A MA A _ A98-35634

AIAA 98-3911Post-Fire Short Circuit PhenomenaOf "NSI Equivalents"

Lien C. YangTRW Strategic Systems DivisionSan Bernardino, CA 92402-1310

34th AIAA/ASME/SAE/ASEEJoint Propulsion Conference & Exhibit

July 13-15,1998 / Cleveland, OH

For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics1801 Alexander Bell Drive, Suite 500, Reston, VA 20191

POST-FIRE SHORT CIRCUIT PHENOMENAOF

"NSI EQUIVALENTS"

Lien C. YangTRW Strategic Systems Division

San Bernardino, CA 92402-1310

ABSTRACT

Recent post-fire electrical short circuiting of initiatorsin NASA Standard Initiator (NSI) "equivalents" in twolaunch vehicles, has highlighted a potential problemarea for all users of electrically initiated pyrotechnicdevices. A high-level firing current continues to flowduring the entire firing command (45 ms to 2 sec),long after the initiator has functioned and thebridgeware has burned out. This phenomena mayintroduce several undesirable side effects and failuremodes. A preliminary assessment has identified anumber of parameters that can affect post-fire shortcircuiting: (1) conductivity of the burning propellantand gases; (2) conductive, unbumed 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) smallinitial volumes in mechanisms into which initiators arefired. This paper presents a compilation of the datacollected on this phenomena and recommendsapproaches to accommodate post-fire short circuitingand to conduct additional diagnostic testing forpossible corrective actions.

INTRODUCTION

Post-fire short circuiting of direct-current, electricallyactuated initiators has long been recognized as apotential problem area in launch vehicle andspacecraft applications. Specifications have beengenerated for both electrical initiators and firingsystems to help reduce the occurrence of thisphenomena. However, data collected on past NSIqualifications, an NSI-derived cartridge, and NSI"equivalents" on two recent launch vehicles indicatethat post-fire short circuiting remains an importantissue.

Post-fire electrical short circuiting occurs in directcurrent firing systems, when the level of currentremains constant or increases after the propellantwithin an initiator has ignited and burned. This levelof current is sustained throughout the duration of theelectronically timed firing pulse, which has been set inlaunch vehicles from as little as 45 milliseconds to as

much as 2 seconds. The cross sectional view of theNSI in Figure 1 shows the path of the electrical firingsignal. The current enters one electrical pin, passesthrough the bridgewire (a 0.002-inch diameter stain-less steel wire), and out the second electrical pin. A5-ampere direct-current input to the NSI typicallyignites the propellant adjacent to the bridgewire withinone millisecond. The bridgewire burns within thattime period and the current soon decreases to zero.However, post-fire short circuiting allows this5-ampere current draw to be sustained, which canintroduce several deleterious side effects:

(1) The time frame for initiating multiple initiators inparallel electrical circuits can be increased. If thecurrent draw remains high in one initiator afterfunctioning, that current cannot be transferred toparallel initiators to accomplish more rapidinitiation of the remaining units.

(2) The electrical batteries can be depleted more thannecessary. The greatest influence occurs withbatteries that are shared in a common bus withother subsequent usages.

(3) The electrical pins through the initiator body canmelt and allow internal hot gases to vent, whichcould lead to failure of rocket motors andmechanisms.

(4) A number of electrical system failure modes canbe introduced. High-current draws on electricalcircuits can damage resistors and batteries, as wellas overload and weld mechanical contacts orstress solid-state relays.

MIL-STD-1512, the specification applied in the1960's, required the initiator to exhibit a post-fire opencircuit (less than 50 mA at 28 Vdc). However thisstandard has been superseded by MIL-STD-1576,DoD-E-83578A, and APR 127-1, which eliminate thisrequirement and allow relays, fuses, or current-limiting resistors to protect the firing systems. TheNSI specification1 still contains a requirement for apost-fire 50 mA electrical current limitation. Althoughsome manufacturers strictly adhere to NSI manu-facturing procedures for NSI equivalents, others havemade changes based on customer requests, the

"Copyright © 1998 by the American Institute of Aeronautics and Astronautics

WELD (RE F)

EPOXY

ELECTRICAL PIN

DISK, SEALING -

EPOXY SEAL BOTH PINS-//

BODY ASSY

Zr/KC104 /PROPELLANT./114-4MG(2 INCREMENTS)

—— .586-396REF ———————————

CUP, CLOSURE

DISK, INSULATING

DISK, INSULATING

BRIDGEWIRE

Figure 1. Cross Sectional View of NASA Standard Initiator (NSI).

relaxation of post-fire electrical inspections, and theinterest of economy. Also, since drawings andassembly procedures are usually not part of pro-curement packages, much of this information isconsidered proprietary.

