exo-atmospheric intercepts: bringing new challenges … · 260 johns hopkins apl technical digest,...

260 JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME22,NUMBER3(2001)

G. A. SULLINS

T

Exo-atmosphericIntercepts:BringingNewChallengestoStandardMissile

Gary A. Sullins

heNavyTheaterWideSystemisbeingdesignedtoprovidedefenseforU.S.forcesandourAlliesagainstmedium- to long-range tacticalballisticmissiles.Aspartof thissystem,anewvariantofStandardMissile,SM-3,willbeintroducedtotheFleet.SM-3willperformahit-to-killinterceptoftheballisticmissilewhileitisinexo-atmosphericflight(i.e.,whileoutsidetheEarth’satmosphere).Exo-atmosphericflightandhit-to-killinterceptshavebroughtnewchallengestotheSMProgram.Thesechallengeshaveintro-ducednewtechnologies,whichinturnhavecreatedtheneedfornewteststobeaddedtoanalreadyrobustSMgroundtestprogram.ThisarticlediscussesthesenewchallengesanddescribestestsgearedtoverifySM-3design,withemphasisgiventothosetestsperformedatAPL.

INTRODUCTIONThe threat of ballistic missile attacks to U.S. forces

and our Allies continues to grow. Currently over 40nations have the capability to launch ballistic missileattacks.MostofthesemissilesarenotcapableofreachingU.S.soil;nevertheless,theydoposeasignificantthreattoour forces stationedoverseas.Manyof thesenationsalso have the ability to build chemical, biological, ornuclearwarheads,makingthethreatevenmoresevere.

The Navy Theater Wide (NTW) System is beingdeveloped to defend against medium- to long-rangetactical ballistic missiles launched against Allied andU.S.forcesonforeignsoil.Thesystemleveragesheav-ilyontheNavy’slargeinvestmentintheAegisWeap-ons System (AWS) and Standard Missile (SM). Theheart of the NTW System is the ability of the AegisAN/SPY-1radartoacquireandtrackballisticmissiles

and the ability of the combat system to engage thembyguidingthemissiletoanintercept.ModificationsarebeingmadetotheAWStochangethelogicconsistentwithtrackingandengagingballisticmissilesratherthanitstraditionalAnti-AirWarfarerole.

InadditiontomodificationstotheAWS,theNTWSystemisdevelopinganewSMvariant,SM-3.SM-3isafour-stagemissilederivingitsheritagefromtheSM-2Block IV used for Anti-Air Warfare as well as tech-nologiesdevelopedundertheStrategicDefenseInitia-tiveOrganizationandlatertheBallisticMissileDefenseOrganization Lightweight Exo-atmospheric Projectile(LEAP)Program.

The SM Program has a legacy dating back to themid-1940s with the advent of the Talos, Terrier, andTartarprograms.Throughoutthemorethan50yearsof

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EXO-ATMOSPHERIC INTERCEPTS

developingsurface-to-airvariants,arobustgroundtestprogramhasbeendeveloped.Manyofthesetestswereimplementedasaresultofproblemsexperiencedduringflighttestsandwere added in an attempt to pre-vent future flight failures. Designverification tests (DVTs) are typi-callyperformedonaninertopera-tionalmissile,whichisidenticaltoa flight round except that there isnoliveordnanceorrocketmotors.DVTs are done to prove that thedesign will maintain functionalitywhile exposed to various environ-mentsandconditionstowhichtheflightroundwillbesubjected.Manyof the extensive ground tests forSM-3arebasedonSMexperiences;however, several tests have beenaddedbecauseofthenewenviron-mentcreatedbythemissile.

Thisarticlediscussesgroundtest-ingaddedtothetypicalSMgroundtest program, specifically for theSM-3 Program, with emphasis ontestsperformedatAPL.Itdoesnotdiscuss the extensive ground test-ing that has been adopted fromthe SM-2 Block IV Program orthe numerous safety tests that arerequired prior to launching a mis-sile from a ship. An evaluation ofthe SM-3 ground test program isdiscussedbyRogers,thisissue.

ALI DEMONSTRATION

Mk 72first-stage

rocket motor

Third-stagerocket motor

Guidancesection

Nosecone

Strakes

Dorsal finsControlsurfaces

Mk 104second-stagerocket motor

Steeringcontrolsection

AttitudeControlSystem(SDACS),andejectorassem-bly.Theseekerassemblycomprisesalong-waveinfrared(IR)sensorwithassociatedopticsandasignalprocessor.Theguidanceassembly includesaguidanceprocessor,valvedriver, telemeter, andbattery.TheSDACShasagasgeneratorwiththreesolidpropellantgrains—sus-tain,pulse1divert,andpulse2divert;thesearedetailedlater in the section. Wrapped around the SDACS isthetelemetryantenna.Theejectorassemblyusesamar-mon-typeclamptoholdtheKWtothethird-stageguid-ance section. Upon command, a nonexplosive actua-tion device allows the clamp to open. Once opened,bellevillewashers(essentiallysprings)atthreelocationsforcetheKWfromthethirdstage.

APListheRound-levelTechnicalDirectionAgentfor SM-3. Other responsible parties are as follows:RaytheonMissileSystemsCompany(RMSC,formerlyHughes Missile Systems Co.), as Design Agent, for

Figure 1. The SM-3 missile.

Figure 2. Kinetic warhead overview.

Sustain grain

Seekerassembly

Guidanceassembly

Belleville washersDivert pulse 1 grain

Marmon clamp

Nonexplosive actuationdevice

Ejector assembly

Telemetryantenna

Solid Divert and Attitude Control SystemDivert pulse 2 grain

Divert nozzles

TheabilityofSM-3,operatinginconjunctionwiththeAWS,isbeingdemonstratedaspartoftheAegisLEAPIntercept(ALI)Program.Atargetwillbelaunchedfromthe Kauai Test Facility, and the USS Lake Erie (CG70),operatingapproximately300milesfromthecoastofKauai,willacquirethetargetusingtheAN/SPY-1B(V)radarandlaunchtheSM-3tointerceptit.

We focus here on the SM-3 missile (Fig. 1), specifi-callytheALIconfiguration.ComponentsusedfromSM-2BlockIVincludethefirst-andsecond-stagerocketmotors(Mk72andMk104,respectively),second-stagesteeringcontrol section, dorsal fins, and Aegis transceiver plateusedforcommunicationwiththeship.Technologiesusedfrom the LEAP Program include the third-stage rocketmotor(TSRM),GPS-AidedInertialNavigationSystem(GAINS),andfourth-stagekineticwarhead(KW).

TheSM-3KW(Fig.2)consistsofaseekerassem-bly, guidance assembly, Solid-propellant Divert and


G. A. SULLINS

round-level design and integration, integration of theKW, and design and fabrication of the IR seeker andsignalprocessor;BoeingNorthAmericanforthedesignof theKWguidanceandejectorassemblies; andAlli-antTechsystemsInc.(formerlyThiokolElkton)fortheTSRMandKWSDACS.

