A New Approach to Propellant Formulation - Copy

7/30/2019 A New Approach to Propellant Formulation - Copy

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1 .ntroductionThe recentQuadrennial Defense Review[1 ]discussed thechallenges faced by theDepartment

ofDefense (DOD) in realizing the new supportstructureneeded to achieve the future military forcesoutlinedintheJointVision2010document[2].nordertoaffordtheincreasingexpendituresassociated with thesenew capabilities, the QDR concludedthatsupportoperations must be"leaner,moreefficient,and morecosteffective.We notonly have theopportunity to change,wehave th erequirementtochange."owhereisthismandatemoreaptthaninthedevelopmentofnew propellantformulationsfo r advanced munitions.nthepast,development ha sbeendependentontrialand errorapproaches,whichare costly,inefficient,and t ime consuming.ompounding theseproblems are new environmental guidelinesand constraintswith which future development programsmust comply.Sinceconventional propellant developmentand manufacture produceslarge amountsof waste, these new requirementscouldhobble the process.During thedevelopmentof XM39 gun propellantduring the1980s,for example, about 50,000 lb of test materialwas produced [3] ,almostallofwhichwaswasteresultingfromthetrialanderrortestingrequired.uringthecurrentmanufactureof M30gun propellant,an estimated 0.3lb of ethanolan d acetoneare released to theatmosphereorverypoundfpropellant4].hesexamplesin tatthecalefpotential environmentalhazardsthatnow mustbeaddressed. smoreperformance isdemanded from gun systems, the margin fo r error in their design decreases,leading to even greater levels of trialan d errorduring development.Clearly,the added modern burden of environmentalresponsibility will renderthe traditionalapproach to propellant development even moreunmanageable.

Thenew environmentalconstraintsare nottrivialadd-onrequirements.hey encompassth emanufactureo feveryingredient,fabricationofthepropellantitself,emissionsintraininganddeployment ,stabilityduring storage, an d demilitarization when no longer useful.Design foresighton issues relating to storage(stabilitysurveillance an demissions)are o f great potentialimportancesince theusefullifeo f propellantsca n be long;16-innavalguns,fo rinstance,still use a propellantknownas pyro,whichwasmanufactured during(o r justafter)World WarII .ropellantsar ealso manufacturedinlargequantities;asinglebatchofartillerypropellantistypicallymorethanahundred thousand pounds.hus,thecradle-to-grave costsassociated with propellants, both toth e


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national treasury and to the environment,are potentially very substantial.While assessing life-cyclecostsfo ranew propellantisdifficult,managingthesecostsusingthetraditionaltrialanderrordevelopmentmethodis allbut impossible.tisarguedin thisreport thattheconflictbetween theneed to developadvanced propellantsfo r more lethal,survivable weaponsand the need to minimizelife-cyclecostscanberesolvedonlybyanewapproach.ustasnew realitieshaveforcedthemaintenanceofthenation'snuclearstockpiletopassfromatesting-basedtoascience-based approach, developing new propellants must transition from a trial-and-error-based to a science-based approach.

Fortunately, thescientific understandingof the microscopicprocesses involved in thestructureand combustion of energeticmaterialsha sseen greatprogressover th elastdecade. lthough thisunderstanding is fa r from complete, sufficient progress ha s been made to permita vision of how new tools fo r the smartdesign o f propellant formulations mightbeused to minimize inefficiencies in thepropellant formulationprocess.uch an exerciseisalso valuablein identifying thosekey aspectsof the problem where investments in futurescientific understanding might be made most profitably.Thedealevelopmentalrocesstilizinghesemergingechnologieswillncorporatehe constraintof reducingthewastestreamsresulting from allthestagesof fielding a new propellantwithpreserving thegiven performance objectives,which are the raison d'etre fo r the process.Thisreport willoutlinesuchastreamlineddevelopmentapproach.

