Joint Milli-Arcsecond Pathfinder Survey (JMAPS): Overview and Application to NWO Mission

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1 Joint Milli-Arcsecond Pathfinder Survey (JMAPS): Overview and Application to NWO Mission B.DorlandandR.Dudik USNavalObservatory 11March MissionOverview TheJointMilli ArcsecondPathfinderSurvey(JMAPS)missionisaDepartmentof Navy(DoN)space based,all skyastrometricbrightstarsurvey.jmapsiscurrently fundedforflight,withat2012launchdate.jmapswillproduceanall sky astrometric,photometricandspectroscopiccatalogcoveringthemagnituderangeof 1 12,withextendedresultsthrough15 th magnitudeatanaccuracyof1 milliarcsecond(mas)positionalaccuracyatameanobservingepochof approximately2013.usinghipparcosandtychopositionaldatafrom1991,proper motionswithaccuraciesof100microarcseconds(umas)peryearshouldbe achievableforallofthebrighteststars,withtheresultthatthecatalogwilldegrade atamuchreducedrateovertimewhencomparedwiththehipparcoscatalog. JMAPSwillaccomplishthiswitharelativelymodestaperture,veryhighaccuracy astrometrictelescopeflowninlowearthorbit(leo)aboardamicrosat.mission baselineisforathree yearmissionlife( )ina900kmsunsynchronous terminatororbit. 1

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 11 MAR REPORT TYPE 3. DATES COVERED to TITLE AND SUBTITLE Joint Milli-Arcsecond Pathfinder Survey (JMAPS): Overview and Apllication to NWO Mission 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) US Naval Observatory,,,, 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 11. SPONSOR/MONITOR S REPORT NUMBER(S) 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified ABSTRACT Public Release 18. NUMBER OF PAGES 14 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 2 MissionStatus 2.1 ProgrammaticOverview WiththereleaseofProgramDecisionMemorandum III(PDM III)inNovember 2008,JMAPSisfullyfundedforflightthrough2015.Theresourcesponsoristhe OceanographeroftheNavy,withprimaryexecutionresponsibilitiesassignedtothe OfficeofNavalResearch(ONR).TheUSNavalObservatory(USNO)hasPrinciple Investigator(PI)anddataprocessingresponsibilities.TheNavalResearch Laboratory(NRL)hasresponsibilityforthespace,launch,groundstationand missionoperationscentersegments. 2.2 Schedule Basedonthecurrentfundingprofile,JMAPSisscheduledforSystem Requirements/SystemDesignreviewincalendaryear2009,PreliminaryDesign Reviewin2010,CriticalDesignandTechnologyReadinessReviewin2011,and launchin2012.alltechnologieswillbeattrl6bytheendofcalendaryear2009. Themissionwilloperatefrom ,withafinalastrometricand photometriccatalogreleasein Outputproducts Therearetworelevantoutputproducts,ordeliverables,fromJMAPS:first,JMAPS willgenerateanastrometricandphotometricstarcatalog,accurateto1masor betterthrough12 th magnitude.second,jmapswillmature,demonstrateandfly attitudesensinginstrumentationthatisaccurateto5mas.inadditiontomaturing largeformatcmos HybridFPA,high stabilitysicoptics,andadvancedelectronics technology,jmapswilldemonstratetheabilitytobuildandoperate10 masclass attitudesensors,allby2012.thecatalog,technologyandinstrumentation demonstrationareallhighlyrelevanttofuturenasamissionssuchasnwo.inthe followingsections,wedescribeinstrumentdesigninmoredetail,anddiscusshow JMAPSmighthavedirectapplicationtoNWO. 4 Spacecraftoverview Asshowinfig.1,JMAPSisasingle instrumentspacecraftconsistingofthe instrumentdeployedonapayloaddeckthatisaffixedtothetopofthebus.the instrument/payloaddeckconsistsoftheopticaltelescopeassembly(ota),thefocal planeassembly(fpa),theinstrumentelectronics(i.e.,processorandmemory), thermalcontrolforthefpa,asunshield,andthecoarsestartracker.the instrumentcomponentoccupiesavolume16.2 (41.1cm)(h)x25.8 (65.5cm)x 24 (61.0cm)withamassof48kg,including25%margin. 2