AtypicalengagementscenariofortheALImissionis shown in Fig. 3. Shortly after launch of the target,theAegiscruiserdetectsthetargetusingtheAN/SPY-1radar.Uponburnoutofthetargetmotor,theAWScal-culates aballistic trajectory andcomputes apredictedintercept point. Knowing the SM-3 kinematics, theAWSdeterminesthebestlaunchtimeforSM-3.AfterSM-3ispreparedforflight,themissileislaunchedfromthe Vertical Launching System (VLS) and is acceler-atedbytheMk72solidpropellantrocketmotor.Duringthis“boost”phase,fourthrustvector–controllednozzlesattheaftendoftheMk72providethemissilecontrol.Themissilepiercesthecanistercoverduringegress,fliesverticallyuntilitreachesasafedistancefromtheship,andthenmaneuverstoflytoapredeterminedpoint.

UponburnoutoftheMk72motor,separationofthefirstandsecondstagesoccurs,andthesecond-stageMk104solidpropellantrocketmotorisignited.Duringthis“endo-midcourse” phase, the vehicle is further accel-eratedbut remainswithintheEarth’satmosphereand

henceusesaerodynamiccontrolcreatedbythetailfins.Accelerationcommands, sent to themissileviaAegisuplinks,arereceivedbythemissileandareturnedintotailcommandsbytheautopilot.Theship,trackingthetargetandmissilewiththeAN/SPY-1radar,attemptstoputthemissileonacollisioncoursewiththetarget.AfterburnoutoftheMk104motor,themissilecoaststoanaltitudeof56km,atwhichtimethethirdstagesepa-ratesfromthesecondstage.Whilecoasting,anin-flightalignment is executed to ensure that the missile andshipcoordinateframesarealigned.Thisisdonebecausethemissilewillprovideitsownguidanceandnavigationsolutionafterthird-stageseparationbutwillcontinuetoreceivetargetpositionandvelocityfromtheship.

Aftersecond-stageseparation,thefirstoftheTSRM’stwopulses is ignited.This portionof flight is referredtoasthe“exo-midcourse”phase.Duringrocketmotoroperation, control ismaintainedby theTSRM thrustvectorcontrol.Immediatelyafterpulse1burnout,theWarmGasAttitudeControlSystem(WGACS)isusedtomaintainpropervehicleorientation.TheWGACSconsistsoffourseparatesolidpropellantgasgeneratorsthat are fired separately and burn for approximately3 s. Four exhaust nozzles in a cruciform orientationallowcontrolinthepitchandyawplanesofthemissile(Fig. 4). The Cold Gas Attitude Control System

Figure 3. ALI engagement sequence.

Second stage

Boost phase (acquire)

En

do

-mid

cou

rse

ph

ase

Third stage,first burn

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-mid

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rse

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Third stage,second burn

Seekercalibration

KW ejection

Acquire, track, divert

SM-3 launch

AWS schedulesSM-3 launch

AWS decision toengage target

Target burnout

Target detected byship’s radar

Pacific MissileRange Facility

SM-3 prelaunchpreparations

Term

inal

ph

ase



(CGACS)provides lower thrust levels usingnitrogenstoredat10,000psi.Thenitrogenisexhaustedthroughsixnozzles tomaintainpitch,yaw,and roll controlathighaltitudes.Twoofthenozzleassemblieshaveacom-binationofwarmandcoldgasnozzles.Eachassemblyhasasinglenozzleforthewarmgasandthreeorthogo-nalnozzles forthecoldgas.BetweentheTSRMpulse1andpulse2burns,theCGACSisusedtoorientthevehicleata30oangleofattacktoejectthenosecone.Thisisreferredtoasthepitch-to-ditchmaneuver.TheWGACSisthenusedtoreorientthevehiclebacktoapathtotheinterceptpoint,andthesecondTSRMpulseisignited.

Afterpulse2burnout,theCGACSisagainusedtoorientthevehicleawayfromthetargetlineofsighttoperformacalibrationoftheKW’sIRseekerwhilepoint-ing it toward a cold space background (i.e., no stars,planets,targetsintheseekerfieldofview).Uponcom-pletionofthecalibration,thevehicleisorientedtowardthetargetlineofsight,andarollmaneuverisdonetoallowanalignmentofthethirdstageandKWinertialmeasurement units (IMUs). Information on the KWpositionandvelocity,alongwiththetargetpositionandvelocity, is passed to the KW in preparation for KWejectionandflight.

Approximately 24 s prior to intercept, the KW isejectedandtheSDACSisignited.Thisisreferredtoasthe“terminal”phaseofflight.TheSDACS’sgasgenera-torusesasolidpropellantandfournozzlesplacednear

thevehiclecenterofgravitytoprovideadivertforcetomaneuvertheKW(Fig.2).SixnozzlesattheaftendoftheKWprovideattitudecontrol.Thesustaingrainofthegasgeneratorisignitedinitiallyandprovidesalim-itedthrusttomaintainsteerage.Thisgrainmustburnuntilinterceptofthetarget,therebylimitingtheflighttimeoftheKW.OncetheIRseekeracquiresthetarget,asecondsolidgrainisignitedtoincreasethethrustlevelfor approximately 10 s.This provides sufficient thrusttodiverttheKWtoacollisioncoursewiththetarget.Afterthedivertpulseburnsout,thesustaingraincon-tinues to burn, allowing small corrections to the KWflight path. A third grain is ignited just prior to KWimpact to again increase the thrust level to allow theKWtomaneuvertoimpactthetargetatthemostlethalspot(i.e., thepositiontodestroy the targetwarhead),referredtoasthelethalaimpoint.

AseriesofnineflightsisplannedaspartoftheALIProgramtodemonstratetheabilityoftheNTWsystemsto intercept a ballistic target during exo-atmosphericflight.Todate, fourSM-3flight testshavebeen con-ducted to demonstrate the readiness of various NTWsystems:controltestvehicle(CTV)1and1Aandflighttestround(FTR)1and1A.Thefirstinterceptattemptwilloccurin2002.Intheseflighttests,thetargetwillbe intercepted during its descent phase of flight (i.e.,afterthetargethasreachedapogee).Aftersuccessfullyinterceptingthetargettwice,thetargetwillbemodifiedtobemorethreat-representative,anda seriesof threetestswillbeperformedtodemonstratetheabilityoftheNTW System to intercept a target during the ascentphaseofflight(i.e.,priortoapogee).Duringthesethreetests theabilityof theKWtohit the lethalaimpointwillalsobedemonstrated.

