testing the sm-3 kinetic warhead in the guidance system ......testing the sm-3 kinetic warhead in...

302 JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME22,NUMBER3(2001)

S. A. GEARHART

S

TestingtheSM-3KineticWarheadintheGuidanceSystemEvaluationLaboratory

Scott A. Gearhart

tandardMissile-3(SM-3)isbeingdevelopedaspartoftheNavy’sAegisLightweightExo-atmosphericProjectileInterceptProgram,knownasALI,whichisintendedtodem-onstrate anAegis shipengagementof a tacticalballisticmissile test target in theexo-atmosphere.AspartoftheLaboratory’slong-establishedroleasSMTechnicalDirectionAgent,weareconductinggroundtestingofkeySM-3components(flightcomputers,guid-ancesystems,navigationsystems,communicationlinks,etc.)inAPL’sGuidanceSystemEvaluationLaboratory(GSEL).Thisarticle focusesontheGSELtestingofthekineticwarhead,theinfrared-guidedfourthstageofSM-3thatisejectedintheterminalphaseofflighttoacquire,track,andinterceptthetarget.

INTRODUCTIONAPL’s Guidance System Evaluation Laboratory

(GSEL)isatestfacilitydedicatedtolong-termsupportof the Navy’s Standard Missile (SM) Program. Sincethe 1960s, the GSEL has performed guidance systemtesting for allSMvariants.These testshaveprovidedmissile flight test risk reduction, postflight test assess-ment, rapid investigation of design and performanceissues, and missile production screening. Because theGSELusespersonnel,testmethods,andtestequipmentthatarenot tied to thecontractor’s testprogram, thefacilityprovidesacomplementarytestcapabilityandasecond,independentassessmentofdesignintegrityandmissileflightreadiness.GSELtestcapabilitiesarecon-tinuallyevolvedtomeettheneedsofeachnewtypeofSM(seethearticlebyMarcotteetal.,thisissue).SM-3is thenewest systembeing tested.This article focusesspecificallyonGSELtestingoftheSM-3’sinfrared(IR)guidedkineticwarhead(KW).

The SM-3 KW is unique in several respects com-paredwithotherIRguidedmissilestestedintheGSEL.First,itisessentiallyaspacecraftwhoseIRseekerdetectsandtracksobjectsagainstcoldspaceasopposedtoter-restrialbackgrounds.Second,theIRseekerhasnogim-balsbutinsteadishard-mountedtotheKWbodyina“strap-down”configuration.Tosearcharegionofinter-est, the entire KW body maneuvers to steer the IRseekerlineofsight,resultingintightercouplingbetweenseeker and guidance functions. Third, the KW’s IRseekeroperates inawavelength regimedifferent fromotherSMIRseekers,andalsohasacomparativelylargeroptical aperture, better sensitivity, and higher opticalresolution. Finally, the KW carries no explosive war-head.Itsdestructiveforcereliesondirectimpactwiththe target at high speed, placing greater demands onguidancesystemresponsiveness.Suchadeparturefromprevioussystemsrequiredthedevelopmentofnewtest

JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME22,NUMBER3(2001) 303

TESTING THE SM-3 KW IN THE GSEL

methodsandequipment.Thisarticlepresentsanover-viewoftheGSEL’sKWtestprogram,includingperti-nentbackgrounddiscussions.

ALI PROGRAMThe objective of the Aegis Lightweight Exo-atmo-

sphericProjectile(LEAP)Intercept(ALI)ProgramistodevelopanddemonstrateanenhancementtotheAegisCombat System that provides the capability to engagea nonseparating tactical ballistic missile test target intheexo-atmosphere(i.e.,aboveabout100kmaltitude).TheALIeffortinvolvesthedevelopmentofnewAegiscomputer programs as well as the development of theSM-3missiletoperformthehit-to-killtargetintercept.It includes a series of control test vehicle flights thatbegan in mid-1999 to incrementally prove ALI systemfunctions,culminatinginaseriesoffull-upsystemteststobegininlate2001.AnumberofdefensecontractorsareparticipatingintheALIProgramincludingLockheedMartinGovernmentElectronicsSystems,RaytheonMis-sileSystems,BoeingNorthAmerica,andThiokol.