2.raditionalPropellant-Formulation ProcessTheraditionalrocedureorormulatingewropellants,uidedargelyyntuition,

experience,and testing,relies heavily on trialand error. andidate propellant mixes must be madean dsubjected to asequenceof tests,manyo f which generatehazardousemissionsand wastes.nadditiontothewastegenerationassociatedwithtestan devaluation,manyof thecandidatesar ediscarded from furtherconsiderationdue to unacceptable levelsofperformanceorotherproblemsthatariseinthequalificationprocedure.orthesecases,wastecostsaccruefo runsuccessfulformulations,ynthesisndtesting,an ddisposingofan yexcessmaterial.I tisclearthatsuchcut-and-tryapproaches, although previouslyunavoidable,are now consideredinefficient,costly,an denvironmentallyundesirable.

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Figure illustratestheconventionalprocesso f developing a new propelling charge.hi sflow chartpresumesthatadequate ingredients(e.g.,energetic materialsandpolymericbinders)are "on theshelfto achieveasuccessful formulation.f this is notthecase, then new ingredientswith thedesired characteristicsmust be developed.Beforeembarking on the procedure outlined in Figure1 ,theweaponsdesignerwillhavespecifiedhi srequirements,whichinthepasthavebeendrivenmainly by performanceorvulnerability requirements.heinitialscreening represented by Loop1 consists o f computations of impetus,flame temperature, an d idealized maximum performance basedon thermodynamic equilibrium,which may be viewed as a limiting case.A t this stage, a formulation canberejectedfitannotmeetperformanceeeds,venssuming theoreticalmaximum performance.f andidateasseshi sevel,owever,hortfallsromheoreticallydealperformance revealed atsubsequent levels may yet causeit to be rejected, in which caseth e burden fallsbackon theformulatorto provide a new candidate to ru n thegauntleto f screeningtestsfrom thebeginning.Note:In thisflow chartan d those to follow,a very complex process is rationalized intoalimitednumbero f discretesteps.uch anidealization isnecessarilyoversimplifiedandisintended to serveonly a heuristicpurpose.)

Oncethesmall-scaleevaluationsaremade,thenmoreextensivetestsandmeasurementsare performed fo rincreasinglylargersamples. sevidentin thisfigure,theconventionalmethod hasa notable degreeof physical testingan d measurement,which could generate a significantamoun tofwaste.lthoughth esmall-scalescreeningprocedurescontainedwithinthefirstfourloopsare relatively inexpensiveon a per-samplebasis in termsof time,material, and equipment requirements,thesemightbecomequitecostintensiveif aseriesof failuresrequirereformulatingandretesting several candidates.Because of the nested natureof these screening loops,an inexpensivesingle-step operation could make theformulation procedurecostprohibitive.

Asnllustrationfthepotentialxpensessociatedwithheepeatedxecutionftheinnermostloopsresultingfrom thetraditionaltrialan derrorapproachto propellantformulation, consider thefollowingictitiouscase of agun-propellantdevelopment.o determinetheexpenseassociatedwithdevelopinganew propellingcharge,costswereassignedtoeachstageo ftheformulationprocedureutlinednigure. Naturally,heseostswillarynormouslyn


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Translationofmunitionperformancegoalsintopropellant specifications

Proposeapropellant formulation-r , Computeimpetus,flame I ,Loop 1Fail-temp.,idealperformance I Developne w ingredientsLoop 2-

-Loop 3

Fabricatepropellantgrains

Measureburningrate

-Loop 4- UseIBHVG2fo rgraindesign& propelling-charge weight

-Loop 5- Performvulnerability testsongrains(HFCIT,BIC)

-Loop6- Perform ballistic-simulator testsofignition & flamespreading

-Loop 7- Designgniter fo rpropelling charge -Loop8- Perform full-scalegu nfirings

-Loop 9- Performfull-scalevulnerability tests

-Loop 10- Large-scale propellantfabrication-Loop 11 - Performacceptancegu nfirings qualitycontrol&bb lerosion

Type-ClassifyPropellant J Figure1 .ConventionalProcedurefo rDevelopmentofaNew Propelling ChargeforGuns.actual cases,butaneffortwasmadeto make reasonableestimatesfo r thesesteps.hese numbersshould be takenwithintheirintended heuristiccontextand nottakenliterally.herelative valuesassigned areintuitively reasonable in that the early "screening" processes are the least expensive,and


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the large-scale processesreflectthe more significantcostsof the procedure.For the purposes of thisillustration,itwasassumedthattheformulatordid no trequirenew energeticmaterialsynthesis.

