Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice...
Transcript of Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice...
![Page 1: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/1.jpg)
RosettaAliceUltravioletSpectrographFlight
OperationsandLessonsLearnedJonP.Pineau1,JoelWm.Parker2,AndrewJ.Steffl2,EricSchindhelm2,RichardMedina2,S.AlanStern2,M.Versteeg3,andEmmaM.Birath2
1StellarSolutions,Inc.,PaloAlto,CA,UnitedStates.2SouthwestResearchInstitute,DepartmentofSpaceStudies,Boulder,CO,UnitedStates.3SouthwestResearchInstitute,6220CulebraRoad,SanAntonio,TX78238,UnitedStates.
AbstractThis paper explores the uniqueness of ESA Rosetta mission operations from the Alice instrument point of view, documents lessons learned, and suggests operations ideas for future missions. The Alice instrument mounted on the Rosetta orbiter is an imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy with the scientific objectives of measuring properties of the escaping gas and dust, and studying the surface properties, including searching for exposed ices. We describe the operations processes during the comet encounter period, the many interfaces to contend with, the constraints that impacted Alice, and how the Alice science goals of measuring the cometary gas characteristics and their evolution were achieved. We provide details that are relevant to the use and interpretation of Alice data and published results. All these flight experiences and lessons learned will be useful for future cometary missions that include ultraviolet spectrographs in particular, and multi-instrument international payloads in general.
![Page 2: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/2.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 2
1TheRosettaMissionandComet67PAtfirstsightofthecomet67P/Churyumov-Gerasimenko,itwasobviousthattheRosettamissionwouldbedifferentfromanythatcamebefore.Whilethiswasexpectedtosomeextentasreflectedinthemissiondesign,theneedforanevenmorecomplexconceptofoperationswasrealizedwhenthehighlyirregularcometbodywasfinallyresolved10.5yearsafterlaunch.Theshapeofcomet67Piscomposedoftwounequallobeswithadeepneckareaconnectingthetwo.Thisaddedcomplexitiesinthegravityfield,thenon-uniformityofmaterialandlightcomingoffthesurface,andthegeolocationmapping.Thecombinationofthesefactorsalongwiththeanticipateddifficultiesoforbitingalowgravity,dynamicbodythatcreatesitsownever-changingenvironmentresultedintrulyuniquemissionchallengesthatrequiredequallyuniqueoperationssolutions.AsamemberoftheJupiterfamilycomets(JFCs),67P’shighlyellipticalorbittakesitjustpastJupiter’sorbit(5.684au)andalmostasclosetotheSunasEarth(1.246au)every6.45years.Theresultisaperiodictransformationbetweenadormant,dark,frozennucleusnearaphelionandaspectacularlydynamicdisplayofsublimatinggasandejecteddustnearperihelion.ThisstrongvariationinactivitydrovemanyRosettamissionattributesandconstraints,addingtothealreadycomplexsystemthatincludedtheRosettaorbiterwith11instrumentpackagesandthePhilaelanderwithitsownsetof10instruments.AsthecometactivityevolvedasitcircledtheSun,theRosettaandAliceoperationsprocessesevolvedthroughthemissiontoprovideasystemthatcouldmeettheever-changingneeds.Toolswereredesigned,interfaceschanged,andprocessesupdatedtooptimizesciencereturn.Afterlaunch,thecircuitouspathofRosettaincludedseveralorbitsintheinnersolarsystemincludingseveralgravitationalassistsfromEarthandMars,thelastofwhichsentRosettatotheoutersolarsystemonarendezvouspathwith67P.AlongthewayinstrumentswereabletomakeobservationsofEarth,cometLINEAR,cometTempel1duringtheDeepImpactevent,Mars,asteroidSteins,andasteroidLutetia,whichallowedtestingoutflightsystemsandgroundprocesses.Shortlyafterwakingfromanunprecedentedpre-primemission2.5yearhibernationperiodthatlastedthroughaphelionwithoutanycommunicationwithgroundstationsonEarth,Rosettabeganstudyingcomet67Pinamannerneverbeforeattemptedatacomet.Wherepreviousmissionshadstudiedcometsfromflybysofseveral100’skmawaytravelingatrelativevelocitiesof10’sofkm/sorperformingabriefsurfaceimpact,Rosetta’stwoyearencounterperiodwasoftenspentat10’sofkmfromthecometnucleuswithrelativevelocitiesofmeters/second.Aslow,controlledsurfaceimpactconcludedthehistoricmissionaddingtothehighsurfaceresolutionmeasurementsthatthePhilaelanderacquiredatthebeginningofencounter.Table1detailssomeoftheimportantRosettamissionandAliceinstrumentevents.
![Page 3: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/3.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 3
Table1:MajorMissionandAliceEvents2004Mar2 Launch
2004Apr-May ObservationsofcometLINEAR2005Mar4 Earthflyby#12005Jul4 ObservationsofDeepImpact
2007Feb25 Marsflyby2007Nov13 Earthflyby#22008Jul19 Ø Aliceupset/resetevent#12008Sep5 AsteroidSteinsflyby2009Sep29 Ø Aliceupset/resetevent#22009Nov13 Earthflyby#32010Jul10 AsteroidLutetiaflyby2011Jun8 • Spacecrafthibernationentry(4.5au)2012Oct3 Aphelion(5.3au)2014Jan20 • Spacecrafthibernationexit(4.5au)2014Mar18 Ø Alice1stpoweronafterhibernation2014Jun6 Ø Alicebeginscontinuouspoweredoperations2014Aug6 Orbitinsertionatcomet67P,startofencounterperiod2014Nov12 • Landerdelivery(3.0au)2014Nov15 • Landerhibernationbegins2015Mar28 • Spacecraftstartrackersafemode–instrumentsoff2015Apr15 Ø Alicereturnstonominaloperationsaftersafemode2015May10 Equinox(Nvernal,Sspring)
2015Jun13–Jul9 • Intermittentlandercontacts2015Aug13 Perihelion(1.2au)2015Sep4 Solstice(Nwinter,Ssummer)
2016Mar20 Equinox(Nspring,Svernal)2016May28 • Spacecraftstartrackersafemode–instrumentsoff2015Jun1 Ø Alicereturnstonominaloperationsaftersafemode
2016Sep30 Endofmission(3.8au)
Ø AliceEvent;�SpacecraftorLandereventInSection2wedescribetheAliceUltravioletSpectrographdesignandscienceobjectives.InSection3wedescribetheoperationsofAliceandthevariousinstrumentalandmissionconstraintsthataffecttheoperations.Section4coversthedifferenttypesofAliceobservations,supportingobservationsbyotherinstruments,andthespecialissuesofregardingmakingobservationswhileorbitinganactivecomet.InSection5wedescribethebroadercontextanddesignofRosettamissionoperations.Section6providessomelessonslearnedandadditionalinformation.
![Page 4: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/4.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 4
2TheAliceUltravioletSpectrograph
2.1AliceDesignDescribedbelowisthedesignoftheNASA-fundedRosettaAliceinstrumentaboardtheESARosettaasteroidflyby/cometrendezvousmission.MostofthetextintheAliceDesignsectionisfromSternetal.,2007[1],butrepeatedhereforstand-alonecompletenessofthisdocument.Aliceisalightweight,low-power,andlow-costimagingspectrographoptimizedforcometaryfar-ultraviolet(FUV)spectroscopy[1].ItwasthefirstofafamilyofsimilarinstrumentscurrentlyincludingAliceonNewHorizons,LAMPUVS(LymanAlphaMappingProjectUltraVioletSpectrograph)onLunarReconnaissanceOrbiter(LRO),UVSonJuno,andtheexpectedUVSinstrumentsontheupcomingJUICEandEuropaClipperMissions.RosettaAlicewasthefirstUVspectrographtostudyacometatcloserange.Itwasdesignedtoobtainspatially-resolvedspectrainthe700–2050Åspectralbandwithaspectralresolutionbetween8Åand12Åforextendedsourcesthatfilltheslit.Anopto-mechanicallayoutofAliceisshowninFigure1.Lightentersthetelescopesectionthrougha40×40mm2entranceapertureatthebottomrightofFigure1andiscollectedandfocusedbyanf/3off-axisparaboloidal(OAP)mirrorontotheentranceslitandthenontoatoroidalholographicgrating,whereitisdispersedontoanimagingphoton-countingmicrochannelplate(MCP)detectorthatusesadouble-delayline(DDL)readoutscheme[2].Thetwo-dimensional(1024×32)-pixelformat,MCPdetectorusesdual,side-by-side,solar-blindphotocathodes:potassiumbromide(KBr;forλ<1200Å)andcesiumiodide(CsI;forλ>1230Å)[3].Themeasuredspectralresolvingpower(λ/Δλ)ofALICEisintherangeof70–170foranextendedsourcethatfillstheinstantaneousfield-of-view(IFOV)definedbythesizeoftheentranceslit.
