury, Fahrenheit 451 . Simon and Sinister,
New York.
(7) Wells, Robert W., Fire and Ice. Two Deadly
Wisconsin Disasters. Fire at Peshtigo . North word,
Madison, WI, 1968.
(8) Gamow, George, Thirty Years That Shook
Physics . Doubleday & Co. (Science Study Series).
New York, N.Y. 1966.
(9) Langdon-Davies, John, Inside the Atom . Harper &
Brothers, New York and London, 1933.
(10) Weast, Robert C. (editor), and Astle, Melvin J.
(associate editor), CRC Handbook of Chemistry and
Physics. 63rd Edition . CRC Press, Inc., Boca Raton,
FL. 1982-1983.
(12) Chapman, D.L., "On the Rate of Explosion of
Gases", Philosophical Magazine (5), V. 47, p. 90,
1999.
(13) Jouguet, E., 4echanique des Rxploszifs" Paris, O.
Doin et Fils, Editeurs, 1817.
(14) The Grolier Society, Grolier Encyclopedia) . Vol.
4, 1931-1951.
(15) Brady, George S., and Clauser, Henry R.,
Materials Handbook . McGraw-Hill Book Co., New
York, etc., etc. 1977.
(16) Soukhanov, Anne M., (Executive Editor), The
American Heritage Dictionary of the English
Language. Houghton-Mifflin . Boston, New York,
Londom, 1972.
(17) Ficket, Wildon, and Davis, William C.
Detonation , University of California Press, Berkeley,
Los Angeles, London, 1979.
(18) Smithsonian Tables .
(19) Henkin, T. "Determination of Explosion
Temperatures", OSRD 1986, November 1943. (Later
published with McGill, R. , in the Journal of
Engineering and Industrial Chemistry 44, 1391, 1952.
(20) Kabik, I., Rosenthal, L. A., and Solem, A.D.,
The Response of Electroexplosive Devices to
Transient Electrical Pulses" 3rd Electrical Initiator
Symposium, Paper #18, 1960.
[Editor's Note: Time and space precludes completion
of Mr, Stresau's paper. He does plan to publish the
entire story as a Stresau Laboratories, Inc. report at
a later date. Interested readers may contact him at:
Stresau Company
W7882 Stresau Lane
Spooner, WI 54801 J
(11) Eschbach, Ovid W., Handbook of Engineering
Fundamentals. Third Edition . Wiley, New York.
371
APPENDIX - List of Participants
Aerojet Propulsion Division Hansen, Jeff
Aerospace Corporation, The Gageby, James
Aerospace Corporation, The Goldstein, Selma
Aerospace Corporation, The Wong, T. Eric
American Safety Flight Systems, Inc. . . . Ziegler, Ron
Analex Corporation Smith, Floyd
Analex Corporation Steffes, Paul
Attenuation Technology, Inc Dow, Robert L.
Boeing Defense & Space Group . . Robinson, Steven P.
Conax Florida Corporation Nowakowski, Don
Consultant Folsom, Mark
Consultant Gans, Werner A.
Consultant O'Barr, Gerald L.
EG&G Mound Applied Tech. . . . Beckman, Thomas M.
EG&G Mound Applied Tech Kramer, Daniel
EG&G Mound Applied Tech Munger, Alan C.
EG&G Mound Applied Tech Spangler, Ed
Energetic Materials Technology .... Ostrowski, Peter
Ensign Bickford Aerospace Co Graham, John A.
Ensign Bickford Aerospace Co Renfro, Steven L.
Ensign Bickford Aerospace Co Rhea, Arthur D.
Franklin Applied Physics Thompson, Ramie
Geo-Centers, Inc Landry, Murphy J.
Halliburton Energy Services
Explosive Products Center . . . Barker, James
Halliburton Energy Services
Explosive Products Center . . . Motley, Jerry
Hercules Aerospace Cole, David A.
Hercules Inc McAllister, Pat V.
Hi-Shear Technology Corp Novotny, Don
Hi-Shear Technology Corp Webster, Richard
Inland Fisher Guide Div. of GM Wirrig, Steven T.
John Hopkins University - CPIA Filliben, Jeff
Los Alamos National Laboratory .... Kennedy, James
Martin Marietta Specialty Components . . . Hinkle, Lane
Martin Marietta Astronautics Wood, Lance
McDonnell Douglas Tierney, Michael
McDonnell Douglas Aerospace Whalley, Ian
McDonnell Douglas Space Sys. . . Parenzan, James E.