Inthisexercise,itwasassumedthattheprogressionthroughtheentireprocesswould requirethreepassesthrougheachloopin Figure1 .nreality,ofcourse,eachloopwillincuradifferentnumber of executions uniquely specific to each propellant-development case.The value of choosinga singlenumber fo r all loopsis purely in the simplicity and transparency it confersto the simulation.The selected value of three passes is arbitrary, but it reflectsthe reality of at leastsome degree o f trialand error.

Theresults of thissimulation are givenin Table1 .n thissimple example,three-fourths of thetotalcostoccursinthefirstthreestagesofthedevelopmentalprocessthroughstepsthat,whenindividuallytaken,are atthree to fourordersof magnitudelessexpensivethanth eprocessesnearthe end of the developmental process.This resultis dramatic evidence of the enormous hidden costsassociatedwithtrial-and-error testing attheearlydevelopmentstages.nactualpractice,thetotalcostsincurred by this inner-loop testing havenever been this large,only becausea complete matrixoftestingwoulderohibitive.hehoroughnessftheormulat ionearchwashereforeconsciously curtailed. ndoubtedly,theincompletenessof thesearch jeopardizesoptimizationoftheformulation.notherreasonthatsuchinner-loopcostshaveneverbeenthislargeisthatperformancerequirementswouldhavebeensacrificedatanearlystageto keepcostsdown.hi sdowngrading of expectationscould have easily compromised the maximum attainable performanceha d morecomplete testing been feasible.

Theinefficienciesinherentinthetrial-and-errorapproachmayhaveconsequencesbeyondexorbitant monetary cost.In the modern era of warfare,a great premium isplaced on agileresponsecapability to new threats.herecould be occasionswhereprotecting somestrategicassetisworthvirtuallyanyexpenditure,yetthet imeneededtoextensivelytestmayprovetobethepacinglimitation. nexampleof thet imeneededto developa new propellantcan beseenin thecaseofM43 ,ahigh-performancetank-gunpropellant.43wasunderdevelopmentfo ralmost20yearsbefore being type classified shortlybeforeOperationDesert Storm.n this case, the presenceof an untried propellant ingredient, cyclotrimemylenetrinitramine(RDX), may have materially lengthened


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Table1 .emonstrationofth eMultiplier EffectAssociated WithRepetitiveExecutionsofLow-Cost,Inner-LoopStepsinTraditionalPropellant-FormulationProcedureofFigure1 Loop No. Per -LoopCost($K)

TotalNo.ofTimes ExecutedDuring EntireProcedure

Tota lCos tofThisStepThroughEntireProcedure (TotalNo.ofTimes ExecutedxCost /Loop) ($K)1 3 3U 177 ,147 531 ,4 4 1 2 5 310-59 ,049 295 ,2453 2 39= 19 ,683 39 ,366 4 5 38= 6 ,561 32 ,805 5 5 37= 2 ,187 10 ,9356 4 0 36=729 29 , 160 7 10 35= 243 2 ,430 8 300 34= 81 24 ,300 9 1 00 33=27 2,700 10 3,000 32= 9 27,000 11 50,000 31= 3 150 ,000

1 TotalCost 1 , 1 45 ,382

the process. ut instead,this lack of experience simply increased the numberof iterationsof testing neededto assurethesafety andconsistency of thenew propellant. bviously,there may likewise becaseswheretheenvironmentalconsequencesof a particularpropellant oringredientmay beso egregiousthatcostand t ime becomeof secondaryimportance.

