Sixth International Conference on Mars (2003) 3287.pdf MROHIGHRESOLUTIONIMAGINGSCIENCEEXPERIMENT(HIRISE): INSTRUMENTDEVELOPMENT.AlanDelamere,IraBecker,JimBergstrom,JonBurkepile,Joe Day,DavidDorn,DennisGallagher,CharlieHamp,JeffreyLasco,BillMeiers,AndrewSievers,Scott StreetmanStevenTarr,MarkTommeraasen,PaulVolmer.BallAerospaceandTechnologyCorp.,PO Box1062,Boulder,CO80306 Focus Introduction:Theprimaryfunctionalre- Mechanism PrimaryMirror quirementoftheHiRISEimager,figure1isto PrimaryMirrorBaffle 2nd Fold allowidentificationofbothpredictedandun- Mirror knownfeaturesonthesurfaceofMarstoa muchfinerresolutionandcontrastthanprevi- ouslypossible[1],[2].Thisresultsinacam- 1st Fold erawithaverywideswathwidth,6kmat Mirror 300kmaltitude,andahighsignaltonoise ratio,>100:1.Generationofterrainmaps,30 Filters cmverticalresolution,fromstereoimages Focal requiresveryaccurategeometriccalibration. Plane Theprojectlimitationsofmass,costand schedulemakethedevelopmentchallenging. FocalPlane SecondaryMirror Inaddition,thespacecraftstability[3]must Electronics TertiaryMirror SecondaryMirrorBaffle notbeamajorlimitationtoimagequality. Thenominalorbitforthesciencephaseofthe missionisa3pmorbitof255by320kmwith Figure1Cameraopticalpathoptimizedforlowmass periapsislockedtothesouthpole.Thetrack Integration(TDI)tocreateveryhigh(100:1)signalnoise velocityisapproximately3,400m/s. ratioimages. HiRISEFeatures:TheHiRISEinstrumentperformance Theimagerdesignisanall-reflectivethreemirrorastig- goalsarelistedinTable1.Thedesignfeaturesa50cm matictelescopewithlight-weightedZeroduropticsanda apertureandadetectorwith128linesofTimeDelayand graphite-compositestructure.TheCassegrainobjective Table1HiRISERequirementsandPerformanceCharacteristics Parameter Performance Comments GroundSampleDistance(GSD) 30cm/pixel From300kmaltitude TelescopeAperture 0.5m,f/24 ForresolutionandSNR Spectralrange 400to600nm Blue-Green(BG) 550to850nm Red 800to1000nm Nearinfra-red(NIR) SNR Blue-Green Typically100:1 AchievedwithTDI,backsidethinnedCCDs,and Red Typically200:1 50cmaperture NIR Typically100:1 Swath Red >6km From300kmaltitude Width Blue-Green&NIR >1.2km From300kmaltitude Swathlength >2×swathwidth Alongtrack DataPrecision 14bitA/D 12to13bitusable DataCompression Real-time14to8bit Look-uptable Upto16×16binning Increasesarealcoverage LosslesscompressionatSSR ~2:1 Datastorage 28Gbits Allchannels Numberofpixelsacrossswath 20,264Red Fromswathwidthandpixelscale 4,048GreenandNIR TDIlinetime ≥76µsec Tomatchgroundtrackspeed CCDreadnoise <50electronsrmsat22°C AchieveSNRatlowsignallevels FOV 1.14°×0.18° IFOV 1×1µrad Detectorangularsubtense 1 Sixth International Conference on Mars (2003) 3287.pdf temprovidesadiffractionlim- itedmodulationtransferfunc- tion(MTF)on12µmpixelsfor all14HiRISEdetectors.The colorfiltersarelocated30mm fromthedetectorsforallthree channels.Thisdistanceavoids problemsduetostraylightand multiplereflectionsfromthe filtersinthef/24quasi- collimatedbeam.ALyotstop, locatedbetweenthetertiarymir- rorandthesecondfoldmirror, ensuresexcellentreductionof straylight. Distortionsinthelargefieldof theredchannelareverysmall. Figure3HiRISETelescopeFlightStructure(Approximately70cminDiameterby1.4minLength) AsHiRISEpointsattheMars’ surface,apointintheimage withrelayopticandtwofoldmirrorsisoptimizedfordif- willremaininasingleCCD fraction-limitedperformanceoverthelong,narrowfield- TDIcolumnwithnocrosscolumnsmearforallCCDs. of-view(FOV)requiredfor“push-broom”scanningand Thetelescopestructureismadeofgraphite-fiber- imaging.Filtersinfrontofthedetectorsprovideimages reinforcedcomposite.Thisproducesastiff,lightweight inthethreewavelengthbands:red(orpanchromatic), structurewithlowmoistureabsorptionpropertiesandlow blue-green(BG),andnearinfrared(NIR). coefficientofmoistureexpansion.Thenegativecoeffi- Thedetector-chip-assemblies(DCA)housingthecharge cientofthermalexpansion(CTE)ofthecompositeele- coupleddevices(CCDs)arestaggeredtoprovidefull ments,inconjunctionwithmetallic,positiveCTEfittings, swathcoveragewithoutgaps.BoththeBGandNIR istailoredtoproducenear-zeroinstrumentCTE.Fig- bandshavetwoDCAseachtogiveatotalswathwidthof ure2showstheflightstructure. 4048pixels,andtheredchannelhastenDCAstoprovide aswathwidthof20,264pixels. HiRISEFocalPlaneSubsystem(FPS):TheFPScon- sistsoftheDCAs,afocalplanesubstrateofaluminum– The50cmdiameterprimarymirrorhasadualarchcon- graphitecompositematerial,aspectralfilterassembly, structionforlowmassandhighrigidity.Theopticalsys- andCCDprocessing/memorymodules(CPMMs).Each 2 Figure2HiRISEFocalPlaneAssembly Sixth International Conference on Mars (2003) 3287.pdf CCDhas204812×12umpixelsinthecross-scandirec- highpixelsrates,inexcessof16megapixelspersecond, tionand128TDIelements(stages)inthealong-track whilesamplingaminimumoftwiceperpixel. direction.The14staggeredCCDsoverlapby48pixelsat Eachofthe14CPMM’susesarad-hardXilinxVirtex eachendasshowninFigure3.Thisprovidesaneffective 300EFieldProgrammableGateArray(FPGA)toperform swathwidthof~20,000pixelsfortheredimagesand thecontrol,signalprocessing,LookUpTablecompres- sion,datastorage&maintenance,andexternalI/O.The 4-StateTDI FPGAisSRAMbasedandusesaFlashSerialProgram- PointSource mableReadOnlyMemory(SPROM)forconfiguration ImageMotion t0 Time uponpower-up.TheSPROMandFPGAarereconfigur- Accumulated 1 t1 ableusingJTAG,sodesignchangesduringdevelopment Chargein1pixel areextremelysimple.TheJTAGportisavailableonan x4TDIElements 2 externalconnectortofacilitatelastminutedesign forSixTimes t2 3 changes,ifrequired. t3 DataSystem&Operations:Targetcoordinatesforanexpo- Aftert4,chargefromthe 4 t4 surewillbeuplinkedtothespacecraft,whichwillthentranslate objectisclockedintothe thetargetcoordinatesintothetimeatwhichthespacecraftwill serialregister t5 flyovertheareaofMarstobeimaged.Attheappropriatemo- Figure4TDIOperationUsinga4-TDIConfigurationto ment,ablockofcommandswillbeexecutedthatwillsetup-for IllustrateChargeAccumulation andtheninitiatetheexposure.Exposuresetupparametersin- cludelinetime,numberoflines,binningfactor,numberofTDI levels,andthelookuptabletobeusedbytheCPMMelectron- ~4,048pixelsfortheblue-greenandNIRimages. icstoconvert14-bitpixeldatainto8-bitpixeldata.About5 UsingtheTDImethodincreasestheexposuretime,allow- secondsinadvanceofthestart-timeoftheexposure,theanalog poweristurnedon ingustoobtainbothveryhighresolutionandahighsig- nal-to-noiseratio.Asthespacecraftmovesabovethe