NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

Pyrotechnic Devices and Firing Circuits

Seminar Announcement: Pyrotechnic Initiators, Applications, and Lessons Learned (June 7, 2005)

Space Shuttle Solid Rocket Booster Pyrotechnic Initiation System Description and Lessons Learned

Charles Webster
AIAA 93-2068
AIAA/SAE/ASME/ASEE 29th Joint Propulsion Conference and Exhibit, June 28-30, 1993, Monterey, CA


In light of interest in developing next-generation space launch vehicle systems, including pyrotechnic initiationn systems, there is a need to review existing systems to determine what has proved to be good and what factors have contributed to concerns or actual problems. The objective of this paper is to describe the existing pyrotechnic initiation systems used on the Space Shuttle Solid Rocket Booster (SRB) and related systems, including strengths and weaknesses as seen over more than 10 years of use, and provide some suggestions for any replacement system.

This paper presents a technical overview of the space shuttle SRB operational and Range Safety electrical initiation system (including ET Range Safety), a more detailed description of key system components and a description of significant assembly and checkout processes. Significant strengths of the existing system are addressed, followed by a description of weaknesses and lessons learned. The lessons learned area addresses potential improvements t o the existing system. In the area of improvements, a key item addressed is an automating checkout and final system connection, which could allow many operations to be improved without reducing safety.

Spacecraft Pyrotechnic Systems

M.J. Falbo and R.L. Robinson
March 1973

Pyrotechnic devices were used successfully in many systems of the Apollo spacecraft. The physical and functional characteristics of each device are described.  The development, qualification, and performance tests of the devices and the ground-support equipment are discussed briefly.  Recommendations for pyrotechnic devices on future space vehicles are given.

ACTS PYRO Separation Band Anomaly (Shuttle Orbiter)


Minor damage to the Shuttle was caused when the firing of the primary explosive cord to deploy the payload from the cargo bay also triggered the backup cord. End-to-end system tests had validated the erroneous design rather than the end function. Document electrical-mechanical interfaces, protect hazardous systems against any possible unintended operation, and consider use of a single cord configuration.

Manned space programs accident/incident summaries (1963 - 1969)

General Electric Co., Daytona-Beach, Florida prepared for NASA

Contract NASW-410 (Safety Task)
March 1970

This summary is a compilation of 508 mishaps assembled from company and NASA records which cover several years of Manned Space Flight Activity. The purpose is to provide information to be applied towards accident prevention. The accident/incident summaries are categorized by the following ten systems: Cryogenic; Electrical; Facility/GSE; Fuel and Propellant; Life Support; Ordnance; Pressure; Propulsion; Structural; and Transport/Handling. Each Accident/Incident summary has been summarized by description, cause and recommended preventive action.

Apollo Tower Jettison Motor Qualification Issue


A firing current of 5 amperes should have been applied to each of two bridgewires that were attached to each initiator. Instead, the improperly used firing harness resulted in the application of approximately 2.5 amperes of firing current to each of two bridgewires that were attached to each initiator. The motor manufacturer did not have adequate definition of current application requirements to design the wiring harness properly.

Unrestrained Separation Nuts May Damage or Hinder Flight Hardware


In testing of both MER1 and MER2, the impact resulted in severe damage to the PYRO cables attached to the bottom of the nuts. The PYRO cabling was damaged sufficiently to cause multiple shorts to chassis that could have over-stressed the PYRO system electronics. Redesign efforts to apply padding to the sep NUT backshells were complicated by the configuration of the adjacent hardware.

Space engineering Mechanical — Part 6: Pyrotechnics ECSS

ECSS-E-30 Part 6A
April 25, 2000
Secretariat ESA-ESTEC Requirements & Standards Division
Noordwijk, The Netherlands


Scope (excerpt)
Part 6 of ECSS--E--30 in the engineering branch of ECSS series of standards defines the requirements for the discipline of pyrotechnics engineering. This part defines the standards to be applied for the use of pyrotechnics on all spacecraft and other space products including launch vehicles. It addresses the aspects of design, analysis, verification, manufacturing, operations and safety. As any pyrotechnic item used for flight can function only once, it can never be fully tested before its crucial mission operation. The required confidence can only be es-tablished indirectly by the testing of identical items. Test results and theoretical justification are essential for demonstration of fulfilment of the requirements. The requirement for repeatability shows that product assurance plays a crucial role in support of technical aspects. The failure or unintentional operation of a pyrotechnic item can be catastrophic for the whole mission and life threatening. Specific requirements can exist for the items associated with it. As all pyrotechnic functions are to be treated similarly, collective control needs to be applied in the manner of a subsystem.