![Page 5: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/5.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 5
Figure1.(a)Theopto-mechanicallayoutofAlice.(b)AphotographoftheAliceflightunit.[1]Theslitdesignisdescribedasa“dogbone”;itis5.53°longinthespatialdimension,thecentral2°ofwhich(calledthe“narrowcenter”)is0.05°wideinthespectraldimension,andthe2°“widebottom”and1.5°“widetop”portionsoftheslitare0.1°wideinthespectraldimension,showninFigure2.Thepinholefeatureatthetopoftheslitwasneverdetectedinflight.
![Page 6: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/6.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 6
Figure2.TheAliceentranceslitdesign[1]Tocapturetheentire700–2050Åbandpassand5.53°spatialfieldofview(FOV),thesizeofthedetector’sactiveareais35mm(inthedispersiondirection)×20mm(inthespatialdimension),withapixelformatof(1024×32)-pixels.The5.53°slit-heightisimagedontothecentral20ofthedetector’s32spatialchannels;theremainingspatialchannelsareusedfordarkcountmonitoring.ThepixelformatallowsaNyquistsampledspectralresolutionof∼3.4Åandaspatialresolutionof0.3°.ThedetectorelectronicsamplifyandconvertthedetectedoutputpulsesfromtheMCPZ-Stacktopixeladdresslocations.InsteadofdiscretephysicalpixelsasinaCCDdetector,thetimeofarrivalofachargeatbothendsoftheorthogonaldelaylinesisusedtodeterminethespectral“pixel”onwhichaphotonlanded.Thesensitivityofthedetectorelectronicstoconvertaphotoneventintoanoutputpulsecanbeadjustedbychangingthedetectorhighvoltagelevel.OnlythoseanalogpulsesoutputfromtheMCPthathaveamplitudesaboveasetthresholdlevel,alsoreferredtoasthediscriminatorlevel,areprocessedandconvertedtopixeladdresslocations.Foreachdetectedandprocessedevent,a10-bitxaddressanda5-bityaddressaregeneratedbythedetectorelectronicsandsenttotheAlicecommand-and-datahandling(C&DH)electronicsfordatastorageandmanipulation.Inadditiontothepixeladdresswords,thedetectorelectronicsalsodigitizestheanalogamplitudeofeachdetectedeventoutputbythepreamplifiersandsendsthisdatatotheC&DHelectronics.Histogrammingthis“pulse-height”datacreatesapulse-height
![Page 7: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/7.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 7
distributionfunctionthatisusedtomonitorthehealthandstatusofthedetectorduringoperation.Abuilt-in“stim-pulser”isalsoincludedintheelectronicsthatsimulatesphotoneventsintwopixellocationsonthearray.ThispulsercanbeturnedonandoffbycommandandallowstestingoftheentireAlicedetectorandC&DHelectronicsignalpathwithouthavingtopoweronthedetectorhigh-voltagepowersupply.Inaddition,thepositionofthestimpixelsprovidesawavelengthfiducialtoaccountforshiftsthatcanoccurwithoperationaltemperaturechanges.
2.2AliceScienceModesTheAliceinstrumenthasthreemodesoftakingdata:histogram,pixellist,andcountrate.Thefirsttwoacquisitionmodesusethesameeventdatareceivedfromthedetectorelectronics,butthedataareprocessedinadifferentway.Thethirdacquisitionmodeonlyusesthenumberofeventsreceivedinagivenperiodoftime–nospectralorspatialinformationisprovided.
Inhistogrammode,theinstrumentcontinuouslycollectsdetectedeventsbypixellocationthroughouttheexposure,muchlikehowaCCDcountsandaccumulatesdetectedphotons.Duringthecourseofahistogramobservation,eachdetectedeventissavedintomemory,wherethememorylocationsmapone-to-onetopixelsonthedetector.Inthisway,anintegratedspatial-spectralimageisaccumulatedoverthecommandedexposuretime.Thismodeisusefulforobservationswithhighcountrates,andwasthemostcommonlyusedmodeduringthemission.Theresultingimagesarethesameformatasthedetector,1024x32pixels,withthelongaxiscorrespondingtowavelengthandtheshortaxisisthespatialdimension.Sincetheouteredgesoftheimagearean“unexposed”partofthedetector,thesoftwareplacesthepulseheightarrayinthisregion,anditalsoprovidesmonitoringofbackground/cosmicrayanddarkcounts.Thehistogramvalues(counts)saturateat65535counts.
Inpixellistmode,theinstrumentseriallyrecordsthex-ylocationofeachphotonandinsertstimetags(“hacks”)inthislistatregular,user-definableintervalstoprovidethetiminginformationforthephotons.Duetodatavolumeconsiderationsandthetimerequiredformemoryreadout,thismodewasusedprimarilyatlowcountrates.Themaximumnumberofentriesis32767(includingphotonsandtimetags),butmaybelessdependingonthecombinationofbrightnessofthetargetandtheexposuretimeoftheparticularobservation.Oncethememoryisfilledtothislimit,nomoredataarerecordeduntiltheexposureisstoppedandthememoryisreadout.ThismodewasemployedprimarilyduringtheBi-MonthlyCrossSlitScanCalibrationduetotheneedfortimeresolutiontodetectwhenthestarcrossedtheedgesoftheslit.
Incountratemode(alsocalled“photometer”mode),thespatialandspectralinformationforeachphotonisignored.Thenumberofphotonsdetectedineachuser-definedtimeintervalaresummedandsavedasasinglenumberinmemory.Thismodewasnotwidelyused,butcouldbeusefulforobservingverybrightultravioletstars.Themaximumnumberofintervalsis32678,butmaybelessdependingonthecombinationoftimeintervalandtotalexposuretimeoftheparticularobservation.(Notethatthenumberofintervalsisindependentofthe
![Page 8: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/8.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 8
brightnessofthetarget.)Thesummedcountspertimeintervalsaturateat65535counts.[4]
2.3AliceScienceObjectivesThescientificobjectivesoftheAliceinvestigationweredefinedasfollowsandfurtherdetailsfoundin[1]:
1. Searchforanddeterminetheevolvedraregascontentofthenucleustoprovideinformationonthetemperatureofformationandthermalhistoryofthecometsinceitsformation.
2. Determinetheproductionratesoftheparentmoleculespecies,H2O,COandCO2,andtheirspatialdistributionsnearthenucleus,therebyallowingthenucleus/comacouplingtobedirectlyobservedandmeasuredonmanytimescales.
3. StudytheatomicbudgetofC,H,O,N,andSinthecomaasafunctionoftime.4. StudytheonsetofnuclearactivityinwaysRosettaotherwisecannot.5. Spectralmappingoftheentirenucleusof67PatFUVwavelengthsinorderto
bothcharacterizethedistributionofUVabsorbersonthesurface,andtomaptheFUVphotometricpropertiesofthenucleus.
6. Studythephotometricandspectrophotometricpropertiesofsmallgrainsinthecomaasanaidtounderstandingtheirsizedistributionandhowtheyvaryintime.
7. MapthespatialandtemporalvariabilityofO+,N+,S+andC+emissionsinthecomaandiontailinordertoconnectnuclearactivitytochangesintailmorphologyandstructurenearperihelion.
3AliceOperationsandConstraints
3.1ContaminationThematerialcomingoffthecometposedaseriousmissionriskasthefinedustandgascouldcoatinstrumentopticsandsolarpanelswhichcouldleadtoseveresciencedegradation,decreasespacecraftpowerproduction,andpreventspacecraftattitudeandlocationknowledgedetermination.Furthermore,duringperiodsofhighcometactivitytherewereunpredictablestrongoutburststhatquicklypropelledconcentratedjetsofmaterialoutward.LargepiecesofmaterialwereseenorbitingthecometandattimesimagesshowedthatRosettawasflyingthroughablizzardofdustparticlesasshowninFigure3.