Figure 1 depicts the ALI mission sequence, whichbegins with the launch of the test target from therange. The shipboard Aegis SPY-1 radar acquires thetarget andestablishes track, and theWeaponsControlSystemissuesamissileengagementorder.TheVertical

Launching System next provides electrical power toSM-3 and transmits prelaunch engagement data. Themissilebatteriesarethenactivated,built-intestsareper-formed,andmissilelaunchoccurs.Duringtheearlyphaseofflight,theSPY-1radartransmitsguidancecommandsto the missile. Later, the missile derives its own guid-ance commandsusinguplinkedSPY-1 target andposi-tiondata.Intheterminalphaseofflight,theKWauton-omouslyguidestothetargetusingitsIRseeker.

SM-3 is a four-stage missile. Stages 1 and 2 includerocketboostersandthesteeringcontrolsystemnecessaryfor achieving exo-atmospheric altitudes. Each motor isseparated from the upper stages after burnout. In addi-tion to the third-stage rocket motor, Stage 3 containsguidance,control,andnavigationsystems,thecommuni-cation link to the Aegis ship, and the nosecone whichprotects the fourth-stageKWduringflyout.AfterStage3 rocket motor burnout and nosecone deployment, theKW is ejected. It then acquires the target with its IRseekerandguidesto interceptusingitsguidancesystemand Solid-rocket Divert and Attitude Control System(SDACS)rocketmotor.ThecombinationofmotorsfromStages1to3providesthekineticenergyneededfortheKWtodestroythetargetonimpact.TheKW’sSDACSprovides lateral thrust maneuverability. Figure 2 illus-tratesthecomponentsoftheKW.

Figure 1. ALI mission sequence.

Second stage

Boost (acquire)

En

do

-mid

cou

rse

ph

ase

Third stage,first burn

Exo

-mid

cou

rse

ph

ase

Noseconeejection

Third stage,second burn

Seekercalibration

KW ejection

Acquire, track, divert

SM-3 launch

GPS hot start(varies withscenario)

Schedule

Engage

Target burnout

Detect

Pacific MissileRange Facility

SM-3 readinesscheckout

(prior to mission)

Term

inal

ph

ase


S. A. GEARHART

KW TEST CONSIDERATIONSThe elements of the GSEL KW test program and

requirementsfornewtestcapabilitiesweredictatedbythe KW’s mission, functions, and operating environ-ment.SomeconsiderationsthatareuniquetotheKWascomparedtootherIRguidancesystemsarediscussedinthefollowingsections.

Coupled Seeker and Guidance FunctionsTypicallyintestingIRguidancesystemsitiscommon

to delineate tests into groups partitioned by compo-nentorfunction(e.g.,seekerfunctions,guidancefunc-tions, etc.). Structuring tests in this manner assumesthat certain functions can be treated as independent,i.e.,notcoupled.Nothavingtosimultaneouslytestcer-tainseekerandguidancefunctionsmakesthetestsetupforeachfunctionalgrouplesscomplexandthetestpro-cess more efficient. Once the tests are completed, acomparativelysmallernumberofmorecomplexsystem-leveltestsisconductedtoassessanyknownorunknowninteractionsamongfunctionalgroups.

KW testing also partitions into convenient testgroups;however,thecouplingbetweenseekerandguid-anceunitfunctionsisgreaterthaninpastexperience,andmorefrequentandextensivesystem-leveltestsarerequired.CouplingamongcomponentfunctionsisduelargelytotheKW’sstrap-downIRseekerdesign,whichrequires the IR seeker line of sight to be steered bycontrolling the KW’s body orientation. In other SMIR seeker designs, the seeker mounts on an inertial-stabilized platform intended to keep the line of sightunperturbed by missile body motion. Although theseother applications need to assess subtle body motioncoupling effects onto the seeker platform, the seeker,for many tests, can be assessed independently of the

guidancesystem.ThissimplificationislessvalidfortheKW’sIRseeker.

ThetightercouplingofKWseekerandguidanceunitfunctions is apparent in the track function.Tomain-tain track on a target image that moves continuouslywithKWbodymotion,theguidanceunitmeasuresbodymotion and feeds these data to the IR seeker, whichpropagatesthetrackgateposition(thewindowoffocal-plane-arraypixelswithinwhichthetargetmustremainto maintain valid track) from one frame to the next.Thus,theappropriatestimulimustbeprovidedtoboththe IR seeker and the guidance unit to fully test thetrackfunction.