HDP System A Pyros Did Not Detonate During STS-112 Launch

IPR 114V -0004

Descriution of Problem

Just after T -0 during the launch of STS-112 on 10/07/02 at approximately 1545 ET, the GLS software in Firing Room 3 annunciated a 'cutoff condition and did not automatically issue the normal post launch sating even though the vehicle had successfully left the mobile launch platform. Real time data review revealed that the erroneous GLS indication and subsequent safing hang-up was triggered by the failure of a MLP 3 GSE indication (GMSX11 07E: SYS A HDP T -0 Bus On Indication) to transition from OFF to ON at T -0. Starting at T -2 seconds, GLS continuously monitors both the SYS A and SYS B HDP T -0 Bus On indications and requires that both (2 of 2) be ON as confirmation that liftoff has occurred and before it will issue post launch safing. More detailed post-launch data review then showed that the MLP 3 Hold Down Post (HDP), ET Vent Arm System (ETV AS) and ETV AS Lanyard' A' circuit pyrotechnic devices did not receive detonation energy as expected from the MLP .3 system A PICs (Pyrotechnic Initiation Controller). TheF1 and F2 switch indicators did not come on, indicating that the F1 and F2 commands were not processed by the PICs. Since the PIC rack did not see all three requisite commands in the proper sequence, it did not issue the detonation energy to the A circuit HDP or ETV AS ordnance. Of the three signals, only the ARM signal could be positively verified as reaching the PICs.

Comparison of Apollo and Soyuz Pyrotechnic Initiators

From the 1975 ASAP Report, Part I - Apollo Soyuz Test Project

The Soyuz Pyrotechnics

From the 1975 ASAP Report, Part I - Apollo Soyuz Test Project

STS-86 USA Simplified Aid for EVA Rescue (SAFER) Failure

Failure Review Board Report

MISHAP DATE: October 1,1997
March 30,1998

Failure and Main Contributing Factor
The NSI in the SAFER (seriall #1005) did not fire. Therefore, the pyrotechnic propellant isolation valve did not open and nitrogen gas was not sent to the SAFER’S thrusters.

The NSI did not fire because there was a change in the NSI resistance as the NSI “fire” current pulse was applied to the NSI by the avionics circuit. This caused the NSI “fire” current level (designed at 4.1 amps) to drop (to 2.8 amps) below the “all fire” (3.5 amps) NSI current specification. The NSI resistance was measured at 1.09 ohms before installation into the SAFER. During application of the “fire” pulse, the resistance changed due to “ohmic heating” to approximately 1.6 ohms. The change in resistance caused the 4.1 amp NSI “fire” pulse to drop to 2.8 amps because of the avionics circuit constant voltage design. At 2.8 amps, the probability of firing the NSI is approximately 60%.

Postfire Short Circuit Phenomena of Electroexplosive Initiators

Lien C. Yang
Journal of Spacecraft and Rockets
Vol. 36, No. 4, July-August 1999
pp. 586-590

Recent postfire electrical short circuiting of initiators in two launch vehicles has highlighted a potential problem area for all users of electrically initiated pyrotechnic devices. A high-level firing current continues to flow during the entire firing command (0.045-2 s), long after the initiator has functioned and the bridgewire has burned out. This phenomenon may introduce several undesirable side effects and failure modes. A preliminary assessment has identified a number of parameters that can affect postfire short circuiting: 1) conductivity of the burning propellant and gases; 2) conductive, unburned fuel and residue; 3) the presence of a slurry mix on the bridgewire; 4) the presence of a Viton binder in the propellant; 5) higher voltage levels in firing circuits; and 6) small initial volumes in mechanisms into which initiators are fired. A compilation is presented of the data collected on this phenomenon, and approaches are recommended to accommodate postfire short circuiting and to conduct additional diagnostic testing for possible corrective actions.