![Page 9: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/9.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 9
Figure3.(a)DustandgasescapingthecometnucleusonMarch272016[5](b)ThedustenvironmentaroundRosettacapturedbyRosetta’sOSIRIS(Optical,Spectroscopic,andInfraredRemoteImagingSystem)cameraonJuly62015[6]Itwasdifficulttostriketherightbalancebetweenwhatwasperceivedtobeasafedistancefromthematerialcomingoffthecometandbeingclosetothenucleustoobtainhighresolutionmeasurementsandsignificantcountsforthedustandgasinstruments.ForAlice,thelocalgaspressureanddustcountmeasurementsneverreachedsustainedlevelsthatwouldcausegreatconcernofcontamination,andthelevelswerealwaysbelowlimitsthatwouldhavetriggeredanAlicesafingeventthatclosestheaperturedoorandturnsoffthedetectorhighvoltage.RegularcalibrationobservationswiththeAliceinstrumentthroughtheescortphasetrackedsensitivitydegradation,whichwasminimal,duetocontaminationandothersources.However,onesystemaffectedbythedirtyenvironmentwasthespacecraftstartrackersthatoccasionallywouldgetconfusedbythebrightdustparticlesandloseattitudeknowledge.Thatresultedintwospacecraftsafeeventsthathaltedallactivitiestoregainattitudeknowledge,andtherewereseveralotherclosecalls(asfurtherdetailedinTable1).Sincesuchspacecraftsafetyeventscouldjeopardizetheentiremission,theprogramerredonthesideofcautionandusuallykeptahealthymarginonthedistancetothecometbasedonactivity.ThistypicallyhelpedAlicesciencebecausethespectrograph’slongslit(5.53°)attheselargerdistancesallowedAlicetohavesomespectralelementsonthenucleusandotherslookingoff-limbattheescapinggasesintandem(asa“ride-along”)withobservationsdesignedbyotherinstrumentteamsthatpreferredsurfacepointing(seetheFigure4example).AnotherfactorthatpossiblyhelpedpreservetheAlicethroughputisthattheinstrumentoperatedincontinuousdecontaminationmodeformostoftheencounterafterverifyingitdidnotimpactinstrumentcalibration.Thismeantthatthemirrorandgratingheaterswereconstantlyenabledtokeepthoseopticalelementswarmsotheywouldnotbecoldtrapsbydrivingoffanydepositedcontamination.However,giventhattherewereveryfewissuesforcomponentsontheRosettaorbiterthroughencounterphasedemonstratesthatencounteringhighconcentrationsofmaterialandlargedestructivechunksofmaterialwasrareeven
![Page 10: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/10.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 10
thoughtheenvironmentwasmuchdirtierthantypicalwhenorbitinglessactivebodiessuchasplanets,moons,andasteroids.
Figure4.ExampleofanOSIRIStargetedsurfaceobservation(landersearch)thatcouldbeusedbyAliceasaride-alongtoviewoff-cometgasses[7].
3.2GainSagAddingsomeuniqueconstraintstotheAliceoperations,theinstrumenthasanun-scrubbedmicrochannelplate(MCP)detector.ThescrubbingprocessexposesthedetectortoUVlightreducingthepixelcharge,aconditioningtechniquethat“burnsin”thepixels,eventuallystabilizingthedetectorresponse.However,ascrubbeddetectorimposessignificantconstraintsinpre-flightgroundhandlingincludingrequiringbeingkeptinconstantvacuum,whichwasnotanoptioninthiscaseastheAlicebandpassintheEUVrequiredanopen-faceddetector.Theconsequenceofflyinganun-scrubbeddetectoristhatitsresponsecontinuallydecreasesthroughthemissionfromexposuretoUVlight,atypicalcharacteristicofMCPscalled“gainsag”.Thegainsagisalsospatiallydependentasafunctionofthetotalfluenceonagivenareaofthedetector,leadingtonon-uniformsensitivitydegradationacrossthedetector.Forexample,thevaryingbrightnessofthecometsurface,theobservationofbrightUVstarsonspecificdetectorrows,ortheconstantexposuretoLyman-alphaemissionfromtheinterplanetarymediumwillcausesomepartsofthedetectortodegradedifferentlyfromotherparts(seeFigure5).Thedegradationwastracked,accountedforinthedatacalibration,andperiodicallycompensatedforbychangingdetectorsettingssuchashighvoltagelevel(adetectorsensitivityadjustment)anddiscriminatorlevel(asignalcutoffadjustment).CharacterizationofthedetectorperformancewasconductedperiodicallyusingmoderatelybrightUVstarsascalibrationsources.
![Page 11: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/11.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 11
Figure5.Theprogressionofdetectorsciencecountsthroughencounter.Theconcentrationofcountsnearcolumn600(1215A)istheLy-αlineandtheregionaroundcolumn~850(~1025Å)correspondstothechameleonartifactregion.Thehighconcentrationofcountsinrows9,15,and21areduetostellarcalibrations.Wavelengthdecreasestotheright,i.e.,tohigherrownumber.
![Page 12: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/12.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 12
Theanticipatedlongtermgainsagdrovestrategicplanningforthedetectorusagetoensurethatthedetectorwouldmaintainadequatesensitivitythroughoutthemissionincriticalbandsanddetectorregionstosatisfythesciencegoals.Thisinitiallydroveanalysis-intenseobservationconstraintsofconductingonlyhighprioritycometmeasurementsandactivelyavoidingexposuretorelativelybrightUVstars.
3.3BadDogsandChameleonContributiontoGainSagSomestarsweresobrightintheUVthattheycouldcauseexcessivecountratesontheAlicedetector.TheseUV-brightstarswerenicknamed“baddogs”.TheAliceteamwouldreceivethepredictedspacecraftattitudeandlocationinformationanduseitdodeterminewhenbaddogstarswouldcrosstheAliceFOVplusamargintoaccountforpointinguncertainty.TheteamwouldthenadjustinstrumentcommandingtosuspendtheAliceobservationsandclosetheaperturedooraroundtheforecastedbaddogencounters.Makingtheprocessevenmorecomplexwasthattheplannedspacecraftattitudecouldchangelateintheproductdevelopmentprocessduetootherinstrumentteamsadjustingtheirprimeobservationsorbythemissionflightdynamicsteamadjustingthecometorbitplans.ThiswouldrequireagilemonitoringandresponsefromtheAliceteamtoquickly(sometimesasshortaswithinacoupledays)identifyandmakecorrespondingAliceobservationchanges.Asthemissionprogressed,itwasdeterminedthatthedetectorgainsagratewaslowerthaninitiallyprojected,whichallowedthegainsagavoidancetechniquestobecomeprogressivelylessconservative.BytheendofthemissionAlicewasobservingalmostcontinuouslyandbrightUVstarswerenolongermanuallyavoided.Insteadofavoidanceplanning,adetectorcountratemonitorwithaconfigurablethresholdwasreliedupontoreactwhenanytoo-brightstarscameintheFOV,autonomouslysafingtheinstrumentbytemporarilypausingtheobservingandclosingtheaperturedoor.Themomentaryexposuretothebrightsourcedidnotsignificantlycontributetotheoveralldetectorgainsagandwasawelcometradeoffbetweensomelossofexposuretimeinexchangeforsignificantlyreducingthelabor-intensivestaravoidanceplanning.Theotherprimarycontributortobrightsafetyeventscamefromasporadicissuereferredtoasthe“chameleon”,whichisthoughttobeduetochargedparticlesenteringtheinstrument,gettingthroughthedetectorelectrongrid,andcausingstrange,high-countmeasurementartifacts(seeFigure5)[8].Becausethechameleonhadstrongtemporalvariations,usuallythebrightsafetyactionoftemporarilyclosingtheaperturedoorandwaitingthesafetytimeoutperiod(typically10minutes)wassufficienttodealwiththeoccasionalhigh-countratechameleons.