4 +),-#$ #./0102/3$!"#$ %&#'(")*&'$ Figure1.JMAPSSpacecraft Thelowerportionofthespacecraftconsistsofthebus,whichsupportsthesolar panelsandhousesthepower,avionics,communications,primarythermalcontrol, reactionwheels,andinertialmeasurementunits(imus).thetotalmassofthe spacecraft,includingcontingency,isapproximately180kg.thespacecraftoccupies avolumeapproximately38 (96.5cm)(h)x28 (71cm)x24 (61cm). IntheJMAPSmissiondesign,theAttitudeDeterminationandControlSystem(ADCS) isintegratedbetweentheinstrumentandthebus.whileslewingorinacquisition mode,coarseattitudeinformationatthe1arcsecondlevelisgeneratedbythestar tracker.thisinformationiscombinedwithdatafromtheinertialreferenceunit (IRU)inthebusandprocessedwithtogeneratepointingknowledgeatorbelowthe 1masaccuracylevel.Duringstandardobservations,theprimaryinstrumentisused toobservereferencestarsandgenerateboresightpointingquaternionsatorbelow 10masinaccuracyat5Hz.The10masattitudesignalisusedbytheADCSsystem todrivethespacecraftpointing.usingasystemofreactionwheelsthespacecraft achievespointingcontrolandstabilityof50mas. TheprimaryrelevanceofthistotheNWOprogramisthattheJMAPSattitude determinationsubsystem thatis,thecomponentsofjmapsthatgenerate 3

5 quaternions arecontainedintheinstrument.thejmapsinstrumentcanbe separatedfromthebusand,inprinciple,usedonotherplatformsforveryhigh accuracyattitudedetermination.thisassumesthattherequisitethermaland powerconnectionsareavailable.theaccuracyofresultantattitudedetermination willbeafunctionofplatformconsiderationssuchasorbit,thermalstability, vibrationalstability,etc. 5 InstrumentDescription Figure2showsthelayoutoftheinstrumentonthepayload.Themajorcomponents areallshown,i.e.:theota,theieb,thestartrackerandthefparadiators.not shownarethesunshield(deployedontherearofthepayloaddecktoprotectthe OTAfromdirectexposuretothesun),thermalinsulationaroundtheOTA,theloop heatpipestructuretocarryheattotheradiators,orthestructureassociatedwith supportingtheradiators.alsonotvisibleisthefpa.thefpaiscontainedinside theota,locatedonthepayloaddeckinrelativelycloseproximitytotheieb.inthe followsubsections,additionaldetailsareprovidedaboutthemajorinstrument subsections.!"#$%&'()*+,&-.,./*0(.&#//.12,3&4'-#5&6789&:$#&;& #%<=&(+*>+?.@&AB@.CB.+89& -D=&C+@7+80C/& <B/8CA1.B8&D,.*8C0B7*/&E0F&4<DE5& -0(& -DG"#&%8+C&-C+*>.C&H&D,.*8C0B7*/& %7@.& :C0B8& Figure2JMAPSInstrument conceptualdesignofpayloaddeck. 4

6 The JMAPS instrument has been designed to meet a 5 mas single measurement systematic error floor, including both local (i.e., centroiding), differential (e.g., residual distortion), and detector error sources. The design and system engineering processes required to meet this specification are currently underway and include high fidelity thermal, vibrational, optical and focal plane modeling. Results of these design and analyses activities will be reported out at appropriate venues and publications. 5.1 Optical Telescope Assembly The high precision and repeatability of the required measurements necessitates an optical system with very low aberrations and very high stability. The JMAPS optical telescope is a 19 cm, f/20, on axis space astrograph designed for a residual aberration and distortion floor of below 5 mas. This is achieved through the use of Silicon Carbide (SiC) optics and metering structure for the powered optics, and through a thermal design that maximizes the thermal stability of the optical elements and structure. 5