Space BackgroundAttheoperationalaltitudeoftheKW,theIRseeker

views a cold space background having low radiance.Consequently,IRradiantemissionsandreflectionsfromits own internal components dominate the seeker’sdetectedbackgroundlevel,whichequatestoanappar-entbackground temperatureof about210K (–63°C).Fromapracticalstandpoint,thisbackgroundtempera-ture is well below laboratory ambient room tempera-ture;hence,amethodtosimulatecoldbackgroundsisrequiredforsometypesoftests.

The most accurate method for simulating a coldspace background necessitates the use of a cryogenicvacuumchamber,oftenwiththeseekerenclosedinthechamberandinaccessibleshouldasystemfailureoccur.Thisapproachrequiresexpensiveequipment,increasestherisktohigh-valuetestassets,andentailsextensiveperiodsforintegrationandcheckout.Fortunately,onlyafewtypesoftestsrequireacoldbackground;themajor-ityofKWtestscanbeperformedintheambientlabo-ratoryenvironment.Moreover,sincehighseekerradio-metric accuracy and sensitivity arenotneeded in theALImission,simplerandlessriskymethodscanbeusedto simulate a cold background (albeit not as cold ascouldbeachievedinaspacechamber).Theapparatusdeveloped in the GSEL to superimpose a test targetontoacoldbackgroundisdescribedlaterinthisarticle.In the future,as theALISystemevolves toa tacticalsystem,somelevelofcryogenicvacuumchambertestingmayberequired.

Hit-to-Kill Target InterceptIn the testing of earlier SM variants, the shape of

thelaboratoryIRtesttargetanditsradiancedistributionwereofminimal importance.Indeed,simpleexpandingapertures back-illuminated by a hot source were ade-quatetoemulatetargetimagegrowthasrangedecreased,becausetargetstructureinarealengagementwouldnotbe discernible until just before intercept. Even if IRseeker tracking errors occurred owing to hot parts onthetargetstructure, theguidancesystemwouldalready

Figure 2. The SM-3 KW.

IR seeker

Guidanceassembly

Lateraldivert

Ejectorassembly

SDACS



becommandingmaximumaccelerationandhencecouldnotrespondtothesetrackanomalies.Thisisnotneces-sarilytruefortheKW.Physicallystrikingapointonthetargetbodyrequiresahighlyresponsiveguidancesystemthatissensitivetotargetimageshapeandradiancedis-tributionjustbeforeimpact.ThisconsiderationpromptstheneedformoresophisticatedandexpensiveIRtargetprojectiondevicesforasubsetoftests.

GSEL APROACH FOR KW TESTINGA KW unit under test in the GSEL is shown in

Fig.3mountedinafixtureonanopticaltable.AlthougharealSDACSisnottestedforsafetyreasons,itseffectsare modeled in the KW hardware-in-the-loop (HIL)simulationdescribedlater.

As Fig. 3 shows, the KW requires an ensemble ofsupport equipment for activation and initialization aswell as video and telemetry data collection. The KWcontrol consoledevelopedbyBoeing emulates power,ordnance, and communications interfaces betweentheKWandStage3prior toKWejection.Thiscon-sole provides the capability to execute user-specifiedsimulatedmissionsequencesfromSM-3launchtotargetintercept, and to vary the contents of KW state ini-tializationmessages.ItalsoemulatesKWbatterypowerandprovidesothersupportfunctionssuchasutilitiesfordownloadingspecial test softwareandnewversionsofflightcomputerprograms.TheKWtelemetryconsole,also developed by Boeing, allows monitoring, collec-tion,andanalysisofKWtelemetry.Similarly,theDAS2000developedbyRaytheonprovidesthecapabilitytocollectandanalyzevideofromtheKWIRsensor.With-outthisensembleofsupportassets,testingoftheKWwouldbeimpossibleoratbestgreatlylimited.