NSIs and NSI equivalents were created to provide theelectrical ignition interface for a wide variety ofpyrotechnic applications. Prior to the Apollo program,NASA, recognizing the myriad problems beingencountered with initiators, decided to create andutilize a NASA Standard Initiator. The NSI wasderived from the dual bridgewire Apollo StandardInitiator (ASI) and the Single Bridgewire ApolloStandard Initiator (SBASI). NASA Johnson SpaceCenter has the management responsibility forproduction and distribution of the NSI to allgovernment agencies and their contractors. Eachmanufacturing lot of NSIs is certified to meet a -420°F

functional requirement; without this certification andrigorous quality assurance documentation, no otherinitiator can be an NSI. NASA policy restricts the saleor transfer of Government property for private use orexposure of the Government to a shared liability forthe success of a commercial project. Therefore,commercial launch vehicle managers requested NSIequivalents, which were subsequently accepted forU.S. Air Force-sponsored programs. The intent wasthat the NSI equivalents met the same form, fit, andfunction, including the same output charge, as the NSI,and were thus interchangeable. However, a number ofpost-fire short circuits have occurred with the use ofNSI equivalents in several recent launches. Becausethe initiator firing circuits in these vehicles weredesigned with current-limiting resistors or couldaccommodate heavy current loads, the phenomena didnot cause electrical system failures.

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The purpose of the effort described in this paper is toprovide information on experiences of post-fire,electrical short-circuit anomalies, to consider thecauses, and to recommend corrective actions to reducethe opportunity of such occurrences. The approach forthe effort was to compile and analyze the directcurrent firing data for the NSI, the NSI-derived GasGenerating Cartridge (a cartridge with the NSIelectrical interface), and NSI equivalents, which areused on the Lockheed Martin-managed Multi-ServiceLaunch System (MSLS) and Atlas Centaur launchvehicles.

DESCRIPTION OF INITIATORS ANDAPPLICATIONS

This section describes the initiators evaluated hi thisstudy: the NASA Standard Initiator, the NSI-derivedGas Generating Cartridge (NGGC), and the NSIequivalents with their applications.

Common to all these initiators/cartridges is the closed-bomb test used for lot acceptance. The initiator isfired into a 10 cc, cylindrical, closed volume(approximately 0.75-inch diameter, 1.25 inches long).This volume is at least an order of magnitude largerthan those normally found in pyrotechnically actuateddevices. Prior to the 1980's, a second closed bombwith a 0.5 cc volume test was required for the NSI. Asstated hi reference 1:

1.3.3 Output Pressure / FunctionThe initiator shall be designed to producethe following pressures and/or functiontime under the conditions listed below:

a. A pressure of 650 +/-125 psig hi a 10 ccvolume within a temperature range of-260 to +300°F.

b. Time to reach 525 psig hi a 10 ccvolume shall not exceed 10 millisecondsfrom -260 to +300°F as measured fromapplication of current (5 to 22 amperesd.c. from -260 to -66°F, 3.5 to 22 am-peres from -65 to +300°F, or withcapacitor ignition circuits).

c. (Prior to 1992) a minimum pressure of5,000 psi hi a 0.5 cc volume at apressure of 10"6 Torr from -260 to+300T. (This requirement has beendeleted.)

Unfortunately, as described hi reference 2, closed-bomb tests do not represent the conditions encounteredin pyrotechnically actuated mechanical devices, suchas small initial free volume and piston stroke. Thecombination of small and changing free volume,decreasing pressure and expanding surface area toincrease heat sinks has a dramatic effect3 on thecombustion process of the propellant.

Three additional differences hi the application of NSIsand NSI equivalents should be highlighted: (1) NSIson the Space Shuttle use capacitor firing circuits, hiwhich post-fire electrical short circuiting would notoccur due to the short-duration pulse, (2) the NASAJSC managers of the NSI recommend that the NSI notbe used as the sole energy source for pyrotechnicmechanisms, as are NSI equivalents. Thus, hi theSpace Shuttle, NSIs are fired into large (0.5 to 10 cc orlarger) volumes or into booster charges, while the NSIequivalents are applied directly to mechanisms thatcontain volumes that are much less than 0.5 cc, and(3) hi most NASA applications, parallel firing ofmultiple initiators is prohibited.