3.heImpactofLife-CycleAnalysison PropellantFormulationThe need to minimizeth e wasteassociated with th e propellantformulationprocess is no longer

driven purely by monetary constraints.Environmental restrictionsan d requirementshave demanded


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that environmentalimpact begivenequalor greater weight in the developmentan d design ofa new gun propellant long withincreasinglyimportant environmentalconsiderationsha scome a focuson the true cradle-to-grave costs of weapons systems.Optimizing the design of a system to minimizedevelopment,manufactur ing,and operationalcostsisaconsiderable challenge. ow,thecostofdemilitarizing th e system at theend of it s usefullifemustalsobe included,ithepast,propellantshavebeendisposedofbyopen-airburning.nthefuture,thismethodofdisposalmayno tbe allowed.herefore,consideringhow the propellantwilleventually bedestroyedorrecycled willhaveto beincludedinitsdesign.hecollectivecradle-to-gravecosts,includingenvironmentalconsiderationsateachstageof manufacture,use,and disposal,havebeen termedlife-cyclecosts.

Toaccountfo r theserequirements,the propellantformulationproceduremustbemodified to reflectthesenewdesignconsiderations.igure2suggestshowtheinclusionofenvironmental constraints(Loops2and6)mightmodifytheconventionalpropellant-developmentflowchart(Figure1 ) .he simulation logic of Table1 assistsin estimating the added burden on the propellantdevelopmentprocessintroduced by theenvironmentalconsiderations.n the modifiedsimulationshown in Table 2, very modest per-loop costs areassigned to the environmental steps.A substantialincrease in totalcostresultsfrom addingonly tw o new steps.ven if it isassumedthat these tw o environmental steps cost nothing, the totalcostof the developmentsequence is increased by a factorof five. bviously,adding environmentalconstraintsca neasilyoverwhelm thepracticalityof thetraditionalut-and-tryevelopmentmethod.Greaterrationalizationfthearlytepsnhe propellant-development procedureis clearly needed to successfully manage this added complexity.

4.ropellantFormulation Through aScience-BasedApproach Priorto th e banonundergroundnuclearweapon tests,theDepartment of Energy(DOE)used

directtests to regularlytestdesign concepts and the safety an d reliabilityof nuclear weaponsin thestrategictockpile.it hthecessationftesting,heseconcernsadobeatisfiedthroughcomputation based on a reliable scientificunderstanding.This strategy is embodied in whatis called


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Translationofmunit ionperformancegoalsintopropellant specificationsProposeapropellant formulationt

_L jComputeimpetus,flame I' temp.,idealperformance IT*Loop2: NEW-oop 3-Loop4

Fabricatepropellant grainsI

Assessfabricationand demi lwastes Fail- Developnewingredients

I-Loop5-

ILoop6:NEW-

MeasureburningrateU se IBHVG2fo rgraindesign&

propelling-chargeweightAssessdeployment,training,

andstorageemissions

-Loop7- Performvulnerabil i tytestson grains(HFCIT,BIC)

-Loop8- Performballistic-simulator testsof ignition&flamespreading

-Loop9- Designgniterforpropellingcharge-Loop 10- Performfull-scale gu nfirings

Loop11-

Loop12

-Loop 13Perform full-scalevulnerabilitytestsLarge-scalepropellant fabricationPerformacceptancegu nfirings-qualitycontrol&bb lerosionType-ClassifyPropellantiFigure 2. onvent ionalProcedure forDevelopingaPropell ing ChargeWiththeAddi t ionofTwo New Loops(2 and 6 )Recognizing Environmenta lConstraints.