3.4AliceObservingStylesThroughoutthemissionAlicewouldobserveduringbothAlice-planned(termed“prime”)observationsaswellasobservationsplannedbyotherinstrumentteams(termed“ridingalong”).Eventhoughmanyobservationsdesignedbyotherteamsweren’toptimizedforAlicesciencegoals,somesciencereturnwasalwayspossible
![Page 13: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/13.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 13
whenobservingthecometanditssurroundings.However,potentialsciencereturnalwayshadtobebalancedwithavailablespacecraftresources,developmenteffort,andtheexpectedgainsagimpact.Aliceobservingconsistedoftwomainstyles.Thefirstwascontinuousobservingwherehistogramsweretakenoneafteranother(withshort~40soverheadforimagereadoutbetweenexposures)forhoursatatime,notcorrelatedtoaspecificsceneorpointingchanges.Thiswassimpletoimplement,butcouldleadtodifficulttousedatasuchaswhenhistogramsbridgedchangesinspacecraftstaringandscanningmotionsormajorscenechanges.Theothertypewastomanuallytimehistogramstocorrelatetheirstart/stoptimeswithspecificviewingconditions.Althoughthistechniquecouldoftenreturnbetterscience,thisstylehadahighcostintermsofdevelopmenteffortandcommandingcomplexity.Thiswasespeciallytruewhentiminghistogramsduringridealongsbecauseotherinstrumentteamswouldoftenchangetheirpointingplansduringthedevelopmentperiod,whichusuallyrequiredcorrespondingadjustmentstoAliceobservations.AtthebeginningofthemissiontheAliceteamfocusedonitsprimesciencerefrainingfromobservingduringpointingplannedbymostoftheotherteams.However,asthemissionprogressed,ridealongsincreasedwhendatavolumeandotherresourceswereavailabletoapointwhereAlicewasobservingalmostcontinuously.Thiswasespeciallytrueafteritwasevidentthatthegainsagprogressionratewaslessthanexpectedandsoftwaretoolswerecreatedtoautomateobservationdevelopmentbasedonplannedpointingcharacteristics.
3.5ApertureDoorUsageandPowerCyclingAliceinstrumentoperationsareunlikealotofotherspaceinstrumentsintermsofpowercyclingandmechanicaldooroperations.Duetotheriskofpowerupfailures,theactionofpowercyclingspaceelectronicshaslongbeenavoidedandonsomemissionsonlydonewhenforcedtobecauseofafailureononestringofaredundantsystem.BynecessitythisoperationalmethodwasnotanoptiononRosetta.Powerconstraintsduringcertainperiodsofthemissionrequiredinstrumentsandsomenon-essentialspacecraftcomponentstoalternatepoweredactivitiesleadingtomanyunavoidablecomponentpowercycles.Infact,duringanunprecedented2.5yearhibernationperiodwhenRosettawasattheoutermostpartofitsorbit,whichtookitouttotheorbitofJupiter,itonlyhadenoughsolarpowertohaveafewvitalheatersandelectronicunitson[9].Therewasnocontactwiththespacecraft,notevenbeaconsduringthathibernationperiod.AnonboardtimerwassettotellRosettatowakeuponJanuary20,2014whentherewouldbeenoughpowertoturnsomesystemsonandcontactEarth.Everyonewasontheedgesoftheirseatsonhibernationexitdaytosaytheleastandamazinglyallsystemsturnedonandproceededwiththecometencounter10.5yearsintothemission.Duringtheescortphase(August2014–September2016)standardAliceoperationsweretopowercycletheinstrumentonaweeklybasis.AnAliceupset/reseteventoccurredtwiceduringthecruiseperiodgettingtothecomet(seeTable1forthedates).TheanomalywouldpowercycleAliceandrestartinadefaultstatedefinedbyhard-codedparameters,andalthoughitwouldreturntothenominalactivitytimeline,sciencedataqualitycollectedafterwardcouldbenegativelyimpacteduntilmanualadjustmentswerecommandedtoseveraloperationalparameters.Therootcauseoftheupset/reseteventswasnotidentified,butitwasthoughtthat
![Page 14: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/14.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 14
periodicallypower-cyclingtheinstrumentperhapscouldpreventsuchaproblemfromoccurringorwouldreturnAlicetoitsnominalstateifanupsetoccurred.WithsomepowercyclesalreadyrequiredandfourseparateEEPROMflightsoftwareimagestobootfrom,itwasdecidedthattheriskwouldbelowertoperformregularpowercyclesratherthanbeingoncontinuously.Additionally,tomitigatetheimpactofanupset/resetevent,activitiesweresplitintosmallindependentsegmentsandseveraloperationalparameterswerereassertedtwicedaily.TheAliceaperturedooroperationsweresimilarlydifferentfrommostotherspacemechanicalsystems.Whereasmostmechanicalsystems,anddoorsespecially,aredesignedforonetimeuse,theAliceaperturedoorwasdesignedtobeopenedandclosedmanytimes,ratedfor10,000such“flaps”,whichgaveafactorof2marginrelativetogroundtests.Alicereliedonarobustlydesignedaperturedoormechanismprovenbyextensivegroundqualificationtestingandsubsequentlybylaterversionsoftheinstrument.TheLAMPUVS,whichisaversionofAliceontheLunarReconnaissanceOrbitermission,hasperformedover95,000cycles.Asasafeguard,Alicealsohadafailsafedoorthatcouldbeopenedpermanentlytoretainsomescienceabilityiftheaperturedoorfailedshut.Drivingallthedoorcycleswastheinstrument’ssusceptibilitytocontaminationanddetectorgainsag.Toavoidcontaminationofinstrumentopticsfromspacecraftthrusterbyproducts,theaperturedoorwasclosedduring,andfor30minutesafter,everyspacecraftpropulsivemaneuver.Toavoidcontaminationfromcometarymaterialtheaperturedoorwasalsoclosedforgapsinobservationsofmorethan15minutesthroughmostoftheencounterandevenshortergapswhenthecometwasespeciallyactive.Monthlydoorperformancetestsconfirmedthemechanismexhibitednomeasurementtrendsthatwouldcauseconcernforcontinuedregularuse.
4AliceObservations
4.1OrbitingaCometTherewasapreliminaryencounterphasetimelineoutliningastrawmanplanofRosetta’sorbitsaroundthecomet,butduetotheuniquecometaryenvironmentittooksometimeforthemissionteamstogetusedtooperatingaroundacometandrefinetheplan.Inadditiontothestandardengineeringandenvironmentmodelsneededforinterplanetarytravel,manyunusualfactorsneededtobeaccountedforincluding:orbitingalowgravitybodywithanasymmetricgravityfieldcreatedbythetwolobedcometshape,variableaerodynamicdragduetotemporalandspatialvariabilityofcometaryactivity,navigationwithstartrackersinanenvironmentwithhighvisualdustconfusion,andcontaminationrisks.Theorbitsvariedquitealottoaccountfortheseconstraintsandtoaccommodatetherequestedobservationalconditions,butthefollowingdescribesthetypicalobittypes:Thespacecraftflewlow(<32kmradius)circularorbitswhenthecometwaslessactive.Thisallowedtheinstrumentstoobtainhigh-resolutionsurfaceinformationwhenthecontaminationriskwaslow,andtoincreasesourcefluxfortheinsituinstruments.
![Page 15: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/15.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 15
Ascometactivityincreased,thespacecraftorbitwasexpandedtoseveralhundredkilometerstoamaximumradiusofabout~600kmaroundperihelionasasafetyprecaution,buttoaccommodatescienceneeds,themissiontriedtokeeptheorbitheightaslowassafetywouldallow.Boundorbitswerenotusedwhenorbitingabove~32kmbothduetothedifficultyofbalancingaccelerationfactorswhenorbitingalow-gravitybodyduringperiodsofhighercometactivity.Abovethatheight,thespacecrafttransitionedtojoinedsegmentsofhyperbolicarcsthattypicallyresultedinfullorbitsthatwereroughlycircularshape.Thismaintainedregularobservationconditionsforscienceplanningwhilealsoprovidingthesecurityofasafetrajectorythatwouldavoidcollisionwiththecometifcontrolofthespacecraftwerelost[9].Theorbitstypicallywerealignedwiththeterminatortominimizegasdragonthespacecraftandavoideclipses.TheorbitorientationallowedthesolarpanelstobecontinuouslypointedtotheSunandresultedintheminimumsurfaceareapointinginthecometdirection.However,angleoffsetswereoccasionallyusedtoobtainavarietyofilluminationconditions.Closecometflybys,ascloseas7kmfromthesurface,wereusedforhighsurfaceresolutionmeasurements.Distant“excursions”to1000kminthetaildirectionand1500kmintheSundirectionwereusedtomeasurethelocalmagneticfieldproperties.Finally,thelowgravitycometbodyallowedforsomeunusualorbittypesthatwouldhaverequiredanexorbitantamountoffueltoaccomplishifRosettaorbitedalargerbodyrequiringhigherrelativespeeds.Forinstance,sharpturnswereusedforspecialactivitiesincludingthePhilaeLanderreleasetrajectoryandRosettasweptbackandforthoverasingleareaabovethesurfaceinanefforttolocatethePhilaeLander(seeFigure6).Becauseoftheloworbitalspeedsofmeterspersecond,alargechangeindirectionactuallycouldinvolveinarelativelylowchangeinmomentum,andthus,notasignificantuseoffuel.