To perform the NTW mission, SM-3 has beendesignedtoflyconsiderablyhigherandfasterthananysurface-launchedmissiletheNavyhaseverbuilt.Figure5showsaplotofaltitudeversusMachnumberforthevariousstagesofSM-3flightduringatypicalALItest.Forcomparison,thespeedregimeofSM-2BlockIVisalso shown. As can be seen, SM-3 will fly more thantwiceasfastandfivetimesashighasSM-2BlockIV.

FlyingatthesespeedsandaltitudeshasbroughtmanynewchallengestotheSMdesign.Aerothermalheatingis significantly increased, requiring new materials toinsulatethemissilecomponents.Likewise,flightoutsidetheEarth’satmospherehasrequiredthedevelopmentofattitudecontrolsystemsforthethirdandfourthstagesofthemissile.ThefactthattheKWmust impactthetarget(“hit-to-kill”),ratherthanusingaconventionalexplosivewarhead,hascreatedchallengestoseveralofthe systems to provide accurate information on mis-sile position and velocity. To increase position andvelocity accuracy, SM-3 carries the GAINS, whichblendsinformationfromtheGPS,theship’sradar,andthemissile’sIMUs.Theuseofthesenewfeatureshas

Figure 4. Hybrid Warm/Cold Gas Attitude Control System.

Warm gasnozzle

Warm/cold gasnozzle combination

Cold gaspressurevessel

Two gasgenerators

Warm gasnozzle

Warm/cold gasnozzle combination

Two gasgenerators

Cold gas nozzles Warm gas nozzle


G. A. SULLINS

requiredadditionalgroundteststoverifySM-3designandoperation.

GROUND TEST PROGRAMAsalreadynoted,SM-3’srobustgroundtestprogram

isderivedfromalegacyofSMtesting.SomeoftheteststhathavebeenaddedspecificallyforSM-3includesepa-ration,hover,andairbearingtests.Theseparationtestwasperformedtoverifyproperactivationofallupper-stage(stagesabovetheMk72rocketmotor)separatingevents, includingsecond-/third-stage separation,nose-cone separation, and KW ejection. Also tested wereotherelectricallyinitiateddevices(e.g.,squibs,batter-ies,explosivebolts,etc.).

ThehovertestisintendedtodemonstrateKWper-formance in a flight test, including target acquisition.ThetestistobeperformedattheNationalHoverTestFacility(NHTF)oftheAirForceResearchLaboratory(AFRL) at Edwards Air Force Base. The KW is ini-tially held down and the SDACS sustain and divertpulses ignited. The KW is then released and allowedto fly autonomously. The KW computer software wasmodifiedforthistesttoprovidea1-gthrustsothattheKWwouldhoverstablyatagivenheight.TheKWwas

programmedtogothroughaseriesofmaneuvers(sidetoside)duringthetest.AheatedtargetispositionedattheheightofthehoveringKWtoallowtargetacquisi-tionandtrackthroughouttheflighttest.Theprimaryobjectiveof thehover test is todemonstrate that theclosedloopcontrolwillmaintainthedesiredpointingaccuracyandstaywithintherequiredbodyrates.ThetestprovidesconfidencethattheSDACSwillrespondascommandedandthattheself-inducedvibrationloadscreatedbytheSDACSwillnotimpacttheabilityoftheseekertoacquireandtrackanobject.

Air bearing tests were performed on both the KWand the third stage to evaluate the autopilot design.Thehardwarewasfixedinacradle,whichallowednear-frictionless rotation about three axes. For third-stageairbearing,openlooporscriptedtestswereperformedinwhichatypicalALImissionwasflown.Commandswere determined by the guidance computer and wereturned intoACSthrustcommands,whichcaused themissile to rotate to the desired orientation. Amongthe maneuvers demonstrated were nosecone pitch-to-ditch, in-flight alignment, pointing toward cold spacefor seeker calibration, and pointing toward the targetpriortoKWeject.Thisdemonstratedproperoperationof the third-stage autopilot and computer. Air was

Figure 5. The ALI flight envelope.

1. First-/second-stage separation2. Mk 104 end of boost3. Mk 104 end of sustain4. Second-/third-stage separation,

start of pulse 15. End of pulse 16. Nosecone eject7. Start of pulse 28. End of pulse 29. KW eject

10. Intercept

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suppliedtotheACStoprovidethrusttorotatethethirdstage.IntheKWairbearingtests,heliumgaswasusedfortheACSratherthanasolidpropellant.Intheseteststheguidance loopwasclosedby the seeker trackingamoving target andproviding information to theguid-anceprocessor,whichinturncreatedthrustcommandstotheACS.Thisresultedinthevehiclerotatingtotheproperorientationtomaintaintargettrack.

Some DVTs were performed at APL. Specifically,theGAINSwastestedinthePowerProjectionSystemDepartment’s Navigation and Guidance System Inte-grationLaboratory(NAVSIL),andthethird-stageguid-ancesectionwastestedintheSpaceDepartment’sther-mal vacuum chamber. End-to-end system tests of allfivemissile computers arebeingperformed in theAirDefenseSystemsDepartment’sGuidanceSystemEval-uation Laboratory (GSEL). These tests are discussedbrieflyinthenextsection.

GSEL TestingTheGSELwasconstructedinthemid-1960stosup-

portSMdevelopment.Itsprimarypurposeistoprovidean independentassessmentof functionalityandrobust-nessofsystemcomponentsandcomputerprogramsforthegovernment.Itisfeltthathavingasecondteam—otherthantheDesignAgent—withdifferentmethods,equip-ment, and personnel increases the level of problemscreening,therebyprovidingriskreductionfortheNavy.Foryears,APLhasperformedtestingofSMguidanceand

navigationcomputersaswellasthecomputerprograms.Morerecently,ontheMissileHomingImprovementPro-gramandSM-2BlockIVARiskReductionFlightDem-onstration,IRseekertestinghasbeenadded.

GSELevaluationsinthepasthaveprimarilyfocusedonendgamemissileguidanceintheendo-atmosphere.The SM-3 missile is unique in that it must operatethroughexo-atmosphericflightatspeedsgreatlyexceed-ingthoseofotherSMvariants.Itusesnewthird-andfourth-stageguidanceandcontrol.WhilethefirstandsecondstagesarecontrolledasbeforebytheAWSonthe launching ship, the third and fourth (KW) stageshave autonomous navigation, guidance, and control.Third-stagenavigationdata(position,velocity,andalti-tudeestimates)aredeterminedonboardusingGAINS.The KW operates autonomously after being ejectedfromthethirdstagetoseek,acquire,track,anddiverttointerceptthetarget.TheKWmusthitthetarget,usingitskineticenergytodestroyit.AllofthesedifferencesputincreaseddemandsonSM-3operation.