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Table 2. ffecton the TotalCost ofDevelopment ofIncluding Two Environmental StepsIntotheTraditionalPropellant-Formulation Procedure(Figure 2)

LoopNo. Per -LoopCost($K)

TotalNo.ofTimesExecuted Dur ing EntireProcedure

TotalCostofThisStep Through EntireProcedure (TotalNo.ofTimes Executed xCost /Loop)($K)

1 3 31 3=,594,323 4,782,9692 2 3 1 2=531 , 441 1 , 0 62 , 8823 5 3U= 177 , 147 885,735 4 2 31 0= 59 ,049 1 1 8 , 0 98 5 5 39= 19 ,683 98,4156 4 38= 6 ,561 26,2447 5 37= 2 , 187 10 ,935 8 4 0 3 6 =729 29,1609 10 35= 243 2,4301 0 300 34= 81 24,30011 1 00 33= 27 2,7001 2 3,000 32= 9 27,0001 3 50 ,000 31=3 150 ,000 Tota lCos t 7,220,868 1

ascience-based stewardship.hi sterm isnotmeantto imply thatsciencewas notformerly used;however,now the burden to assure an accurate, detailed understanding of th e microscopic processesiscute,astotalrelianceisbeingplacedon it.heDOEhasredirectedfundsformerly usedin testingintoexperimentsandtheorydesignedtobolstergapsinfundamentalunderstandingo fphenomena related to designand agingissues.Whiletestingin thedevelopment of propellantsis permissiblendmportant,tsxpensivenollars,ime,ndnvironmentalmpact.he propellant-formulationcommunitycouldprofitablyadoptthepiritofth eDOEscience-based strategy.


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Effortsto developpredictivetechnologiesleadingto smartdesignhavebeenunderwayforseveral years within DODmiss ion programs.hese efforts include developing molecu la r -dynamicmodel s5-7]fRDXandCL20 )tructurendaggregateproperties,heoreticaltools8]orpredicting th e stability andheats offormationfornot ional energet icmater ia ls ,models[9] to predictth e burning rateofa propellantfrom it singredients,and models[10,11]to compute th eeffectsoffinite-rateineticsnl amepreadingn ropell ingharge.hesemergingredictive technologies can formthebasis ofth e science-basedapproach to propellant development , which can inurnminimizeheostfth epropellantormulat ionrocedureyreducingynthesisnd measurement .Unfortunately,theseeffortshavefocusedalmostsolelyonperformance,withoutregardto envi ronmenta lhazard . continuedand leveragedeffortto develop thesecapabilit iesto incorporateenvi ronmenta lconst ra intsshouldbeunder taken.

To minimize propellant-development costs(whether they be moneta ry ,t ime,or environmental) ,th edevelopmenta lproceduremus tbeoptimized.uchanopt imizat ion canbeachieved if :

(1 )he numbe roft imesth einnerloopsare accessed is minimized ,and (2 )heprocessesincludedininnerloopsareeitherel iminatedo rmadeascostefficientas

possible.

These tw o requirements forachieving optimizationcan be met by extensively uti l izing model ing and simulat ion. esults frommodel ing andsimulationprov ideth einsightneeded forth esmar t design ofmater ia ls .Modelingand simulat ion arerelatively cheap and fast .hereis no needto fabricate testmater ialandnoneedfo rth elaborandexpenseofmann ingand maintainingtestequipment . Addit ional ly , there is noexpense associatedwithhazardousmater ial ,including synthesis,handl ing,cleanup,or disposalcosts .

Figure3showsa flowdiagram attemptingto opt imize th e propellantformulat ion procedure by replacing early-phase testingand measurementwithmodelingandsimulat ion.ont inuingin th espiritofth etw osimulationspreviouslymentioned,it wasassumed thata mode lfo r predicting th e

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burning rateha s been developed an d that it was incorporated into Loop1 .The capability to computetheburningratewouldobviatetheneedfo rfabricatingpropel lantgrainsortheburningratemeasurementand themeasurement itself.Next, it was assumed that vulnerabilitymodelsexist thatca n at leastscreencandidates at the Loop1 level.inally, it wasassumed that modelsexistthatca npredict f lamespreading and igniter functioning well enough to eliminate thetesting associated withthesesteps and incorporate these functions into Loop 4.The per-loop executioncost in Loops1 an d4 was increased to reflect theadded modeling effort.heseactivities are all areasof active researchunder missionprogramsof the U.S.Army Research Laboratory(ARL)and have realisticchancesfo rsuccess.

