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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
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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
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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
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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.
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306 JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME22,NUMBER3(2001)
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.
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TESTING THE SM-3 KW IN THE GSEL
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
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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
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TESTING THE SM-3 KW IN THE GSEL
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.
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310 JOHNSHOPKINSAPLTECHNICALDIGEST,VOLUME22,NUMBER3(2001)
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.