7 TheOTAconsistsofaplane parallelentranceaperturewindow,madeoffusedsilica. Thiswindowprovidesbotharedbandcutoffatabout920nmaswellasmechanical supportform2,withminimalstraylighteffects.therearethreepoweredelements andsixfoldflatsthatareusedtocontainthe3.8meffectivefocallengthinavolume thatisapproximately25 alongthelongaxis.thesystemincludesarotatingfilter wheelwithfourpositions.thefirstpositionisawide openvisibleband(~ nm),thesecondpositionistheprimaryastrometricbandpassbluecutoff(itpasses light>700nm),thethirdisalowresolutionspectralgrating(r~15)usedforbasic colorsensing,andthefourthistbd. Thedesignresidualwavefronterror(WFE)iswellbelow0.05wavesat633nm, whiletheas builtwfeisbetween0.05and0.067wavesat633nm.residual centroidingerrorduetostatic(e.g.,psfundersampling)andvarying(e.g., thermally induceddefocus)sourcesoferrorwillnotexceed3masrms.residual distortionandothersourcesofdifferentialastrometryerrorduetobothstaticand varyingeffectswilllikewisebekeptbelow3mas.thesesourcesoferrorrollupto4 masfortheoptics inducedsingle measurementjmapssystematicfloor contribution. Figure4:(left)JMAPSInternalOpticalTelescopeAssembly(OTA)and(right)opticalraytrace 5.2 FocalPlaneAssembly ThebaselineJMAPSfocalplaneassembly(FPA)consistsofa2x2mosaicof TeledyneImagingSensor(TIS)H4RG 10sensorchipassemblies(SCAs),asshownin Figure5.TheH4RG 10isa4192x4192,10micronpixelCMOS HybridSCA.JMAPS willusetheb0,or3 rd generationdesignofthesca.thefirstgenerationsca(a1) hasbeenfabricatedandtestedatbothgoddardspaceflightcenter(gsfc)and USNOandreportedonintheliterature.USNOwilltakedeliveryofthesecond generationsca(a2)in2009andimmediatelybeginlaboratory,skyandradiation testingworkingwithbothgsfcandtheairforceresearchlaboratory(afrl).by 6

8 earlysummer,initialresultswillbeavailableforthea2design.atthispoint,thea2 designwillhaveachievedatrlof6. TheflightSCAswillbemountedonanintegratedFPAthatwillprovideelectric, thermalandmechanicalinterfacestothepackagedscas.thefpawillbecooledto atemperatureofapproximately193k,withastabilityspecificationof10mk.the FPAheatwillbedumpedtospaceusingdedicatedFPAradiatorsonthefront apertureandabovetheota(seefigure2). TheFPAisallocated3masofsystematicerrorforcentroidingmeasurements.This includestheeffectsofchargediffusion,intra andinter pixelquantumefficiency variations,hotpixels,inter pixelelectroniccross talk,andscamotion.these requirementsdrivetheperformancespecificationsfortheflightunitsaswellasthe thermalandmechanicalstabilityrequirementsonthefpa.fparequirementsand performancearecurrentlybeingvalidatedusinganumberoftools,includingahighfidelityfocalplanesimulator. Figure5:JMAPSFPA4K2X2MosaicConcept 5.3 ReadoutASICS ThebaselineJMAPSreadoutandFPAcontrolelectronicsaretheTISSIDECARASICS (seefigure6).jmapswillutilizeatotaloffourtooperatethefpa.thesidecars digitizethedatacomingoffthefpa,witha16 bitdepth.multipleoutput connectionswillbeusedtoreadoutthefpainapproximately1second.inaddition, forbothguidestarandbrightstarapplications,thesidecarswillreadoutsmaller windowsonthefpaathigherframerates.guidestar(approximately10starsper 7