Consistentwithestablishedpractice in theGSEL,evaluationoftheKWprogressesfromtestsofselectedlow-level functions to more complicated system-leveltests.Inthiscontext,low-levelfunctionsarebasicoper-ationsthatareeitherprerequisite toor fundamentallyinherent to the execution of high-level mission func-tions. Once the selected set of low-level functions isconfirmed,testsofmissionfunctionsareconductedbyiteratively traversing through increasingly larger por-tions of the ALI mission timeline in simulated flightsequences,culminatinginfull-upHILsimulationsfrommissile launch to target intercept. Table 1 providesexamplesofIRseekerandguidanceunitlow-levelfunc-tions tested during initial KW checkout and lists theassociatedALImissionfunctionsequence.

Thisincrementalapproach,progressingfromsimpletomorecomplextests,hasbeenshownfromourexpe-rience to build fundamental knowledge and intuitionthatisessentialtorecognizingandisolatinganomaliesobservedinthelatermorecomplextestconfigurations.Resultsfromearlytestsarealsousedtodevelopandval-idatemodelsused indigital simulations.Digital simu-lation resultsprovideakeyprimer to interpreting theresults of more complex system-level tests like HILsimulation.

EquipmenttotesttheKWvariesincomplexityfromsimple IRcollimatorsandblackbody sources, topointtarget generators, to complex IR scene projectors andHIL simulations. The GSEL test equipment is eitherdeveloped in house or built to GSEL-specific require-mentsbyoutsidevendors.Testequipment typically isdesignedtoprovidemodularityandflexibility,assumingthatitwilllaterneedtobereconfiguredoraugmentedtoaddressnewtestneeds.Ingeneral,itisnotpossibletoforeseeallequipmentneedsatthestartofatestpro-gram;a test requirementmaybediscoveredonlyaftertestexperiencewiththeKWisattained.

Asarule,thecriterionforchoosingaparticulartestequipmentconfiguration is toselect theonethatpro-vides the highest-fidelity representation of the flightenvironmentattributes importanttothespecificcom-ponentorfunctionbeingtested.Forexample,asimplecollimator with a moving pinhole target more accur-atelyrepresentsadistantmovingIRtargetfordetailedacquisition and track studies than a complex resis-tor-arrayIRsceneprojector thatmightexhibit spatialanomaliesassociatedwithitsdiscretepixels.Conversely,the latter device is more appropriate for testing IRseekerprocessorloadingwhiletrackingmultipleobjectsortestingendgametrackperformancewhentheseekerviews details of the target shape. Experience suggeststhatbuildingasinglepieceoftestapparatusthatsuitsalltestneedsisimpractical;thus,acollectionofdiffer-enttestassetsisrequired.

ThefiveprimaryKWtestconfigurationsintheGSEL(Table1)areasfollows:

Telemetry

SDACS loademulator

DAS 2000KW control console(Stage 3 emulator)

Compressednitrogen

IR seekervideo

PowerInitialization dataOrdnance activationFlight computer programs

KW telemetrycontrol

KW

Vortexcooler

Vacuumpump

Figure 3. The KW unit-under-test configuration in the GSEL, showing test support equipment.


S. A. GEARHART

1. Floodillumination2. Pointtargetonambientorcoldbackground3. KWonratetableviewingpointtarget4. KWconnectedtoStage3avionics5. HIL

Configuration 1 uses a cryogenic, temperature-con-trolled,extended-areablackbodysourcethatisplaceddirectlyinfrontoftheKWtocharacterizesensorper-formance.Configuration2isanAPL-developedpointtargetgeneratorincorporatinganovelapproachthatsuperimposes the target on a cold background, wellbelowambientroomtemperature,withoutemployinga spacevacuumchamberorcooledoptics.TheKW

typicallymountsonamechanizedplatformthatnu-tatestheKWbodyanalogoustoflight.InConfigura-tion3,theKWisattachedtoaprecisionsingle-axisrate table for characterizing body motion couplinginto the KW’s reported target positions and rates.Duringthesetests,theKWtracksapointtargetgen-eratedwiththeapparatusofConfiguration2.Config-uration4linkstheKWtotheStage3avionics(beingtested elsewhere in the GSEL) to confirm this crit-ical interface. (During most other KW tests in theGSEL, the KW control console emulates the Stage3interface.)Finally,Configuration5isaHILsimu-lationthat includesaresistor-arrayIRsceneprojec-tor capable of projecting complex and dynamic IR

Table 1. KW testing in the GSEL.