NASA STANDARD INITIATOR

The NSI, as shown hi Figure 1, is the unit of choice forNASA and some DoD programs, required for theSpace Shuttle vehicle, and the recommended unit forShuttle payloads. A 0.002-inch diameter, 304 stainlesssteel bridgewire provides a highly controlled 1-ohmresistance for the heat source to initiate thezirconium/potassium perchlorate propellant. Thispropellant, which contains 5% Viton B binder and 1%carbon, is highly stable and has a fast reaction rate.Intimate contact between the bridgewire andpropellant is assured through a slurry preparationprocess, painted and cured on the bridgewire. The leftend of the housing is a standard electrical connectorwith a number of keyway configurations to reduce theopportunity for mismatching connections.

Two manufacturers are currently certified to produceNSIs, Universal Propulsion Co. (UPCO, was SpaceOrdnance Systems, Inc.) and Hi-Shear TechnologyCorp. To date, approximately 200,000 units havefunctioned successfully. Special manufacturing pro-cedures provide several advantages. The size of theproduction lots are usually large, 1,500 unitsmaximum. The numbers of sample units tested for lotacceptance are also large, 154 units, resulting hi morethorough testing. These production lots allow dedi-cated engineering and quality personnel more time fordetailed monitoring of production.

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NSI-DERTVED GAS GENERATING CARTRIDGE

The NGGC4, also manufactured by UPCO and Hi-Shear, was developed to deliver a greater output thanthe NSI. It utilizes the same housing and bridgewireinterface as the NSI, including the slurry mix.However, the output charge consists of 40 milligramsof zirconium/potassium perchlorate and 90 milligramsof a gas-generating propellant. The NGGC is initiatedwith a direct current, 200-volt power supply; thevoltage and current-limiting resistors can be set toprovide constant-current inputs at preset levels. TheNGGC as yet has no applications.

NSI EQUIVALENTS

Two major launch vehicle programs, both managed byLockheed Martin, use standard initiators which arebased primarily on the NSI. The two NSI equivalentsin this study were manufactured by Hi ShearTechnology. Hi-Shear uses a company-standardhousing, the PC23, which is modified to meetcustomer requirements and given a "dash number" foreach configuration. For example, the unit that mostclosely matches the NSI (without the NASAcertification process) is the PC23-23. The Hi Shearpart numbers for each unit, along with the differencesfrom the NSI, are described below.

PC23 used on MSLSThis initiator was purchased as "any PC23." Nodetailed requirements were made on the electricalinitiation interface or the zirconium/potassiumperchlorate propellant formulation. Therefore, sinceany PC23 type was acceptable, 4 or 5 differentavailable lots, including different "dash numbers,"were provided. Two PC23 initiators are used in eachof four 3/8-inch and eight 1/2-inch separation nuts andone isolation valve for the MSLS. Also used wereseparation thrusters that employ PC 178-1 cartridges,containing dual, one-ohm bridgewires. The applica-tions hi the mission require 3, 4 and 6 initiators to befired in parallel. The working volume within the 1/2-inch nut is 70% greater than that of the 3/8-inch nut.Each electrical firing circuit employs a 28 +/- 4 voltbattery with current limiting resistors to provide5.5 amperes, 45-millisecond gated pulse for eachbridgewire. The current drawn in each of theredundant firing systems on the MSLS were measuredduring flight and transmitted to ground recorders.

General Dynamics Standard Initiator (GDSD usedon the Atlas Centaur VehicleThe GDSI, General Dynamics part number 55-07261-1(Hi Shear PC23-34), is identical to the NSI, exceptthere is no slurry on the bridgewire, the first incrementof propellant against the bridgewire contains no Vitonbinder, and the pin configuration hi the connector isslightly different. The devices used on this vehicle aresimilar to those on the MSLS. Again, a 28-volt, 5.5amperes, current-limited pulse is provided. However,the gated firing pulse duration is 2 seconds. Firingcurrents were measured in flight and transmitted toground recorders.

STUDY PROCEDURE

Functional data on the available post-fire short circuitphenomena for the NSI, the NGGC, and each of theNSI equivalents in each respective application werecollected and reviewed. The potential causes for theobserved short circuit phenomena then were analyzed,based on each particular configuration.

RESULTS

The results of this effort are presented hi the aboveorder: the NSI, the NGGC, and the NSI equivalents.