9 fieldofview)windowswillbereadoutat5framespersecond(fps),whilebright star(<5 th magnitude)windowswillbereadoutatframeratesofupto200fps. Figure6:SidecarASIC 5.4 InstrumentElectronicsBox TheInstrumentElectronicsBox(IEB)housestheprimaryon boardprocessing systemfortheinstrumentandspacecraft.theiebcombinesthepowerconversion, mechanismandthermalcontrol,dataprocessinganddatastoragefunctions.the IEBreceivesfull framedatafromtheasics.cdsprocessingisperformedby differencingscienceobservationsfromtheresetreadoutframe.theprocessorthen stepsthroughtheimageanddetectsstars.foreachdetectedstar,a10x10pixel windowsisretainedandstoredinthesolidstatedatarecorder(ssdr)forlater downlinktotheground.attitudedeterminationcalculationsareperformedinthe IEB,andquaternionsaregeneratedtodrivetheADCS.Dataratesforthewindows aretypicallyabout5.6mbitsperminute.dataaredownlinkedtothegroundstation viatheon baordtransmitterduringregularpasses.onepassperdayoverthe groundstationissufficienttodownloadoneday sworthofastrometricdata. 5.5 IntegratedInstrumentConceptofOperationsandPredictedPerformance TheJMAPSinstrumentisoperatedinafashionsimilartostandardstartrackers.A starfieldisimaged inthecaseofjmaps,integrationtimesof1,4.5and20seconds areused individualstarpositionsarecalculated,andtheboresightpointing calculatedevery200msec.asdescribedintable1,theintegratedinstrumenthasa fieldofviewof1.24 x1.24.eachpixelsubtendsapproximately0.5secondsofarc. Theprimaryastrometricbandpassis nm,approximatelyequivalentto astrometriciband.thetypicalpointspreadfunction(psf)fullwidthathalf maximum(fwhm)is0.87arcseconds,forasamplingof1.6pixelsperfwhm. 8

10 Usingacombinationoffocalplaneandcentroidingmodelscombinedwithanalyses ofthepsfs,instrumentthroughput,etc.,wecanpredictcentroidingaccuracyfor singlemeasurementsasafunctionofibandmagnitude.theseresultsareshownin Figure7.Theresultsconsideronlythe bestcase foradiscreterangeofexposure times(0.01,0.2,1.0,4.5and20seconds).here,bestcaseisdefinedasthelongest, non saturatedexposuretime. TheADCSsystemusesthetenbrighteststarsonthefocalplanetocalculatea boresightattitudeata5hzrate.usingtypicalnumbersandi bandbrightnesses, boresightaccuraciesofbetterthan10masata5hzratecanbeachievedaccording tojmapsattitudedeterminationsimulationresults. Theinstrumentperformanceestimatesarebasedondetailedsimulationsofthe focalplane,optics,centroidingprocessandarealisticattitudedeterminationsystem simulator.theresultsincludeboththermalandvibrationseffects. Parameter Spec Units Optics Optical Aperture 19 cm Collecting Area cm^2 central obscuration 9 cm Focal length. 3.8 m Focal Ratio Optical Field of View (FOV) 1.24 square degrees Survival Temperature K Operating Temperature K Single Measure Instrument Error Floor 5 mas Mission Systematic Error Floor 0.5 mas Focal Plane Size of FPA (pixels) 8192 square pixels Size of FPA (mm) square mm Pixel size 10 um Pixel subtense arcseconds FPA Read noise 10 e- Mode of dark current distribution <1 e/s/pix Operating Temperature. 193 K Survival Temperature 180 K Temperature stability < 0.01 K Spectral Range nm Full Well e- Residual uncorrected detector effects < 3.5 mas Instrument Data Rate Per Day 93 kbits/sec Per Minute 5.6 Mbits/min Per Day 7.5 Gbits/day FPA Readout time! 1 seconds Digitization noise!10 e- Overall instrument read noise!14 e- Table1.Instrumentperformanceparameters(notional). 9