A schematic of the test setup in GSEL for ALI isshowninFig.6.Testingfallsintooneoftwocategories:

1. Avionicssuitetesting,whichincludesfirst-,second-,and third-stage guidance performance; third-stageguidance integrationwithGAINS; andKWhand-overaccuracy

2. KW testing, which includes KW target acquisitionand tracking as well as KW navigation, guidance,anddivertaccuracy

AWSsimulation

GPS hot startsimulation

GPS RFsimulation

IMUsimulation

GSELreal-time computer

IR environmentsimulation

Targetsimulation

IR scene projector

KW

IMUsimulation

KW flightsimulation

IRHandover

Target state

KW test set

KW state

Test/telemetry

GPS RF

GPS initialization

Missile initialization

Aegis RF

Aegisuplink

generator

Control and data collection equipment

Hardware under test

Simulation of other system elements

Avionics suite

Figure 6. GSEL test configuration.


G. A. SULLINS

KW and avionics suite testing are performed in sepa-ratepartsofGSELtoallowindependenttestingofeachcomponent;however,theyareconnectedelectricallytoalsoallowacompleteend-to-endtestingcapabilityasisshowninthefigure.

The primary objective of the laboratory evaluationof the computer programs and hardware is twofold: (1)to reduce flight risk through an extensive characteriza-tionofnominalend-to-endsystemperformanceand(2)toidentifyperformanceboundariesofthesystemoperat-ing in realistic simulatedflightenvironments.Emphasisisplacedonverifyingtheperformanceofthefunctionalinterfacesbetweenthemissileandtheship.Onlyinspe-cial cases, i.e., when the risk is felt to be high, are thephysicalinterfacesalsotestedintheGSEL.Somephysi-calinterfaceshavebeentestedinNAVSILtoensurethatthe GPS “hot start” function has been properly imple-mented(NAVSILtestsarediscussedlaterinthisarticle).

AsecondaryobjectiveofGSEListoprovideafacil-itythatismaintainedthroughtheentirelifecycleofthemissile(includingdeployment).HardwareandsoftwarearemaintainedintheGSELsuchthatifanewthreatshouldemergeorifnewcountermeasuresaredeveloped,the effect on the missile can be readily determined.GSELandNAVSILalsoprovideresourcesforflighttestdataanalysisinvestigationsofanyflightanomalies.

Avionics Suite TestingTheSM-3guidance sectionprovides thecapability

forprelaunchroundinitialization,in-flightmissile/shipcommunication,boostphasecontrolcommands,endo-and exo-midcourse guidance/control commands, andthetransferofdatatotheKWassemblypriortothird-andfourth-stageseparation.Twoindependentcomput-ersaccomplishflightguidanceandcontrolforthefirstthreestages.Onecomputer,CentralProcessingUnit2(CPU2), is dedicated to controlling the guidance forthefirsttwostagesofflight,andanother,CPU3,isded-icated to controlling the guidance for the third stage.Theguidancesectionincludestheavionicssuite,whichhousesCPU2andCPU3aswellastheGAINSReceiverProcessor Unit (RPU). The GAINS RPU includes aGPSreceiverandnavigationprocessorwhichprovidesaccurate inertial data. The navigation processor usesGPS,radar,andIMUdatatoestimateandcorrect forIMU misalignments and biases. The processor uses aKalmanfiltertominimizeprocessingnoise.

The GSEL provides testing for actual missile guid-ancehardwareinrealtime.Theavionicssuitemaintainsthe latest-released version of the missile software fortheCPU2,CPU3,andGAINSRPU.Forcomponentsthatarenotincludedintheavionicssuite,theGSELtestsetupincludescustom-designedreal-timesimulatorsthatpossess the specified hardware characteristics requiredtoemulatetheexternalinterfaces.Themajorinterfaces

include Aegis Weapons Control System (WCS), ini-tialization, uplink, and downlink messages; telemetryand steering control section; inertial instrument unit;accelerometer;andgyrodataandpowersupplies.Allofthese interfaces are controlledby theGSEL real-timecomputer(Fig.6).

TheAPLsix-degree-of-freedom(6-DOF)simulationisasupportingtoolthatisneededfortheavionicseval-uationperformed inGSEL.The simulation is ahigh-fidelityrepresentationofthekinematicsandfunctionaldesign of the SM-3 missile. It also contains medium-fidelitymodelsoftheremainderoftheweaponsystem,targetvehicle,andenvironment.Thesimulationisusedto generate trajectory files that become input files foropen loop testing. Missile dynamic data are recordedfromthesimulationand fed intotheGSELtest setuptosimulatethemotionofthemissile.Analysisofopenloop testing provides an opportunity to validate theimplementation of the functional design in both thesimulationandthemissilesoftware.

Forclosedlooptesting,the6-DOFsimulationactu-allytakesinputsfromthemissilesoftwareandprovidesdynamicoutputbacktothemissileto“closetheloop.”In this testing, the 6-DOF functional algorithms arereplaced with the actual missile software. This allowsthe performance of the missile software to affect thesimulatedtrajectory.Asinthecasewithopenlooptest-ing,thisactsasanotherleveloffidelityinvalidatingthe6-DOFsimulationandmissilesoftware.

In addition to evaluatingfirst-, second-, and third-stageguidanceandcontrolperformance,GSELevalu-ations characterize and verify the performance of theavionicssuite interfacesandmissile-to-shipcommuni-cations.Avionicssuitetestingevaluatesthe initializa-tionoftheKWpriortoejectionaswell.ResultsofthistestingalsoservetovalidateandrefinetheSM-3digi-tal6-DOFsimulation.Theavionicssuitehasalloftheexternalinterfacesattachedtoactualmissilehardwareorsimulators.Testinterfacesareavailabletoeachoftheprocessors for softwaredownloads, control, andmoni-toring.Testingisperformedinbothopenloop(scriptedscenarios)orclosed loop fashion, inwhichthedigitalsimulationiswrappedaroundtheguidanceprocessors.

Simulatedtrajectoryinputsarederivedfromthedig-ital 6-DOF simulation. The 6-DOF outputs are usedas stimuli to evaluate themissile software (e.g., simu-lated IMU measurements). In addition to testing formissile performance, tests are performed to exercisecriticalalgorithmsandfunctions,especiallythosethatarenewtoSM-3.Amongthemajorareasofconcentra-tionarebuilt-in-testprocessing,Stage1control(iner-tialboostguidance),Stage2control(Aegismidcourseguidance), Stage 3 control (TSRM/ACS guidance),AegistargetandGAINSmissilestateprocessing,mes-sage processing (initialization, uplink, and downlink),IMUdataprocessing,KWinitialization,andKWeject.



Outputdatafromthesetestsarecomparedwithdigital6-DOFresultstovalidatethealgorithmsandsimulationmodels.