Morton International Inc Hansen, David
Morton International Inc Richardson, Bill
NASA Headquarters Schulze, Norman R.
NASA Goddard Space Flight Center . . Bajpayee, Jaya
NASA Johnson Space Center Hoffman, William
NASA Kennedy Space Center Rayburn, Larry
NASA Langley Research Center Bement, Larry
NASA Lewis Research Center Seeholzer, Tom
NASA Stennis Space Center .... St. Cyr, William W.
Naval Surface Warfare Center
Indian Head Division Blachowski, Tom
Naval Surface Warfare Center
Indian Head Division Hinds, Jeffery L.
Naval Surface Warfare Center
Indian Head Division Krivitsky, Damn
Naval Surface Warfare Center
Indian Head Division Martin, Steve
Naval Surface Warfare Center
Crane Division Schlamp, Jan N.
A- 1
Olin Rocket Research Co Mo ran, Joe
Olin Rocket Research Co Watson, Bruce
Pacific Scientific Corp Cunnington, Rick
Pacific Scientific Corp Day, Bob
Pacific Scientific Corp Greenslade, John T.
Pacific Scientific Corp LaFrance, Bob
Pacific Scientific Corp Schuman, Alex
Pacific Scientific Corp Smith, Bob
Pacific Scientific Corp Spomer, Ed
Pacific Scientific Corp Todd, Michael C.
Pacific Scientific Corp VonDerAhe, Ken
Pacific Scientific Corp Walsh, Tom
Quantic Industries, Inc Willis, Kenneth E.
Reynolds Industries Systems, Inc Varosh, Ron
Rockwell International Corp Cascadden, Raymond
Rockwell International Corp Erazo, Anibal
Sandia National Laboratories Andrews, Larry A.
Sandia National Laboratories . . . Bickes Jr., Robert W.
Sandia National Laboratories Bonzon, Lloyd L.
Sandia National Laboratories .... Brigham, William P.
Sandia National Laboratories Chow, Weng W.
Sandia National Laboratories Cooper, Paul
Sandia National Laboratories Curtis, William
Sandia National Laboratories Fleming, Kevin J.
Sandia National Laboratories GrubelicH, M. C.
Sandia National Laboratories Harlan, Jere G.
Sandia National Laboratories .... Holswade, Scott C.
Sandia National Laboratories Kass, William
Sandia National Laboratories Merson, John A.
Sandia National Laboratories Metzinger, Kurt
Sandia National Laboratories Mitchell, Dennis E.
Sandia National Laboratories Salas, F. Jim
Sandia National Laboratories Setchell, Robert E.
Sandia National Laboratories .... Stichman, Dr. John
Sandia National Laboratories Troh, Wayne M.
Sandia National Laboratories Williams, T. J.
Santa Barbara Research Center Gonzales, Roman
Santa Barbara Research Center Jeter, James
SCB Technologies, Inc McCampbell, C. B.
Schimmel Company Schimmel, Morry L.
Special Devices, Inc Sipes, William J.
Special Devices, Inc Telle, Dennis
Stresau Company Stresau, Richard
Teledyne McCormick Selph Ingnam, Robert W.
Teledyne McCormick Selph Marshall, Clyde
Teledyne McCormick Selph Smith, Brian
TPL Inc Brown, Ralph
United Technologies/USBI Webster, Charles F.
Universal Propulsion Co., Inc Barlog, Stan
Universal Propulsion Co., Inc. . . . Magenot, Michael C.
Universal Propulsion Co., Inc Mayville, Wayne
Universal Propulsion Co., Inc Wergen, Tom
University of Notre Dame Gonthier, Keith A.
University of Notre Dame Powers, Joseph M.
USAF/30 SW/SESX Gotfraind, Mark
USAF/45SPW/SESE Wadzinski, Mike
USAF/B-1B Engineering Branch Tipton, Steve
USAF/Ogden Air Logistics Center .... Kangas, Charles
UTC/Chemical Systems Division Lai, K. S.
ZZY2X Potter, Jed
Larry A. Andrews
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-5800
J ay a Bajpayee
NASA Goddard Space Flight Center
Wallops Flight Facility - Bldg N-159
Wallops Island, VA 23337
(804) 824-2374 (FAX) 824-1 51 8
James Barker
Halliburton Energy Services
Explosive Products Center
2001 S. I35
Alvarado, TX 76009
(817)783-5111 (FAX) 783-5812
Stan Barlog
Universal Propulsion Co., Inc.
