Development of Supercam Calibration Target and scientific capabilities of combined and standoff instruments: Raman and LIBS
Abstract
Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía
Full text
DEVELOPMENTOFSUPERCAMCALIBRATIONTARGETANDSCIENTIFICCAPABILITIES OFCOMBINEDANDSTANDOFFINSTRUMENTS:RAMANANDLIBS TESISDOCTORALPRESENTADAPOR D.JoséA.ManriqueMartínez PARALAOBTENCIÓNDELTÍTULODEDOCTORENCIENCIASFÍSICAS DIRIGIDAPOR: FernandoRullPérez GuillermoEduardoLópezReyes TESISFINANCIADAPOR: ESP2013‐48427‐C3‐2‐R ESP2017‐87690‐C3‐1‐R
AKNOWLEDGEMENTS Iwouldliketostartthissectionofacknowledgementsbythankingtheexternalrevisors andthemembersoftheboardthathavehelpedmeimprovingandevaluatingthiswork. ToallofthemIhavenothingbutthedeepestscientificrespect.Thisrespectistobe extendedtothetutorsofthethesis,F.RullandG.LópezReyes,andthemoraltutorJ. Medina,whogavemetheopportunitytoworkinwhatIlikeandgetaPhDintheprocess. Nothinghappensinsciencenowbyindividualwork,andbecauseofthatIwouldliketo thankmycolleaguesfromtheresearchgroup,presentandpast,thathaveinfluenced andtaughtmealot:Jesús,Antonio,Rafa,Álvaroandlastbutnotleast,Marco,thanks foryourelf‐sightforscienceandpapers,ithelpedmealotinthisthesis.Specialthanks toAurelio,forseveralaislelecturesonhowaRamanmeasurementhastobedone,and thehoursofhistimegettingthebestofmysamples.Tomycolleague/tutor,andpartner incrimeineverythingrelatedtospace,Guillermo,thereisnoexpressionofgratitude thatmakesjusticetoyourhelp.Iamlookingforwardtokeepingworkingwithyou.To Pablo,thanksforyourhelpandeverythingI’velearnedfromyou…andmanybeersin severalcontinents,Ihopetokeepworkingtheimpossiblewithyouinthefuture. ThankstoThomasandAndresforyourhardworkthatturnedintogreatscience,best wishesforyourfuture.ThankstoINTAandJose,Andoni,Alice…youwereofgreathelp withtheSCCT,itmighthadbeenimpossibletodoitwithoutyourhelp.Also,SCCT couldn’tbearealitywithoutthehelpofAVS,andthebestengineerIhaveeverseen, Charlton. Finalmente,enespañol,enunaclavemáspersonal,debodargraciasalasmujeresde mivida:Caro,mamáyVir.Amimadreyhermanaquemedemostraronconsucariño queelinfinitonoesunaabstracciónmatemática.Graciasporcuidardetodocuandono estuvedondedebí.AmimujerCarolina,solopuedodarlelasgraciasporsuapoyo,por supaciencia,yperdónporlasmuchashorasqueheestadolejosdecasa.Esperodarte elfuturoquetemerecesamilado.Teamo. Dejounaúltimanotaparamialfaymisomegas.Graciasamipadreporayudarmea convertir,trasdemasiadosaños(loadmito),unosjuegosylacuriosidaddeunniñoen unatesisdoctoral.Medistelasbasesparallegarmáslejosdeloquenuncaimaginé.A mishijos,Isabela,quehassidounadistracciónmaravillosaestosúltimostresaños,ymi primerpensamientocadadía,yalqueestáporvenirydistraerme,esperoserpara vosotrosalmenosunafraccióndeloquemipadrefueparamí. Siaalguienmedejé...fuesinquerer,simelohaderecordaresperomesepaperdonar
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vii Prologue ThepresentmanuscriptdescribestheworksthatIhavedoneaspartoftheparticipation oftheUniversityofValladolidinMars2020mission,aspartoftheinstrumentSuperCam. Thisisanatypicalthesiswork,astherearetwowelldifferentiatedaspectsinit:Onepart morerelatedtothedevelopmentofhardwareforspaceuse,alwayswithinthecontext ofthesciencetobedonewiththathardware;andanotherpartrelatedtothescientific supporttoinstrumentationasSuperCam,orotherdevelopmentsdonebytheResearch groupwhichIbelongto. IsthisactivityofthisresearchgroupthatIhavetriedtoremarkinthiswork,toputin valuethepotentialofagroupthat,despiteitssmallsize,isinvolved(asNov2019)in threemissionsforMarsexplorationandfuturedevelopmentsofinstrumentation.This groupcomposedbyresearchersfromdifferentbackgrounds,coveringfromchemistry tosoftwareengineering,andofcoursephysics,hasparticipatedinverydifferentareas ofresearchandtechnologydevelopment.Thatcharacteristicisreflectedinthisthesis andthewidevarietyofworksthatIhavedoneinthelastfiveyears. Ithasbeenmywork,andstillis,tobetheProjectManageroftheSuperCamCalibration Target.Thistaskhasbeendonetoawiderextentofpureprojectmanagement,reason whyitwasassignedtoaprofilelikemine,farfromengineeringmanagement,although with some experience on it. With help from other partners for some tasks, the responsibilityofthetechnicalaspectsoftheprojecthasfallen onthebacksoftwo researcherofthisgroup,mytutorGuillermoLopez,andmyself.Thisworkhasbeendone inparalleltomorescientificrelatedactivities,astheScienceLeadoftheCalibration targetismyothertutor,Prof.FernandoRull,andwedoparticipateinbothendsofthe project. Thepositioncovered,beingintheengineeringsideoneday,andinthesciencesidethe other,hasbeenajoyformeandIvaluetheexperienceacquiredinthisprocess. Saidthis,Ihaveseparatedthecontentofthethesisinthreebigsections,afirstsection asintroduction,inwhich,despiteoftheorybackgroundthatevaluatingexpertsknow deeply, I tried to summarize the different developments that have positioned our researchgroupaspioneerofstandoffRamanspectroscopy.DuringthestateoftheartI alsoremarktheinterestofanewbranchinspectroscopy,whichisthedatafusion.Not onlyweareintostandoffinstrumentation,butthisinstrumentation,asSuperCam,can useseveraltechniques.Thelineofworkinwhichthescienceoutcomeofanexperiment, takingintoaccountallthetechniques,isbetterthanthesumoftheindividualanalyses
xiv demonstratethatthetechnologywillbeabletoperformthe tasksforwhatitwasdesignedintherequiredenvironments. ‐ Chapter3:CombinedandstandoffRaman‐LIBSspectroscopy:some experiments. This section covers the different experiments performed as part of this thesis that is intended to support the SuperCammissionobjectives,usingthetechnologyortechniquesof theSuperCaminstrument. o 3.2Anewinterestingapplicationofamaterialispresented. Worksdoneinourresearchgrouparesummarizedtopresent an interesting candidate for Raman Standard Reference Materialthatwouldallowtocalibrateinintensityawiderange instrument, survive to pulsed laser and environmental conditionsofPlanetaryExploration. o 3.3PresentsexamplesonhowaStandoffsystemdetects biomarkers, and the difficulties behind this detection using standoff instruments. In vivo detection of interesting biomarkersisachieved. o 3.4PresentsaworkdoneonhowstandoffRamancouldassess thegeologicalcontextofanarea.Thisworkhasdirect implications in the selection a site for sample caching, and gives an example of the operational advantages of these developmentsinspaceexploration. o 3.5presentsworksdoneinthechemometriccalculationsdone usingRamanandLIBS:fromstandardunivariateanalysesin binarymixtures,multivariateanalysesonbinaryandternary mixtures, and also data fusion with LIBS. Each individual analysis sets the different capabilities of each technique separately,andthegreatpotentialoffusedanalysis.Thiswork hassetapathforimmediatefutureworks. ‐ Chapter4:Conclusions.Thissectionsummarizestheresultsofthis thesis,andrelatesthemtotheobjectivesofthethesis,aswellashowthis workswillbecontinuedinthefollowingyears,asacomplementtothe participationintheExoMarsandMars2020operations.
1 1 Introductionandcontext
2 1.1 Introducción El presente texto refleja los trabajos realizados en desarrollodesistemasremotos basadosenespectroscopíaRaman,ycomoestostrabajosnoshanllevadoaparticipar enuninstrumentocomoSuperCam,yatenerlaresponsabilidaddedesarrollarunode suscomponentes. Eldesarrollodelamuestradecalibración,desdeelconceptohastasu fabricacióny entrega,hasidoeltrabajomásexigenteentiempoydedicacióndelapresentetesis. Representaademásunobjetivocumplidodealtarelevancia,alsignificareliniciodela contribución española en SuperCam, y la entrega de material desarrollado desde ValladolidyqueformarápartedelRoverMars2020. He querido abordar también el tipo de trabajos que pueden realizarse mediante instrumentacióndeestetipo.Abarcandoinstrumentaciónremota,einstrumentación combinada,abordaremosunaseriedeexperimentosquesirvendecienciadesoportey ejemplodelascapacidadesqueSuperCampuedetenerunavezestéoperativoenla superficiedeMarte Objetivosdelatesis Enlapresentetesissehanqueridofijarlossiguientesobjetivos: 1‐ SentarlasbasesdetrásdeldiseñodesistemasRaman‐LIBSremotosydesarrollar unsistemadelaboratorioquesirvadesoportecientíficoparaSuperCam. 2‐ Desarrollodeunsistemadecalibraciónparauninstrumentomultianalíticocomo SuperCam. Demostrar que el diseño cumple con las especificaciones, tanto científicas como técnicas. Fabricar un modelo de vuelo que se aceptado por JPL/NASA. Esto constituye la parte española de responsabilidad en el instrumentoyquesirvedeentradaalaparticipaciónenoperaciones. 3‐ DemostrarqueenelcontextodelosobjetivosdelamisiónMars2020 los desarrolloscomoSuperCamsonunaayudadealtointerésenlaconsecuciónde losobjetivosdemisión. 4‐ Proporcionarresultadosydesarrollosdealgoritmosdeanálisisquepuedanser empleadoscondatosobtenidosporSuperCam. “… si alguien tiene pleno conocimiento de que la “entropía de un sistema aislado aumenta constantemente”, no sólo buscará una estufa para calentarse —resultado muy magro para veinte años de estudio— sino que podrá resolver una enorme cantidad de problemas, desde el funcionamiento de un motor hasta la evolución del Universo. Ernesto Sábato, El uno y el Universo.
3 Objetivo1:Enprimerlugarsehaqueridorealizarundesarrolloteóricoorientadoa instrumentoscombinadosRaman‐LIBS,yainstrumentaciónRamanremota.Estaclase dedesarrollosganaránprotagonismoenelfuturo,ysehanqueridocondensarenun textolasleccionesderelevanciaobtenidasennuestrosdesarrollos. Almismotiempo,elgrupodeinvestigaciónERICAhadedicadomuchotiempoyesfuerzo aldesarrolloyusodesistemasRamanremotos.Estetrabajoenelqueestegrupoque hasidopionero,alserunodelosprimerosgruposenelmundodesarrollandoestos conceptos,nosehavistoreflejadoadecuadamenteenpublicaciones,obteniendopoca visibilidad. En la introducción del presente trabajo se ha pretendido hacer una recopilacióndelosdesarrollosrealizadosporestegrupodeinvestigación,asícomolos trabajosrealizadosconestosdesarrollos. Estosdesarrolloshanafianzadolaposicióndeliderazgodeestegrupoenlaaplicación de técnicas espectroscópicas a la exploración planetaria. Fruto de este liderazgo, a octubrede2019,elgrupoylaUniversidaddeValladolidformanpartedetresmisiones deexploracióndelsistemasolar,cumpliendodiferentesroles.Desdelaparticipaciónde liderazgoenelinstrumentoRLSdeExomars,delquelostutoresdeestatesissonIPy responsablecientíficodeoperación,laresponsabilidadcomoequipodecienciaenla misiónMMX,contandoconF.RullcomoCo‐IyG.Lópezcomocolaborador,oeltrabajo másdirectamenterelacionadoconlapresentetesis:elliderazgotécnicoycientíficoen unodelossubsistemasdelinstrumentoSuperCam. Objetivo 2: Porlacantidaddetrabajoyesfuerzosqueimplicaba,asícomopor su relevancia institucional y científica, el objetivo fundamental de esta tesis ha sido precisamentelorelacionadoconelúltimoinstrumentomencionado.Siendoelobjetivo prioritario proporcionar soporte científico al instrumento SuperCam, y sobre todo proveeruncomponentequepermitasucorrectacalibraciónenMarte,laSuperCam CalibrationTarget(SCCT).Esteinstrumento,queespartedelacargaútildelamisión Mars2020,consisteenuninstrumentoremotoqueutilizamúltiplestécnicasanalíticas, incluyendoRamanyLIBS,razónporlaquelaexperienciayconocimientosdeestegrupo deinvestigaciónsondealtarelevancia. Objetivos3y4:UnadelascaracterísticasdelgrupodeinvestigaciónERICAesladeser ungrupomultidisciplinarenelquenosolamentesecuentaconlapartededesarrollo instrumental, sino también con trabajo orientado al retorno científico de la instrumentación que se desarrolla. En esta línea de trabajo, en la presente tesis se muestranalgunosresultadosdelostrabajoscientíficosrealizadosenlalíneadelestudio in situdeMarte,enconcretolacienciadesoporteaSuperCamyengeneral a los desarrollos remotos Raman‐LIBS. Así pues se presentarán algunosejemplosde investigacionesrelacionadasconladeteccióndebiomarcadoresmedianteestatécnica,
4 aunquelasprevisionesdeunadeteccióndirectaenlasuperficiedeMarteseanbajas.Se continúatambiénconlostrabajosorientadosaunamejoridentificación y caracterización mineralógica que permite, por ejemplo, identificar y cuantificar mediante espectroscopía Raman procesos de alteración geológica directamente relacionadosconlaaparicióndevida.Olacaracterizacióngeoquímicausandodatos Raman y técnicas de análisis novedosas, o una combinación de varias técnicas con Raman para potenciar el retorno analítico y que permita una comprensión más pormenorizadadelacomposicióndeáreasdeinterésastrobiológico,tantoparaMarte comoparafuturasmisionesquepuedanvisitarotroscuerposplanetariosdelSistema Solar. Ramanremoto LaespectroscopíaRamanhademostradoyaserunatécnicadereferenciaenciencias planetarias.Pordiversosmotivos,peroprincipalmenteporsupolivalencia,siendocapaz dedetectarmúltiplescompuestosconlamismatécnica,oporsuversatilidad,alno necesitarunapreparaciónpreviaespecialdelamuestra,estatécnicasehaidoganando adeptosenlacomunidaddeastrobiólogíaycosmogeoquímica. F IGURE 1‐1 D IFFERENTCOMPOUNDSTHATCANBEDETECTEDBY R AMANSPECTROSCOPY Unadesusventajasparticularesesestarbasadaenunainteracciónmeramenteóptica con la muestra a analizar. Al no requerir contacto ni interacción con la muestra de ningúnotrotipo,permite,simplificandomucho,poderanalizarcualquiermuestracon laúnicacondicióndequeestáenelcampovisualdelinstrumento. Sedesarrollaráenulterioressecciones,peroelRamanremotoesunarealidad,todavez queseseacapazdelidiarconunacantidaddefotonesextremadamentebaja.