AGSELsimulationofactualflightscenariosisper-formed to assess the readiness of the operational soft-wareforanupcomingflight.Thistestingexaminesthepropertimingofeventsinaflightscenarioandcompat-ibilitywiththeWCS.TheflightprofileisconstructedwithrawIMUdataderivedfromthedigital6-DOFsim-ulation, and from actual Aegis ship messages derivedfrom the Combat Systems Engineering DevelopmentSite (CSEDS). These data are synchronized and fedintotheavionicssuiteasifanactualflightweretakingplace,andthemissileoutputsarecomparedwithdigi-tal6-DOFresults.Figure7 illustrates samplecompari-sonsofGSELand6-DOFdataforasimulatedflighttest.Sincethe6-DOFsimulationisbeingusedastheinputtothesoftware,onewouldexpectthe6-DOFandGSELresults tocompare favorably, ascanbe seen inFig.7;however,thisisnotalwaysthecase.Whendifferencesoccur,theyareduetoerrorsineitherthe6-DOFresults,theGSELsetup,orthemissilesoftware.Ifthesoftwareissuspected,resultsareforwardedtotheDesignAgentfor review. GSEL has been successful in highlightingerrors in the 6-DOF data, missile software, and AWScomputerprograms.

In addition to nominal flight conditions, modifica-tionstothescriptaremadetoexamineperformanceincriticalareasunderoff-nominalconditions(e.g.,lossofAegisuplink).Frompastexperience,manypossiblefail-uremodeshavebeenidentifiedwhicharenotaddressedin all of the normal testing modes. On the basis offlightscenarios,additionalpotentialfailuremodeswillbeidentifiedandtestsdevelopedtocharacterizeperfor-manceunderthoseconditions.

KW TestingTheALIKWbeingtestedintheGSELhasafunc-

tioningIRsensor,signalprocessor,andguidanceproces-sor.TheunitdoesnotincludeanSDACSbutratheranSDACS emulator. Likewise, the telemetry antenna isomittedandsignalsaresentdirectlytotheKWteleme-tryconsole.Aspreviouslynoted,KWandavionicssuitetestingaredoneinseparatelaboratorieswithinGSEL;however, they are tied together electrically to allowcommunicationspriortoKWeject.

TheobjectivesofKWtestingareto

•CharacterizetheIRsensor• Assess coordinated IR seeker and guidance unit

functionality

Inertial data processing

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Figure 7. Sample data from GSEL avionics suite testing.


G. A. SULLINS

• Confirmline-of-sightstabilizationinthepresenceofKWbodymotion

• ConfirmKW/third-stageinterfaces

APL’s approach to IR guidance system testing in theGSEL is discussed in more detail by Gearhart in thisissue,andonlyseveralkeypointsarevisitedhere.

Again,GSELtestresultsareintendedtoprovideanindependent functional confirmation of the KW andcomputerprogramspriortoeachALIflighttest.Empha-sisisonidentifyingpotentialvulnerabilities,andwhereappropriate,definingperformanceboundaries.SincetheGSELiscurrentlytheonlytestactivitythatwillmoni-tortheperformanceofasingleKWtestarticleoveralongperiod,dataarealsocollectedtoassessfunctionalstabilityovertime,inparticularfortheIRseeker.

GSELKWtestingisalsotiedcloselytoAPL’shigh-fidelity digital simulation activities. For example, theGSEL characterization of the seeker optical system isused to derive and validate optical system models inthe digital simulation. Viewed from another perspec-tive,theoutputsofthedigitalsimulationareoftenusedasinputstotheGSELhardware-in-the-loop(HIL)sim-ulationforopenloopguidancestudies.Inaddition,thedigitalsimulationhasproventobeessentialinseveralcases to performing trade studies for designing GSELtestequipment(e.g.,derivingdatalatencyrequirementsfortheHILsimulationcomputers).

GSEL testing involves an ensemble of test assets.Different assets are used because one type of IR targetprojection device may provide good fidelity for sometargetattributesbutnotforothers.Specifically,aresistiveheater IRdisplayprovidesexcellentfidelity foragrow-ingtargetimageduringaimpointselectionandthefinalintercept phase of flight, but because of potential pix-elizationeffects(i.e.,spatialsamplinglimitations),suchdevices are less desirable for emulating accurate pointtargetphenomenology.Thussimplepointtargetgenera-tion devices are favored to provide better accuracy forfunctionsearlyinKWflightthatinvolvepointtargets.

Ingeneral,nosingletestconfigurationprovidesthehighestpossiblefidelityemulationofrelevantenviron-mentalattributesovertheentireKWflighttimeline.Forthis reason, a methodical piece-wise evaluation usinga variety of tests and test devices is necessary. GSELtestsarestructuredonthebasisofadecompositionofKWfunctionsinflighttimelinesequence(forexample,seekercalibration,targetacquisition,targettrack,etc.).

Since the SM-3 KW has a body-fixed IR seeker(i.e.,nogimbals),theKWismountedonamotorizedgimbalplatformforsometypesoftests.Thegimbalplat-formiscontrolledbydrivesignalsderivedfrombufferedKWattitudecontrolcommands.RatherthanmountingtheKWonacarcotableas isdone insomefacilities,analternativeapproachbeingused in theGSEL is tohard-mounttheKWandemulateitsmotionbymoving

the target appropriately and sending synthesized IMUoutputstotheKWguidanceprocessor.

Openloopandscriptedtestinginboththeavionicssection and the KW have been performed separately,with a simulator as the interface to the section notbeingtested.Whenthetwoaretestedtogether,testingis aimed at verifying data transfer and control com-mandsbetweenthethirdandfourthstage.

Similar to avionics suite testing, the APL 6-DOFsimulation is a supporting tool that is needed for theKW evaluation performed in the GSEL. The 6-DOFsimulationisahigh-fidelityrepresentationofthekine-maticsandfunctionaldesignoftheKW.Fortheclosedloop portion of testing, the simulation actually takesinputs from the KW software and provides dynamicoutputbacktothemissiletoclosetheloop.Withval-idation data being provided by open loop and closedlooptesting,andwithadditionaldatasuppliedbyDVTs(bythecontractor),the6-DOFsimulationcanbeusedto predict preflight performance and to perform post-flightanalysis.

AnexampleofhowtheGSELcanbeusedoccurredpriortoFTR-1A,whenRaytheonsuggestedchangingthenominaltimelinesothattheKWremainedlongeron the third stage to allow it to image the target.BecausetheKWwasinert(noSDACS)onFTR-1A,it had no control and therefore would tumble afterKW eject. Since a target would be flown during themission,itpresentedanopportunitytoprovideseekerdataiftheKWremainedattachedtothethirdstage,whichhadcontrol.TheNavyaskedAPLtoassessthisoption.TheLaboratoryfirstused the6-DOF simula-tiontoshowthatthethirdstagehadadequatecontroltomaintainthetargetwithintheseeker’sfieldofview.ThesimulationwasthenusedtoestablishopenloopscenariosfortheGSELsceneprojector.TestsinGSELshowed that the target remained in thefieldofviewforamajorityofthetimeandthattheseekerwasabletoacquireandtrackthetarget.Theseresultsindicatedthat greater than 10 s of seeker imaging data shouldbe available. On the basis of these and Raytheon’sresults theNavydecided toextend the timeline.On25January2001,FTR-1AwasflownandtheKWoper-atedaspredictedbythe6-DOFsimulationandGSEL.TheKWacquiredandtrackedthetargetandgathered13.5sofIRdataonthetarget.