Theresultsofthissimulationaregivenin Table3,an dtheyshowadramaticdropin totaldevelopmentcostsby a factorof almost 30.Notice thatthenew emphasisonsmartdesign returnsthe heaviestcost burden to thelarge-scale testing and acceptance firings. oncern over troop safetywilllwaysdemandextensivequalityassurancetestingatthisndfthedevelopmentcycle.Modeling an d simulation are most effectivelyused in the beginning stages of the developmentcycle.Thesenumbers are notintendedto be taken to o literally.he totalcosts are obviously a function ofthenumberof steps in eachchart,and thedegree o f simplificationinherentin thesechartsdoesnotpermitthem tobe unique.ntheotherhand,theconceptbehindthenumbersissound.dding environmentalconstraints unambiguouslyaddssteps to thedevelopment process,which increasescosts.Innermost loop functions are exercised the mos t and are th e mos t susceptible to having testing replaced by models.Replacing relativelyexpensive testing with relatively inexpensive models leadsto either totalelimination of inner-loopsteps(suchas propellantfabricationfo r burning-rate tests)or consolidated inner-loop functions.he en d result is an unambiguousreduction in money,time,and environmentalimpact.

5.mplementation The simplified flow chartsillustrate the nested-loop natureo f the propellant-development process

and the total cost reduction that willbe realized by modelingvarious combust ion characteristics and

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Translation ofmunitionperformancegoalsintopropellantspecifications

Proposeapropellant formulation>*-Loop1-

-Loop 2-

Loop3-

-Loop4-

Loop5-

Loop6

-Loop7

-Loop8-

Computeimpetus,flametemp.,idealperformance, burningrateAssessfabricationan ddemilwastes I Fail-

UseIBHVG2fo rgraindesign&propelling-charge weight;flamespreadingan dignitercodesAssessdeployment,training,and storageemissionsPerform full-scale gunfirings1

Performfull-scale vulnerabilitytestsILarge-scale propellantfabricationT JPerformacceptance gunfiringsqualitycontrol&bblerosion

Type-ClassifyPropellantJ

Developnewingredients

Figure 3.StreamlinedPropelling-ChargeDevelopmentUtilizingModel ingDuringEarlyPhases .

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Table3. ffectofStreamliningthePropellent-Formulation ProcedureThroughth eUse ofModeling andSimulation(Figure 3)

Loop No. Per-Loop Cos t($K)

TotalNo.ofTimesExecutedDur ingEntireProcedure

Tota lCos t ofThisStep Through EntireProcedure(TotalNo.ofTimes Executed x Cost /Loop) ($K)

1 5 38= 6 ,561 32,805 2 2 37= 2 , 187 4,374 3 7 3=729 5,1034 4 35= 243 972 5 300 34=81 24,3006 100 33= 27 2,700 7 3,000 32=9 27,0008 50 ,000 31= 3 150,000

TotalCost 214 , 449

behavior.hey donot,however,conveythefactthatahierarchyof modelsexistwithdifferingsophistication anddiffering requirements fo r theinputinformation.orexample,IBHVG2isan interior-ballisticcode usefulin th e preliminary designof a propelling charge,butit cannotpredictproblemswith ignition delaysarising from finite-ratechemical kinetics. n theotherhand, it also doesotequirehemicalineticmechanismssnput,souldhemoreophisticatedXNOVAKTC/NGENcodes.heXNOVAKTC/NGENcodesalsoconsume considerablygreatercomputer resourcesand requiremoreskillto use properly.hus,fo r theoptimumcandidate,themostefficientapproachtoortingthrough largenumberofexistingpropellantsstouseasuccession ofcodeso f increasing sophistication.Eliminateasmany candidates as possible by using simpler codes first;reserve the more detailed, data-hungry,and operator-intensivecodes fo r the morepromisingcandidates. flowdiagramillustratingthishierarchy o fsophisticationin evaluation codesisgivenin Figure4. eferencesfo r thecomputercodesidentifiedin Figure4 are givenin Table4.