![Page 16: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/16.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 16
Figure6.Rosettaorbitdiversityexample[10].ThedarkbluecolordisplaystheapproachbeginningJuly312014andearlyencountercloseorbits.ThelightbluecolordisplaysmoredistantorbitsaroundperihelionthroughAugust92016andthelandersearch.
4.2PointingUncertaintyAnotheruniquechallengethismissionhadtocontendwithwhileplanningobservationswasfairlylargepointinguncertainties.Asisthecaseformostspacemissions,thespacecraftflightdynamicsteamprovidedthescienceteamsmanyorbitalparameterstouseforplanningobservations.However,uniquetothismissionwasthetaskofunderstandingthecraft’srelativelocationandattitudewithrespecttothecometinlightofsignificantnon-gravitationalforces.ThespacecraftinertiallocationandattitudewasknownverywellfromthestartrackerdataandenabledcommunicationwithgroundstationsonEarthandprecisepointingatstarsforinstrumentcalibrations.However,therewereoftenlargeuncertaintiesforthespacecraftpointingrelativetoacometreferencepointsuchasnadir,limb,orsurfacelocationsandthishadasignificantimpactonobservationplanningatseverallevels.Thepointinguncertaintysourcecamefromthecombinationofenvironmentandcometmodeluncertainties,thrusterefficiencyuncertaintiesforupcomingorbitcorrectionmaneuvers,andthequalityofthecomet-relativelocationknowledgeasascertainedfromnavigationimagesofthecomet.Thepointinguncertaintycontinuallychanged,beingbestjustafterthecurrentspacecraftlocationwasdeterminedandupdatedonthespacecraftcomputerand
![Page 17: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/17.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 17
thenitwouldgrowuntilthenextupdateastheuncertaintiescompoundedinthemodels.Theprojectedcomet-relativepointinguncertaintyrangewastypicallybetween0.1°–4.0°formostofthemission,butwhenthespacecrafttraveledveryclosetothecometsurface(under10km)theuncertaintyforecastcouldgrowmuchlargerupto~16°.Inpracticeitwasfoundthatthedifferencebetweenthedesiredandactualpointingcouldoccasionallygrowlargeforshortperiodsoftime,howeverconservativefactorsinthemodelstypicallyresultedinalargeoverestimateforthepointinguncertainty,typicallybyafactorof0.5ormore.Evenifobservationswereplannedusingpointinguncertaintyvaluesofhalftheforecastedlevel,thescaleoftheuncertaintieswasverydifficultforsomeoftheinstrumentteamstoincorporateintheirplanning.Negotiationsforprimeobservationslotsbytheremote-observinginstrumentteamsoftenprioritizedslotswithlowpointinguncertaintyvaluestoreduceobservationsmear.However,Aliceplanningwasabletobemoreflexiblethanthatforotherinstrumentteamsregardingpointingconstraintsandacquiredalotofprimeobservationswithhighpointinguncertaintyperiods.MakinguseoftheseslotswasmadepossiblesincetheAliceFOVwasmuchlargerthanmostoftheotherinstruments(5.53°long)andittookrelativelylongexposures(5-10minutes)makingobservationsofspecificlocationslessimportantthangettinggoodregionalcoverage.Also,severalAliceobservationtypeswereoff-comet,includinginertialor360°GreatCirclesthatwerenotimpactedbythecomet-relativepointinguncertainty.ThismadeAliceobservingmuchlessdependentonthepointinguncertaintyvaluescomparedtotheothersandAlicewasabletoputmanyoftheworsepointinguncertaintyblockstogooduse.
4.3ObservationTypesSpecificpointingcouldbedevelopedoncetheorbittypewasdefinedandthetrajectoryandsub-spacecraftparameterdetailsfrozen,suchasorbitheight,phaseangle,latitude,longitude,andpointinguncertainty.Afternegotiationsforobservationtimewerecompleted,theinstrumentteamsturnedtheirattentiontoimplementingtheplans.Eachinstrumentteamwouldtailorthepointingduringtheirprimeobservationstooptimizesciencereturn.Teamscouldverifyanditeratethepointingproductsusingmissionsimulatortools,thenaftertheyweredeliveredtheywereverifiedandapprovedbytheRosettaScienceGroundSegment(RSGS)groupatESA’sEuropeanSpaceAstronomyCentre(ESAC)inSpainandtheRosettaMissionOperationsCenter(RMOC)groupattheEuropeanSpaceOperationsCentre(ESOC)inGermany.Therewerequitearangeofobservationtypesimplementedbythevariousinstrumentteams,butmostwerevariationsonthese:
• Staringatthesurfacewiththecometrotatingunderneaththespacecraft• Matchingthecomet’srotationratetotrackasurfacelocation• Scanningacrossthesurface• Staringatoneofthecometlimbs• Pointingoffcomet
BelowaredetailsofsomeofthevariantsoftheseobservationtypesthatAliceutilized.ForreferencetheobservationnamesarealsousedinAlicedatanomenclature,whichisdiscussedfurtherattheendofthepaperintheAliceLogbookSection.
![Page 18: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/18.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 18
4.4AliceObservationTypes:GasObservationsAprimaryAlicescienceobjectivewastocharacterizethegassescomingoffthecomettobetterunderstandthesolarsystem’sprimordialconstituentsandenvironment.Thisrequiredmeasuringthedifferentgastypes,theirrelativeabundances,andhowtheyvariedthroughtheevolutionofthecometduringitsorbitaroundtheSun.Todothis,avarietyofobservationtypesweredesignedtoviewthegassesagainstadarkbackground(eitherlookingoffcometorashadowedregiononthecomet)wherethecometsurfacereflectancewouldn’tinterferewiththemeasurements.Thestylesvariedandwererefinedbasedondistancetothecomet,gasabundance,andtheunderstandingofthecometenvironment.VolatileAbundanceCampaign.AprimarystyleofgasobservationusedforAliceandotherinstrumentswasnamedVolatileAbundanceCampaign(VAC),whichwasdesignedtomeasureilluminatedgassesagainstthedeepspacebackground(a“DeepVAC”wasalongexposureversionofsuchpointing).ThiswasastablestaringobservationwheretheAliceslitwouldbepositionedsuchthatitwasapproximatelyhalfonthecometsurfaceforlocationcontextandhalfoffthesunwardlimb,thoughtheexactpositionvariedduetopointingerrorandnegotiationswithotherinstrumentteams.InnerComaRaster.Whenthecometwasmoreactive,InnerComaRasterobservationswouldbeused,whichwouldstareinseverallocationssteppingoffthecometinaradialline,typicallysunward,totrackhowthegasabundancefallsoffwithrespecttodistancefromthecomet.GreatCircle.SinceRosettawasnearthecenterofthecomet’scomathroughouttheencounterperiod,theAliceinstrumenttookfull360°“GreatCircle”observationstomeasurethedistributionofthegassesitwasimmersedinandhowtheychangedthroughouttheorbitaroundtheSun.NightStares.Theseobservationsweredesignedtolookattheilluminatedgasbetweenthespacecraftandthecometsurfaceeitheronthenightsideofthecometoroverlargeshadowedregions,whichhadtheusefuleffectofcuttingouttheskybackground.ComaRide-Alongs.TheAliceteamalsorodealongonsimilarobservationsplannedbyotherinstrumentteamssuchastheOSIRIS-ledVACs(termedDiurnalVACs)thatscannedbackandforthalongthesunlitcometlimblookingforconcentrationsofactivityandtheVIRTIS(VisibleandInfraredImagingSpectrometer)instrumentSnowflakesthatwereacombinationmanyoff-cometstares.StellarOccultations.AlthoughobservingstellaroccultationswasalwayspartoftheobservationconceptforAliceandotherinstrumentstomeasurecomagasesinabsorption,planningthoseprovedtobeunfeasibleduetotheuncertaintiesinthepredictedspacecraftorbitandattitude.However,asUVstarsweremonitoredpassingthroughtheAliceFOV,itwasrealizedthatitwasstillvaluabletoobservestellarappulsesevenifthestardidn’tgettotheabsolutelowestlayersofthecomajustabovethenucleus.TheAliceteamwasabletomodel(withinuncertainties)the
![Page 19: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/19.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 19
tangentialdistancesfromthenucleusofvariousUV-brightO-andB-typestarstotargetthosethatcouldbeobservedthroughthecolumnofgasnearthesunwardlimbofthecomet.Thelargepointinguncertaintiesandfrequentpointingplanchangesmadeplanningtheseobservationsdifficult,butwhensuchobservationsweresuccessful,thesamestarwasobservedagainatalatertimefarawayfromthecometasabaselinemeasurement.Thesetwospectrawerecomparedtomeasurethelevelofattenuationinspecificbandstocharacterizegastypeabundance.Thetechniquewasinitiatedlateinthemissionafterperihelion,soatimehistoryofthesemeasurementsthroughoutthecomet’sactivitycyclecouldnotobtained,butH2OandO2abundancesweremeasuredfromseveralofthe29stellarappulsemeasurementsets[11].