NAVSIL Navigation Testing GAINSprovidesposition,velocity,andattitudeesti-

mates for use by the third-stage guidance and as ini-tialization data to the KW. The SM-3 GAINS is adirectderivativeofthesuccessfullyflownTerrier/LEAPGAINS. GAINS forms these estimates by combiningmeasurementsfromanonboardGPSreceiver,uplinkeddata fromtheAegisradar,andanonboardIMU.TheavailabilityofhighlyaccurateGPSmeasurementsallows



GAINStoperformaprecisein-flightalignment,therebyimprovingonitsrelativelycourseinitialization.

The IMU is a combination of accelerometers andgyros that provide inertial motion measurements toGAINS.AnavigationalgorithminGAINSintegratesthe IMUsensormeasurements starting froman initialconditionprovidedby two ship systemmeasurements.This navigation solution is updated by measurementsfromaGPSreceiveranduplinkedAegisradardata.AmultistateKalmanfiltercorrectsforestimatederrorsinallthreesetsofmeasurements.Theresultingoutputistheposition,velocity,andattitudeestimateusedbythethird-stageguidance.

A system called the VLS GPS integrator (VGI) isinstalledon the ship forSM-3. Itprovidesahot starttotheGAINSGPSreceiverandinitializespositionandvelocityinthenavigator.Togenerateanavigationsolu-tion with small error, the GPS receiver must providemeasurementsasquicklyafter launchaspossible.TheVGIhotstartallowsrapidGPSsatelliteacquisitionandtrack, thus generating measurements much earlier inflight.TheVGIcontainsitsownGPSreceiver,whichoperates continuously using signals froma ship’smastantenna.TheGPSreceiverprovidesbothprecisetimeandsatellitedigitaldataneededbythemissile’sreceiver.The information ispassed into themissileviaahigh-speedfiber-opticcable,resultinginveryhighhotstartGPStimingaccuracy.

APL’sNAVSILisaGAINSHILsimulationandtestfacility.Itwasoriginallydevelopedinthelate1980stosupport the addition of GPS to Tomahawk. Over theyearsNAVSILhascontinuedtosupportTomahawkevo-lution while also contributing to SM-3, SM-4 (LandAttackStandardMissile,LASM),JointDefendedAreaMunition(JDAM),theThermosphere-Ionosphere-Meso-sphere Energetics and Dynamics (TIMED) spacecraft,andotherprograms.NAVSILalsoprovidedriskreduc-tion assessments for GAINS during the Terrier/LEAPTechnologyDemonstration.Staffanalystsworkingwiththeprimecontractor’steamperformedHILteststohelpimprovetheGAINSdesign.PredictedGAINSaccuracymatchedobservedflighttestperformance.

The primary objective of NAVSIL testing is tocharacterize theperformanceof theGPSreceiverandGAINS navigation under ALI flight conditions. Thisalso includes testing VLS hot start sensitivities, GPShold-fire issues, and GAINS navigation performancein the event that GPS signals are lost after launch.The tests identify and address technical issues associ-atedwithGPSaswellasGAINSperformancesuitabil-ityandmargin.VLS-basedGPShotstartischaracter-izedwithrespecttospecificationsandGPSacquisitionunder flight-representative conditions. GAINS accu-racyandrobustnessareassessedinresponsetoinitializa-tion errors,GPS receiver performance and anomalies,andAegisuplinkdataerrors.

GroundtestsoftheSM-3GAINSinNAVSILhaveinvolved assessing the performance of the supportingVGIhotstartsystemaswellasGAINSitself.Theaccu-racy and robustness of the VGI are evaluated in manycontexts.GAINSnavigationerrorversustimeinflightisevaluatedby simulatingGAINSwith inputs like thoseitwouldreceiveduringanactualmission.Forexample,hotstartdataareprovidedoverafiber-opticcable,sim-ulated IMU output data are injected, simulated GPSradio-frequencydataaregenerated,andsimulatedAegisuplinks are inserted.Realistic sensormisalignmentandothererrorsareincludedinallofthesedatastreams.Inthecaseofthehotstartinput,eitheractualshipequip-ment(aVGIandfiber-opticantennalink)oraspecial-purpose“hotstartemulator”canbeused.

Figure8showsthefunctionaltestbedusedinNAVSIL.Dataareextractedfrommultiplepointsinthistestbed,allowingathoroughpost-testevaluation.Thisabilitytoextractdataatmultiplepointsprovedusefulintrouble-shootingaproblemobservedinGSEL.Theproblemwasrepeated in NAVSIL and the data were extracted andsent to theDesignAgent,whichwasable to track theproblemtoamathematicalerrorintheGPSreceiver.Asaresult,apatchwasmadetotheGAINSsoftwaretopre-ventapotentialflightfailure.

As in theGSEL, theAPL6-DOF simulation is anintricatepartofNAVSILtesting,usedtoprovideIMUandAegisradardatatoGAINS.NAVSILrunsthetra-jectoryintheopenloopconfigurationandcomparesthepositionandvelocityinformationcalculatedbyGAINSwiththe6-DOF–suppliedtrajectorytodeterminenav-igation accuracy. Figure 9 shows normalized exampleGAINS navigator performance for cases of GPS withAegisradaruplinks.WhenGPSsatellitesareacquired,theerrordropssignificantlyforbothpositionandveloc-ity.FortheALImission,GPSenhancesthenavigationperformance, but the system has sufficient accuracywith radar and IMUalone tohit the target.ThishasbeendemonstratedinNAVSIL.However,severalothertacticalscenariosrequireGPS.Forinstance, for inter-cepts during target ascent, the nominal missile cross-rangemotionissmallandnoteasilyvisibletotheradarbecause of its angle measurement noise. Thus radar-onlynavigationaccuracyfortheseascentintercepts isdegradedwithouttheuseofothertechniques(e.g.,tra-jectoryshaping)toimproveobservability.

The NAVSIL was instrumental in finding a problemafter CTV-1A when VGI data indicated that the GPSreceiverhadstoppedupdatingsatellites.Thefacilitywasable to duplicate the symptom, and the data were pro-videdtotheGPSreceivermanufacturer.ThesoftwarewasrepairedandtestswereperformedatAPLtoverifythefix.