GSELtestconfigurationsa

1 2 3 4 5Low-levelfunctionstested Flood Point Rate KW/Stage3duringKWcheckout ilumination target table connect HILb

Seeker Imaging X Sensing X X Noise X XGuidanceunit Initialization X Statepropagation X Attitudeprocessing X Inertialstabilization X X

ALImission-levelfunctionsequencePre-eject 1. Activate X X 2. Cooldownfocalplanearray Limitedtesting 3. Receive/processtimesync X X 4. Transferalignment X X 5. Initialize X X 6. Calibrateinflight X X X X 7. Activatebattery Emulated:realbatterynottestedPost-eject 8. Eject Ejectornottested 9. IgniteSDACSsustain Emulated:realSDACSnottested 10. Navigate X X 11. Control X 12. Search X X 13. Acquiretarget X X X X 14. Selecttarget X X X 15. Tracktarget X X X 16. IgniteSDACSdivert Emulated:realSDACSnottested 17. Guidetotarget X 18. Selectaimpoint X 19. Trackextendedtrack X 20. Hittarget X 21. Assessmissionsuccess XaTestconfigurationsaredetailedinthetext.bPerformedwithandwithouttheKWconnectedtoStage3.



scenes.Theunique testapparatusused in these testconfigurationsisdiscussedinthenextsection.

Simple equipment configurations are used in theearlytestspartly forexpedience,sincetheintent istoprovide a quick assessment of basic operations beforeproceedingwithmorecomplicatedtests.Also,insomecases, the simple test configuration provides the bestfidelity for the low-level function tested. In addition,somefunctionsareassessedinmorethanonetestcon-figuration. For example, mission functions in Table1 such as “acquire target,” “select target,” and “tracktarget”aretestedbothinConfiguration2,whichpro-videsahigher-fidelitypointtargetrepresentation,andin Configuration 5, which provides a test of “end-to-end”functionalcontinuity.

UNIQUE TEST CAPABILITIESAs driven by considerations discussed previously,

testingoftheKWrequiredupgradestotheGSEL’stestcapability.Thissectiondescribessomespecificsonthemoreuniqueandinnovativeupgrades.

Cold Background Point Target GeneratorFigure4 isadiagramof thecoldbackgroundpoint

target generator devised by GSEL engineers. TheKW seeker views into an enclosure whose interior isreflective. As shown in the figure, a highly reflectivebeamsplitter(apartiallyreflectingmirror)mountedintheenclosure reflects coldblackbody radiation fromacryogenicallycooledplateintotheKWseekeraperture.Sincetheenclosure is reflective,wallblackbodyemis-sionsintotheKWarelow.Furthermore,ambientroomtemperature radiationthatwouldnormallyenter fromoutsidetheenclosureisreflectedawaybythebeamsplit-terwhichactsasaradiationseal.Inthisway,theKWeffectivelyviewsabackgroundtemperaturewellbelow

ambientroomtemperaturewithoutemployingaspacevacuumchamberorcooledoptics.

Pointtargetradiationgeneratedoutsidetheenclo-sure enters through the beamsplitter, which, thoughmostlyreflective,doestransmitabout5%.(Theinten-sityofthetesttargetisincreasedtocompensateforthelowbeamsplittertransmission.)Thetesttargetassem-blycomprisesasmoothgold-coatedplatethatcontainsasmallholeback-illuminatedbythetargetblackbodysource.AsFig.4shows,asecondlarge-areacryogenicsourcereflectsfromthegoldfaceintotheKWseeker’sfieldofviewtofurtheremulateacoldbackgroundsur-roundingthetarget.ThetargetassemblyalsoincludesanAPL-designedcollimatinglens,amotorizedtargetintensityattenuator,andamotionstagetoprovideoneaxisoftargetmotion.Topreventfrostingandmistingof the cold air near the cryogenic source, the entireapparatus is enclosed in a Plexiglas box purged withnitrogen.

Measurementsshowthatamovingpointtargetcanbesuperimposedonabackground-equivalentblackbodytemperatureofabout182K(–91°C),comparedtoambi-ent room temperature, which is about 293 K (20°C).Althoughbetterperformancewouldbeachievableusinganopticalsuiteinacryogenicallycooledvacuumcham-ber,theapproachdescribedhereisadequateformanytypesoftestsatrelativelylowcostandrisktotheKW.Inaddition,theapparatusrequireslittlesetupandcanbeusedonaday-to-daybasis.