4.5AliceObservationTypes:SurfaceStudiesAsecondaryAlicescienceobjectivewastocharacterizethecometsurfacereflectanceintheUVandsearchforsurfaceicestobetterunderstandthecomet’scompositionandmorphologicalprocesses.Fortheseinvestigationstwotypesofobservationsoftheilluminatedcometsurfacewereplanned.SurfaceCenter.Thisstyleofobservationwouldstareatthesurfaceeitherdirectlynadirorwithadefinedoffsetfromnadirandtakecontinuoushistogramsasthecometrotatedunderneaththespacecraftwithaperiodof12hours24minutes.Ifthecomet’srotationaxiswasnotalignedsothatthescenewouldvarythroughtheobservationperiod,theobservationtypewouldbechangedtoaSurfaceScan.SurfaceScan.Thisstylewouldscanveryslowlyat0.01°/sbackandforthfromthesunwardlimbtotheanti-sunwardlimb(spacecraftY-axis,perpendiculartotheALICEslit)orasfarascouldbescannedwithinanobservationwindowwhenclosetothecomet.SurfaceRide-Alongs.AlicerodealongonanassortmentofotherinstrumentobservationsespeciallyonlongstaresandtheTargetsofOpportunity(ToO),wherespecificinterestingsurfacefeatureswerestaredatandmostinstrumentsrecordeddatatoprovideacomprehensivestudyofthearea.TherewereafairamountofobservationsoptimizedforotherinstrumentsthatAlicedidnottypicallyridealongbecausetheywouldn’tyieldhighqualityAlicedata.Forinstance,observationsthatincludedhighscanratesorshortstaresoflessthan5minutesforfastmappingofthesurfacewouldsmeartoomuchsurfaceareatobeofmuchuseforAliceanalysis.Alicetypicallyused5-10minutehistogramsforsurfaceobservationsand10-20minutehistogramsforgasobservationstobalancemeasurementsignalandspatialresolution.
4.6AliceObservationTypes:CalibrationsItwasveryimportantforseveralRosettainstrumentsincludingAlicetocharacterizetheirperformancewithregularcalibrations.Inadditiontothetypicalinstrumentopticsdegradationandalignmentchanges,eachAliceobservationcontributedtoanon-uniformdetectorgainsageffectthatneededtobetrackedandaccountedfor.ModeratelybrightUVstarswereusedasstablecalibrationsourcesforAlice,howevertheytypicallywerefaroff-cometanditwouldtakealotoftimeto
![Page 20: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/20.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 20
slewtoacalibrationstar’sposition.Sincealltheinstrumentteamspreferredtospendasmuchtimeaspossibleobservingthecomet,calibrationobservationswerecoordinatedtominimizeoff-cometpointingtime.OSIRIS,VIRTIS,andAlicewereabletocombinestellarcalibrationrequirementsreducingthetotalnumberofinstances.TheAliceinstrumentperformedseveraltypesofstellarcalibrationstotrackchangesinperformance:Bi-WeeklyStellarCalibrationswereusedtomeasuretheeffectivearea(instrumentsensitivity)byperiodicallystaringatcalibrationstarsandmeasuringchangesinresponseforthreerepresentativelocationsonthedetector.Bi-MonthlyFlatFieldCalibrationswereconductedasarasterscanalongthelengthoftheslitofacalibrationstartomeasurerelativesensitivitydifferencesacrossthe2Ddetector.Thissetofbi-weeklystellarandbi-monthlyflatfieldmeasurementsallowedfortheeffectiveareachangestobeappliedacrossthefulldetectorprovidingamethodofcorrectingfordetectorgainsagonaperpixelbasis.Bi-MonthlyCrossSlitScanCalibrationswereperformedthatconsistedofrasterscansperpendiculartotheslitofacalibrationstarusingpixellistmeasurementstopreciselydefinetheinstrumentfieldofview.Thiswasimportanttobeabletotrackandaccountfortheinstrumentflexureduetochangesinthermalenvironmentthroughoutthemission.Bi-MonthlyHighVoltage/DiscriminatorCalibrationswereperformedbystaringatacalibrationstarandmakingobservationswithasetofdetectorhighvoltage(HV)levelsanddiscriminatorlevels,settingsthatcanbeadjustedtochangethedetectorsensitivity.Theseinstrumentsettingscouldthenbeoptimizedtomitigategainsageffects.ThestandardoperationalhighvoltageanddiscriminatorvaluewerechangedseveraltimesduringthecourseofthemissionasshowninTable2.Thesechangesaretakenintoaccountinthecalibrateddata,butmaybeofinterestifworkingwiththerawAlicedata.
Table2:NominalAliceHighVoltageandDiscriminatorSettingsfortheRosettaMission
InitialSettings HV-3.8kV,Discriminator0.09V
2006Dec3 HV-3.7kV,Discriminator0.34V2007Feb23 HV-3.8kV,Discriminator0.09V2007Sep13 HV-3.9kV,Discriminator0.09V2014Apr2 HV-4.0kV,Discriminator0.09V
2014May12 HV-4.0kV,Discriminator0.45V2015June25 HV-4.1kV,Discriminator0.45V2016Feb23 HV-4.2kV,Discriminator0.45V
![Page 21: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/21.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 21
Bi-WeeklyDarkCalibrationswerealsoperformedwherehistogramsweretakentomeasureandaccountforthedetectorresponsewiththeaperturedoorclosed.
4.7NCIRandOCIRContextImagesEventothetrainedeye,Alicehistogramscanbedifficulttointerpret,especiallywhenviewingpartiallyshadowedterrainandthevariableconcentrationsandstructuresofgasanddustcomingoffthecomet.Toaidintheinterpretationofhistograms,itwasveryusefulexamineNavigationCamera(NavCam)andOSIRISWide-AngleCamera(WAC)imagestakenaroundthesametimetoprovidecontexttothesceneasshowninFigure7.ThetimingoftheimagesplannedbytheSpacecraftandOSIRISteamswereoftennotwellcorrelatedtoimportantAliceobservations.Soinanotherexampleofcooperationwithinthemissiontoachievethebestsciencepossible,theAliceteamwaspermittedtoplanadditionalNavCamandOSIRISImagesRequests(NCIRsandOCIRs)withtheconstraintthattheimagedatavolumewascoveredbyAliceresourceallocations.TheNavCamwasusedsolelyforAlicecontextimaginguntilMay11th2016,wheredatavolumeconstraintsstartedtosignificantlyincrease.AtthatpointtherewasatransitiontouseOSIRISWACimages,whichcouldbecompressed,savingalargeamountofdatavolumetoberepurposedasadditionalAlicescienceobservations.
Figure7.ExampleofanAlicehistogram(left)of67PandaNavCamcontextimage[12]withanoverlaidAliceFOV(right)acquiredon08/18/2014(2014DOY230).Thecontextimagecanhelpidentificationofscenecharacteristicstocorrelatehistogramfeatures.
4.8HEETMeasurementsAsasecondarysciencepursuit,Alicewasperiodicallyconfiguredtomeasurethehigh-energyelectron,or“HEET”,componentofthespaceenvironment.TheAlicedetectorcouldsensepenetratingelectronsandwouldrecordtheminthedetectorcountratedata.ThiswasaccomplishedatlowdatavolumecostsincethecountrateisincludedintheAlicehousekeepingdatapacket.HEETmeasurementsweremadewiththeAliceaperturedoorclosed,thedetectorhighvoltageon,andatanelevated
![Page 22: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/22.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 22
housekeepingrateof1Hzinanattempttocaptureshort-termelectrondensitychanges.