25401 North Central Ave.
Phoenix, AZ 85027-7837
(602) 869-8067 (FAX) 869-8176
Thomas M. Beckman
EG&G Mound Applied Technologies
P.O. Box 3000
Miamisburg, OH 45343-0987
(513)865-4551 (FAX) 865-3491
Larry Bement
NASA Langley Research Center
Code 433
Hampton, VA 23681-0001
(804) 864-7084 (FAX) 864-7009
Robert W. Bickes Jr.
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0326
(505) 844-0423 (FAX) 844-5924
Tom Blachowski
Naval Surface Warefare Center
Indian Head Division - Code 5240E
101 Strauss Ave.
Indian Head, MD 20640-5035
(301) 743-4243 (FAX) 743-4881
Lloyd L. Bonzon
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0327
(505) 845-8989 (FAX) 844-5924
William P. Brigham
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0327
(505) 845-9107 (FAX) 844-0820
Ralph Brown
TPL Inc.
Raymond Cascadden
Rockwell International Corporation
201 N. Douglas St.
El Segundo. CA 90245
(310)414-1655 (FAX) 414-2077
Weng W. Chow
Sandia National Laboratories
Division 2235
P.O. Box 5800
Albuquerque, NM 87185-5800
(505)844-9088 (FAX) 844-8168
David A. Cole
Hercules Aerospace
P.O. Box 210
Rocket Center, WV
(304) 726-5489
26726
(FAX) 726-4730
Paul Cooper
Sandia National Laboratories
M/S 1 1 56
P.O. Box 5800
Albuquerque, NM 87185-5800
(505) 845-7210 (FAX) 845-7602
Rick Cunnington
Pacific Scientific Corp.
Energy Dynamics Division
7073 West Willis Road, Box 5002
Chandler, AZ 85226-5111
(602) 796-1 100 (FAX) 796-0754
A-2
William Curtis
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185
(505) 845-9649 (FAX) 844-4616
Werner A. Gans
Consultant
1015 Lanark Ct.
Sunnyvale, CA 94089
(408) 245-2857
Bob Day
Pacific Scientific Corp.
7073 West Willis Road, Box 5002
Chandler, AZ 85226-5111
Robert L. Dow
Attenuation Technology, Inc.
9674 Charles Street
La Plata, MD 20646
(301) 934-3725 (FAX) 934-3725
Anibal Erazo
Rockwell International Corporation
201 N. Douglas St.
El Segundo, CA 90245
(310) 647-2756 (FAX) 647-6824
Jeff Filliben
John Hopkins University - CPIA
10630 Little Patukxent Parkway
Suite 202
Columbia, MD 21044-3200
(410) 992-7305 (FAX) 730-4969
Kevin J. Fleming
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0327
(505) 845-8763 (FAX) 844-0820
Mark Folsom
Consultant
25747 Carmel Knolls Drive
Carmel, CA 93923
(408) 626-8252 (FAX) 626-1652
James Gageby
The Aerospace Corporation
MS M4/907
2350 E. El Segondo Blvd.
El Segondo, CA 90245
(310) 336-7227 (FAX) 336-1474
Selma Goldstein
The Aerospace Corporation
MS M4-907
P.O. Box 92957
Los Angeles, CA 90009-2957
(310) 336-1013 (FAX) 336-1474
Keith A. Gonthier
University of Notre Dame
Aerospace & Mechanical Engineering
365 Fitzpatrick Hall
Notre Dame, IN 46556-5637
(219) 239-6426 (FAX) 239-8341
Roman Gonzales
Santa Barbara Research Center
Hughes Aircraft Company
75 Coromar Drive B30/12
Goleta, CA 93117
(805) 562-7705 (FAX) 562-7882
Mark Gotfraind
U. S. Air Force/30th Space Wing
30 SW/SESX
922 N. Brian St.
Santa Maria, CA 93454
(805) 928-9637
John A. Graham
Ensign Bickford Aerospace Co.
640 Hopmeadow St.
P.O. Box 427
Simsbury, CT 06070
(203) 843-2325
John T. Greenslade
Pacific Scientific Corp.
Energy Dynamics Division
7073 West Willis Road, Box 5002
Chandler, AZ 85226-5111
(602) 796-1100 (FAX) 796-0754
M. C. Grubelich
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0326
(505) 844-9052 (FAX) 844-4709
A-3
David Hansen
Morton International Inc.