IR Scene Projection SystemThe IR scene projection system used in the GSEL

hastwocomponents:theSceneGenerationComputingSystem(SGCS)developedbyMatra/BritishAerospaceandtheThermalPictureSynthesizer(TPS),aresistor-arrayIRsceneprojectordevelopedbyBritishAerospaceSowerby Research Center. Capabilities for dynamicIR sceneprojectionarepossessedbyonly a fewother

Gold targetplate

Targetradiation

Cryogenicsources

Enclosurewith reflective

interior

Motionstage

Highly reflectivebeamsplitter

Ambient radiationrejected

Nitrogen-purgedbox

Collimatinglens

Cold backgroundradiation

Target intensityattenuator

KW

Figure 4. Cold background point target generator concept.

organizationsworldwide.The SGCS renders multiple IR

objects on a background and pro-ducesacorrespondingdigitalimagethatprovidestheinputtotheTPS.Objectmodelsarefilescontainingvertexcoordinatesthatdefinetheobject surface facetsandthetem-perature of those vertices. For acommandedviewinggeometry,theSGCStransformstheviewofobjectfacetsintotheobserver’s(i.e.,theIRseeker’s)fieldofviewandcom-putestheapparenttemperaturesofeach facet, including the effectsof blackbody emission, solar andEarthreflections,andatmosphericattenuation(ifneeded).Thescene


S. A. GEARHART

isnextconvertedtoa10-bitgray-level digital image and output tothe TPS in a video line-by-lineformat starting at the center ofthe display and progressing out-ward. The SGCS is synchronizedto operate at the frame rate ofthe IR seeker under test. It canrender up to 350 facets in thescene at up to a 120-Hz framerate.TheSGCStotaldatalatency,from scene geometry commandinput to digital image output, isabout17ms.

The TPS includes drive elec-tronics,watercoolingandargongashandling systems, and the displayunit. The display has 256256pixels, which are vacuum-sealedbehindanIRtransmissivewindow.The architecture of each pixel isa serpentineheatingcoil (akin toa heating element on an electricrange stove) that is suspended forthermalisolationabovethelower-layer address circuitry by smallposts.TheTPSiscalibratedtoradi-ateuptoanequivalentblackbodytemperatureof473K(200°C),at

Figure 5. KW HIL simulation.

frameratesofupto120Hz.Itsaddressingarchitectureuses 256 digital-to-analog converters to update eachvideoline.Theentiredisplaycanbeupdatedin6ms.

KW HIL SimulationThe KW HIL simulation (Fig. 5) is an ensemble

ofcomputersandemulatorsintendedtoprovideavir-tual flight environment to the KW. Core to the HILsimulationisaflightdynamicssimulatorthatprocessesbodymotioncommandsfromtheKWguidancesystem,computes the SDACS propulsion and body motionresponse,andrelaysthisinformationtoemulatorsthatprovidestimulibacktotheKW,therebyclosingcon-trolandguidanceloops.OneemulatorintheHILsim-ulation is the inertial measurement unit (IMU) thatprovidesbodymotionmeasurementstotheKWanalo-goustoitsownIMU(whichisdisconnectedfromtheguidance unit during HIL testing). The second emu-lator is the IR scene projection system that providesdynamic IR scenes to the KW’s IR seeker using theSGCS and TPS discussed previously. The motion ofobjectsprojectedintotheseeker’sfieldofviewincludesthecombinedeffectsoftargetandKWbodymotion.

TheKWHILsimulationisoperatedineitheroftwomodes: open loop using scripted IMU emulator dataandIRscenegeometryinputs,orclosedloopasalreadydescribed.Theopenloopmodeisusefulfortestingthe

IR seeker without the complexities of a closed looptest.Inparticular,parametricstudiescanbeperformedtoassesstheIRseeker’sresponsetovaryingKWbodymotionperturbations.Theclosedloopmode,althoughmorecomplex,capturesseekerandguidanceunitinter-actions as well as real-time sensitivity to off-nominalpropulsion conditions (e.g., stuck or leaking SDACSthrustervalves).