5MissionPlanningandProductDevelopment
5.1MissionPlanningCoordinationAtfirstglancetheprospectofbalancingtheneedsofthe21Rosettamissioninstrumentsseemsdaunting,especiallywitheachbasedatseparateinstitutionsscatteredacrossEuropeandtheUS,indifferenttimezones,andstaffedbyteamspassionateabouttheiranticipatedscience.Nonetheless,themissionwasaresoundingsuccessanddatawererecordedtosatisfytheAliceinstrumentsciencegoals.Thiswasachievedthroughtirelessoperationsdesign,development,andplanningsupportfromalltheinstrumentteamsandtheESAscienceoperationsteam.Additionally,thefreedomtoself-harmonizescienceplanningwithintheRosettasciencecommunityinsteadofbeingdirectedbymanagementledtoholisticallybalancedsolutions.Anobservationimportancehierarchybetweeninstrumentswasnotalwaysclearasmissionsciencegoalsweren’trequirementsororderedbypriority.However,teamsusuallycametoanagreementontheirownwhenscienceprioritiesweremadebasedondatasetuniquenessandcontinuity.Oftentheteamsmadecompromisestomergeobservationtypesforhighlydesiredperiodssuchasaddingperiodicstaresduringscans,adjustingscanrates,starelocations,etc.Fortunately,thistaskbecamemoremanageableasonlyasubsetofinstrumentteamsactivelyparticipatedinresourcenegotiationsincludingAlice,MIRO(MicrowaveInstrumentfortheRosettaOrbiter),OSIRIS,ROSINA(RosettaOrbiterSpectrometerforIonandNeutralAnalysis),RPC(RosettaPlasmaConsortium),VIRTIS,andsometimesthePhilaeLanderTeam.Theresourcesthattheremaininginstrumentstypicallyrequiredwerelowenoughthattheywereautomaticallygrantedortheywereabletoachievetheirdesiredobservationsbyridingalongonthepointingdesignedbytheotherteams.Therewereexceptionstothetypicalnegotiationprocess,thebiggestbeinghowtobalancethepotentialresourceneedsofthePhilaeLanderandits10instrumentsifandwhenitbecamefunctionalagaininthemonthsafterthelanding.Sometimes,thisledtoresourcesandschedulingtosearchfortheLanderorrecoveraLandersignaltakingpriorityoverotherRosettaspacecraftplans.Thatinturnresultedinlatechangestothetrajectorytooptimizecommunicationandviewopportunities,addedmultiple-caseplanning,droveadditionalpointingconstraints,andrequiredresourcestobereserved.Unfortunately,amongthemanycontactattemptstherewereonlybriefadditionalcontactswithPhilaeroughly7andthen8monthsafterlanding(seeTable1forthedates),thecontactswerenotsufficienttocommandextendedadditionallanderscienceactivities.
5.2Long,Medium,andShortTermPlanningPhasesEachinstrumenthaditsownmasterscienceplanthatdefinedmeasurementgoals,theirrelativeimportance,andobservationmethodstoaccomplishthem.Toachievethesegoalseachteamwouldfirstmakerequestsfortheneededresourcesatthe
![Page 23: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/23.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 23
LongTermPlanning(LTP)phaseincludingspacecraftpointing,datavolume,power,andtelecommandcount.Thiswasdonewitharesourceandrequesttrackingspreadsheettypicallycovering4weeksofoperationsandwassubdividedintoshortblocksoftimedefiningspacecraftactivitiesorblocksavailableforinstrumentteamstorequest.Thistypicallyresultedin3-4hourinstrumentobservationblocksseparatedby30-70minutespacecraftactivityblocksthatinstrumentobservingmayormaynotneedtoavoidduetopropulsionandnon-optimalpointingactivities.Everyobservationblockfortheentiretwo-yearencounterwasreviewedandnegotiatedforbytheinstrumentandspacecraftteams.HarmonizationofplanstookplacewithRSGSliaisonscientistsmoderatingtheprocessfromESA’sESACfacilityinSpainwhilethevariousinstrumentteamsdialedinfromaroundtheglobe.Harmonizingtheobservationrequestsoftentookalotoftimeandcompromises,andoccasionallygotheatedwhendesignscouldn’tachieveeveryone’sneeds.However,itwasatestamenttointernationalcollaborationandcooperationthatmostnegotiationswereattainedsmoothlyandwithenoughtimetoimplement.AfterharmonizationtheliaisonscientistswouldhandofftheplantotheMediumTermPlanning(MTP)counterpartswherecommandingproductswouldbebuilt,refined,andvalidated.MTPperiodsweretypically4weekslong,correspondingtotheLTPplanningspreadsheetperiods.Finallytherewasopportunityfornon-standardoremergencyactivitiesandchangestobeaddedattheShortTermPlanning(STP)phase,typically1-weekduration.
5.3EvolutionofOperationsPlanningDuringthefirst9monthsofencounterthecometaryactivitywaslowandthespacecraftorbitaltrajectoryplanningwasverystable,excludingthevariousPhilaelandingscenarios.Thisallowedforlongdevelopmentprocessdurations,forexampletheLTPphasestarted6monthsbeforetheexecutionoftheplannedactivities,theMTPphasekickedoff2.5monthsbeforeexecution,andtherewereseveralweeksforSTPadjustments.ThisledtoconcurrentplanningofseveralMTPperiods,butplentyoftimeforleisurelyplanning.However,thisluxurywasshort-livedasthecometbecameactiveandtheorbitaltrajectoryneededtobeadjustedonamuchshortertimeframetokeepasafedistancefromthecometandparticularlyactiveareassuchasthecometneckandthesideofthecometpointedtotheSunwherethegasanddustdensitieswerehigher.Planningphaseswerehighlycompressedafterthispoint,butthemissionwasabletomaintaintheabilitytoplanobservationsthatcorrelatedtospecificcometphaseangles,locations,andothercharacteristics,whichresultedinmuchbetterformulateddatasetswhencomparedtoarbitrarypointingscheduling.Theremaining16monthsofthemissionplanningproceededatafranticpacewiththeLTPphasestarting2monthsbeforeexecutionandtheMTPandSTPphasesmergedandkickedoffamonthbeforeexecution.Unfortunately,lastminutechangestopointingattheSTPlevelbyotherinstrumentteamswerenotrareandusuallyrequiredascrambletoaccommodateinthecommandingforAliceandotherinstruments.However,theAliceteamwasappreciativefortheopportunitytomakeSTPlevelchangestothepointingaswelltooptimizesomeobservations,especiallystellarappulses,whicharediscussedinthe“AliceObservationTypes:GasObservations”Section.
![Page 24: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/24.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 24
Thecompressionoftheplanningtimeframeimpactedallfacetsofoperationsfromobservationdesign,resourceharmonization,implementation,developmenttools,productreviewtiming,andproductvalidationtiming.Itrequiredthatprocessesandsystemsbedevelopedthatcouldbeefficient,adaptable,reliable,andmodular.AmongtheAliceteam,awikiwasusedforefficientcommunicationofproductstatusandSubversion(svn)wasusedforproductversiontracking.ModularPython,Perl,andbashscriptswereusedforproductdevelopmentandverificationthatallowedforquickadjustmentsandtestingasmissioninputsandformatschangedandnewcapabilitywasneeded.ESAmissionsimulationmodels(includingESA'sMappingAndPlanningPayloadScience(MAPPS)software[7]),SatelliteToolKit(STK)scenarios,andanAliceEngineeringQualificationUnitwerealsousedforproductvalidation.