5 FIGURE1‐2FLUJOLUMÍNICOENFUNCIÓNDELADISTANCIA YesqueelefectoRaman,queesunefectobastantedébildeporsí,damuypocos fotonescuandoalejamosdelamuestra,requiriendológicamenteounamejoraenlos mediosdedetección,olageneracióndemásfotonesfrutodeladispersiónRaman. Comoserverádespués,ambasaproximacionessetomanalahorade desarrollar instrumentosremotos.Porunladoelusodeláserespulsadospermiteconcentraren lapsosmuycortosdetiempounagrancantidaddeenergíayproducirunagrancantidad de fotones Ramanprovenientesdelamuestra.Porotrolado,laaparicióndelos intensificadores en el mundo de los detectores ha hecho que técnicamente no sea infrecuenteencontrarenelmercadocámarasCCDcapacesdellegarallímitedelsingle photon,esdecir,llegaradetectarunúnicofotónprovenientedelamuestra. Dejando aparte el reto técnico y la mejor manera de salvarlo, es conveniente preguntarseporlasposiblesaplicacionesdeestetipodedesarrollos. LainstrumentaciónRamanremotahasidounpartededesarrollos instrumentales llevadosacabopordiversosgruposdeinvestigaciónyaplicadaadiferentescampoy problemas.Principalmenteesútilcuandoelcontactoconlamuestraescomplicadoo noesunaopción.Ejemplosdeestecasopuedeserelanálisisde materiales muy calientescomocoladasdelava,omaterialesradiactivos,comoloscompuestosdeuranio que se forman en los elementos de combustible de centrales nucleares. Incluso se planteadesdealgunasindustriascomounatécnicadeutilidadparaanalizarexplosivos permitiendounadistanciadeseguridadaloperador.Peroesquetambiénpuedeser aplicadoparaaccederazonasmásampliasconunasimplicidaddeoperaciones. Un instrumento Raman remoto establecido en un punto podría realizar mapeos alrededoryproveerunmapadeunazonamuyamplia,porejemplounentornode terrenode10metrosderadio.Dequereradquiriresainformaciónconelementosde contactorequeriríadesplazamientosdeequipoypersonal,mientrasqueestetipode
6 desarrollos solo requerirían el movimiento de algunos elementosópticos.Esta capacidadesdegraninterésensusaplicacionesparaexploraciónplanetaria.Así,un hipotéticoinstrumentocapazdeRamanRemotopodríareconocertodoelentornode unaterrizadorsinnecesidaddedesplazamiento.Oenelcasodetenercapacidadde desplazamientopodríaproveerinformacióndeutilidadenoperacionesmáscomplejas comosonlasdemovimiento. PortodosestosmotivoslaespectroscopíaRamanremotahaidoganandointerésenla comunidad científica. Pero es que no solo acaba su interés en lo referente a las capacidadespropiasdelaespectroscopíaRaman,sinotambiénensusposiblessinergias conotrastécnicas. EsteeselcasodelaespectroscopíaLIBS.Estatécnicaespectroscópicautilizaunpulso deluzconcentradoenunapequeñaáreadelamuestraparainducirunplasma,yanalizar despuéslaluzprovenientedeesteplasmaparaidentificarlacomposiciónelementalde lamisma.Desdeelpuntodevistainstrumentalsoloalgunaspequeñasdiferenciasla separan de la espectroscopía Raman a distancia, lo que hace queconunamínima complicaciónañadida,eldesarrollodeinstrumentoscombinadosseafactible.Algode altointeréssisetieneencuentaqueambastécnicasdaninformaciónmuydiferente,y complementaria,delamuestra. SuperCam SuperCamesunejemplodeestosinstrumentoscombinadoscomentadospreviamente. Elinstrumentosedescribiráenlasección2delpresentetrabajo,peroamodoresumen basta con comentar que es un instrumento derivado de otro que llevadesde2012 operandoyobteniendodatosdelasuperficiedeMarte:ChemCam. Éste es un instrumentoLIBSadistancia,enelqueseaprovechalaaltacantidaddeluzproveniente delaablaciónlaserdelamuestraparahacerunanálisisdelaslíneasdeemisióndel plasmagenerado.Graciasaesteinstrumentosehandetectadofases minerales en Marteconteniendocalcioyazufre,muyseguramenteyesooalgunaformadeshidratada delmismo,formandovenasentreotrosmateriales.Estaclasede evidencias son testimoniodeunaposibleactividadhidrotermalpasadayportantosondealtointerés astrobiológico. ChemCamformapartedelMarsScienceLaboratory,elroverCuriosity,yestamisiónha servido de predecesora para otra misión con una alta carga de herencia, la misión Mars2020. El éxito alcanzado por el instrumento ChemCam animó a su equipo de desarrollo a realizar un instrumento que, basándose en parte delosdesarrollos realizadosparaChemCam,pudieseincorporarunamayorcapacidadanalítica,ysiempre conlacapacidaddehacerestosanálisisadistancia.EsasícomonaceSuperCam,quea latécnicaLIBSylaobtencióndeimágenesdealtoaumentoenblancoynegro,ambas
7 enChemCam,ahorasumanossololasimágenescolor,sinoademáslacapacidadde obtenerespectrosRaman,fluorescencia,espectrosdereflectanciaVISIRosonidosdela superficiedeMarte. EsteinstrumentoquefueseleccionadoporNASAen2014paraformarpartedelamisión gemeladeMSLqueselanzaríaen2020,hacontadodesdesufasedeconceptoconla participacióndeEspañaymásconcretamentedelaUniversidaddeValladolid. Contextodeexploraciónplanetaria Enelmomentodelaredaccióndeestatesishaycuatromisionespreparándoseparasu lanzamiento en2020, y otras dos misiones, planeadaspara el futuroinmediato, sin contarconlasmisionesimplicadasenelretornodemuestras. Las cuatro misiones planeadas para su lanzamiento en 2020 pertenecen a cuatro agenciasespacialesdiferentes.ExomarsdeESAyROSCOSMOS,Mars2020deNASAy HX‐1delaagenciaespacialChina,CNSA,planeanponerunroverenlasuperficiede Marte, mientras que esta última misión y HOPE de la agencia espacial de Emiratos Árabes,planeanponerorbitadoresenlaórbitadelplanetarojo.Atrásquedanlosaños enquelaexploracióndelsistemasolareraunabatallaentredosagencias,elaño2020 significaráunhitoalmandartresmisionesalasuperficiedeMarteydosorbitadores, conlaimplicacióndecincoagenciasespacialesdiferentes.Estasmisionessesumarána misionespasadastantodeESA,NASAyROSCOSMOS,unamisióndelaagenciaespacial India.EnelfuturounanuevamisióndelaagenciajaponesaJAXAtrataráderetornar muestrasdesdePhobos,satélitedeMarte.Unmomentocomoelactualnuncaantesse habíadadoenlaexploracióndelSistemaSolar. LaexploraciónrobóticadeMartecomienzaenladécadadelossesenta,yenaquellos añoslacarreraespacialestabacopadaporNASAylaUniónSoviética.Estosúltimosno contabanentoncesconunaagenciaespacialpropiamentedichaquecentralizasesus esfuerzos,enlugardeellosuprogramadeexploraciónestabadescentralizado,yfueasí hastaeldesmembramientodelaURSS. FuelaURSSquiencomenzóconlosesfuerzosporexplorarMartemediantesondas,ylo hizoconsupocoexitosoprogramaMarsentrelosaños1960y1973.Deesteprograma ysuscincointentosdeponerunaterrizadorenMartesolouno,elMars3,alcanzóel gradodeéxitoparcialalpoderseposardemaneracontroladaenMarteyrealizarun envíoparcialdeunaimagendesusuperficie.Losorbitadoresencambiotuvieronalgo másdesuerteyconsiguieroninsertarlaMars2yMars3enlaórbitamarciana.Éxitoque serepetiríaconsusmisionesMars6yMars7,queademásdeunfallidoaterrizador llevabanunorbitadorpararealizarunsobrevueloporMarte.
8 DosfallidasmisionesmásalossatélitesdeMarte,Phobos1yPhobos2,afinalesdelos 80, una misión que explotó en el lanzamiento, Mars96, y una misión que no pudo abandonarlaórbitaterrestrebaja,Phobos‐Grunt,completaronlosesfuerzosrusospor laexploracióndeMarte,yfueronsusúltimasmisionesaMartehasta la posterior implicacióndeROSCOSMOSenExomars. NASAencambiotuvomássuerteycompletaronunexitosoprogramadeexploraciónen lasdécadasdelos60ylos70.ElprogramaMarinerrealizósobrevuelosdeMarteconla Mariner4(1965)yconsiguiólaprimerainsercióndeunorbitadorenlaórbitadeMarte con el Mariner 9. Gracias al programa Mariner se pudo comprenderalfinquelos cambiosenelalbedodeMartesedebíanatormentasdepolvoglobales. PeroelgranéxitodeNASAenladécadadelos70fueelprogramaViking.Viking1y2 fueronlasprimerasmisionescapacesdeoperarunlaboratorioanalíticoautomatizado enlasuperficiedeMarte.Estelaboratoriocontabacondiferentesinstrumentospara realizarlaprimeracaracterizacióndelentornomarciano: ‐ Sensoresclimáticos ‐ Cámaraacolor ‐ Sismómetro ‐ SistemadefluorescenciaderayosX ‐ Cromatógrafodegases ‐ Experimentobiológico. EsteúltimoexperimentoesdegranimportanciadadalafaltadedatossobreMarteysu superficieenaquellaépoca.Antesdeconocerlasdurascondicionesalasqueorgánicos osmicroorganismodeberíanenfrentarseenlasuperficiedeMarte(Klein,1978). Solounodelostresexperimentosdiounpositivo,elLabeledRelease(Ballou,1978).Este resultadosehaatribuidoalaposiblepresenciadeorgánicosenelregolitomarcianoque pudieron pasar desapercibidos para el cromatógrafo, debido a laaccióndelos percloratosquelosdegradaríandurante el calentamientoprevioalamedida.Estos compuestos son unos poderos oxidantes de los que futuras misiones detectaron cantidadesimportantesenMarte. LosresultadosdelasVikingfuerondegranrelevanciaymantuvieronelinteréssobre Marte,aunquenosemandaríaotramisiónconunaterrizadorhastafinalesdelosaños 90conPathfinder. Entre medias, numerosos orbitadores fueron lanzados a Marte, consiguiendo datos morfológicosdelplaneta,asícomodatosespectroscópicosdeinfrarrojo.
9 Focalizandolaatenciónenlosaterrizadoresylastécnicasquedesplegaron,Pathfinder incluyóunpequeñorover,Sojourner,concapacidaddehacerdiversosexperimentos. Entre la base Pathfinder y Sojourner se desplegaron cámaras de imagen, sensores climatológicos, experimentos de adherencia de materiales, magnetómetros, anemómetroyuninstrumentoAPXS. APXS, acrónimo de Alpha Proton X‐ray Spectrometer, analiza la composición de la muestramedianteelbombardeoconradiación,provenientedeunafuenteradiactiva,y analizandodespuéslaspartículasalfadispersadas,asícomolosRayosXproducidospor estaradiaciónenlamuestra.Esunatécnicaactivaquepermitióhacermedicionesdela composiciónelementaldediversasmuestrasalrededordePathfinder. Después de Pathfinder dos misiones muy exitosas de NASA llevaron diversos experimentosendosroverindependientes,losMER,queestavezsindependerdeuna baseenlasuperficiedeMartepudieronexplorargrandesextensionesdeesteplaneta. SpirityOpportunityfueronlanzadosen2003ydesplegaronenlasuperficiedeMartela siguienteinstrumentación: ‐ Cámaraspanorámicas,Pancam,ycámarasdenavegación,Navcam. ‐ Espectrómetrodeinfrarrojos,Mini‐TES ‐ EspectrómetroMossbauer ‐ InstrumentoAPXS ‐ Microscopio ‐ Experimentomagnéticoparaelpolvo ‐ Herramientadeabrasión Lacargaútilenestasdosmisionesibamuyorientadaalacaracterizacióngeoquímicade lasuperficiedeMarte.Ningúninstrumentoabordoestabapreparadoparaelanálisisde orgánicos,aligualquepasabaconPathfinderySojourner.Además,dentrodelosanálisis decaráctergeoquímico,lastécnicasactivaselegidas estaban limitadas.APXSqueda limitadaaladeteccióndeelementosmáspesados,yMossbaueresunatécnicamuy orientadaamineralesdehierro. EsconlallegadadelMarsScienceLaboratorycuandolaexploracióndeMartedaun saltoencomplejidadtécnicayanalítica,haciendoqueestamisiónseacomparable,por suambición,alasprimerasmisionesViking. ElroverCuriositymarcaunagrandiferenciaconsuspredecesores,fundamentalmente porelsaltotécnico,alserunroveralimentadoporbateríasde radioisótopos (las anterioressevieronlimitadasporlospanelessolares),eltamañoycomplejidaddelos instrumentospuedoaumentar.