Challenges todeveloping theKWHILsimulationincludedtightsynchronizationofemulateddatastreamsand the control and compensation of data latency.Here,data latency is thedelaybetweenthe timethattheKWguidancesystemissuesacommandandwhentheHILemulatorsprovidearesponsebacktotheKW.Becauseofthecomputationsrequired,IRsceneprojec-tion latency is the largest contributor. The effects ofscenelatencyarecompoundedbytheKW’sstrap-downIR seeker configuration, since the target imagemoveswith KW body motion. If uncompensated latency islargeenoughortheimagemotionperturbationssevere,thetargetcouldbeplacedinthesceneoutsidetheseek-er’s time-propagated track gate, causing loss of targettrack.Characterizingandcompensatingfordatalatencysources, and achieving precise synchronization of theHILsimulationelements,tookmanymonthsofmetic-ulous integration testing before successful closed loopsimulationrunsweredemonstrated.

Scenegeometryand frame

sync

Control andguidancecommands

Thermalpicture

synthesizer(IR display)

IMU emulator

KW

Video and telemetry

Target dynamics

Sync and I/O

SDACS propulsion

Flight dynamicssimulator

SDACSignition signal

KW HIL simulationcontrol computer

Emulated IMU

Syncsignals

IRscene loop IMU loop

KW control console(Stage 3 emulator)

SGCS

Optics



STATUS OF THE TEST PROGRAMAPLreceivedtheKWanditssupportequipmentfrom

RaytheonandBoeing in late July1999.After aperiodforintegrationandcheckout,aswellastrainingforAPLpersonnel in KW and support equipment operations,testing began in the fall of 1999 with detailed charac-terizationoftheIRseekerlow-levelfunctions.Measure-mentsofseekerimagingattributeslikeopticalefficiency,distortion, and magnification were completed, as weremeasurements of sensor function parameters includingresponsivity,spectralresponse,temporalnoise,andfixedpatternnoise.SomeofthesefundamentalmeasurementswererepeatedinApril2000toquantifychangesinseekerperformanceaftera5-month interval.Since theGSEListheonlyfacilitytestingasingleKWoveranextendedperiod,measurementsoftimestabilityoftheIRseeker’soriginalfactorycalibrationandanydegradationintheIRfocalplanearrayovertimeareofkeyimportance.

Afterconfirmationofthelow-levelseekerandguid-anceunitfunctionslistedinTable1,KWmissionfunc-tion testing began in preparation for two flight testrounds (1 and 1A). Since these flight exercises wereaimed at testing SM-3 Stage 1 through 3 functions,operational requirements for the KW were minimal.Nevertheless,bothflight rounds includeda functionalKWwithaninertSDACS,andtherewaspotentialtocollectKWtelemetrydatausefulforriskreductiononfutureflighttests.Furthermore,FTR-1AincludedatesttargetidenticaltotheonetobeusedforthelaterALIinterceptflights,andcollectionofKWseekerdatawasofgreatinterest.Accordingly,openloopKWHILtestswereconductedtoverifyKWmissionfunctionsshownin Table 1 from activation through track target. Inaddition,GSELtestingwasperformed toassessapro-posedmodificationtotheFTR-1AmissionthatwoulddelayejectionoftheKWtoprovidealongertargetview-ing opportunity. Based partly on GSEL test data, themission modification was adopted and was ultimatelysuccessful.

Closed loop KW HIL test capability was demon-strated in November 2000, and tests are now beingperformed from KW activation through target inter-ceptusingtheapproachpresentedearlierofincremen-tallyprogressingthroughlargerportionsofthemission

timeline. Timeline testing is being performed for anumber of scenarios that include off-nominal condi-tions like multiple objects in the seeker field of viewandpotentialmissed-switchingoftheSDACSvalves.Aspartofthesetests,aconnectionhasalsobeenmadebetweentheKWandtheSM-3Stage3avionicssuitetestedelsewhereintheGSELtoverifytheKWtoStage3interface.

KWcomputerprogramsthatwillbeusedinthenextSM-3flightmissiletest,FM-2,wererecentlydeliveredto the GSEL. The FM-2 missile will include a fullyfunctionalKW,includingaliveSDACSrocketmotor.GSELriskreductiontestingforFM-2isunderway.