NSIDirect current, closed bomb, lot acceptance data onover 1,000 firings of Apollo Standard Initiators andSingle Bridgewire Apollo Standard Initiators (prede-cessors to the NSI), references 5 and 6, indicated adifference in post-functioning decay of currentbetween firings hi 10 and 0.5 cc closed bombs. Itshould be noted that the firing system used hi thesetests was a solid-state system, which maintained thepreset current level, as the resistance at the bridgewireinterface changed, until the 50-volt limit voltage wasexceeded. As shown hi Figure 2, the 10 cc firings, thecurrent at 3.5-amperes decreased exponentially to zerohi 2 milliseconds after bridgewire burnout. Thecurrent in the 22-ampere firings dropped to zero hi 0.3millisecond after bridgewire burnout. However, hi the0.5 cc bomb (Figure 3), the current decays were 12 msfor 3.5 amperes, 13 ms for 5 amperes; the 22-amperefiring trace indicated an 8-ampere current draw at 0.43ms, at which time it exceeded the recorder's timelimit.

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25 r-

/- 22 *mp», 1Dec bomb

t

/-.Z.

as amps, 10 cc bomb

Figure 2. Typical ASI/SBASI Firing CurrentTraces in 10 Cubic Centimeter Bomb Tests.

Electrical conductivity between the electrical pinsoccurs during the combustion of the zirconium/potassium perchlorate propellant. The followingobservations have been made. The burning of thezirconium/potassium perchlorate produces a highlyconductive plasma and creates a temporary short-circuit between the pins and between the pins and theinitiator body. The level of voltage available in thefiring system has a significant effect; when thebridgewire burns away, the full voltage of the firingsource appears across the pins to drive an electricalcurrent through the plasma. Conductivity is furtherenhanced when two cartridges are fired simultaneouslyin redundant devices. As long as the gases remain hot,conductivity continues. Firing into smaller volumes,as described in the previous paragraph, produceshigher pressures and requires longer times for thegases to cool. The products of combustion of astoichiometric zirconium/potassium perchlorate (ZPP)composition are non-conductive solids, ZrO2 and KC1,and gaseous CO2 (due to the 5% Viton and 1%graphite additives). The ZrO2 and KC1 can only be"gases" in the vapor state at thousands of degrees hitemperature; they quickly condense on the cool wallsof the containment volume. However, since thecomposition is formulated to be fuel (zirconium) rich,the unburned zirconium is highly conductive.

Fuel-rich mixtures were selected to achieve a fast burnrate. The dissimilarity in particle size (zirconium 1 to8 microns, versus potassium perchlorate 15 to 20microns) increases the opportunity for heterogeneity,reduces physical fuel-to-oxidizer contact, andultimately yields fuel-rich residue. Heterogeneity isfurther exacerbated by the differences in material

25 r-

20

15

10

/~22 amps, 0.5 cc bomb

- 5 amps, Oi cc bomb- 3.5 amps, OJS cc bomb

decay extend* to 13m*decay extend* to 12m*

0 1 2 3 4 5 6Time, mllllMeonds

Figure 3. Typical ASI/SBASI Firing CurrentTraces in 0.5 Cubic Centimeter Bomb Tests.

density (zirconium is 6.5 g/cm3 and potassiumperchlorate is 2.52 g/cm3). The presence of unreactedzirconium is virtually inevitable. The addition of 5%Viton and 1% carbon slows the burn rate and enhancesthe opportunity for more complete combustion.

Ignition, burn rate, and combustion efficiency aredramatically affected3 by the size and shape of thevolume into which the NSI is fired. The ZPPformulation is very sensitive to ambient pressure andthe thermal conductivity of the housing materials. Thehigher the pressure and the lower the thermal losses(as provided by small initial free volumes), the fasterand more completely it burns—an avalanching effect.Large volumes induce lower ignition and combustionefficiencies, but do allow the burning material to beexpelled from the NSI to reduce the opportunity ofzirconium deposits on its electrical pins.

The presence of a bridgewire slurry mix could have anaffect on post-fire short circuiting. The slurry, beingthe first to ignite, could assist in the expulsion of themam portion of the propellant load and the reductionof combustion residue from the electrical pins,particularly in large initial free volumes.

NSI-derived Gas Generating CartridgeAs described in reference 4, the NGGC exactlyduplicated the electrical ignition characteristics of theNSI. At higher current levels (15 and 20 amperes),however, a number of post-fire short circuits wereobserved. These short circuits can be attributed to thehigh voltages applied (up to 200 volts) and to firinginto devices with small initial free volumes.