16 de longitud de onda a desplazamiento Raman, nos lleva a otra conclusión sobre la resoluciónalcanzable:cuantomenorsealalongituddeondadellaser,másestrecho (monocromático) tendrá que ser éste para mantener la resoluciónentérminosde desplazamientoRaman. Aefectosdeestatesis,esimportanteremarcarlagrandiferenciaentrelasanchuras espectralesdelosláserescontinuostípicos,yladelosláseres pulsados (los no semillados). Estosdosresultados,encombinaciónconelintroducidoenlasecciónanteriorhacen que no exista una respuesta válida en cuanto a qué laser es mejor para usarlo en espectroscopía Raman. Dejando la selección de la longitud de ondadelmismoen funcióndelaaplicaciónconcreta, y en general, sereduciráauncompromisoentre límitesdedetecciónyresolución. 1.2.1.3 Lafluorescencia Enlafigura1.4(B),eneldiagramadeniveles,habríasidomáscorrectoincluirotros nivelesrelativosalastransicioneselectrónicas.Estastransicioneselectrónicastambién puedenserexcitadasporellaserconqueseiluminalamuestra,conloquesurgeotro efectoatenerencuentaenlainteraccióndenuestraradiaciónincidenteconlamuestra. La fluorescencia se produce cuando niveles vibracionales realesdelamuestrason excitados. Estos niveles de energía, a diferencia de lo que ocurreconlosniveles energéticosasociadosconelefectoRaman,sonnivelesenergéticosreales,yportanto tienen asociado un tiempo de permanencia del sistema en ese estado antes de su decaimientoalestado fundamental, y la emisión de un fotón. En contraposición, el efecto Raman se produce de manera instantánea ya que los niveles energéticos asociadossonvirtuales,yportantonoconllevantiempodepermanencia. FIGURE 1‐5DISTRIBUCIÓN ESPECTRAL DE LA FLUORESCENCIA Y LOS DIFERENTES RANGOS DE MEDIDA DEPENDIENDODELLASERUSADOPARAESPECTROSCOPÍARAMAN(AZOMATERIALS).
17 Encuantoalanaturalezaespectraldeesafluorescencia,esunfenómenoqueocurre fundamentalmente en el visible, y aunque para algunos compuestos tiene una naturalezamásomenosdiscreta(Venkateswaran,1935),engeneralesteefectotiene una distribución continua a lo largo de la zona de luz visible del espectro electromagnético. Lafluorescenciaesunproblemaserioalahoradecaracterizar algunas muestras medianteespectroscopíaRaman,alserunefectoquecompiteconelRamanypuede sermásintensoqueéste,tapándolo. Sienelapartadoanterior1.2.1.2hablábamosdenoteneruncandidatoclaroparala mejorfuentedeexcitaciónenuninstrumentoRaman,ahoraladecisiónsecomplicaalgo más.Lafluorescenciasesitúajustoentremediasdelosdosextremosqueantes se evaluaban,entremediasdelosinstrumentosinfrarrojos,congranresoluciónperopeor límitededetección,ylosUVconmejorlímitededetecciónperopeorresolución. UninstrumentoRamanUVpuedenoverseafectadoporlafluorescenciaalestarelrango de medida fuera de la zona de emisión de este último efecto, mientras que en un instrumentoinfrarrojolaenergíadelaradiaciónincidentenoessuficienteparaexcitar losnivelesvibracionalesqueoriginanlafluorescencia.Noobstante,entremedias,y aunque la fluorescencia pueda jugar en contra de láseres en el rango visible, sus particularidadeseneldominiotemporalhacenqueciertosdesarrollostecnológicosnos permitaneliminarla. AlprincipiodeesteapartadohablábamosdelainmediatezdelefectoRamancontra ciertoretrasoenlaemisióndefluorescenciadesdequellegalaondaincidenteala muestra.Estetiempodepermanenciadenuevodependedeltipodefluorescencia,y puede variar entre unos pocos nanosegundos y los microsegundos.Estadiferencia introduceunanuevavariantedelaespectroscopíaRamanqueesdeinterésparala presentetesis:laEspectroscopíaRamanResueltaenTiempo,oTRRS,porsussiglasen inglés. EnlaTRRSsepuedeutilizarunpulsolaserdeunospocosnanosegundos,yundetector concapacidaddegating,luegoseexplicará,paratomarpulsosmuycortosdeluz,de maneraquepodemosajustarlaadquisicióndeluzennuestrodetectoralmomentoen queseproducelaemisiónRamanperoaúnnohaempezadolafluorescencia. 1.2.1.4 DescripcióndeuninstrumentoRamanporbloques. Comoehadiscutidopreviamente,paradesarrollaruninstrumentoRamanloprimeroes contar con una fuente de luz coherente, es decir, un laser. Láseres hay muchos, pudiendo ser pulsados, continuos, de gas, de estado sólido… cada láser tiene sus particularidades,ycadalasernospermitiráhacerespectroscopíaRamandeunamanera
18 diferente.Estelaserhadeserfocalizadoodirigidohacialamuestraporalgúnsistema ópticoasociado. Despuésdehaberexcitadolamuestraconestelaser,yhabergeneradoladispersión Raman,esnecesariodiscriminarlaluzprovenientedeladispersiónRayleigh,carentede informaciónestructural,delaprovenientededispersiónRaman.Paraelloesnecesario colectarlaluzprovenientedelamuestramediantealgúnsistemaópticodecolección,y despuéssepararmediantefiltrosinterferométricos(notchoEdge)ladispersiónRayleigh delaRaman. EnmuchosdelossistemasRamanmodernoslasópticasdefocalizacióndellaseryde coleccióndelaluzdelamuestrayfiltrado,estánintegradasenunúnicosistemallamado cabezalRaman. Finalmente la luz, debidamente recolectada y filtrada, debe pasar por un monocromadorparasepararespacialmentelaluzenfuncióndesulongituddeonda,y serdetectadaporalgúnelementofotosensible. Todosycadaunodeloselementosarribadescritossonelementosgenerales,ycadauno de esos elementos puede ser escalado y adaptado a diferentes aplicaciones y desarrollos.EstohacedelosinstrumentosRamaninstrumentosmodulares,conuna granadaptabilidadalasnecesidadesdlproyecto.Enlasección1.2.3veremoscomoesta modularidad se aprovecha para adecuarse a las características concretas de un instrumentoremoto. FIGURE1‐6BLOCKSOFATYPICALRAMANINSTRUMENT
19 EspectroscopíaLIBS Existenvariastécnicasquepuedenserempleadasparaproporcionarlacomposición elementaldeunamuestra,comolafluorescenciadeRayosXolaespectroscopíade masas,LIBSmereceserpuestaenunlugarespecialentreestastécnicas. LIBS,acrónimodeLaserInducedBreakdownSpectroscopy,esunatécnicaanalíticaque, virtualmente,tienecapacidaddedetectarcualquierelementodelatablaperiódica,en cualquier estado de agregación, y hacerlo además con una preparación nula de la muestrayconunarelativasimplicidadinstrumental. Elestudiodelosespectrosdeemisióndeplasmasesdegraninterésenlacomunidad científica,ysonnumerososlosestudiosquesehacensobreplasmasinducidosdemuy diversasmaneras.LIBSesuncasoparticulardeestosestudios,inicialmentepropuesto enladécadadelosaños60(Schurig,2006),yconundesarrolloparalelo,pormotivos evidentes,aldesarrollodelláser. Enestatécnicasefocalizaunpulsolaserenunáreamuyreducidodelamuestra.Dada la naturaleza electromagnética de la luz ésta tiene asociado uncampoeléctrico,al concentrarseenunpequeñospotelhazdellaserlaintensidaddeestecampopuedeser comparablealcampoelectrostáticoporelqueloselectronesestánunidosalosátomos. Comoconsecuenciaenlamuestraseproducelaablacióndeunapequeñacantidadde lamisma,yportantoseinduceunplasmaenelquesetienelíneasdeemisióndelos componenteselementalesdelamuestra. 1.2.2.1 EventosduranteunamedidaLIBS RepasaremoslosdiferenteseventosqueocurrenduranteunamedidaLIBS,empezando porlaablaciónlaser.Partiendodelaablación,enestafaseunapequeñapartedela muestraesarrancadadelrestoylosvolátilescomienzanaevaporarseeionizarse.Esta fasesecaracterizaporuncaráctertérmico:ellaseresabsorbidoporlamuestrayesto inducecambiosdefase,alllegaralestadodegaselmaterialsepuedeionizarporla presenciadelcampoeléctricodelaluz,generándoseunplasma.Cabedestacarenesta fasequeeltiemporequeridoparalageneracióndelplasmaestápordebajodelorden losnanosegundos,motivoporelqueenláseresconduracionesdepulsoeneseorden elrestodelaenergíaunavezgeneradoelplasmaseempleaencalentarestevapor generadoyportantoelplasma,alavezqueseaumentaelgradodeionización. Segeneraenestemomentotambiénunaondadechoqueyelplasma,generadoenla superficiedelamuestracomienzaaexpandirse.Debidoaestaexpansión,amedidaque laburbujadeplasmaocupamásvolumensutemperaturaempiezaacaerdesdelos 20.00Kalosquepudoencontrarseenelmomentodelainducción.Enestafasede expansióntieneunefectoclarolapresióndelmedioenqueseproduceelplasma.En
20 vacío la expansión es rápida como lo es el enfriamiento, mientrasqueapresión atmosféricalaexpansiónesmáslenta. Entodoesteproceso,dentrodelplasma,haypartículascargadasqueestánmoviéndose ychocandounasconotras,onunadistribuciónuniformedeenergía.Debidoalaleyes delaelectrodinámicaclásica,unacargaqueseaceleraodeceleraemitiráradiación electromagnética.Esteefectosellamaradiacióndebremsstrahlung,quevienedela palabraalemanaquesignifica“frenado”. Todasestasemisiones ocasionadasporlas aceleracionessufridasporlasdiferentescargasemitenunfondocontinuoque,como pasabaenelcasodelRamanconlafluorescencia,compiteconlaemisionesatómicas quenosinteresacaptarparalaidentificación.Estefondonoaportainformaciónsobre lamuestraycarecedeinterés,portanto. Es a medida que el plasma se expande y enfría que estos choquesentrepartículas cargadas bajan en número e intensidad, reduciendo el fondo de bremsstrahlung, y permitiendoalaslíneasdeemisióndelosátomosdelamuestraaparecer. F IGURE 1‐7 LIBS SPECTRUMWITHDIFFERENTDELAYS Se puede conseguir obtener un espectro con un fondo reducido si la captación del espectrolahacemosuntiempodespuésdelageneracióndelplasma.Dependedela muestra,peroengeneral,parasólidosenatmósferaterrestrenosotrosusamosretrasos enelrangodelosmicrosegundos. LIBSesportantounatécnicadeunmarcadocaráctertemporal,esdecir,requierela capacidad de obtener los datos en un lapso de tiempo concreto. Aunque algunos instrumentosenelmercadopuedenfuncionarsinnecesidaddeestesincronismo,esto
21 sipuedetenerunefectoadversoenladeteccióndeelementosconemisionesdébiles quenopuedanversesobreelfondocontinuo. Esinteresanteademásintroducirestecarácterderesolucióntemporalporotrofactora mayores,yesqueamedidaqueelplasmaseenfríaocurrencosasdiferentes.Enprimer lugarlaslíneasquerecibimossonaquellasprocedentesdelaionización,yposterior recapturaelectrónica,delosátomosdenuestramuestra,esta emisióndeluzsuele ocurrirduranteunospocosmicrosegundosdespuésdelageneracióndelplasma.Entre elmicrosegundoyalgunadecenademicrosegundostenemosemisionesprovenientes delasrelajacionesdelosestadosexcitadosenlosátomosdelamuestra.Finalmente,y siendolasmáslongevas,seemitenlaslíneasmoleculares. Estasúltimassongeneralmentemenosintensasymásdificultosasdecaptar.Motivopor elqueLIBSsueleserusadoexclusivamentecomotécnicadeanálisiselemental,aunque tienelacapacidaddeidentificarmoléculas.Uncampointeresantedeestacapacidades ladetecciónycaracterizacióndehidrocarburos. 1.2.2.2 EsquemadeuninstrumentoLIBS F IGURE 1‐8 S CHEMATICDIAGRAMOFLIBSSYSTEM (X IAONA , 2014). TalcomovimosenlaintroducciónteóricadelatécnicaLIBS,elprocesodeobtenciónde unespectroLIBSes,generalmente,resueltoeneltiempo.Estacaracterísticaparticular introduceciertasnecesidadesinstrumentalesdegestiónderetardosysincronismo. EngeneraluninstrumentoLIBScuentaconlossiguienteselementos: ‐ Láser:eslafuentedeenergíautilizadaparainducirelplasmaenlamuestra. EltipodelásermásfrecuenteeselNd:YAGusandosufrecuencia fundamentalde1064nm.Unacaracterísticainteresantedeestoslásereses sufacilidadparaobtenerotrosarmónicosmediantecristalesnolineales.Para LIBSnosueleserinteresanteestedesarrolloporqueparaestatécnicalomás
22 interesanteescontarconunabuenacantidaddeenergía.Generalmenteen losláseresNd:YAGenelmercado,laenergíaporpulsounavezsedoblala frecuenciaparaobtener532nmeslamitaddelaqueelláserproporcionaen sufrecuenciafundamental.Otromotivoamayoresparausarel1064esque estáfueradelrangodemedidatípico,queparaunespectroLIBSestáentre 200y850nm.Aunquenodeberíaserunproblemadebidoaqueelpulsodel lasertieneunaduracióntípicadenanosegundos,ylaadquisicióndelespectro se hace unos cuantos microsegundos después, pueden aparecer interferencias.Enmiexperienciaconnuestrosistemausando532nm,en muestras translúcidas (hielos) las diferentes reflexiones internas en la muestra hacen que todavía en el momento de adquisición del espectro aparezcan fotones del láser. Eso si, existen ventajas en usar láseres de frecuenciasmásaltas,yaqueellímitededifracciónquemarcaeltamaño mínimodespotdeanálisisesinversamenteproporcionalalafrecuenciadel láser,existiendodesarrollosmicro‐LIBSqueempleanláseresUV (Singh, 2018). ‐ Espectrómetrooespectrómetros:dadoelgranrangoacubrir,ylaresolución típicaenelordendelos0.5nm,puedeemplearseunespectrómetrodegran rangocomolosdetipoEchelle,outilizardiversasventanasdeadquisiciónen diferentesespectrómetros. ‐ Detector:eldetectorsueleserintensificadodadoqueestossistemastienen lacapacidaddehacergating,adquisicionesultracortasdetiempo.Existenno obstanteinstrumentosque,acostededesempeño,puedenprescindirde estatecnología.Encualquiercasodebeadmitirelcomandadoexternopara sincronizaciónconelláser. ‐ Generadorderetardos:estesistemaeselencargadoderecibirlaseñaldel láserydespuésintroducirelretardodeseadoentreéstaylaseñaldedisparo aldetector. ‐ Ópticas:lasópticassuelenincluirunalenteosistemaconvergente para focalizarelláser,yópticasdecolecciónparamandarlaluzdelplasmaalolos espectrómetros. El primer elemento debe soportar las altas energías, y debenevitarsedobletesdelentespegadasyaqueelpegamentotiendea degradarconellaser.Paraelsegundoelementosidebetenerseencuentael rango de medida, es difícil encontrar sistemas que permitan una buena transmitanciadesdeelUVhastaelIR.