Altitude TestingSinceSM-3willflyoutsidetheEarth’satmosphere,

preparation is required for flight in the vacuum. At


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Figure 9. Position and velocity errors with GAINS.

an altitude of approximately 200,000 to 300,000 ft,the combination of low pressure and high voltage inelectroniccomponentscancausearcingduetocoronaeffects. If any voids are present in the printed circuitboards, the vacuum will cause the void to expand,

whichcoulddelaminatetheboard,creatingafailureina circuit. Finally, the vacuum of space will accelerateoutgassingofhydrocarbonsfromcondensablematerials.For these reasons,analtitude testof theSM-3upper-stage components was considered desirable. Although



BoeingNorthAmericanperformsaltitudetestingoftheKW, their facility was too small to also include thethirdstage.TheAPLeastverticalvacuumchamberwasthereforeusedtotesttheguidancesection.

Figure10showstheSM-3guidancesectioninstalledin the chamber. The chamber was pumped down to6105 torr, simulating an altitude of approximately340,000ft.Powertotheguidancesectionwasturnedoffattimesduringthetesttoavoidoverheatingduetothelongtimeassociatedwithpumpingthechamberdowntosimulatedaltitude(i.e.,thetimetopumpthecham-berdownwasgreaterthanthetypicaloperatingtimeoftheguidancesection).Dataweretakenatthreedistinctintervalsduringthetest.Powerwasturnedonpriortothe test to perform a baseline run; during the initialpump-downtotestfromlaunchthroughthemaximumcoronadischargeregion;andagainoncetheminimumpressureof6105 torrwasattained.Finally, apost-test baseline was taken 3 min after the chamber hadreachedsea-levelconditions.

The guidance section performed without problemduring the test. Contamination samples were takenandanalyzed.Althoughthecontaminationdidincreasethroughout the test, it was determined to be withinacceptablelevels.

Aerothermal TestingInadditiontotheDVTsnotedearlier,criticalexper-

imentswereperformedtoensurethedesignadequacy,i.e.,properstructuralstrengthandfunctionality,ofeachcomponent. The considerably faster speeds that theSM-3willfly(seeFig.5)createthermalchallengesforthe missile structure due to aerothermal heating andforcetheneedtoincludeinsulationontheupperstages

ofthemissile.Componentsofparticularconcernwerethe nosecone, guidance section, strakes, and TSRM.APL’sResearchandTechnologyDevelopmentCenter’swind tunnel was uniquely qualified to perform theseaerothermaltests.

When a vehicle flies at high supersonic speeds it isheatedbythecompressionoftheairasthevehiclefliesthrough it. This canbe simulated in awind tunnel byheating high-pressure air and then accelerating it tosupersonic speedsprior toexposure to thewind tunnelmodel.Testcell2ofAPL’sAveryAdvancedTechnologyDevelopment Laboratory (AATDL) uses high-pressureair heated by the combustion of hydrogen in a heater,referred to as a vitiated air heater. Makeup oxygen issometimesaddedtotheheatersothattheoxygenmolefraction represents that of standard air. This is impor-tantforanymaterialsthatmightreactinanoxygenenvi-ronment. Vitiated air differs from standard air in thatnitrogen is replaced with steam which is generated bythecombustionprocess(5.5to18.4bymolepercentforthesetests).Downstreamoftheheater,theflowisaccel-erated through a converging/diverging nozzle which issizedtoproduceaMach6flowfield(seeFig.11).Thegasesarecontrolledbycomputer,allowingconditionstobeprogrammedtovarywithtesttimetosimulatevehicleacceleration. The test duration at the AATDL can beupto3min.

Nosecone TestsThe nosecone, developed by RMSC, provides

aerodynamic/aerothermalprotectionfortheKWduringtheendo-atmosphericflight.Itisacompositefabricatedwith a graphite bismaleimide (Gr/BMI) shell with asilicon resin quartz fiber (SM8029) insulating outer

Figure 10. The SM-3 guidance section (a) under test in the APL Space Department’s thermal vacuum chamber and (b) pressure profile during simulated high-altitude testing (shaded regions indicate time when guidance section was powered).

layer.A thinmolybdenumcoatingontheinsidereducesthermalradia-tiontotheKWandprovidesprotec-tion against electromagnetic inter-ference.The total thicknessof thenoseconeisnominally0.2in.

Stagnation-point heating wasvaried with time to simulate theheating that the nosecone wouldexperienceduringanALIflighttra-jectory.Thecell2facilitydemon-stratedtheabilitytosimulateflightconditionsreasonablywellthroughtheexo-midcoursephaseofflight.Becauseof the sizeof the facility,only the forward section of thenosecone could be tested in thewindtunnel.Figure12isaphoto-graphtakenwithastandardvideocamera of the nosecone during atypical test at maximum heatingconditions.Thistruncatedsection

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Figure 11. Schematic of the AATDL wind tunnel facility. Test setup for SM-3 third-stage insulation materials is shown.

ofthenoseconecontainedthecriticalportions,whichwerethetitaniumtip,theinterfacebetweenthetita-niumandthecomposite,andthepointofthehighestheat transfer. Heating decreases rapidly farther fromthetipandthereforeisnotascriticaltotest.

Threeseparatetestentriesofthenoseconewereper-formed during 1997 and 1998 to improve the design.Inthefirst,10testswereexecutedtoevaluatethecom-positenosecones.Duringtheearliestteststhewindpat-ternofthequartzfiberwasmodifiedtoimproveitsstruc-turalperformanceunderthehigh-speedflowfield.Theconeswereinstrumentedwithupto16thermocouplesto define the thermal environment. Deposits of con-densed material were observed on the back plate ofthe fixture assembly for each of the nosecones tested.

Figure 12. Photograph of the nosecone during wind tunnel testing.

ThesedepositsweredeterminedtobearesultofoutgassingoftheBMIresin.

Sinceoutgassingcoulddegradethe performance of the IR seekerin the flight vehicle, the graphiteBMIcoatingwascuredatahighertemperature (600°F instead of450°F)toreduceit,andacoverwasdesigned and built to protect theoptics incasetheoutgassingcouldnotbeeliminated.Thecoverpro-vides a flexible, non-airtight sealovertheopticalsectionoftheKWduring transportation and storage,throughtheendo-midcoursephaseofflight, and throughaportionofthe exo-midcourse phase of flight.Itisdeployedwiththenoseconeatejection (Fig 2). RMSC designedthecoverandAPL’sSpaceDepart-ment fabricated several covers forwind tunnel testing as well as for

the DVTs. Once the final design was completed andverified inthewindtunnel,30coverswere fabricatedby APL during the first 6 months of 1999 to be usedon inertoperationalmissiles aswell as theALIflightrounds.

Inthesecondandthirdseriesoftests,thenoseconeswere instrumented to allow thermal assessment and toquantifycontaminationduetooutgassingofthecompos-itematerial.Theconeswereinstrumentedwithupto16thermocouplestodefinethethermalenvironmentofthenosecone,sunshade,andradiationshield,andthetem-peratureof theatmosphere inside thenosecone.Threetypesofinstrumentationwereemployedtomeasurethedegreeofoutgassinganditseffectontheseeker:

1. Optic samples were placed inside the sunshade toquantifytheamountofcontaminationandtheeffecton the IR seeker optics. These samples were thenanalyzedusingaBomemFouriertransforminterfer-ometertodeterminetheeffectofcontaminationonopticaltransmissioninthelong-waveIR.