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PC23 in the Multi-Service Launch SystemAlthough the electrical initiation characteristics of thePC23 were normal (comparable to Figure 2) during10 cc firings for lot acceptance testing, actual flightdata showed otherwise. In the first, or demonstrationflight of the MSLS, firing circuit A was free of post-fire short circuiting, while the identical circuit B hadsevere shorting. A typical current trace for the firingof three PC23's in parallel in system A is shown hiFigure 4, where very little post-fire current drawoccurred. All three of the units hi system B shortcircuited (Figure 5), to draw 5 amperes each, or a totalof 15 amperes of current. After the initial currentdecrease, indicating the bridgewire burnout, thecurrent stayed at a high level throughout the firingcommand of 45 ms. Figure 6 shows three currentdraws in three sequential events, curve "a" shows thecurrent drawn for four PC23's in parallel in two3/8-inch and two 1/2-inch separation nuts, indicatingtransient shorting and finally complete shorting of allfour PC23's for the duration of the 45-millisecondgated pulse. Curve "b" shows no indication ofshorting of four PC23's hi four 1/2-inch separationnuts. Curve "c" has no indication of shorting of twoparalleled PC23's in two 1/2-inch separation nuts andin one bridgewire each of four PC178-l-actuatedthrusters. Subsequent flights experienced moreshorting hi 3/8-inch separation nuts than did the1/2-inch separation nuts with the 70% larger internalworking volume. Again, it must be pointed out thatseveral lots of PC23's were used on these missions; thepossibility exists that more than one PC23 type wasused (with and without a slurry and with and without aViton binder).

10 20 30Tim*, milllMConds

40 50

Figure 4. Current Drawn in Firing 3 PC23's inParallel in MSLS, Flight 1, System A: 2 PC23's

in 3/8-inch Nuts and 1 in an Isovalve.

18

1614

10

8

10 20 30Time, mllllMcond*

40 SO

Figure 5. Current Drawn in Firing 3 PC23's inParallel in MSLS, Flight 1, System B: 2 PC23's

In 3/8-inch Nuts and 1 in an Isovalve.

60 80 100 120 140 160TifiM) (will seconds

Figure 6. Current Drawn in Three MSLSFlight 1 Firing Circuits:

a = 4 PC23's in 2 3/8-inch and 2 1/2-inch Nutsb = 4 PC23's in 4 1/2-inch Nutsc = 2 PC23's in 2 1/2 -inch Nuts and 4 PC178-1

Bridgewires

10

§ 8

: 6j-I *3 2

-

-

-

-

-

\0 2 4 6 8

Tlnw, milliseconds

Figure 7. Typical GDSI 5-ampere FiringCurrent Trace in a 10 cc Closed Bomb.

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General Dynamics Standard Initiator in the Atlas-CentaurThe GDSI exhibited post-fire short circuiting in 10 ccclosed bomb firings in lot acceptance testing, as shownin Figure 7. The constant current firing circuit used inthese tests was a solid-state system that could controlthe current level until the voltage source of 28 voltswas exceeded. The firing level was set at 5 amperesfor the 6-millisecond gated pulse, but the system wasclearly unable to control the level once the bridgewireburned out and short circuiting occurred. In seven ofthe last eight flights, these initiators experienced post-fire short circuiting for the entire 2-second duration ofthe firing signal. Figure 8 shows three traces of thecurrents drawn in flight with three GDSIs in parallel.The first trace indicates all three units experiencedpost-fire short circuiting to draw 16.5 amperes shortlyafter bridgewire burnout. The second trace indicatesintermittent, and finally a complete short circuit of allthree units. The bottom trace indicates that only oneunit shorted to draw 5.5 amperes. The lack of Viton inthe GDSI propellant was the likely leading contributorto short circuiting. This lack of Viton resulted in acomposition that exhibited a higher initiation sen-sitivity, a faster bum rate, a higher combustiontemperature, and higher electrical conductivity in theburning material and post-combustion residue.

".10

8.15

1 10*§ 53

-I

' i ___ >^ ———— ,\J- i i . 1 i

0 .5 1.0 1.5 2.0 2.5Time, seconds

Figure 8. Typical Currents Drawn in Firing 3Parallel GDSI's in Atlas Centaur Flights.