23 Elpasoainstrumentosremotos Unavezqueyahemosintroducidolosconceptosbásicosdecadaunadelasdostécnicas quecuentanconelprotagonismoenestatesis,enestasecciónnoscentraremosenel usoconcretodelasmismaseninstrumentosremotos. Hasidoyadescritocomoelproblemadeladistanciaafectaalflujolumínicodeseñal querecogemosdeunamuestra,variandoconlaleydelcuadradodeladistancia.En ambos casos nos encontramos con fuentes luminosas que son hasta cierto punto isótropas,esdecir,notienenunadirecciónpredominanteparalaemisióndeluz.Enel casodelLIBStodalaplumadelplasmaemiteentodaslasdirecciones.Enelcasodel Raman,estadispersiónpuedeocurrirencasitodaslasdirecciones,aunquesireviste cierta predominancia en la dirección de incidencia. Así pues, a modo de estudio cualitativo,podemosevaluareláreadeunasemiesferaadiferentesdistanciasparaver suinfluenciaenlairradianciaquelaatraviesa. Considerandolairradianciarecibidaaladistanciade1cmcomoparámetroyéstaigual a1w/m2,porejemplo,unafuenteluminosaconunaemisiónisótropaatravésdeesta semiesferaproporcionarálassiguientesirradianciasenfuncióndeladistancia: Dist.(m) 0,01 0,1 0,5 1 2 5 7 Irr.(w/m2) 1 0,01 0,0004 0,0001 0,000025 0,000004 2,04082E‐06 T ABLE 1‐1 I RRADIANCIAENFUNCIÓNDELADISTANCIA Delatabla anterior sepuedeobservar como paraunadistancia querondelos diez metrosestamosrecibiendolamillonésimapartedeirradianciaquelaqueobtendríamos conuninstrumentodecontacto.Estotieneefectosparticularmenteimportantesenel casodeladispersiónRaman,yaquecomoyasehadiscutido,lacantidaddefotones disponiblesesmuchomenorqueenelcasodelLIBS. Siconsideramosunlásertípicode15mJporpulso,yconsideramos532nmcomoláser deexcitación,cadafotónde532tendrá3,7x10 ‐16 mJdeenergía.Estonosdauntotal aproximadode4x10 16 fotones.Esteeselnúmerototaldefotonesparalaexcitación. AhorasiconsideramosunaeficienciaenladispersiónRamandeunfotónporcada10 6 o 10 9 fotonesdeexcitación,estonospermitecalcularquelamuestradevuelveentre10 10 y10 7 fotonesdeRaman,enelpeorescenario,a7metros,estamosrecibiendounostres fotonesporcentímetrocuadradoydisparo.Ademáshayotrosefectosadversos,yes quenosólo lleganfotonesRamanprovenientesdelamuestra, lo que acrecientael problemadedetección.
24 Este modelo nos permite ver que amayorsuperficiedecolecciónmásnúmerode fotonesparadetectar,yenelcasodeópticascircularesclásicas,estointroduceuna dependenciaconelcuadradodelradio.Asíunaópticade10cmdediámetroestará captandomásde200fotonespordisparo,mientrasqueunade20captarámásde900. Elproblemadelcuadradodeladistanciapuedenossertalsisiempreycuandoel equipooperedentrodeloslímitesdedistanciashiperfocales,entendiendoladistancia hiperfocaldeunsistemaópticocomoladistanciamínimadeenfoqueconlacuál conseguimosunamayorprofundidaddecampo,obteniendounenfoquequese extiendedesdelamitaddeestadistancia,hastaelinfinito.Laexpresiónmatemática quenospermitecalcularestadistanciaes: 𝐻𝑓 𝑁𝑐 DondefeslafocaldelSistemaópticoempleado,Nsuaperturanumérica,ycelllamado círculodeconfusión.Esteúltimoconceptoeselcírculomínimoquesepuededistinguir enelplanofocaldelsistema,yestárelacionadoconlaprofundidaddefocodelmismo. De esta expresión Podemos sacar dos conclusiones claras, la primeraesqueesta distanciadentrodelacualelcuadradodeladistancianoaplicaserámayorcuantomayor sealafocaldelsistema,ycuandomenorseasuapertura(relación entre su focal y diámetro),esdecir,focalesmuylargasconsistemasmuyluminosos(Hirschfeld,1974). ElpasoahacerRamanadistanciasdelordendelosmetrosrequiere,ademásdeadaptar laópticadecolección,aumentarlapotenciadelafuentedeexcitación.Enesteejemplo, siesos15mJserepartenenunpulsode10ns,lapotenciaestáenelordendelos megawatios. FIGURE1‐9CHANGESINHARDWAREFORSTANDOFFRAMAN Estaintensidadluminosa,oflujodefotonesquellegandelamuestralohacentambién acompañadosdefotonesprovenientesdelailuminacióndifusa,considerandoquenose
25 operaráesteinstrumentoencondicionesdeoscuridad,yquenoharáapuntandoalSol. Estaradiaciónescontinua,notienenaturalezapulsadacomoelláserdelejemplo,y aunqueseveráminimizadasiseadaptabienelenfoquedeláreadecolecciónaldelárea de excitación (Hirschfeld, 1974), existe esta contribución. Así pues, cuanto más nos ciñamosalpulsodelláser,másventajaledamosalosfotonesRamanfrenteala radiacióndeotraíndole.Estoportantointroducelanecesidaddecerraralmáximola adquisiciónalpulsodelláser,yencondicionesideales,unamedidaresueltaentiempo quepermitacontrarrestarladistancia,losretardosinternosde los instrumentos, y sincronizar al máximo la adquisición con la llegada del pulso láser de vuelta al instrumento. El planteamiento ideal es entonces el de contar con un detector intensificado con función de gating, y capacidad de sincronizarseconelláser. Condicionesporotroladoque,comoseintrodujoenlaseccióndeteoría,sontípicas parauninstrumentoLIBS.Dehecho,esterequerimientoeselquepermitehaceruntipo diferentedeanálisisRaman,queeselRamanResultoenTiempo. Asípues,amodoresumen,elnecesitarcontrarrestarlosefectosdeladistancianos implica contar con un láser pulsado, un detector intensificado con capacidad de sincronismoconelláser,yópticasdecolecciónmásgrandes. Unaopciónmássimple,peronocarentedelimitaciones,esladecontarconundetector normalquepermitalaadquisiciónentiemposmuycortos.Cuantomáscortoseael tiempo,sinllegaraceñirsealpulsodelláser,másselimitalacontribucióndelaluz ambiental.Siademásapoyamosestoconunláserconunaaltatasaderepetición(10 KHz),podemosconseguirqueenunaadquisicióndeunmilisegundoseconcentren10 eventoslaser.DemaneraquesepuedeadquirirespectrosRamansinnecesidadde sincronismoointensificador.Unejemplorealizadoconunmontajemuchomássencillo, a30Hzcon60mJporpulso,puedeverseenlasección0. HastaelmomentonosehatenidoencuentaelLIBSyaquedemomentosoloestábamos evaluandolaintensidadlumínicaacaptar.EnelcasodelLIBS,elplasmaesmuchomás luminosoqueelefectoRaman(variosórdenesdemagnitud)yportantoloquefunciona paraRaman,funcionarátambiénparaLIBS(inclusopuedequedemasiado). Unacuestióndiferenteeselcómonecesitamosllevarlaenergíadenuestrafuente,bien elláserparalaablación,bienelláserparalaexcitaciónRaman,hastalamuestra.Enel casodelRamanydadalaintensidaddelláserlomejoresmantenerelhazdelláser colimado y en valores de irradiancia altos. Un láser colimado nospermitirállevar irradianciaselevadasagrandesdistanciasconunmínimoincrementoeneltamañode spot. EstenoeselcasodelLIBS,enestecasoesnecesarioconcentrarlomáximoposiblela energíadelláserenunspotmuyreducido.Parainstrumentosremotosesnecesario
32 de 60 mJ, y se monta un expansor variable del haz. En este sistema el láser no se introduceenelejeóptico,siendounsistemaexclusivamentedelaboratorio,enqueel operadordesplazaensistemadecolecciónparaadecuarsealaposicióndelláseralas diferentesdistancias. FIGURE1‐14SISTEMAREMOTOCONLENTEDE300MM Elpodercontarconunamayorenergíadelláseryunexpansordehazpermiteadecuar eltamañodellásersobrelamuestraaltamañodeláreadecolección,manteniendounos valoresdeirradianciarazonablementealtos. Enestesistemauncambioadicionalocurreeneldetector,pasando de un sistema intensificadoaunaCCDAndorNewton,noEMCCDcomolamayoríadeesaserie,pero siunaCCDconcapacidadderealizarlecturasaunaelevadatasaderefrescoytiempos deadquisiciónmuycortos,siendocapazdealcanzarlos1600Hzdecaptación. Estesistemapermiteoperarelláser,queahoraalcanzalos30Hzfrentealos10Hzde losprimerosdesarrollos,asumáximatasaderepetición,ajustando el tiempo de adquisiciónalmáximoparacaptarunpulsodelláserypocaluzdefondo.Adiferencia deloqueocurreenlosdesarrollosqueempleanunintensificador,laCCDempleadaen estedesarrollonotienecapacidaddehacergatingnidebajaral límite de los nanosegundos, por lo que este desarrollo no tiene la capacidad de hacer estudios resueltosentiempo.NopermiteportantodiscriminarentrefluorescenciayRaman,y nopermiteadaptarsealosdiferentestiemposdevuelodelláser en función de la distancia.Enlugardeestasincronización,seadaptaeltiempodeexposición,aunque conelmínimo,ycomandandoeldisparodelaCCDmediantelaseñandeentradadel láser,secubrenlasdistanciasdentrodeesos10metrosdereferenciasinadaptación.
33 FIGURE1‐15PRINCIPIODEOPERACIÓNDELINSTRUMENTOREMOTONOSINCRONIZADO Enlafigura1‐15semuestraelprincipiodeoperacióndeesteinstrumento, y una comparativadediferentesespectrosenquesecómo,amedidaquesereduceeltiempo deadquisición,sedisminuyeelfondo. Con este instrumento he podido realizar diversas pruebas y ensayos, incluyendo la pruebadedeteccióndebiomarcadoresen3.3.Permiteestesistemaobtenerunbuen compromisoentresimplicidad,distanciaoperativayresoluciónparaequiposremotos. Finalmente,conlaentradadenuestrogrupodeinvestigaciónenelgrupodecienciade SuperCam,yconlaresponsabilidadtécnicaasociadadeldesarrollodesumuestrade calibración, de la que soy responsable técnico, bajo la direccióndelresponsable científico,F.Rull,sehacenecesarioactualizarelsistemaremoto. Elnuevosistemahallegadoconretrasopordiferentesproblemasfinancierosdelgrupo, asícomoporlacargadetrabajoquehaimplicadoeldesarrollodelSCCT.Pero actualmenteelgrupoyacuentaconunsistemacombinadoRaman‐LIBS,concapacidad de hacer análisis en rango similares a los de SuperCam, aunque actualmente se encuentrafijadoaladistanciadelamuestradecalibracióndelMastUnit. Enestenuevodesarrollosevuelveaundetectorintensificado,peroestavezseacopla unasegundaópticaconunacopledirectoafibraparahacerLIBS.Elmismoláserantes descritoseempleaenestaocasiónparahacerRaman,adaptandoeltamañodestpotal decolección,oparahacerLIBS,reduciendoelspotatamañospordebajodelmilímetro.