2. Mk21quartzcrystalmicrobalances(QCMs)wereusedto measure particulate and condensable contamina-tioninthesunshadeasafunctionoftimeforselectedtests.TheseQCMswerealsoflownonCTV-1Aasafinalassessmentofin-flightcontamination.

3. A small (1.261.261.33 in.) black-and-whitevideo camera was installed inside the cone toprovide a real-time visual record of the internalenvironment.

Thesecondtestentrycontinuedthedevelopmentofthenoseconedesigntowithstandthehigh-speedflowfield and reduce outgassing as well as to develop the



instrumentation necessary to quantify the contamina-tiondeveloped.Thethirdentrydemonstratedthattheimprovements made to the nosecone had eliminatedtheoutgassingproblem.Itwasdecidedthattheseekercover would still be used as added assurance againstcontamination.

On 24 September 1999, CTV-1A was performedwithQCMsensorsinstalledontheinertKW.Sensorswereplacedontheoptics,wheretheywereprotectedbytheseekercover,aswellasontheSDACS,wheretheywerenotprotected.Contamination levelswerebarelydetectable,indicatingthattheoutgassingproblemhadbeeneliminated.

Strakes TestsStrakes protect cables that run from the guidance

section across the TSRM (Fig. 1). They are elevatedfromthevehiclebodyandthereforedirectlyexposedtothehypersonicflowfield.Twoseparatetestentrieswereperformedonthestrakestoevaluatethedesignsoftwosuppliers.AforebodydesignedtosimulatetheguidancesectionandTSRMwasbuiltbyRaytheonforthesetests(Fig. 11). Similar to the nosecone, the strake modelwasstationaryinthetestsectionduringtestingandthestagnation-pointheating ratewas varied with time tosimulateaflighttrajectory.Forthestraketests,amoreseveretrajectorywasusedthantheALIflighttrajectorytodemonstratemarginforthetacticaldesign.Figure13showsthestrakeduringatestatthemaximumheatingrate.Thecell2facilitydemonstratedtheabilitytosim-ulatetheflightconditionsreasonablywellthroughtheexo-midcoursephaseofflight.

Thefirst straketestentrywasperformedtoevaluatethree designs from two different vendors. Each vendorbuilt three strakes, one with a solid titanium base andphenolicinsulation,onewithatitaniumtruss(i.e.,cut-outs in the titanium to reduce weight) covered with

Figure 13. Photograph of the strake at maximum heating condition.

phenolicinsulation,andoneall-compositedesign.Ther-mocouples were placed at various locations within thestraketocharacterizethethermalenvironment.Inaddi-tion,asampleofthecablethatthestrakeprotectswasincludedbeneaththestrake.Thiscablewasalsoinstru-mentedwiththermocouples.Allstrakesperformedade-quately and since the composite design was lighter inweightitwaschosen.Asecondtestentrywasperformedusingcompositestrakesfromeachvendor,whichresultedina“down-select”toasinglevendor.

Third-Stage Insulation TestsThethirdstageconsistsoftheguidancesectionand

TSRM.Thealuminumguidancesectionwithglassphe-nolic insulation houses the Tri-Band antenna, whichincludesantennasfortheGPS,telemetry,andflightter-mination system.TheTri-Band antennahas a duroidinsulatoroveranaluminumshell.TheTSRMinterstageisa0.1-in.-thickglassepoxycompositewitha0.187-in.-thickcorkexterior insulation.RMSCbuilta frametohousea70osectorofthethird-stageoutershell,includ-ingastrake,foraerothermaltesting(Fig.14,left).The

Figure 14. Before (left) and after (right) photographs of the TSRM test sample.

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conditionsusedforthesetestswerethesameasthoseforthestraketests(stressingtacticaltrajectory).Inadditiontotheinsulationmaterials,aDC93-104ablativecom-poundusedforsealingjointsonthemissilewasappliedtosealthestrakeandthejointsbetweentheguidancesectionandTSRM.

All insulation materials successfully withstood theconditions produced by the simulated tactical trajec-tory. Figure 14 (right) shows the test setup after thetest.Onecornerofthecorkinsulationsustaineddamageduring the tunnel shutdown. Under this condition ashock wave translates upstream of the model, whichcreatesamuchmoreviolentconditionthanwouldbeexperiencedinflight.

SUMMARYSM-3isauniquevariantofSMdesignedtointercept

tacticalballisticmissileswhileoutsidetheEarth’satmo-sphere.BecauseitflieshigherandfasterthananyotherNavysurface-launchedmissileandmusthitthetargetto

THE AUTHOR

GARY A. SULLINS is a member of APL’s Principal Professional Staff and theProgramManagerforStandardMissile-3intheAirDefenseSystemsDepartment.He receivedB.S.andM.S.degrees inaerospaceengineering fromtheUniversityofMaryland in1980and1981, respectively, and aPh.D. in1988, also from theUniversityofMaryland.He joinedAPL in1982andhasworked in the areasofair-breathingpropulsion,high-speedfluiddynamics,aerothermaltesting,andmis-silesystemsengineering.Hise-mailaddressisgary.sullins@jhuapl.edu.

destroy it,SM-3presentsuniquechallenges.StandardMissileanditspredecessorshavehadalonghistoryofsuccess, in large part due to the development of arobust ground test program to ensure adequate designprior to flight testing and deployment. The SM-3Program has adopted this legacy test program, butbecauseof itsuniqueattributes severalnewtestshavebeen added. APL test facilities have been used onseveral occasions to perform various critical experi-mentsandDVTs.Thesetestshaveprovidedadditionalconfidence inthesystemprior toflightand inseveralinstanceshaveresultedinimprovementstothedesign.

ACKNOWLEDGMENTS:Theworkpresentedherewasmadepossiblebyagroupofhardworkinganddedicatedpeople.TheSM-3TeamatAPLhasmadenumer-ouscontributionstotheprogramindesignevaluation,testandevaluation,pre-flightpredictions,andpostflightanalyses.Theauthoristrulyindebtedtothisteamfortheirefforts.Severalpeopleprovidedideas,figures,andwordsforthisarticleandmeritrecognition:ScottGearhart,RonGriesmar,JamesJohnson,TomJohn-son,GeorgeStupp,TomWolf, andDaveZotian.RaytheonProgramManagersRosemaryBadianandMikeLealareacknowledgedfortheircontinuedsupportofGSELandNAVSIL.TheauthorwishestoexpresshisappreciationtoNavySM-3ProjectManagerClayCrappsforhiscontinuedbackingoftheprogramatAPL.

exo-atmospheric intercepts: bringing new challenges … · 260 johns hopkins apl technical digest,...

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