M/SX1830
3350 Airport Road
Ogden, UT 84405
(801) 625-9222 (FAX) 625-4949
Jeff Hansen
Aerojet Propulsion Division
Bldg. 201 9A2, Dept. 5274
P.O. Box 13222
Sacramento. CA 95813-6000
(916) 355-6102 (FAX) 355-6543
Jere G. Harlan
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0329
(505) 844-4401 (FAX) 844-4709
Jeffery L. Hinds
Naval Surface Warfare Center
Indian Head Division - Code 520
101 Strauss Ave.
Indian Head, MD 20640-5035
(301)743-6530 (FAX) 743-4881
James Jeter
Santa Barbara Research Center
Hughes Aircraft Company
75 Coromar Drive
Goleta, CA 93117
(805) 562-7539 (FAX) 562-7740
Charles Kangas
USAF/Ogden Air Logistics Center
OO-ALC/LIWCE
6033 Elm Lane
Hill AFB, UT 84056
(801)777-4135 (FAX) 777-9484
William Kass
Sandia National Laboratories
Division 2234
P.O. Box 5800
Albuquerque, NM 87185-5800
(505)844-6844 (FAX) 844-8168
James E. Kennedy
Los Alamos National Laboratory
MS - P950
Los Alamos, NM 87545
(505) 667-1468 (FAX)667-6301
Lane Hinkle
Martin Marietta Specialty Components
P.O. Box 2908
Largo, FL 34649-2908
(813) 541-8222 (FAX) 545-6757
William Hoffman
NASA Johnson Space Center
Code EP5
2201 NASA Road One
Houston, TX 77058
(713) 483-9056 (FAX) 483-3096
Scott C. Holswade
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0328
Robert W. Ingnam
Teledyne McCormick Selph
3601 Union Road
P.O. Box 6
Hollister, CA 95024-0006
(408) 637-3731 (FAX) 637-5494
Daniel Kramer
EG&G Mound Applied Technologies
P.O. Box 3000
Miamisburg, OH 45343-0987
(513)865-3558 (FAX) 865-3680
Darrin Krivitsky
Naval Surface Warfare Center
Indian Head Division - Code 5240E
101 Strauss Ave.
Indian Head, MD 20640-5035
Bob La France
Pacific Scientific Corp.
Energy Systems Division
7073 West Willis Road, Box 5002
Chandler, AZ 85226-51 1 1
(602) 961-0023 (FAX) 961-0577
K. S. Lai
UTC/Chemical Systems Division
P.O. Box 49028
San Jose, CA 95161-9028
(408) 776-4327 (FAX) 776-4444
A-4
Murphy J. Landry
Geo-Centers, Inc.
2201 Buena Vista Dr., SE
Albuquerque, NM 87106
(505) 243-3483 (FAX) 242-9497
Michael C. Magenot
Universal Propulsion Co., Inc.
25401 North Central Ave.
Phoenix, AZ 85027-7837
Clyde Marshall
Teledyne McCormick Selph
8920 Quartz Ave.
Northridge, CA 91324
(818) 718-6643 (FAX) 998-3312
Steve Martin
Naval Surface Warfare Center
Indian Head Division
101 Strauss Ave.
Indian Head, MD 20640-5000
(301) 743-4243 (FAX) 743-4881
Wayne Mayville
Universal Propulsion Co., Inc.
25401 North Central Ave.
Phoenix, AZ 85027-7837
(602) 869-8067 (FAX) 869-8176
Pat V. McAllister
Hercules Inc.
M/SN1EA1
P.O. Box 98
Magna, UT 84044
(801) 251-6192
(FAX) 251-6676
C. B. McCampbell
SCB Technologies, Inc.
1009 Bradbury Dr. S.E.
Albuquerque, NM 87106
John A. Merson
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0329
(505) 844-2756 (FAX) 844-4709
Kurt Metzinger
Sandia National Laboratories
Structrual Mechanics Group 1562
P.O. Box 5800
Albuquerque, NM 87185-5800
(505) 844-5077
Dennis E. Mitchell
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0522
(505) 845-8656 (FAX) 844-3894
Joe Moran
Olin Rocket Research Co.