Attheprescribedmoment,allDCAsbeginclockingsi- surfaceofMars,TDIintegratesthesignalasitpasses multaneously.WhentheexposureonthelastDCAis acrosstheCCDdetectorbyshiftingtheaccumulatedsig- completed,theanalogpoweristurnedoff,andthestored nalintothenextrow(line)oftheCCDatthesamerateas pixeldataisthenreadoutsequentiallyfromeachCPMM theimagemoves(seeFigure4).Thelinerateof tothespacecraftsolid-staterecorder,inpreparationfor 13,000lines/seccorrespondstoalinetimeof76microsec downlinktotheground.Sciencedataheadersaccompany for250kmaltitude.Thepixelintegrationtimeissetto thesciencedatasothatthesciencedatacanbeproperly matchthegroundvelocitysothatchargefromoneimage interpreted.Optionally,thepixeldatacanbecompressed regionissequentiallyclockedintothenextcorresponding byalosslesshardwarecompressorattachedtothesolid- elementinthealong-trackdirection.Theimagercanuse staterecorder. 8,32,64or128TDIstages(detectorelementsinthe Thenominalhighresolutionimageis20,000pixelsby along-trackdirection)tomatchsceneradiancetothe 40,000linesandcantakefrom4to48hoursoftransmis- CCDfullwellcapacity.Spacecraftorientationinyaw siontimedependingonrangetoearthandcompression willcompensateforimagesmearingduringtheintegra- factors. tionperiod.Apracticallimitisreachedwhenresidual imagesmearandspacecraftpointingjitterseriouslyde- gradetherequiredresolution.The128linesisthelargest numberoflinesthatmeetsallrequirements.Imageswith higherSNRandlowerresolutionimageswillbeobtained bybinningthesignalfromadjacentlinesandpixels withintheCCD,uptoamaximumof16×16pixels. HiRISECameraElectronicsOverview:TheCCDProc- essingandMemoryModule(CPMM)electronicsap- proachistominimizethenumberofactiveandpassive componentsthatcontributetonoise.Theobligatoryana- logsignalprocessingchainbetweentheCCDoutputam- plifierandthe80MSPS14bitA/Dhasbeendesignedso thatitaddslessnoisethantheCCD,whilebeingradia- tiontolerantandreasonablylowpower.TheDigitalCor- relatedDoubleSample(CDS)schemeiscapableofvery 3 Sixth International Conference on Mars (2003) 3287.pdf HiRISEPerformance:Thepredictedmaximumsignalis flightstructureandthecustomCCDdesignbeingcompleted. 76,000electronsfortheredchannelat300kmwithno Breadboardsofalltheflightelectronicsareintest.Assembly binning.Figures5showtheexpectedun-binnedSNR andtestofthecamerawillbecompletedbyJune2004. capabilityasafunctionofspacecraftlatitudeandregional Acknowledgments:ThisworkwasperformedattheUniver- albedofortheblue-green,red(pan)andNIRbands. sityofArizonaandBallAerospaceandTechnologiesCorp., underNASA/JPLcontractNAS7-1407.Manythanksgotothe Themodulationtransferfunctionisshowninfigure6. manyengineersandscientistsatE2VTechnologies,Light Notethattheresolutionislimitedbytheaperturere- WorksOptics,CompositeOptics,Inc,UniversityofArizonaand sponseofthepixel,thediffusionintheCCDandthedif- BallAerospacewhoareparticipatinginthedevelopmentofthe fractionofthetelescopemodifiedbythe18cmobscura- HIRISEcamera.Wealsoacknowledgethestrongsupportgiven tionofthesecondarymirrorbaffle. tothedevelopmentgivenbyJimGrafandhisteamattheJet Conclusion:InAugust2005theMarsReconnaissanceOrbiter PropulsionLaboratory,CaliforniaInstituteofTechnology, spacecraftwillembarkonitsambitiousjourneytoexplore References: Mars.Thespacecraftwillcarryanimpressivearrayofinstru-