CONCLUSIONS

This study has documented and analyzed theoccurrence of post-fire short circuiting of the electricalinitiators used in pyrotechnically actuated devices.This short circuiting not only can degrade theperformance of the pyrotechnic devices, but also canaffect the electrical firing circuit itself. Both canpotentially degrade the success of flight programs.The current levels drawn from 28-volt firing circuits intwo launch vehicles, utilizing two different NSIequivalents, indicated that short circuiting occurredfrequently. Several parameters affect post-fire shortcircuiting: (1) highly conductive plasma and hot gasesare generated during the burning of the zirconium/potassium perchlorate propellant, causing conductionbetween the electrical phis, as well as between theelectrical phis and the initiator body; (2) the propellantis fuel (zirconium) rich, which leave deposits ofconductive, unburned fuel and residue; (3) the pre-sence of a slurry mix on the bridgewire apparentlyassists in jettisoning conductive, unburned fuel andresidue; (4) the presence of a Viton binder hi thepropellant enhances combustion and reduces theamount of conductive unburned fuel and residue; hicontrast, the lack of Viton causes a more rapidcombustion and higher conductivity of the burninggases and propellant residue; (5) higher voltage levelshi firing circuits force greater conduction through theplasma and hot gases of burning propellant; and(6) small initial volumes in mechanisms into whichinitiators are fired induce more vigorous and morecomplete combustion, as well as higher, longer-duration pressure pulses to prolong conductivity.Although the electrical interface to the propellant ofthe NSI was not totally immune to short circuiting hithis evaluation, the two types of NSI equivalentsexhibited a much higher sensitivity to the aboveparameters. The most likely cause is the lack of aslurry mix on the bridgewire, and elimination of theViton binder. Although there is apparently a low-frequency occurrence of post-fire short circuiting withthe NSI electrical interface (only observed with high-voltage firing systems), this study can offer noguarantees. The parameters hi manufacturing andapplications could eventually produce the conditionsthat allow post-fire short circuiting.

RECOMMENDATIONS

Recommendations from this study fall into twocategories: coping with the potential of post-fire shortcircuiting of initiators, and investigating theopportunities to reduce this phenomenon.

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Users of any electrical initiator should be aware of thepotential for experiencing short circuiting and shoulddesign and demonstrate that their systems canaccommodate this phenomenon. The electricalinitiation characteristics of initiators should beevaluated in the actual pyrotechnic mechanisms, usingthe actual electrical circuits intended for flight.Capacitor-discharge firing circuits with short-durationgated pulses will reduce the possibility of currentoverloads and long-term conduction.

To reduce the opportunity of post-fire short circuitingthrough initiator redesign, further investigations areneeded to determine the effects of the six parameterslisted above.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the support of thefollowing in providing historical, management, design,and performance information: Barry Wittschen andCarl Hohmann of NASA Johnson Space Center; FredSilverman of Hi-Shear Technology; Stan Barlog ofUPCO; Eric G. Anderson and Mike Kirchoff ofLockheed Martin; and John J. Dougherty, BruceKliewer, J. N. Mason, J. C. McMunn, John W. Wee,and E. J. Kovacic of TRW.

A special acknowledgement is due to Mr. Laurence J.Bement of NASA Langley Research Center for hisencouragement hi writing this paper, providing thebulk of the references, many discussions and a criticalreview of this paper.

REFERENCES

1) Design and Performance Specification for NSI-1(NASA Standard Initiator-1), SKB26100066,Revision D, March 27, 1992.

2) Bement, Laurence J. and Schimmel, Morry L.:Cartridge Output Testing: Methods to OvercomeClosed-Bomb Shortcomings. Presented at the 1990SAFE Symposium, San Antonio, Texas,December 11-13, 1990.

3) Bement, Laurence J. and Schimmel, Morry L.:A Manual for Pyrotechnic Design, Developmentand Qualification. NASA Technical Memorandum110172, June 1995.

4) Bement, Laurence J.; Schimmel, Morry L.; Karp,Harold; and Magenot, Michael C.: Developmentand Demonstration of an NSI-Derived GasGenerating Cartridge (NGGC). Presented at the1994 NASA Pyrotechnic Systems Workshop, Albu-querque, New Mexico, February 8 and 9, 1994.

5) Qualification Test Report 1055, Initiator, ElectricalHotwire, Space Ordnance Systems, Inc.,May 21, 1965. Summary of 611 firings of Dual-Bridgewire Apollo Standard Initiators (ASIs).

6) Qualification Test Report 6068, Single BridgewireApollo Standard Initiator (SBASI), Space OrdnanceSystems, Inc., October 10, 1966. Summary of 488firings.

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