A Manual for Pyrotechnic Design, Development and Qualification

L.J. Bement and M.L. Schimmel
NASA TM 110172
June 1995

Requesting ...

TM 106810: Applications Catalog of Pyrotechnically Actuated Devices-Systems

January 1995.

A compilation of basic information on pyrotechnically actuated devices/systems used in NASA aerospace and aeronautic applications was forrnated into a catalog. The intent is to provide (1) a quick reference digest of the types of operational pyro mechanisms and (2) a source of contacts for further details. Data on these items was furnished by the NASA Centers that developed and/or utilized such devices to perform specific functions on spacecraft, launch vehicles, aircraft and ground support equipment. Information entries include an item title, user center name, commercial contractor/vendor, identifying part number(s), a basic figure, briefly described purpose and operation, previous usage, and operational limits/requirements.
WIRE_Report.PDF Small Explorer WIRE Failure Investigation Report.  This is Appendix F of the WIRE Mishap Investigation Board Report, June 8, 1999.

Use of FPGAs in Critical Space Flight Applications— A Hard Lesson

W. Gibbons and H. Ames

1999 MAPLD International Conference, Laurel, MD


Abstract (excerpt)
In early March of 1999, the NASA Wide Field Infrared Explorer (WIRE) experiment was launched on a Pegasus air launch vehicle from a location in the Pacific Ocean just west of Vandenberg Air Force Base. The launch itself was successful, but a system anomaly prematurely opened the aperture cover of the telescope. This premature opening resulted in excessive venting of gaseous hydrogen from the WIRE instrument. The escaping gas increased the torque rates to the spacecraft to such an extent that the spacecraft could not control them. All the solid-hydrogen cryogen in the instrument was vented within a few hours rather than within the projected four months of nominal mission life. Days after the anomaly, the spacecraft was stabilized, and it is currently being used as an attitude control test vehicle by its builder, Goddard Space Flight Center (GSFC).
NASA Johnson Space Center www site for pyrotechnics initiators.
Nedelin disasterXL

R-16 Family: Nedelin Disaster

It took almost three decades before the first publication in the official Soviet press shed the light on what really happened in October 1960. In 1989, Ogonyok magazine, a mouthpiece of Gorbachev's "perestroika," run a story called "Sorok Pervaya Ploshadka," (or Site 42 in English). The article revealed to the Soviet people that Nedelin died in the explosion of a ballistic missile in Tyuratam along with numerous other nameless victims.

Some interesting excerpts:

To make matters worse, several minutes after the membranes blew up, pyrotechnic devices on the valves of one of three engines in the first stage fired spontaneously.

The commission concluded that the management of the testing was overly confident in the safe performance of the complex vehicle, which resulted in the decisions taken without thorough analysis.

(Added 10/9/01)

NASA Standard Initiator User's guide

JSC-28596A, 2/29/00



The purpose for this document is to provide a quick reference and a source of corporate knowledge for the users of the pyrotechnic device called the NASA Standard Initiator (NSI). The contents deal strictly with this one government furnished (GFE) item. The information contained herein contains design, manufacturing and test information.

Design and Performance Specification for NSI-1




Military Standard, Electroexplosive Subsystems, Electrically Initiated, Design Requirements and Test Methods


U.S. Air Force
March 1972

Military Standard, Electroexplosive Subsystems, Safety Requirements and Test Methods for Space Systems


U.S. Air Force
July 1984

Military Specification, Explosive Ordnance for Space Vehicles (Metric), General Specification for