P.O. Box 97009
Redmond, WA 98073-9709
(206) 885-5000 (FAX) 882-5744
Jerry Motley
Halliburton Energy Services
Explosive Products Center
2001 S. I35
Alvarado, TX 76009
(817) 783-5111 (FAX) 783-5812
Alan C, Munger
EG&G Mound Applied Technologies
P.O. Box 3000
Miamisburg, OH 45343-0987
(513) 865-3544 (FAX) 865-3491
Don Novotny
Hi-Shear Technology Corp.
24225 Gamier Street
Torrance, CA 90509-5323
(310) 784-7857 (FAX) 325-5354
Don Nowakowski
Conax Florida Corporation
2801 75th Street North
St. Petersburg, FL 33710
(813)345-8000 FAX: 345-4217
Gerald L. O'Barr
6441 Dennison St.
San Diego, CA 92122
(619)453-0071
A-5
Peter Ostrowski
Energetic Materials Technology
P.O. Box 6931
Alexandria, VA 22306-0931
(703) 780-5854 (FAX) 780-4955
James E. Parenzan
McDonnell Douglas Space Systems Co.
MSA3/11-1/L292
5301 Bolsa Ave.
Huntington Beach, CA 92647
(714)896-5778 (FAX) 896-1597
Jed Potter
ZZYZX
25341 Via Oriol
Valencia, CA 91355
(805) 259-9491
Joseph M. Powers
University of Notre Dame
Aerospace & Mechanical Engineering
365 Fitzpatrick Hall
Notre Dame, IN 46556-5637
(219)631-5978 (FAX) 631-8341
Larry Rayburn
NASA Kennedy Space Center
NASA Shuttle Pyrotechnic Engineering
Code TV. MS D-23
Kennedy Space Center, FL 32899
(407)861-3652 (FAX) 867-2167
Steven L. Renfro
Ensign Bickford Aerospace Co.
640 Hopmeadow St.
P.O. Box 427
Simsbury. CT 06070
(203) 843-2403 (FAX) 843-2621
Arthur D. Rhea
Ensign Bickford Aerospace Co.
640 Hopmeadow St.
P.O. Box 427
Simsbury, CT 06070
(203) 843-2360 (FAX) 843-2621
Bill Richardson
Morton International Inc.
M/SX1870
3350 Airport Road
Ogden, UT 84405
(801) 625-8222 (FAX) 625-4949
Steven P. Robinson
Boeing Defense & Space Group
M/S 81-05
P.O. Box 3999
Seattle, WA 98124-2499
(206) 773-1894 (FAX) 773-4846
William W. St. Cyr
NASA Stennis Space Center
Code KA22 Building 1100
Stennis Space Center, MS 39529-6000
(601 ) 688-1 1 34 (FAX) 688-33 1 2
F. Jim Salas
Sandia National Laboratories
P.O. Box 5800
Albuquerque, NM 87185-0329
(505) 844-3265 (FAX) 844-4709
Morry L. Schimmel
Schimmel Company
8127 Amherst Avenue
St. Louis, MO 63130
(314)863-7725 (FAX) 727-8107
Jan N. Schlamp
Naval Surface Warfare Center
Code 4073
300 Highway 361
Crane, IN 47522-5001
(812) 854-5431 (FAX) 854-171 1
Norman R. Schulze
National Aeronautics
and Space Administration
Code QW
Washington, DC 20546
(202) 358-0537 (FAX) 358-2778
Alex Schuman
Pacific Scientific Corp.
Energy Dynamics Division
Box 750
Litchfield Park. AZ 85340
(602) 932-8409 (FAX) 932-8949
Tom Seeholzer
NASA Lewis Research Center
Code 4330 M/S 86-10
21000 Brookpark Road
Cleveland, Ohio 44135
(216) 433-2523 FAX 433-6382
A-6
Robert E. Setchell
Sandia National Laboratories
Department 5166
P.O. Box 5800
Albuquerque, NM 87185-0445
(505) 844-3847 (FAX) 844-7431
William J. Sipes
Special Devices, Inc.
16830 West Placerita Canyon Road
Newhall, CA 91321
(805) 259-0753 (FAX) 254-4721
Dr. John Stichman
Sandia National Laboratories
Surety Components and
Instrumentation Center
P.O. Box 5800
Albuquerque, NM 87185-5800
Richard Stresau
Stresau Company
Star Route
Spooner, Wl 54801
(715)635-8497
Bob Smith
Pacific Scientific Corp.
102 South Litchfield Road
Goodyear, AZ 85338-1295
(602) 932-8450 (FAX) 932-8949
Dennis Talle
Special Devices, Inc.