1 3


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Inigure,heirstetfmodelsabeledpreliminarycreeningmodels"reth eeastsophisticatedodelstheyrequiretheleastextensiveinputdataandarethereforeexpected to produceheeastccurateesults.oreventheejectionfgoodandidatesecausefinaccuraciesin thesemodels,andidatesat thislevelshouldbeeliminatedaccordingto th eleaststrictcreeningolerances.sheophisticationandenceccuracy)mproveswithheintermediateand advanced evaluation models,thescreening tolerances representedby thediamond shapeswould likewisedecreaseappropriately.

A paralleldemonstration study [12] used the logicembodiedin Figure 4 (preliminaryscreeningand intermediateevaluationmodelsonly)to identify the bestexisting gun propellant fo r a realgunsystem with user requirements.In this work, theuser-supplied requirementsincluded the maximum pressurelimitationand minimum muzzleenergy required bya propellingchargefo raNavy5-in,54-cal .gun. candidatese tof10existing propellantformulationsrepresentingsingle,double,triple-based,andcompositenitraminepropellantswasusedfo rthedown-selectprocedure.ll combust ionpropertieso fthislistof propellantsareknown.heprocedurebeganbyassessing environmentallynacceptablengredientsnheropellantsthisliminatedwoandidates.Thermodynamicropertynformation asbtainedromxistingiteratureossessdealperformance(i.e., muzzlevelocity assuming constantmaximum pressure during thefiring).heseestimatesllowed urtherullingfcandidates.dditionalnsuccessfulandidateswereeliminated from the next stageof screening,which is a calculationof interior ballistics performanceassumingpropel lantgraindesign.ttheendof theexercise,theuserwasleftwithonlyafew candidatesfo rfurtherstudy.tthisstage,usersca nrankthesecandidatesaccordingtotheirspecifications,and more advanced modelscan be employed to make the finalsuitability assessment.Thus,this exerciseillustrated how the procedure outlined in Figure 4 ca n be used to reduce the wastestream in the formulation process,whilecontinuing to meetthe performance objectives fo r th e gun.

The tasknow remainsto transitionthisprocedurefrom anidealizedconceptintoaworking methodology.achoftheboxesinFigure4representanopportunitytoperformatheoretical analysisinlieuofmorecostlytesting.an yofthemodelsdescribedareunderdevelopment; however,thereare many more thatneed to bedeveloped.orexample,thesuccesso f the parallel

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USERREQUIREMENTSMuzzlevelocity,projectiledesign,gun design,specialvulnerabiltyand environmentalconstraints

MASTEROPTIMIZATIONALGORITHM(Generatestrialformulationsand selectsthe one oflowestcost&leastwaste whichmeetsperformanceand vunerabililyrequirements.

)K Full-Scale XTesting J

Figure4 . FlowChartI l lustratingth erogressiveWinnowingofPropellantCandidates ThroughaHierarchyof ModelsofIncreasing Sophist ication.1 5


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Table4 .dentification ofCodesUsed in Figure4 Code Description " 1 Reference

BLAKE Equilibrium thermochemistry [ 13 ] CONPRESS Constant -pressureidealgun [ 1 4 ]

EBHVG2 Lumped-paramete rinteriorballistics [ 1 5 ] XNOVAKTC Quasi -1 -D interiorball isticswithf lamespreading [8,9]