34 ParaelanálisisdeluzprocedentedelplasmaseusaunespectrómetroEchelle,deAndor, conunrangodelecturaentre200y850nm,yunaresoluciónmejorde0,1nm.Elacople sehacemedianteunalentede50mmaf:1,8.Eldetectoresotra cámara Andor intensificada. Estesistemahaservidoparahacernumerosaspruebasquehanconstatadounproblema quetambiénSuperCamtuvoqueabordar,yqueestuvopresenteenanterioresdiseños denuestrogrupo:lainclusióndelintensificadoracarreaunagranpérdidaderesolución. Estoesdebidoalaaparicióndebordesdifusosenelfósforodelintensificadorquehacen quelaimagendelarendijadelespectrómetropuedaaumentarsuanchuraenelplano focal. F IGURE 1‐16 E SPECTROSOBTENIDOSCONELSISTEMAREMOTORESUELTOENTIEMPODE : YESO ( AZUL ), DIOPSIDO ( ROJO ) YORTOCLASA ( VERDE ). Enconcreto,connuestrosistema,conunafibrade200micrasactuandocomorendija obtenemos resoluciones, en Raman, superiores a los 25 cm ‐1 , 40 cm ‐1 enlabanda principal del yeso mostrado en Fig. 1‐16. Esta resolución es inaceptable para aplicacionesenmineralogía,dehecho,casinosedistinguenlabandaprincipaldelyeso yeldiópsido.Lasustitucióndeunafibrade200micrasporunade50micrasacarreauna pérdidadeluzdeun75%,aunquesolucionaenparteelproblemadelaresolución.Para ellocontamosconunamejoraquenohepodidoimplementarenlapreparacióndeesta tesis: una fibra multi núcleo con siete núcleos de 50 micras que en un lado tienen configuracióncircular,aumentandoeláreadecaptacióndeluzenelladodelalente,y configuraciónlinealenelotro,simulandounarendijade50micras.Nosehanrealizado pruebas,peroestaconfiguración,similaralaempleadaporSuperCam,puedemejorar laresolucióndelsistemaydejarloenvaloresdelentornode10cm ‐1 .Elmaterialnoha
35 estadodisponibleparapublicarresultadosenestetesis,peroesunamejoradelsistema arealizardemanerainmediata. Desarrollosremotosenexploraciónplanetaria. Finalmente,yfocalizándomeenlosdesarrollosdesistemasremotosparaexploración planetaria,hagounrepasoalossistemaspropuestoshastalafechaylosquevolaránen unfuturoinmediato. SihayunamisiónquehasignificadounpuntodeinflexiónparalaespectroscopíaRaman aplicadaacienciasplanetarias,esaesExomars.Enmomentospreviosdedefiniciónde la misión Exomars contaba con un sistema combinado Raman‐LIBS que además era remoto, como se relata en (Rull, 2017). Llegando incluso a desarrollarse un espectrómetroparaabarcartodoelrango,diseñoacargodelaempresaTNO.Cambios en la misión al final decantaron la balanza del lado de un instrumento Raman de contacto,peroconstituyelaprimeravezqueunsistemacombinadoRaman‐LIBSestaba consideradoparaunamisióndeexploraciónplanetaria. LIBSentraríadespuésalanunciarselainclusióndeChemCam(Wiens,2012),contando con la colaboración de IRAP, que ya participaban en Exomars en RLS,yquehabían jugado un papel importante en lo tocante a LIBS remoto. Chemcam es el primer instrumento LIBS remoto que se emplea en exploración planetaria, y lleva dando espectrosdelasuperficiemarcianadesdeelaño2012hastalaactualidad. Añosdespués,conladecisióndeNASAdelanzarunasegundamisiónconunagrancarga deherencia(Mars2020)sellegaaSuperCam,(Wiens,2017),queahorasiconstituyeel primer instrumento combinado Raman‐LIBS y remoto para ambas técnicas, que se incluyeenunacargaútildeexploraciónplanetaria. Duranteelaño2020selanzaráademásotramisiónChina,HX‐1,queconstituyeelprimer intentodesuagenciaespacialdeaterrizarcargaútilenMarte.Dentrodelroverque formapartedelamisiónsehaincluidouninstrumentoLIBSmuysimilaraChemCam, perodelquenohepodidoencontrarbibliografíarelevante. Paraelfuturonoexisten,almenosdemomento,misionesplanteadas que puedan incluir desarrollos remotos. MMX incorporará un Raman de contactoensurover MASCOT,yparaunhipotéticoEuropaLandersehapropuetotambiénuninstrumento Raman,perodadoelconceptodemisiónseríadecontacto,yparecidoaSherlocoRLS (JPL,2016).
36
37 2 SuperCamandthe SuperCamCalibrationTarget
38 2.1 MARS2020mission Mars2020missionisflagshipmissionfromNASAwithahighheritagefromtheprevious, andhighlysuccessful,missionMarsScienceLaboratory.Themissionisincludedinalong termplanthathasasgoalthehumanexplorationofMars. FIGURE2‐1PLANETSKNOWNINHABITABLEZONE SinceVikingmissions,thepositionofMarswithinwhatcanbecalledaconservative habitable zone of our solar System has made the red planet of great interest for astrobiology. Later missions have contributed to know more about its habitability increasingitsastrobiologicalinterest.NowweknowthatwaterflowedinMarsin a distantpast,thattherewasanactivegeology,athickeratmosphere,andconditionsthat could lead to the emergence of life. Mars 2020 will focus on the past and present habitabilityofMars,participatingintheMarsSampleReturnProgram(Foust,2019)and alsohelpinthedevelopmentoftoolsandknowledgecapitalforhumanexploration. Thepayloadwasselectedaccordingtotheseobjectivesandincludesseveralanalytical techniques,witharemarkablepresenceofanewtechniqueinplanetaryexplorationas Ramanspectroscopy,presentintwooftheinstruments.Again,thehighheritageofthe missionisevidentinpartoftheselectedpayload,withsomespacetonewconcepts. Definitionandbackground In2011theMarsScienceLaboratorywaslaunched,forthatmissionwithaestimated costof2600millionsofDollarsseveralkeycomponentsandtechnologyweredeveloped.
39 ForfirsttimeamobileplatformwaspoweredwithaRTG(Radioisotopes Thermal Generator)allowinghighermassandpowerconsumptionofsciencepayloadthanin previousmissions.SinceitsdeploymentonthesurfaceofMarsin2012topresentdays, MSL (Mars Science Laboratory) has contributed to a better knowledge of Mars exceedingitsinitialmissiontimeof23monthsrepresentingagreatsuccessfromthe scientificpointofviewandtheengineeringdevelopmentofthemission. ThissuccessandsomeofthetechnologicaldevelopmentsusedinMSLwerefoundtobe usefulinthedefinitionofanewflagshipmissiontoMars,Mars2020.Thismissionwould takeadvantageofthedevelopmentsmadefortheMSLrover,thearmandthemobility systemamongothers,anditsEDL(EntryandDescentModule,theskycrane),todevelop anewroverwithanimprovedpayloadthatcouldplayaroleinthenexttwochallenges tobefacedbyNASA:thesamplesreturn(allowingagreaterscientificoutcomeusing earthbasedlaboratories)andthehumanexplorationofMars.Inaefforttocontainthe costsassociatedtothedevelopmentinsomeareas,partofthesparecomponentsfrom MSLhavebeenusedintheassemblyofMars2020. FromMSLscientificoutcomeitwasevidentthatatleastsomeregionsofMarscould havebeenhabitableinthepast.Althoughthereissomelackofdefinitiononthetime frameofthishabitability,andiflifefinallycouldappearornot.Tofillthisgapinthe knowledgeofMarsthebestpossibleoptionistoleavebehindtheconstrainsderived fromtheinstrumentationthatcouldbesenttoMars,andtakeselectedsamplesfrom MarstoEarthwherecouldbeanalyzedwithgroundbasedequipment. With this in mid, the science payload could be then defined not to directly find biomarkers,butwiththeobjectiveofanalyzingthegeologicalcontextlookingforthe bestoutcropswherebiomarkerscouldbepreserved(JPL,2013).Thepayloadwasthen announced in July 2014, also reflecting MSL heritage in the final selection of some instruments,leavingspaceforthenewrequirementsonpayload.Ifthisscientific payloadiscomparedtothescientificpayloadonMSLitisevidenthowresourceshave beenredistributedfrominstrumentationtocoveroneofthemainobjectivesofthe mission,thecollectionofsamplesfortheirlaterreturntoEarth.
40 Objectivesandcontextinfuturemissions NASA’sseekingforsignsoflifeonMarsisevidentinthe definitionoftheobjectivesoftheMars2020mission.As commented before, and once identified the need of takingsamplesbacktoEarth,needalsoidentifiedinthe PlanetaryDecadalsurveyforthedecadeof2013‐2022 asagreatpriority,thissearchofbiomarkerscanbe addressedinadifferentway.Thiswayimpliestogive someeffortstotheidentificationofthebestcontextin which life could have existed on Mars, and the evidencesofthispastlifecouldhavebeenpreserved fromtheharshenvironmentofMars,butnotnecessarilytryingto detect these signaturesinsitu.Intheobjectivesdefinedforthemissionthereisalsoaspottohuman exploration,assometechnologydevelopmentscouldbetestedinthismission,aswell asgettingadeeper,andmorehumanexplorationoriented,scientificknowledgeofthe planet. Can water be found in low latitudes? What can be extracted from the undergroundonMars?DoweknowenoughabouttheMartianclimate?Allofthese havebeenconsideredandsummarizedinfourmainobjectivesforthemissionthatare asfollows: ‐ ObjectiveA:ExploreanastrobiologicallyrelevantancientenvironmentonMars, itsgeologicalprocessesandhistory,includingtheassessmentofpasthabitability.Itwas alreadydiscussed,thereareevidencesofpastwaterflowingonmars,andwehave enoughdatatosaythatinthepastsomeregionsofMarscouldhost life, but unfortunately, more data is needed on the geological history oftheseregions.Itis necessarythentohaveagoodunderstandingofthegeologicalprocessesthathappened inadeterminedarea,andalsotohaveagoodideaofitshistoryandtimescale. Thisbetterunderstandingofthegeologyoftheareaneedstobedoneatdifferentscales, andthisalessonlearnedfromdifferentmission.Thereisalwaysachangingpictureof Marswhenanalyzingtheorbiterdataandcomparingthemtothedatacollectedinsitu by landers and rovers. The full picture could only be obtained with multiscale observations,placinginthecontextofmorphologyandotherdatafromorbiters,the moredetailedfindingsandmeasurementsfromtherover. Theaimofthisefforttobetterunderstandthegeologicalpastofaregionofinterestof Marssurfaceistogetabetterassessmentofpasthabitability. F IGURE 2. 1 M ARS 2020 LOGO F IGURE 2‐2 MARS 2020 LOGO
41 Habitability requires the confluence of four different factors:thepresenceofraw materialsthatcouldbeturnedintoorganicchemistry (socalledCHONPS),anenergysourcetopowerallthe chemical transformations that life means, the presenceofliquidwatertobeusedbutpossiblelife forms, and favorable conditions for the emergence, evolution and persistence of life. In this last requirement we can include the presence of liquid water for sustained period of time, this is not a seasonalappearance,thesalinityofthatwater,pH, temperature,energyofthewater(wasitstill,orwas itarawstream)… Oncethehabitabilityhas been assessed,thereis another geological factor to study whichisthepotentialpreservationofthishabitability.Inthiscase,thegeologyofthe areamayhaverecordedseveralenvironmentsduringMarsgeologicalhistory,soagood geologicalstudyofdifferentlayersandunitsisofcapitalimportancetounderstandif theregionwashabitableduringatimeenoughtoallowlifeforms. To accomplish this objective, it has been found by NASA that the following measurementsneedtobedone(JPL,2013): o Contextimaging o Contextmineralogy o Fine‐scaleimaging o Fine‐scalemineralogy o Fine‐scalechemistry Thepayloadselectedshouldbeabletoaddressthesekindsofmeasurementsrequired tounderstandbetterthegeologyandhabitabilityofMars. ‐ ObjectiveB:Assesthebiosignaturepotentialpreservationwithintheselected geologicalenvironmentandsearchforpotentialbiosignatures.Thecurrentconditions ofMarsarenotthebestplacetopreservecomplexorganiccompoundsthatareusually relatedtolife.UVradiationandotheroxidantscanhavedegradedtheorganicsinto smallersimplercompoundsandtherefore,itisparticularlyimportanttolookforthese biomarkers in places where they could have survived while protected from the environment. Notonlyisimportantforthesecompoundstobepreserved,butalsotheconditionsin whichtheyappeared,whichcouldbecrossedwiththegeologicalhistoryofthezoneand provideabetterunderstandingofthemomentandconditionsinwhichlifeemerged. So, first, it is needed to define what compounds are directly understood as a consequence of past lifeforms. The scientific report distinguish between two main F IGURE 2‐3 CONDITIONS OF A HABITABLE ENVIRONMENT (JPL)
48 F IGURE 2‐9 S AMPLESANDWHITENESSTUBESOFTHE SCS (JPL) Along with the samples witness tubes will be stored to monitor the possible contamination that has been accumulated, and have this into account in the measurementstobedoneonearth. AfinalinterestingfeaturethatwilltravelwithMars2020Roverisanothertechnological demonstrator:theheliscout.Martianatmosphereisover100timeslighterthanEarth’s atmosphere,andthatmakesarealchallengetoanyflyinghardware.JPListakingthis opportunitytofly alightweight,solarpowered, double rotorhelicopterthat willfly aroundtheMars2020Roverandwilloperateduringthefirstdaysofthemission.The technologiesandlessonslearnedcanbeusedinthefutureforanewbreedofexploring drones. Payload AfterthesettingoftheobjectivesofthemissionNASAcoulddefinethebestpayloadto servethoseobjectives.Initspreliminaryreport(JPL,2013),beforethefinalselection,it wasdiscussedthekindofmeasurementsthatmightbeneededdependingoneach objective: T ABLE 2‐2 O BJECTIVESOFTHEMISSIONVSMEASUREMENTSNEEDED (JPL)
49 Thefirstthreeobjectivessharethesamekindofmeasurements,whilethelastone,the onerelatedtohumanexploration,mayneedspecificdevelopmentstobeaddressed. Apartfromthisobjective‐orienteddefinitionofthepayload,theoperationoftherover canbealsotakenintoaccountforthedefinitionofthepayload.Giventhecomplexityof anyoperationincluding the displacementofthe rover, previous datahelpinginthe decisionmakingonwheretogowiththeroverisalwayswelcomed.InthecaseofMSL, the availability of a complete imaging suite from navcams, along with Mastacm (incorporating some spectroscopical features) and ChemCam providing high magnificationimagesandelementalcompositiondataaroundtherover,helpedinthe decisionmakingonwheretomovetheroverandproceedwithcontacttechniques. AnotherfactortoremarkbeforedescribingthecompletepayloadtobesenttoMarsis the high heritage of the mission. This heritage takes profit oftheexperience, developmentsandlessonslearnedfromMSLtoreducerisksinthedevelopmentand manufacturingofthenewrover.Saidthis,thesciencepayloadofMars2020missionis composedbythefollowinginstruments: FIGURE2‐10SCIENCEPAYLOADOFTHEMARS2020ROVER(JPL)