6MissionPerspectives
6.1LessonsLearnedSummaryCooperationandjointplanningbetweenteamsleadtobetteroverallscience.ToOs,contextimages,starcalibrations,andothercasesofcorrelatingseveralinstrumentmeasurementsledtoamorecompleteunderstandingofthecometprocessesandobservedscenes.Transparencyintheoperationsplanningforallinstrumentteamshelpedwithunderstandingeachother’sgoalsandhelpedmaketheharmonizationprocessmoreefficient.Thiswasachievedbydocumentingobservingstyles,labelingobservationsinastandardizedway,andcollectingobservationrequestsinoneplaceforside-by-sidereviewandharmonizing.Itisimportanttoautomateplanningandcommandingasmuchaspossibletominimizemanualeffort.Thisleadstomoreefficientplanningandreducesoperationalrisk.Itwasfoundthatrollingoutcapabilityincrementallyanduseofopensourcesoftwarequickenedimplementationofautomationsoftware.ArecommendationforfutureAlice-likeinstrumentswouldbetoupdateflightsoftwaresoitisflexibleenoughtocreateadditionalinstrumentsequencesthatcombinesetsofcommandsusedregularlytoreduceriskincommandloadsandmakeoperationsdevelopmentmoreefficient.Intermsofpersonnelitwasfoundthatitwasworththeresourcestohavesomeonewhoisworkingonoperationsdevelopmentwithintimatefamiliaritythesystemsanditsneedswithsufficienttimetobuildandtestoperationstoolstoimprovetheprocess.Thereisalsostrongvalueinhavingaliaisonbetweenoperationsteamandscienceteamwhocanhelptranslaterequirements,constraints,jargon,etc.betweenthetwoteams.Havingainstrumentflexibleinpointing(madepossiblewithalargeFOVandlongexposuretimes)meanttheAliceinstrumentcouldtakeadvantageofobservation
![Page 25: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/25.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 25
blocksthatwereoflittleusetootherinstruments,givingAlicemoreprimepointingthanitwouldhaveotherwisesecured.Implementinganongoingprocessofassessingoperationalconstraintsandassumptionshelptoidentifyareastooptimize.Forinstance,thegainsagratewasreassessedresultinginadjustmentsinBadDogavoidanceandridealongobservationplanning.Thefreedomtoself-harmonizescienceplanningwithintheRosettasciencecommunityinsteadofusingarbitraryschedulingorsolutionsbeingdirectedbymanagementledtoholisticallybalancedsolutionsandadditionalcollaborations-notjustcompromises.Beingclearwithcommunicationandschedulingdeadlineswasveryimportanttoreduceissuesforaninternationalmissionwithteammembersspanningmanytimezonesandnativelanguages,butrequiringmanyweeklymeetingsforplanningcoordinationandquick-turnaroundresponses.OneareaofcommunicationsthatcouldbeimprovedonRosettawasoccasionallyESAmissionsoftwareusedforproductdevelopmentandmodelingwouldchangewithoutaheadoftimenoticeimpactingongoingdevelopment.Thiswouldrequirechangestointerfaceanddevelopmentsoftwareinaveryshorttimeframe.Bettertransparencyintomissionsoftwarechangesbeforetheyareimplementedwouldhavereducedrushchanges,softwareworkaroundsandrollbacks,andriskofcommanderrors.Havingmission-commonvisualizationandresourcetrackingtoolsareimportanttoprovideasingleframeofreferenceforallteamsfacilitatingcompatiblesolutionstoend-to-endoperationsdevelopmentfromobservationdesignthroughimplementation.Participationinmeetingsisnecessaryforallteamsthatdesiretohaveavoiceindecisionsbeingmade.Revisitingdecisionscanwastealotofpeople’stime.
6.2AliceLogbookForfurtherAliceoperationaleventdetailspleaserefertotheRosettaAliceLogbookthatwillbeintheRosettaAliceArchive.ItcontainsdetailsforAliceevents,majorspacecraftevents,allobservationsbynameandbydate,andotherinformationvaluabletousingandunderstandingAlicedata.
7AcknowledgementsRosettaisanESAmissionwithcontributionsfromitsmemberstatesandNASA.WewouldliketothankthemembersoftheRosettaScienceGroundSegmentandMissionOperationsCenterteamsfortheirexpertanddedicatedhelpinplanningandexecutingtheAliceobservations.WewouldliketothankthededicatedscienceandengineeringstaffatSwRIforalltheircontributionsthroughtheyears.TheAliceteamacknowledgescontinuingsupportfromNASAviaJetPropulsionLaboratorycontract1336850totheSouthwestResearchInstitute.
![Page 26: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/26.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 26
8References[1]S.A.Stern,D.C.Slater,J.Scherrer,J.Stone,M.Versteeg,M.F.A’Hearn,J.L.Bertaux,P.D.Feldman,M.C.Festou,JoelWM.ParkerandO.H.W.Siegmund,“ALICE:THEROSETTAULTRAVIOLETIMAGINGSPECTROGRAPH”,SpaceScienceReviews(2007)128,pp.507–527[2]Siegmund,O.W.H.,Stock,J.,Raffanti,R.,Marsh,D.,andLampton,M.,“UVandX-RaySpectroscopyofAstrophysicalandLaboratoryPlasmas”,Proceedingsfromthe10thInternationalColloquium,Berkeley,CA3–5February1992,inSilver,E.andKahn,S.(eds.),p.383.[3]Siegmund,O.W.H.,Everman,E.,Vallerga,J.,andLampton,M.,“OptoelectronicTechnologiesforRemoteSensingfromSpace”,ProceedingsoftheSPIE,SPIE,Bellingham,Washington,USA,1987Vol.868,p.17.[4]JoelWm.Parker,AndrewJ.Steffl,S.AlanStern.“ROSETTA-ALICETOPLANETARYSCIENCEARCHIVEINTERFACECONTROLDOCUMENT”RosettaPSADocumentNo.8225-EAICD-01,March2016Rev4Chg0[5]Cometon27March2016–NavCam,CopyrightESA/Rosetta/NavCam–CCBY-SAIGO3.0,Id358019,Released01/04/2016,http://www.esa.int/spaceinimages/Images/2016/04/Comet_on_27_March_2016_NavCam[6]Comet’sdustyenvironment,CopyrightESA/Rosetta/MPSforOSIRISTeamMPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA,Id345498,Released13/08/2015,http://www.esa.int/spaceinimages/Images/2015/08/Comet_s_dusty_environment[7]MikeAshman,MaudBarthélémy,LaurenceO'Rourke,MiguelAlmeida,NicolasAltobelli,MarcCostaSitjà,JuanJoséGarcíaBeteta,BernhardGeiger,BjörnGrieger,DavidHeather,RaymondHoofs,MichaelKüppers,PatrickMartin,RichardMoissl,ClaudioMúñozCrego,MiguelPérez-Ayúcar,EduardoSanchezSuarez,MattTaylor,ClaireVallat,“RosettascienceoperationsinsupportofthePhilaemission”,ActaAstronautica,Volume125,August–September2016,Pages41-64[8]JohnNoonan,EricSchindhelm,JoelWm.Parker,AndrewSteffl,MichaelDavis,S.AlanStern,ZuniLevin,SaschaKempf,MihalyHoryani,“AninvestigationintopotentialcausesoftheanomalisticfeatureobservedbytheRosettaAlicespectrographaround67P/Churyumov–Gerasimenko”,ActaAstronauticaVolume125,August–September2016,Pages3-10[9]AndreaAccomazzo,SylvainLodiot,VicenteCompanys,“Rosettamissionoperationsforlanding”,ActaAstronautica,Volume125,August–September2016,Pages30-40
![Page 27: Rosetta Alice Ultraviolet Spectrograph Flight Operations ... · PDF fileRosetta Alice Ultraviolet Spectrograph Flight Operations and Lessons Learned 2 1 The Rosetta Mission and Comet](https://reader033.fdocuments.us/reader033/viewer/2022051718/5a7132687f8b9abb538c9a3b/html5/thumbnails/27.jpg)
RosettaAliceUltravioletSpectrographFlightOperationsandLessonsLearned 27
[10]Rosetta’sjourneyaroundthecomet,CopyrightESA,Released:05/08/2016,http://www.esa.int/spaceinvideos/Videos/2016/08/Rosetta_s_journey_around_the_comet[11]BrianA.Keeney,S.AlanStern,MichaelF.A’Hearn,Jean-LoupBertaux,LoriM.Feaga,PaulD.Feldman,RichardA.Medina,JoelWm.Parker,JonP.Pineau,EricSchindhelm,AndrewJ.Steffl,M.Versteeg,andHaroldA.Weaver,“H2OandO2AbsorptionintheComaofComet67P/Churyumov-GerasimenkoMeasuredbytheAliceFar-UltravioletSpectrographonRosetta”,2017,MonNotRAstronSocstx1426.doi:10.1093/mnras/stx1426[12]Cometon18August2014–NavCam,ROS_CAM1_20140818T200718,CopyrightESA/Rosetta/NavCam–CCBY-SAIGO3.0,horizontallyinvertedtomatchAlicehistogramorientation,https://imagearchives.esac.esa.int/picture.php?/7204/categories/created-monthly-calendar-2014-8-18