NGEN 2-D/3-D advanced interiorballistics [16,17]

exercisew ascompletely dependen t on knowledgeofthetoxicity ofth e ingredients and knowledge ofth e combustionproperties(such as burning rate,etc.)to performth e screening tests.Fornot ionalmater ia lsthatmightbedeveloped foradvanced propulsionconcepts ,thisinformat ion wil lno tbereadily available,anda need existsforpredictive modelsofsuch. lso,thecurrentmodel s do notaccurately predictproductemiss ions from th e gun intotheatmosphere after gunfir ing events ,which would beanimpor tan tfactor in an environmental ly drivendeve lopmentprocedure .Themos t thatcurrent modelscan do is assume that th e combus t ion productsare in thermal equi l ibr ium,a situationthatm aynotexistin agun-fir ingenvironment .hisdeficiency could beremediedbyenhancing exist ingnteriorballist icsodesoalculateiniteatehemist rytth emuzzle .hearalleldemonstra t ion also makesuseofpreviously measuredburning rates.irst-principlesburning ratemodelsare underdevelopmenta tARLto r emovedependencyonc losed-bombandst rand-burnermeasurement s ,whichrequires fabricating any new propellantand synthesizing any new ingredient . Ifmodels are developed fo r all of th e boxes in Figure4 , one could replace thefirstsix steps of Figure3couldbe replacedby th ehierarchicalevaluat ionmodelsofFigure4 to achieveevenhigher costsavings thansuggested by Table 3.This end goa l is illustratedby th e new chargedeve lopment chartin Figure 5,whereall ofth e model s and logic ofFigure4 are represented by thebox termed "Mas te rOptimizat ion Algor i thm."hus ,Figure 5represents thefull measure ofstreamlining thatmight beachieved by fully implement ing th e science-based designapproach.The savings in t ime and moneyimpliedy ompar isonfigure oheraditionalpproachfFigure sramatic .

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Translationofmunitionperformance goalsintopropellantspecifications

'Loopl- MASTER OPTIMIZATION AL GO RI T HM (Generates trialformulations andselects the one ot lowestcost& leastwaste which meets performance and vunerability requirements.) H Develop ne w ingredientsLoop2-

Loop3

1Loop 4Perform full-scale gu nfirings

Perform full-scalevulnerabilitytests1 Large-scalepropellantfabrication

Loop 5- Performacceptancegu nfirings -qualitycontrol&bblerosion Type-Classify Propellant|

Figure 5. Simplification of Propelling-Charge Development Possible With FullImplementation ofScience-BasedDesign (Compare to Figure 2). Thisreport hasnotdiscusseddeveloping new propellantingredients,energeticmaterials,and

polymericbinders.tmay well happen that performanceobjectivescannot be met witha propellantmadefrom existing ingredients.l thoughrepresentedin Figures1 -3 asasinglebox,thereisasimilarnested-loopprocedurerequiredtodevelopthese.ngredientdevelopmentca nlikewisebenefitfrom strongtheoreticalguidanceduringit searlyphases.esearcheffortsatARLare addressinga number of relevant areas such as theoretical chemistry, detonability,an d thermophysicalpropertiesof polymers.heoreticalchemistry methodsca n be used to predictpropertiesof novelmaterialsanddeterminewhetheraspeciesisstable.hesemethodscanalsobeusedtoguideexperimentalsynthesisby predicting favorablereaction routes,hi fact, these methods would reducetheneedfo r chemicalsynthesis,a potentially costlyand t ime-consuming step.

Implement ing ascience-based approach to propel lantformulationwillnot be trivialorwithoutitsownconsiderablecostand delay.or example,he rangeof chemistry and physics involvedin interior-ballisticphenomenaisaunting. Interior-ballisticodeshaveongbeenunderactive

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weaponscapabilities in the face of declining resources,thereappearsto be littlechoice butto pursueascience-basedstrategytominimizingtheselife-cyclecosts.gainechoingthewordsoftheQuadrennialReview,"W enotonlyhaveth eopportunitytochange,wehavetherequirementto change."

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A New Approach to Propellant Formulation - Copy