CONCLUSIONKWtestingintheGSELwillcontinuethroughthe

ALI test flights, with a later shift to the collection oftestdatapertinenttothedevelopmentofmoresophisti-catedSM-3tacticalvariants.PlanningisbeginningnowtoascertainwhatGSELenhancementsarerequiredforthetestingofthesemoreadvancedsystems.

TheNavySMsponsorreliesonGSELengineersandtestactivitiestoaidinmissiledevelopmentandflight-readinessdecisions.TheGSELisakeyelementinful-fillingAPL’strustedagentrole.Itcannotbeoverempha-sizedthattheGSEL’scredibilityandvalueinthisregardhingeonthecontinuedhands-onexperienceofGSELengineers working the practical problems involved indevelopingandtestingrealsystems.

ACKNOWLEDGMENTS: The author acknowledges the GSEL KW test andequipmentdevelopmentteamsfortheirworkanddedicationtothiseffort:Chris-tinaChomel,LaurelFunk,JamesGarcia,MichaelMattix,ToddNeighoff,RobertPatchan,RickTschiegg,KatyVogel,andDuaneWinters.Inaddition,theauthoracknowledgesTerryHipp(nolongeratAPL)wholedearlyKWHILdevelop-mentefforts.ThanksalsotoKWtestanddevelopmentteamsatRaytheonMis-sileSystems,Tucson,AZ,andatBoeing,CanogaPark,CA, ledbyMikeLealandDanTubbs,respectively,fortheircollectivesupport.SpecialthankstoHansAcosta(Raytheon),PhilPagliara(Raytheon),MattRyan(Boeing),andTerrySapp(Raytheon),whowereourprimaryliaisonsandmadenoteworthyeffortstoensurethatourneedsweremet.OurappreciationalsotoBillBaurer,PatBuckley,RobinLewis,andBrianMaloneofBoeingwhohavebeenofgreatassistanceinmaintaining,augmenting,andtroubleshootingKWsupportequipmentonsite.TheauthoralsoacknowledgesAPL’sBillMehlman,whowaskeytogettingtheKWtesteffortstartedduringhistenureasSM-3ProgramManager,andcurrentAPLProgramManagersTomEubanksandGarySullinsfortheirunwaveringsup-portandpatience.Finally,ourthankstoourNAVSEAPMS422sponsorsCAPTC.M.BourneandClayCrappsfortheopportunitytoperformstimulatingandrelevantwork.


S. A. GEARHART

THE AUTHOR

SCOTTA.GEARHARTreceivedaB.S.inengineeringsciencefromthePennsyl-vaniaStateUniversityin1982andanM.S.inelectricalengineeringfromtheUni-versityofMarylandin1987.HeisamemberofAPL’sPrincipalProfessionalStaffandasectionsupervisorinADSD’sElectro-OpticalSystemsGroup.Mr.GearhartjoinedAPLin1983andhasworkedprimarilyonthedevelopment,test,andevalu-ationofopticalandinfraredguidancesystems.HehasledseveraleffortsinAPL’sGSEL todevelop infrared system test capabilities in supportof theNavy’sStan-dardMissileProgram.Mostrecently,Mr.GearhartledAPL’seffortindevelopingcapabilitiesfortestingtheStandardMissile-3infrared-guidedkineticwarhead.Hise-mailaddressisscott.gearhart@jhuapl.edu.

Testing the SM-3 Kinetic Warhead in the Guidance System Evaluation LaboratoryScott A. GearhartINTRODUCTIONALI PROGRAMKW TEST CONSIDERATIONSCoupled Seeker and Guidance FunctionsSpace BackgroundHit-to-Kill Target Intercept

GSEL APROACH FOR KW TESTINGUNIQUE TEST CAPABILITIESCold Background Point Target GeneratorIR Scene Projection SystemKW HIL Simulation

STATUS OF THE TEST PROGRAMCONCLUSIONTHE AUTHORFIGURES and TABLESFigure 1. ALI mission sequence.Figure 2. The SM-3 KW.Figure 3. The KW unit-under-test configuration in the GSEL,showing test support equipment.Figure 4. Cold background point target generator concept.Figure 5. KW HIL simulation.Table 1. KW testing in the GSEL.

testing the sm-3 kinetic warhead in the guidance system ......testing the sm-3 kinetic warhead in...

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