11 Figure7.SinglemeasurementprecisionpredictionsforJMAPSasafunctionofsouceI bandmagnitude. 6 NWO SpecificApplications 6.1 SimilaritiesandDifferencesbetweenbaselineJMAPSandNWO implementation Thedescriptionprovidedin 4and5refertothebaselineJMAPSmission.This missionwillflyinthe timeframe.By2013alltechnologyandconcepts willbedemonstratedattrl9andby2016afinalcatalogwillbereleasedwith stellarpositionsaccurateatthe1maslevel. Asnotedin 5,theinstrumentisessentiallyadiscretecomponentandcanbe thoughtofasanextremelyaccurateattitudesensor/startracker.asecondinstance oftheinstrumentcanbebuiltanddeployed,inprinciple,onotherplatforms. Assumingthepropermechanical,thermalandelectronicinterface,itcanthenserve asanextremelyaccuratestarsensor.ifflownafter2016,itwillalsobeabletotake advantageofthejmapsstarcatalog.basedonextensivecostmodelingusingboth thenasainstrumentmodel(developedbyjpl)andaerospacecorporation s ConceptDesignCenter,theinstrumentdevelopmentcostisestimatedatunder $40M($FY08).Asignificantportionofthisisnon recurringexpenses,soasecond unitwouldlikelycost$30morless.adoptinga$40mnot to exceedlimitwouldbea veryconservativeestimate,andwouldallowforsomemodificationstobemade basedonlessonslearnedwiththefirstunit. 10

12 ForpurposesoftheNWOanalysis,weassumethatasecondinstrumentisbuiltand deployedasstarsensoronboardthenwostarshade.theinstrumentwouldbe usedtonavigatethestarshadeduringthealignmentphaseoftheoccultation.the originalinstrumentisdesignedtosupport5massinglemeasurementaccuracyfora LEO classmission.mostofthesourcesofsystematicerrorarerelatedtovarying thermalconditionsovertheorbit.asimilarunitdeployedatl2wouldbeina significantlymorebenignthermalenvironment.assuch,wewouldexpectthe systematicerrorfloortobewellbelow5mas.forpurposesofthisanalysis, however,wewillcontinuetousethe5masvaluefromthebaselinemission.wewill continuetheanalysisforthel2caseandwillpublishtheseresultsinthe appropriateforumoncetheanalysisiscompleted. 6.2 Starshadealignment TheprimaryapplicationoftheJMAPSinstrumenttoNWOistosupportthe alignmentofthestarshade(seefigure8).theoverallprocessisdiscussedindetail elsewhereinthemainbodyofthenworeport;werestrictourdescriptionhereto thejmapscomponent.inthecaseofdisagreementbetweenthedescription presentedhereandthatpresentedelsewhereinthenworeport,thelattertakes precedenceoverthisone. Inordertosuppressthestarlightandrevealthereflectedlightfromtheexoplanets, thenwostarshadehastobeaccuratelymaneuveredinfrontofthetelescopeat distancesof50 100Megameters(50, ,000km).TheJMAPSinstrument willbedeployedonthestarshadeandorientedtowardsthetelescope.inorderto ensuretherequiredsignal,ani bandbeaconwithamaximumapparentmagnitude of12atthemaximumalignmentdistancewillbeaffixedtothetelescopeand directedatthestarshade. Figure8:IllustrationofNWOalignmentproblem 11