50 2.1.4.1 MastcamZ: MastcamZisadirectsuccessorofMastcam,andasinthelatest,thegeneraldescription ofthisinstrumentcouldbeastereoscopiccamerasystemcapableoftakingcolorimages andshortvideos,orprovidingsomespectroscopicdataoftheobjectsthankstoafilter wheel.ThemaindifferenceinMastcamZistheincorporationofzoomcapabilitiesanda betterimagequality. TheprincipalinvestigatorisJimBell,fromArizonaStateUniversity,andthetechnical andscienceteamofMastCamZincludesresearchersfromJPLandNielsBohrInstitute amongotherinstitutions(Bell,2016). MastcamZwillbemountedontherovermast,rightundertheMastUnitofSuperCam (tobedescribedfurtheron).Itconsistontwocamerasmountedat2meterheightand separatedby24cm,thatwillprovide3DstereoscopicimagesofthesurfaceofMars. Thetotalweightofthesystemy4kilogramsandregardingthetechnicalcapabilities,the cameraswillprovidecolorimageswitharesolutionof1600by1200maximum.Thefinal resolutioncanbechangedbytakingROIs.Regardingthecolor,thequalitywouldbe similartoaconsumercamerabasedonabayerfiltermatrix.Thankstothezooming capabilitiesofMastcamZ,nowtheachievableresolutioncanvaryfrom150micronsper pixelto500micronsmmperpixelat2meterdistance,orbetween0.74and2.7cmper pixelat100meters. ThecamerasofMastCamZwillcoveraspectralrangefrom400to1000nm,andthis rangecanbesweptbymeansof11narrowbandfilters. Thisinstrumentwillbeabletocharacterizethemartianlandscapemorphology,givena contextforothermeasurements.Willbeusedtoassesthetopography,stratigraphyand ingeneraltoobtainagoodpictureofthepastgeologicprocessesthathappenedinthe analysisarea.Atthesametimeitwillprovideinformationaboutthetextureandmore concisecharacteristicsofoutcrops.Itwillalsoobservethesky,characterizingtheopacity oftheatmosphere,observecloudsorduststormsthatwillhelpinthestudyofmartian FIGURE2‐11MASTCAMZOPTICALDESIGNANDMODEL
51 weather.Finally,MastcamZwillgivesupporttooperationsprovidinginformationthat willhelpwithrovernavigation,andprovidinginformationfromwhathasbeencalled “remotescience”suite. Giventhecharacteristicsoftheinstrument,itsimagingcapabilitiescanmeananasset fortheobjectivesA,BandC,identifyingthebestcontextforbiomarkersandgeological processes,aswellasobjectiveDhelpingwithabetterunderstandingoftheclimate dynamicsofMars. 2.1.4.2 MEDA: FIGURE2‐12MEDASENSORS(JPL) Continuing with the heritage instruments, MEDA, standing for Mars Environmental Dynamics Analyzer represents the evolution of the weather station on board MSL, REMS.MEDAisalsothemaincontributionofSpaintoMars2020mission,thePIisJ.A. ManfredifromtheAstrobiologyCenter,CAB.MEDAincorporatesseveralsensorsonthe mastandtheroverdeckallowingtoinvestigate(Manfredi,2013):characteristicsofthe dustandthetransparencyoftheatmosphere,dynamicsofdustliftinganddeposition, dust storms; general weather dynamicsinMars,withmeasurements of pressure, temperature, humidity or wind direction and speed; Correlate local atmospheric dynamicswithlargescaleweather;thecycleofwaterinpresentMars;studyofthe irradianceonMarsdependingoftheseasons;possibleweatheringconditionsofthe samples candidate for a caching, cooperate in the better understanding of the measurementsandoperationsofotherinstrumentsasMoxie. MEDAwillprovideusefulinformationnotonlyfortheoperationsandobjectiveC,also forobjectiveD.Asitwasexplainedbefore,thedustisofgreatinterestwhenstudying Marsinpreparationofhumanexploration.Inabsenceofwater,thatisafactorthat modulatestheweatheronEarth,thedustinsuspensionintheatmosphereonMars,for
52 example,changestheirradiancereceivedbythesurface,meaningthatthedynamicsof thedustmighthaveagreatimpactinthelocalandglobalclimateofMars.Also,thedust, itsgrainsizeandabundanceamongothercharacteristics,areofgreatinterestwhen designingfunctionaldevicesorstructurestohostahumanmissiononmars. 2.1.4.3 MOXIE: MoxierepresentsadirectapproachtotheobjectiveD,asitconsistsonaconceptmodel ofatechnologythatisdirectlyintendedtobeusedinthehumanexplorationofMars. FIGURE2‐13MOXIEWORKINGSCHEMATICS MoxieisatechnologicaldemonstratorforasystemthatcouldbeusedonMarstoobtain O2(Hecht,2015)frommartianatmosphere.Thisoxygenwillbeneedednotonlyforthe habitat of the astronauts, that will have to spenda long time onMars,butalsoas propellantforthereturnmission.Inthisline,theminimumestimationisthatatleast30 tonsofoxygenwouldbeneededforthelaunchfromMars,andthismeansthatthe transportationofthatresourcefromEarthmakesnosenseatall.Thebestwaytosolve thisistheInSituResourceUtilization(ISRU),andproducetheneededoxygenonMars. MoxiewillbeabletocollectCO2fromtheatmosphere,compressitandheatitupto800 ºC,adaptingtothevariableconditionsonMars,andobtaintheoxygenbyelectrolysis tochecklaterthepurityoftheproducts.AtMoxiescale,aminimumof10gramsof oxygenperhourwillbeproduced,andthisissupposedtobea1%scaleoftheintended hardwaretobeusedatthehumanexplorationstage. Duringtheoperationofthelargescalesystem,itwillneedtoworkcontinuouslyfora longtimetoproducetheneededamountofoxygen.Thiscontinuousoperationimplies
53 a need of adaptability to a very extrem environment with abrupt changes in temperature,atmosphericconditions,dustquantity,etc.Forthatreasonthistechnology demonstratorneedstobetestedatMarsbeforesendingafullscaletechnology. 2.1.4.4 PIXL: PIXL stands for Planetary Instrument for X‐ray Lithochemistry, and it is one of the instrumentsmountedonthearmoftherover,makingpartofthecalled“proximity science”instrumentationofthemission.Itsmeasurementsaredirectlyrelatedtothe geochemistrycharacterizationofMars,andthereforewiththeobjectivesA,BandC, providing fine scale imaging and elemental composition in image context.Butalsocouldplayitsrole intheobjectiveDidentifying interesting materials that could be processedonMarsintheframework ofISRU,asMoxie.Forexample titanium oxides can be used for manufacturing of mechanical parts ifaprocessingisdeveloped. PIXL is an imaging XRF instrument with a submillimeter resolution, in fact,theXraybeamwillhavea120 microns diameter. This beam will scanthesurfaceofthesamples allowingalsoflexibilityinthemeasurement,beingabletoprovideafullmap,apointor aline.Ashappenswiththetechnique,lighterelementsaredifficulttobedetected,but elementsfromNacanbedetected(Allwood,2015). 2.1.4.5 SHERLOC: Sherlocis,appartfromthedrill,theothertooltobeplacedinthearm,andalongwith PIXLcompletestheproximitysciencesuiteonboardMars2020.SHERLOCstandingfor F IGURE 2‐14 E XAMPLEOFA XRF IMAGEOBTAINEDWITH PIXL F IGURE 2‐15 S HERLOC I NSTRUMENT
54 Scanning Habitable Environments with Raman & Luminescence for Organics & ChemicalswillbeabletoobtainRamanspectraina50micronsspot,anduseitsscan capabilitytoobtainaRamanimageofthesampleinaareaof7x7mm.theexcitation sourceofthisRamaninstrumentisaUV(248.6nm)laser,andthewholesystemhas beendesignedtominimizethedetectionlimitof organics (Beegle, 2015).Asitwas covered in the introductory section, the Raman cross section getsbiggerwhenthe excitationsourceshiftstoshorterwavelengths,andtobemoreconcise,thisrelationis inverselyproportionaltothefourthpowerofitswavelength. AnotheradvantageoftheUVexcitationsource,asdiscussedpreviously,isthefactthat whenobtainingaRamanspectrum,thespectralrangetobemeasuredcoversfrom250 to270nm,andthatregionsisfarfromthefluorescenceemissions.Furthermore,the highenergyoftheexcitationsourceenablesresonancesmoreeasilythatcanimprove thesignalstrength.However,theuseofUValsoimpliesdifficultiestoobtainagood resolutionandcouldbeproblematicformineralogy,andforthatreasonthisfeature couldbemorerelatedtotheobjectiveB,andC.anyway,tothedate,noresultsfrom thisinstrumentcouldexaminedbytheauthornorwerepublished,sothefinalresolution ofthisinstrumentcouldnotbefairlyevaluated.Ontheotherhand,SHERLOCwillalso be available to study the fluorescence induced by the laser, givingextraanalytical information. Anotherfeaturefromthisinstrumentisitscapabilitytoobtaincontextimageswitha great magnification thanks to the add on called WATSON, standing for Wide Angle TopographicSensorforOperationsandeNgineering,thatisadirectsuccessorofMSL’s MAHLI.Withthisaddon,thisinstrumentwillhaveaimagingsystemmountedonthe armwithaspatialresolutionof30microns,coveringanareaof2.3x1.5cm.Thisimaging capability will have, as MAHLI did, several applications in the study of textures of samples,andalsointheinspectionstobedoneintherover,helping with the engineeringduringoperations.
55 2.1.4.6 RIMFAX: TheRadarImagerforMars'SubsurFAceeXperimentitsaninterestinginstrumentfor large scale geology, for objectiveA,andalsoforobjectiveD.Italsohasasimilar instrument on board another mission, ExoMars in this case, calledWISDOM.This instrumentwillbeabletouseGroundPenetrationRadartomaptheverticalunderthe roverdownto10metersdepth(Eide,2019).Incombinationwiththedisplacementof theroveritwillbeabletoprovidecutoffsofthelandingsiteat10cmofhorizontal resolution,givinginformationofthelayersundertheroverandsomeideaofthekindof materials.Itisspeciallyinterestinginthepursueofundergroundwaterreservoirs.More specifically,RIMFAXwillbeabletoprovidethefollowinginformation:thedepthofthe regolith layer, identify the different layers and relate them to visible outcrops, characterizethestratigraphyofthearea(keytounderstandpastenvironmentonMars). Inthefigure2.15,asimulationofatypicalmeasurementofRIMFAX during the displacement of the rover is shown. Different layers of deposits on Jezero will be measuredbyRIMFAX. 2.1.4.7 SUPERCAM: ThefinalinstrumenttobedescribedinthepresentworkisSuperCam,theinstrument thatcountswiththecollaborationoftheUniversityofValladolidandhadcopedmostof thetimeoftheauthorduetohistechnicalresponsibilitiesandmanagementrole,reason forithasbeencoveredinitsownsection. Anyhow,asageneraldescriptionoftheinstrument,itispartoftheremotesciencesuite oftheRover,andwillbeabletouseseveralspectroscopictechniqueatdistancesof somemetersaroundtherover.Itsuniquecombinationofspectroscopicinformationof theelementalcompositionofatarget,andalsoitsstructure,givesthepowerofhaving apre‐analysisonsometargetsthatwillbesimilar(withlimitationsfromitsstand‐off operation)tothecombinedmeasurementsofPIXLandSHERLOC. F IGURE 2‐16 S IMULATIONOFACUTOFFMEASUREMENTOF RIMFAX IN J EZERO
56 2.2 SuperCaminstrument Thequoteabove,fromSteveJobs,couldnotonlydescribehisrestlesspursuetoconquer themarketofconsumerelectronics,butthecurrentenvironmentofspacesciences.Go further,domore,doitbetter. TheSuperCaminstrumentistheMars2020successorofChemCaminstrumentonMSL‐ Curiosity.ChemCamusesLIBSspectroscopy,alreadydescribedin the introduction chapter,togetelementalcompositionoftargetsaroundtherover,andalsoprovides highmagnificationimagesofthetargets.Thisinstrumentmeantabreakthroughinthe wayoperationsandscienceweredoneinroboticexploration.Forthefirsttimeanactive spectroscopictechniquecouldbeusedtocharacterizetargetsinthe rangeofsome meters.Thesestandoffmeasurementsmeanagreatadvantagenotonlyhelpinginthe selectionoftheplacestogowiththerover,butalsointhequantityofdatathatcanbe done,sincefromtheoperationalpointofview,agratareaaroundtherovercanbe assessed without moving the rover, increasing the data available covering more samples. Now in SuperCam, in addition to LIBS, other spectroscopic techniques have been includedsuchas:TimeResolvedRamanSpectroscopy,TimeResolved Luminiscence, Visible‐Infra Red reflectance spectroscopy, microimaging and sound recording. This completesuiteofanalyticaltechniqueshasincreasedthecomplexityofSCAMwhen comparedtoChemCam. Background TalkingaboutthebackgroundofSupeCamnecessarilyshouldstartwithitspredecessor, andalmosttwininstrument,ChemCam.ThisinstrumentisajointventurebetweenLos AlamosNationalLaboratoryintheUS,andL’InstitutdeRechercheenAstrophysiqueet PlanétologieinFrance.ThelastinstitutionisalsoinvolvedinExoMars,andwasthere whentheconceptofRLSinstrumentwasalsoacombinedinstrumentcalledExLIBRIS. BothinstitutionshavegreatexperienceintheuseofLIBSappliedtoPlanetarySciences andworkedtogetherinthedevelopmentofaStand‐offLIBSinstrumenttobeincluded inMSL,andareworkingtogetheragainforSuperCam.Sowhentalking about the background and the situation behind SuperCam it should be remarked that the instrumenthassomeheritagefromanotherinstrument,andmoreimportant,hasacore teamthathavebeenworkingtogethersinceMSLwithagreatlysuccessfulinstrument. “I think if you do something and it turns out pretty good, then you should go do something else wonderful, not dwell on it for too long. Just figure out what’s next.”. Steve Jobs
57 ChemCamthenhasbeenprovidingremoteelementalcompositionofthetargetson Marssince2012thankstoitsstandoffLIBScapabilities,andalso,thankstotheRMI, highmagnificationcontextimagesofthetarget.ChemCamwasthefirstinstrumentever tousethistechniqueinaplanetaryexplorationmission,atechniquethatisvirtuallyable todetectanyelementandmeantadifferentapproachtothepreviousspectroscopic techniquesdeployedonMars. PrevioustoChemCamandSuperCam,themineralogydoneonMarswasdoneusing techniquessuchasSojourner’sAPXS,standingforAlpha‐protonX‐raySpectrometer, thatusedaradioactivesourcetoirradiatethesamplewithalphaparticlesandmeasured thebackscatteredparticlesandX‐Raygenerated,ortheMössbauerspectrometersthat werepartofMERrovers.Thosetwotechniquesrequiredcontactwiththesampleand longtimesfordataacquisition,lagerthan10hoursinbothcases,alsointhecaseof Mössbauerinstrumenttherewerelimitsofthetechnique,veryorientedtoironbearing minerals. A different approach was given by Mini‐TES, providingthermalinfrared spectroscopicdatafromthesurface,butagainthistechniquehasitslimitations,orthe massspectrometeronboardPhoenix.Solookingattheprevioustechniquesitisclear thatstand‐offLIBSmeantachangeinthewaythingsweredoneinoperations.ChemCam isasimplerinstrumentformtheoperationalpointofview(notthetechnical),givesa completeinformationofthesamples,inashorttimeandwithoutcontact,andalsoata smallerscalethanthementionedtechniques.Thismeansmoresamplesanalyzedper solandmoresciencedatatounderstandMarsandhelpoperations. This kind of developmentsstartedinthelate80’sandhavebecamemoreandmorepopularasthe technicaladvancesallowedmorecompactlasersanddetectors,makingtheirwayto Mars with ChemCam, and will be followed by SuperCam and another stand‐off libs instrumentfromChina,alsotobelaunchedin2020. ChemCamusedaQswitchedNdYAGlaser(1064nm),focalizedusingatelescope(both locatedinthemast)toreachthelimitofplasmainduction,andusedthesamefocalizing opticstocollectthelightfromtheplasma.Theemissionfromtheplasmawasthen analyzedinthethreespectrometersinthebodyofCuriosity(Wiens,2012)(Maurice, 2012). The Mast Unit in ChemCam was developed by CNES and IRAP, and included the telescope,thelaserandtheRMI.StartingwiththeRMI,itusedamonochromesensor, thatmeansthattheimagesareinblackandwhite.TheothercompanionoftheRMIin theMastUnitThelaserinChemCamprovides24mJduring8nspulses, with the capabilityofoperatingupto10Hz.Withthispower,itwasabletoreachtheGW/cm2 requiredtoinducetheplasma.BothusetheSchmidt‐Cassegraintelescopeof110mm asopticalelement.