U.S. Air Force Space Div.
Los Angeles AFB, CA
Oct. 1979 and Oct. 1987

Hi-Shear Technology CorporationXL



Products - NASA Standard Initiator

A Manual for Pyrotechnic Design, Development, and Qualification

NASA Technical Memorandum 110172

Laurence J. Bement
Langley Research Center, Hampton, Virginia

Morry L. Schimmel
Schimmel Company, St. Louis, Missouri

June 1995


Although pyrotechnic devices have been singularly responsible for the success of many of the critical mechanical functions in aerospace programs for over 30 years, ground and in-flight failures continue to occur. Subsequent investigations reveal that little or no quantitative information is available on measuring the effects on performance of system variables or on determining functional margins. The three following examples amplify these points. A pin puller design, that was used for the successful deployment of an antenna on the surface of Mars in 1976 in the Viking Lander Program, failed to function in a second application in 1986 and was abandoned. A spacecraft separation joint failed to function in a 1984 ground test after more than 20 years of flight successes; the same joint, which is designed for full containment of explosive products, burst in 1994 during release of a payload from the Space Shuttle cargo bay. A “fully qualified” valve design, that was created for the Gemini Program in the early 1960’s, structurally failed and ignited hydrazine in 1994 through previously unrecognized failure modes. Improved guidelines for pyrotechnic design, development and qualification are clearly needed.

The purpose of this manual is to provide an overview of and recommendations for the design, development and qualification of pyrotechnic components and the systems in which they are used. This is a complex field in which there are few specialists and even fewer guidelines on the approach to create a device and assure it will perform its required task. The field of pyrotechnics is generally considered to be an art, not a science or engineering discipline. Also, pyrotechnics are considered to be readily available, and, therefore, can be managed by any subsystem in which they are applied, such as structure, propulsion, electric power or life support. This presentation is intended to dispel these misconceptions.

The objectives of this manual are:

  1. Remove the art from pyrotechnic applications.
  2. Introduce engineering approaches.
  3. Provide the logic for improved procurement, design, development, qualification, integration and use.

Tests methods and logic are recommended that quantify performance to improve widely cited go/ no-go testing of under and over-loaded energy sources. References are noted throughout to allow the reader to obtain more detailed information on all test methods.

This manual does not provide “cookbook” answers and approaches for any aspect of pyrotechnic operations. Not only are devices unique, requiring individualized approaches for design, development and qualification, but systems and operational procedures are also specialized. The contents of this man-ual are not intended for direct incorporation into pyrotechnic specifications.

Magellan AACS RAM Upset During SRM Pyrotechnic Initiation



On August 12, 1990, 7.3 seconds after the SRM separation pyros were activated on Magellan, erroneous alert codes were received by CDS. These alerts were caused by the failure of the AACS Memory B of at least 2K of the TCC244 RAM.

Functional Performance of Pyrovalves

Laurence J. Bement
NASA Langley Research Center Hampton, VA


Following several flight and ground test failures of spacecraft systems using single-shot, "normally closed" pyrotechnically actuated valves (pyrovalves), a Government/Industry cooperative program was initiated to assess the functional performance of five qualified designs. The goal of the program was to provide information on functional performance of pyrovalves to allow users the opportunity to improve procurement requirements. Specific objectives included the demonstration of performance test methods, the measurement of "blowby" (the passage of gasses from the pyrotechnic energy source around the activating piston into the valve's fluid path), and the quantification of functional margins for each design. Experiments were conducted at NASA Langley Research Center on several units for each of the five valve designs. The test methods used for this program measured the forces and energies required to actuate the valves, as well as the energies and the pressures (where possible) delivered by the pyrotechnic sources. Functional performance ranged widely among the designs. Blowby cannot be prevented by o-ring seals; metal-to-metal seals were effective. Functional margin was determined by dividing the energy delivered by the pyrotechnic sources in excess to that required to accomplish the function by the energy required for that function. Two of the five designs had inadequate functional margins with the pyrotechnic cartridges evaluated.

Fusing Element Failure resulting from Test Integration, Test, Pyrotechnic Devices, PYRO, Electrical Explosive Devices, EED, Command CIRCUIT, Drive Circuit



Introduction (excerpt)
Recently on a Goddard Space Flight Center (GSFC) spacecraft program, a contractor had concluded successful live fire tests on the EEDs (Electrical Explosive Devices, also called Pyros). Subsequently it was found that the live fire tests had not only fired the EEDs but had also damaged the drive CIRCUIT. The damaged component was the EED CIRCUIT fusing element. This component would not provide sufficient energy to fire an EED when required during the mission.

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