13 TheJMAPSinstrumentwillobservethetelescopebeaconagainstthebackground fieldofreferencestars.assumingatypicalbackgroundguidingsignalupdaterateof 0.1Hz,theJMAPSinstrumentwillaveragetheboresightpointingresultsover50 observations,andgenerateameanboresightmeasurementofaccuracy1mas. Ifweadopta10secondintegrationtime,wecancalculatethesinglemeasurement accuracyforindividual,stellar likesources.resultsarepresentedforthreetypical NWOrangesinTable2.ThenominalNWO12 th magnitudebeaconishighlightedin thetable.theconclusionisthattheinstrumentiscapableof8masposition determinationgivenatensecondexposure.whencombinedwiththeboresight accuracyof1masoverthesameperiod,alignmentaccuracies(1 σ)ofbetween2 and4metersareexpected(seethetable).theinstrumentwillperformboththe positionandboresightcalculationsinternallyandgenerateboresightandtelescope positionsforthestarshadespacecraftonceeverytenseconds. Increasedexposuretime,abrighterbeaconandareducedsystematicerrorfloor duetothemorebenignthermalenvironmentatl2woulddrivedowntheerror.in principle,alignmenterrorsof1metermaybepossible,butadditionalanalysis includingdetailedthermalsimulation arerequiredtosupportthisresult. Magnitude SMP Range (megameters) (I band) (mas) tint = Table2.PredictedsinglemeasurementaccuraciesforstellarsourcesovertypicalNWO ranges.resultsarepresentedinunitsofmeters. 12

14 6.3 Navigation AsecondaryapplicationofJMAPStoNWOisspacecraftnavigation.Asshownin Figure9,theJMAPSinstrumentcanbeusedtoobserveSolarsystemobjects.By combiningobservationsofmultipleobjects,thepositionoftheinstrumentwithin thesolarsystemcanbedetermined.thisisanalogoustoworkcurrentlybedonein thedepartmentofdefensewhichusesobjectsinorbitaroundtheearthto determinepositionsofsensorsinearth svicinity.inthiscase,weareusingmuch moredistantsolarsystemobjectstodeterminepositionwithinthesolarsystem. Aninitialfeasibilityanalysishasbeenperformed.Possibletargetsincludetheouter planets,theirsatellitesandminorplanets.keysourcesoferrorinclude:howto determine position forresolvedtargetssuchasthegasgiants,theerrors associatedwiththeephemeridesofoutersolarsystemobjects,thesignalsfor variouscandidatetargets,andtheeffectsofphotocentermotiononsub pixel centroiding.initialanalysisindicatesthatwithsufficientsignal,1/100 th pixel centroidingonquasi pointsourcessuchasasteroids,andfewaubaselines, positionswitherrorellipseaxesoforder50kmorlessarefeasible.moredetailed analysisisunderwaytorefineatargetlist,developanapproachforout of plane positionandassessaccuracieswithmorefidelity.wewilllikelyperformnavigation experimentswiththebaselinejmapsmissionwhileonorbitinordertodefinitively determinethefeasibilityofthisapproachforsolarsystemnavigation :28:33! Figure9:Simulationofsolarsystemorbits.JMAPScanbeusedtodeterminethepositionoftheoccultor toaccuraciesof50kmorless. 13

15 7 Summary TheJMAPSmissionisafunded,DepartmentofNavyall skyastrometricand photometricsurveymissionscheduledforlaunchinthe2012timeframe.the missionwilldeliveranupdatedbrightstarcatalogby2016.themissionwill developandflyanewclassofastrometricinstrumentationthatwillsupport measurementofindividualstarpositionsatthe5maslevelandattitude determinationatthe10maslevelata5hzrate.theinstrument,describedindetail inthispaper,canbedeployedonotherplatformsandusedforbothboresight attitudedetermination(i.e.,attitudesensing)andindividualstarposition measurement(i.e.,startracking).initialanalysisindicatesthatthecatalogand technologycanbeappliedtothenwomissiontosupportbothalignmentofthe Starshadespacecraftatthe2 4maccuracylevelatdistancesofupto100Mm,and forsolarsystemnavigation,witherrorellipsesof50kmorless. 14