64 ensuresthatwhenthetelescopeisfocusingonapoint,thelaserisalsofocusedonthat point.Theuseofthisgalileanexpanderisusualwhendealingwithhighpowerlasers thatcouldinducedamagesintheopticsifthebeamistooconcentrated.Theobjective istobeabletofocalizethelaserintospotsofasimilarsizetoChemCam,thisisbetween 350and550micronsdependingonthedistanceandmaterial. In the case of the green line, the 1064 nm is introduced in the second harmonic generatorwherethebeamisturnedinto532nmandfilteredtoeliminatetheremaining 1064nmlaser.Typicallyincommerciallasersthisconversionisapproximatelya50% efficientintermsofenergy,thatmeansthattheenergyperpulseofgreenlaseristhe halfoftheenergyofthegroundinfraredwavelength,inthecaseofSuperCam,the groundenergyis14mJperpulse(4ns)for1064nmand11mJperpulseforthe532nm (Wiens,2017).Thebeaminthiscasewillremaincollimatedalthoughisexpandedto limitdamagesintheoptics.Asdifferencewiththeredline,itisnotintroducedinthe opticalpathofthetelescopebutintroducedintheopticalaxisofthesystembymeans ofamirrorsituatedinthecenteroftheSchmidtplate. ThelightcollectedfromtheLIBSevent,theRamananalysis,orsimpleforimagingcan gothenthroughthreedifferentpaths.Inthefirstoneandmoreobvious,thecollected lightisfilteredthroughanotchfilerandfocalizedintheopticalfiberthatwilltakeitto thespectrometers.Thenotchfilterisnecessarytoavoidtheentranceoflaserinthe fiberthatcouldinduceparasiteemissions.Theotheroptionforthislightistobeused toobtainanimageintheRMI,nowprovidingcolorimages,HDRcapabilities and coveringthevisiblespectrum. AthirdoptionistointroducethecollectedlightintotheIRspectrometer. FIGURE2.26SUPERCAMIRSPECTROMETER(J.M.REESS,LESIA)
65 TheIRspectrometerinSuperCamusesanAcoustoOpticalTunableFiltertofocusthe lightinalightdetectingelementandmeasureintensityduringthespectralsweepofthe filter(Reess,2019).TheAOTFusescrystalsthatactasbandpassfiltersbutcanchange thespectralpositionofthisbanddependingonthefrequencyonanacousticwavethat isintroducedinthecrystal.Varyingthisfrequencyitispossibletoseepthespectral rangeandcollectintensitymeasurementsinanystep.Thissamekindoffiltersareused forhyperspectralimaginginotherinstruments. Finally,amicrophoneisimplementedtorecordthesoundmadebytheLIBSsparkinthe material.Thecharacteristicsofthesoundwavecollectedcangiveinformationofthe texture and physical characteristics of the material that has been shot. Also this microphone will be able to record sounds of the rover and wind, helping with the weatherstudiesandtheengineeringduringoperations. SCBU: TheSuperCamBodyUnitisthesubsystemofSuperCamwherethespectrometersare placed.Herethelughtcomingfromthedifferentmeasuresisanalyzed. ThelightcollectedbytheSCMUandcarriedtotheSCBUthroughtheopticalfiberneeds tobeseparatedintothreedifferentspectralwindows.AshappenedinChemCam,due tothebroadareaoftheelectromagneticspectrumthatneedstobeanalyzedinLIBS measurements,theincomingsignalissplitintothreedifferentwindowsaccordingtoits wavelength,andtheneachofthosewindowsanalyzedinadedicatedspectrometer. This separation in the three spectral windows is done by means of an optical demultiplexer.Inthiselementthelightexitingthefiberiscollimated,andthenpasses throughthreelowpassopticalfilters.Thelightisthenrefocusedinadedicatedfiberand carriedtoeachspecificspectrometer. IntheSCBUthreespectrometersareusedforthemeasurement,quitesimilartoque onesusedinChemCam,withonebigexception,theVisiblespectrometer. The two shorter wavelength spectrometers keep the same optical design used in ChemCamwithgreatresults.Thevisiblespectrometer,ontheotherhand,neededa differentapproachgiventheconstrainsassociatedwithRamanspectroscopy,basically demandingahighersensitivity. Thefollowingtableshowsthemaincharacteristicsofeachofthesespectrometers:
66 T ABLE 2‐3 M AINCHARACTERISTICSOFTHESPECTROMETERSINTHE SCBU ANDTHE IR (R. W IENS , 2017) ThevisiblespectrometeristheonecoveringalltheRamanrange.Typicallywhenusing 532nmexcitationsourceandaRamaninstrumentcoverarangeof4000cm ‐1 maximum, thatisfrom532to675nm,butinthecaseofSuperCamseveralinterestingLIBSlines occurintheIRrange,reasonwhytherangeofthisspectrometerisextended.Thegreat distinct characteristic of this spectrometer, besides its opticaldesign,rangeand resolution,it’sthedetectionpart,thatneedstoprovidethetimeresolvingpowertothe instrument. F IGURE 2.27 S UPER C AM V ISIBLE S PECTROMETER (LANL) TimeresolvinginSCAMhappensthankstoatime‐gatedintensifierincludedbetween themonochromatorandtheCCD.Themainreasonforhavinganintensifieddetectoris notonlythetimeresolvingcapabilities,alsothefactthatRamaneffectisaweaksignal
67 and that faint light is really hard to collect when using standoffRaman.Tisalso introducesanextrarequirementonthehardwarethatisadaptability,sincethesignal strengthcomingfromRamanandLIBSareseveralordersofmagnitudedifferent.This adaptabilityisintroducedbychangingthegainintheintensifierfromitsmaximumvalue forRamantoitsminimumforLIBSandVISIR(Perez,2017).Theintroductionofthis intensifier,however,comeswithapriceintermsofresolution. Theintensifiersusuallymeanareductionoftheresolutionduetosomeghostingeffects thathappeninthephosphorscreen.Asaresult,astraightlinebecomesblurryand spectralresolutionislost.ThiseffectwasdramaticinthedevelopmentoftheTime ResolvedRamansystematUVA,withFWHMbandwidthsintheorderof30cm‐1.This needs to be taken into account when dimensioning the monocromator, and it is a difficulteffecttomeasurewithanticipation.InthecaseofSCAMthiswassolvedby spreadingthespectralrangeintothreetracksinthespectrometer,decisiontakenwith theaidoftestsonadevelopmentunit,EDU.Thischangealsoallowedtoincreasethe slitwidthfrom20to30microns,introducingmorelightintothespectrometerwhile improvingthenresolution(thepixelresolutionisbetterthan2.5cm‐1)(Wiens,2017). Theresultingspectrometersuite,thethreespectrometersintheSCBUandtheAOTFIR mountedonthemastcovermorethan1900nmofrange,givingservicetofourdifferent spectroscopictechniques.Thiscouldbeagooddefinitionatfirstsightofthecomplexity ofSuperCam. SCCT: InwordsofChemCam’sandSuperCam’sPI,RogerWiens,theonlythingfromChemCam thathewouldhavechangedistheCalibrationTarget.Thecaliobration target in an instrumentlikeChemCam,orSuperCam,servesnotonlyforawavelengthcalibrationof thespectrometers,butalsoforthechemometriccalculations.LIBSmeasurementsare affected by matrix effects, environmental conditions and other factors that make advisabletohaveagoodsetofsamplestodocalibrationcurvesofsomeelementsin situ.SuperCamisplannedtoprovideestimationsofconcentrationofsomekeyelements withanaccuracybetterthanthe10%,andapartoftheresponsibilitytoachievethat performancefallsonthecalibrationtarget. TheSuperCamcalibrationtargetisthesubsystemunderSpanishresponsibility.ThePI of this elementis Prof. Fernando Rull, from theUniversity of Valladolid,andfor its developmentandmanufacturingthisinstitutioncountedonthecollaborationofseveral other institutions from five countries. In Spain a complete team including four universities,INTAandatechnologicalpartner(AVS)wasarranged.
68 FIGURE2.28SCCTDEVELOPMENTTEAMCHART AddedValueSolutions,AVS,providedthetechnicalsupportinthestructuraldesignand manufacturingofthedifferentpartsoftheSCCTholder.Severalresearchgroupsin Francehelpedwiththemanufacturingofthesamples,undercoordinationofIRAPand thereflectancesampleswereprovidedbyNiehlsBhorInstitute.InSpain,thescience groupincludingtheUniversityofValladolid(UVA),UniversityofBasqueCountry(EHU), ComplutenseUniversityofMadrid(UCM)andtheUniversityofMalaga(UMA),took chargeofthecharacterizationandscientificassessmentofthesamples,alongwiththe generalparticipationinthescienceoftheinstrument.INTAgaveitssupportduringAIT activities.UVAtookchargeofthetechnicalcoordination,withtheMissionAssurance and Project Management under its responsibility (this last one being author’s responsibility). ThetechnicaldetailsoftheSCCTareintroducedinthefollowingsection2.3.
69 Finalremarksandstatus: FIGURE2.29FOOTPRINTSOFDIFFERENT SPECTRALTECHNIQUES(R.WIENS2017). SuperCam instrument presents a uniqueopportunitytounderstand better the geological processes andpastofMars.Notonlywillbe able to use different analytical techniques, each of one shows a differentfeatureofthesamples,it will be able to do all these measurements coaligned. The different techniques may have a different measuring scale, Raman analysisspotwillnotbeassmallas LIBS,buttheywillbedoneonthe samesample,onthesamespot,openinganewlineofpossibilitieswhenusingdatafrom different techniques to be combined in chemometric calculations. Again, in this capability an important role is played by the calibration target, since it will make availablethesamesetofsamplestobemeasuredbyallthetechniques,givingacross calibrationbetweenmeasurements.Infigure2.27thedifferentsizesforeachtechnique canbeseenforasampleat2.5meters(Wiens,2017).Theyellowcircleshowsthearea thatwillbecleanofdustafteritsremovalwiththefirstlasershots.Pleaseobservethat thesizeoftheLIBSspotwillremainconstantwithdistance,tosomeextent,becauseit isfocalizedateachdistancebythetelescopeoftheSCMU.TheRamanspotwillget biggerwithdistanceasitisnotfocalized,itiscollimated,andtheVISIRdependsonthe fieldofview,thatofcoursegetsawiderareawhendistanceincreases. Whilewritingthepresentwork,theflightmodelofSuperCamwasalreadydeliveredto JPL and integrated in the rover. Due to schedule constrains only limited functional testingcouldbedonewithbothflightmodelsoftheSCMUandSCBUandresultsarenot forpublicdisclosureatthemoment.However,aspecialissueofSpaceScienceReviews willincludethreepapersfromSuperCamwithmoredetailedresultsanddescriptions.