16830 West Placerita Canyon Road
Newhall, CA 91321
(805) 259-0753 (FAX) 254-4721
Brian Smith
Teledyne McCormick Selph
3601 Union Road
P.O. Box 6
Hollister, CA 95024-0006
(408) 637-3731 (FAX) 637-5494
Ramie Thompson
Franklin Applied Physics
98 Highland Ave.
P.O. Box 313
Oaks, PA 19456
(215) 666-6645 (FAX) 666-0173
Floyd Smith
Analex Corporation
3001 Aerospace Parkway
Brookpark, OH 44142-1003
(216) 977-0201 (FAX) 977-0200
Michael Tierney
McDonnell Douglas
10171 Halawa Dr.
Huntington Beach, CA 92646
(714) 963-7242 (FAX) 896-6995
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EG&G Mound Applied Technologies
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Ed Spomer
Pacific Scientific Corp.
Energy Dynamics Division
102 South Litchfield Road
Goodyear, AZ 85338-1295
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Paul Steffes
Analex Corporation
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USAF/B-1B Engineering Branch
Air Logistics Center (AFMC)
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Pacific Scientific Corp.
Energy Systems Division
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Sandia National Laboratories
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A-7
Ron Varosh
Reynolds Industries Systems, Inc.
3420 Fostoria Way
San Ramon, CA 94583
(510) 866-0650 (FAX) 866-0564
Ken VonDerAhe
Pacific Scientific Corp.
Energy Systems Division
7073 West Willis Road, Box 5002
Chandler, AZ 85226-5111
(602) 796-1 100 (FAX) 796-0754
Mike Wadzinski
USAF/45SPW/SESE
1201 Minuteman St.
Patrick Air Force Base, FL 32925
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Pacific Scientific Corp.
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Olin Rocket Research Co.
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Redmond, WA 98073-9709
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United Technologies/USBI
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Richard Webster
Hi-Shear Technology Corp.
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Tom Wergen
Universal Propulsion Co., Inc.
25401 North Central Ave.
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McDonnell Douglas Aerospace
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T. J. Williams
Sandia National Laboratories
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Quantic Industries, Inc.
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Inland Fisher Guide Division of GM
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The Aerospace Corporation
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Martin Marietta Astronautics
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American Safety Flight Systems, Inc.
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REPORT DOCUMENTATION PAGE
Form Approved
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1. AGENCY USE ONLY (Leave blank)
4. TITLE AND SUBTITLE
2. REPORT DATE
February L994
3. REPORT TYPE AND DATES COVERED
CP February 8-9, 1995
Second NASA Aerospace Pyrotechnics Systems Workshop
6. AUTHOR(S)
William W. St. Cyr, compiler
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESSES)
National Aeronautics and Space Administration
John C. Stennis Space Center
CodeKA60 Building 1100
Stennis Space Center, MS 39529-6000
5. FUNDING NUMBERS
8. PERFORMING ORGANIZATION
REPORT NUMBER
CP 3258
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESSES)
Office of Safety and Mission Quality
CodeQW
NASA Headquarters
Washington, D.C. 20546
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
11. SUPPLEMENTARY NOTES
Hosted by Sandia National Laboratories
Albuquerque, New Mexico
12a. DISTRIBUTION/AVAILABILITY STATEMENT
Unlimited
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words)
This NASA Conference Publication contains the proceedings of the Second NASA Aerospace Pyrotechnics Systems
Workshop held at Sandia National Laboratories, Albuquerque, New Mexico, February 8-9, 1994. The papers are grouped
by sessions:
Session 1 - Laser Initiation and Laser Systems
Session 2 - Electric Initiation
Session 3 - Mechanisms & Explosively Actuated Devices
Session 4 - Analytical Methods and Studies
Session 5 - Miscellaneous
A sixth session, a panel discussion and open forum, concluded the workshop.
14. SUBJECT TERMS
Pyrotechnics, laser ordnance, safety, pyrotechnic database
and catalogue, electric initiation, explosively actuated devices, laser
safe and arm system, mechanisms, modeling of pvros.
15. NUMBER OF PA^ES
3M.
16. PRICE CODE
17. SECURITY CLASSIFICATION
OF REPORT
Unclassified
18. SECURITY CLASSIFICATION
OF THIS PAGE
Unclassified
19. SECURITY CLASSIFICATION
OF ABSTRACT
Unclassified
20. LIMITATION OF ABSTRACT
NSN 7540-01-280-5500
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