70 2.3 SuperCamCalibrationTarget RobertD.Harededicatedhislifetopsychiatry,afieldofknowledgefarfromphysics,but hisrealizationabouttheimportanceofmeasurement,capitalinphysics,ledhimtothe developmentofthePsychopathyChecklist,PCL,awaytomeasureandhaveabetter diagnosticofpossiblepsychopaths.Inhisquote,hestatestheimportanceinscienceof areliableand accuratemeasurement,something thatisin the coreofscienceslike physiscsorchemistry.Infirstplaceitisabsolutelynecessarythetoolthatwillprovide themeasurement,itisimpossibletothinkaboutmeasuringmasswithoutascale,or lengthwithoutaruler.Insecondplace,andasimportantasthefirst,isthecalibration ofthemeasuringtool,sotheresultscanbegivenwithcertainty. InthecaseofSuperCam,acompleteandmultianalyticaltoollikethisinstrumentwould beincompletewithoutapropercalibration,accuratechemometriccalculationsdepend on a good calibration, the Raman spectra cannot be properly provided without knowledge of the excitation source, the VISIR are impossible without a good characterizationoftheilumationspectrumandblackcurrent...Ifthatcalibrationwas importantforChemCam,theinclusionofmoretechniqueshasmadeitcrucialin SuperCamtohavegoodcalibrationtarget.Thisimportantcomponentoftheinstrument has received great support and careful planning and design fromthescienceteam, remarkingitscapitalimportanceintheperformanceofSCAMinstrumentinMars. Description SuperCaminstrument,whichwasdeeplydescribedintheprevioussection(3.2),willbe abletousesixdifferentanalyticaltechniquestocharacterizesamplesinthesurfaceof Mars,andwilldothatwithoutcontact,uptodistancesofseveralmeters,expandingthe sciencerangeoftheMars2020roverandprovidingmoreinformationduringoperations. ThesixdifferenttechniquestobeusedbySuperCamare: ‐LaserInducedBreakdownSpectroscopy(LIBS):providingelementalcompositionofthe target and based on emission lines from a plasma induced on the sample by concentratingthelightfromapulsedlightsourceinaspotofafewmicrons. ‐TimeresolvedRaman:providingstructuralinformationofthesample,itisavibrational spectroscopytechniquebasedontheinelasticinteractionoflightandmatter.Whenthe Science cannot progress without reliable and accurate measurement of what it is you are trying to study. The key is measurement, simple as that. Robert D. Hare
71 excitationsourceisapulsedlaserandthedetectorisgated,andsynchronizedwiththe laser,itispossibletoseparatedifferentmomentsoftheinteractionofthesamplewith thepulse. ‐ViSibleInfraRedspectroscopy(VISIR):alsoavibrationalspectroscopytechnique,inthis caseitisbasedontheselectiveabsorptionsbythesampleofparts of the electromagnetic spectrum. This technique has been used by orbiters due to its simplicity,sincetheonlythingneededistohavesampleilluminatedbyacontinuous spectralsourceliketheSun.itprovidesstructuralinformationofthesample. ‐Inducedfluorescence:Inthiscasetheuseofahighfrequencylaserallowstoinduce electronic transitions on the target. The relaxation of those excitations can provide additionalinformationofthesampleasthepresenceofrareearthelements. ‐Sound:thesparks of the inducedplasmabyLIBSanalysis producea characteristic sound.Bytheanalysisofthissound,eveninthefaintatmosphereofMars,canprovide informationofthetextureofthesample. ‐Image:Imagesoftheanalyzedareaareimportanttounderstandmorphologyofthe sample,andalsotohaveanideaofthepossibleindividualcomponentsofacomplex sample. This analytical suite of SCAM has global needs but also particular needs for each techniquewhenitcomestocalibration.Exampleofaglobalneedforalltechniquesisto haveacalibrationtocalculatetheassignmentofawavelengthto each pixel in the detectorsofthespectrometers.Anexampleofaparticularneedofatechniqueisto calibratethespectrumoftheincidentlightonthesampleforVISIR.Alltheseneeds,in additiontoothers,shouldbeaddressedbythecalibrationtarget.Thecomplexityofthis elementhasbeenincreasedforthisreasonwhencomparedtoChemCam’s. Alltheseneeds,sciencerequirements,needtobeaddressedwithtechnicalconstrains inmind.ThedesignoftheSuperCamCalibrationTarget,SCCT,needstomeettechnical requirementsfromdifferentorigins,fromthespaceandmassavailable for the hardware,tothosedependingontheenvironmentalconditionsthatthesystemwill face.Asageneraldescription,theSCCTneedstobeunder270gramsofmass,andthe size,althoughisnotcriticalgiventhatthereisnootherhardwarearoundthatcouldbe interferedbytheSCCT,needstobeascontainedaspossible. TheSCCTiscompletedwithafinalelementthatisnotintendedtoflyandservesas protectiondeviceduringtheintegrationandtestingoperations.ThisRemoveBeforeFly orRedTagCover,needstocovertheSCCTcompletely,protectingitfromimpactsof toolsorfastenersduringintegration,alsoallowingasafehandlingoftheunit,butdoes notneedtobehermeticandserveascontaminationcontrolmeasure.Sinceitisnotan
72 operationalelementitdoesnotimpactinthemasslimit,butsomeelementsduring ATLOcouldbeclosetoit,sothiselementneedstobetakenintoaccountwhentalking aboutmaximumdimensions. Alltheserequirementsareexplainedanddiscussedinthefollowingsection. RequirementsthatdefinetheSCCT 2.3.2.1 TechnicalRequirements Startingwiththetechnicalrequirements,thefirsttopictobeaddressedisthetechnical resourcesthatthehardwaretobedevelopedwillconsume.Typically,inthisgroupare included the mass, power consumption, volume, and heat. The SCCT is a passive elementfromthepointofviewofpowerandheat,thereisnoneedorprevisionof includinganypowerconsumingelementintheSCCTormeasurestoconductheatfrom onepointoftherovertotheSCCT.Butthemassandvolumearetechnicalresources thatneedtobeaddressed. Massandenvelope:Startingwiththemass,themaximummasswithmarginsthatwas assignedatthebeginningoftheprojectwas240grams.Atdifferentstagesoftheproject themasshaschanged,ashavedonethemarginsapplicable,from20%attheinitial stagesofdesignto10%atthefinalstage.Anyhow,themassallocation is not be exceeded,oranincreaseneedstobejustifiedandrequestedtotheresponsibleofthe uppersystem,inthiscasetheMars2020rover. ThiswasthecasefortheSCCT,asthose240gramswerefoundnotsufficientdueto changesintroducedbyJPLinthepossiblelocationintherover.In2016atPDRlevel,this isPreliminaryDesignReview,JPLhadimplementedanantennatocontroltheheliscout thatwasproposedforMars2020mission,andthatantennainterferedwiththeSCCTby shadowingthesamplesintendedtobeusedtocharacterizetheambientlight,whatis notacceptable.Asaresult,atradewasopenedatinstrumentleveltovaluatepossible solutionstothisissue,solutionsthatincludedtherelocationofthewholecalibration target,oraredesign,thatallowedthereflectancestandardstobeinashadow‐free locationontheroverdeck.Thisrelocationchangedthedynamicsenvironmentofthe SCCT,basicallyincreasingtheshockleveltobefacebythehardware.Tosolvethisissue two solutions were considered, or ruggedize the design, or split the SCCT into two separated targets, so the sensitive samples could be separated in a ruggedized separatedholder,whiletheothercouldstayintheinitiallocation, anyhow, both solutionsrequiredmoremasstobeimplemented.Asaresultthemaximummasswas increasedfrom240to270grams.
73 Regardingthevolume,orsize,aswasalreadycommented,inthepossiblelocationsof theSCCTintheroverdeckitsdifficulttofindelementsthatcould be mechanically interfered,sothesizewasjustagreedwithJPLwithoutaNotTo Exceed envelope requirementperse.Again,andasanexampleofhowaliveaprojectofthiskindis,once thedesignwasvalidatedanewrequirementwasidentifiedatinstrument level. To preventdamagesontheopticsoftheMastUnit,acertainminimumdistancewasset, andtheSCCTwascloserthanthatdistanceatthatmoment.Thistimetheimpactfellon JPLsmechanicalteamthatneededtoredesignthebrackettoaccommodatetheSCCT, butdoingthisthecalibrationtargetgotclosertosomegroundsupportequipmentthat couldharmthehardwareduringATLOactivities.Thisintroducedspecialrequirements intheenvelope,thatwasdefinedwiththeremovebeforeflycoveronplace. 2.3.2.2 Environmentalrequirementsoverview TheSCCTwillneedtofaceverydifferentenvironmentsduringitsassembly,cleaning, launch,cruise,landingandoperationtime,andthehardwareneedstobeprovento surviveinthoseenvironments.Theserequirementscanbeverifiedbyanalysisortest, andwillcovertheretheonesdirectlyrelatedtodemonstratethatthehardwarewillbe abletosurvive(Qualification),asothertestsarejustdonetoverifyworkmanship(Flight Acceptance)andareusuallylesssevere. Startingwiththeassembly,therearenotspeciallyharmfulenvironmentsduringthis phase,butitisatthelaststage,whenthehardwareiscleaned to accomplishwith PlanetaryProtectionrequirements,thattheSCCTfacesthehighesttemperatureofits wholeoperationaltime.ThePPprocedureswillbeexplainedlater,buttosummarize, during this process, the SCCT is introduced in a vacuum chamber at 115 ºC of temperatureforatleast120hours.Thistemperaturecouldbeariskforanyadhesive, thatusuallytrendtobehaveplasticallyathightemperatures,orinworstcases,degrade completely. Continuing with the launch, the main stress received by the hardware due to the experienceofbeinglaunchedintospacebyarocketismechanical,mainlyinformof vibrationsofdifferentkind. Duringitscruisestagethehardwareisunderlowtemperaturesandvacuum,itisinthis stagewhenlowesttemperaturesmightbereached,andisalsoduringthisstagethatany outgassingmaterialcouldbeacontaminationriskforotherpartsoftheRover,butthat willbecoveredinadifferentsection. DuringthedescentandlandingonMars,theSCCTwillsufferagainvibrations,butthe most demanding requirement appears in this stage, which is shocks. The SCCT is mountednearthepyrotechnicwheelrestrainoftheMars2020Rover,whatintroduces
80 Theserequirementsaretobetakenintoaccountateverymomentoftheintegration, assemblyandtestingofthehardware,andaremeasuredoverwitnesses,asthedirect measurementonthehardwarecouldbeacontaminationsourceitself. 2.3.2.3 Sciencerequirements Iamgoingtocoverherethedifferentneedsandrequirementsthatthecalibrationtarget needstofulfil,andthataredirectlyrelatedtothescienceoutcomeoftheinstrument. Wavelengthcalibration: Duringtheoverviewoftheinstrument,andintheblockdiagram(Fig.2.21),wereshown thedifferentspectrometersthatneedtobecalibrated.AllthespectrometersbuttheIR spectrometer(whichispartoftheSCMU)arelocatedintheSCBU.Startingwiththese spectrometers,allofthemwork,inasimplisticdescription,byintroducingadispersive element,agrating,thatdispersethelightindifferentanglesaccordingtoitswavelength. Withtheappropriateopticaldesignapolychromaticlightspotintheentranceofthe monochromatorwillhavedifferentimagesintheoutputofthespectrometer,spatially separatedaccordingtothedifferentwavelengths.ByplacingaCCDinthisimageplane, oroutputofthemonochromator,whatwehaveisanarrayoflightdetectingelements (pixels),eachofonemeasuringtheamountoflightinacertainrangeofwavelengths (dependingontheresolutionoftheinstrument).So,thefirstthingneededtohavea calibrated instrument is to obtain a unique relation between wavelength and pixel numberinourarray.Usuallyinthelaboratorythisisdoneusingspectrallampsthat provideasetofknownandfixedspectrallinesthatcanbeusedtoobtaindecalibration polynom, ideally of 3rd grade or higher, providing an expression that assigns a wavelengthtoeachpixel.That’sthefirstneedintermsofcalibration, to provide a known,stablesourceofspectrallinesthatcoversthewholerangeofSCAM. RamanRayleighcalibration: During the theoretical introduction, when the Raman effect was introduced, it was shownthatthiseffectisaneffectrelativetotheexcitationsource.Thismeansthatthe sameRamanscatteringhappeningforacertainmolecularvibrationwillhavethesame value when talking about Raman shift, not depending on the wavelength of the excitationsource,butthisofcoursemeansthatusingdifferentexcitationsources,that same Raman band will have different wavelengths. When calibratingaRaman instrumentusingonlyRamanbandsofwell‐knowncompounds,anyeffectdepending onthelaserisautomaticallytakenintoaccount,butinthecaseofSCAM,thecalibration ofthespectrometersneedstocoverawiderangeofwavelengths,andLIBSneedsa calibrationinwavelength,so,ourcalibrationpolynomwillgivethepixel/nmrelation,
81 butnotdirectlythepixel/Ramanshiftrelation.TheRamanshiftcanbecalculatedthen usingtheknownexpression: 𝑅𝑎𝑚𝑎𝑛𝑆ℎ𝑖𝑓𝑡𝑐𝑚 – ThewavelengthoftheRamanbandwillbeknown,butthereisadependenceonthe wavelengthoftheexcitationsource,λex,toprovidetheRamanshift,thateveninthe caseoflaser,supposedtobestableandfixed,canvaryintime.Oneinitialapproach couldbetomeasurethepositionofthelaserdirectly,butthisoperationcannotbe performedbySCAM duetothedifferentinterferometricfilters that arepartofthe instrument.SotheapproachtakeninthiscaseistoincludeasamplewithaRamanband withahighRamancrosssection,thatprovidesahighintensitywhenshotwiththegreen laser,andalsoneedstobeabandrelatedtoavibrationthatisnotsensitivetopressure ortemperatureanddoesnotchangewithenvironmentalconditions,thisRamanband couldbeusedtocalculatethewavelengthofthelaserthenandcorrect,ifneeded,the calibration in Raman spectra. This gives, In my point of view, a second need for calibration,asamplethatisagoodRamanscatterer,allowingshortintegrationtimes andhighintensitysignals,andprovidesaRamanbandthatcanbeconsideredfixedand willnotdegradewhenexposedtoUVradiation. VISIRcalibration: VisibleandInfraredreflectancespectroscopyisatechniquewithalonghistoryinspace explorationduetoitscapabilityofprovidingmineralogicalcharacterization(tosome extent)ofthesurfaceofplanetsfromorbit.InthecaseofSuperCamthistechniqueis, alongwiththeimaging, thetechnique withthe farthestrange,beingabletoobtain spectrafromafewmetersto“infinity”. Thewaythistechniqueworksisbyanalyzingthereflectancespectraofthesamples irradiatedbyacontinuouslightsource,consideringthatsomegapsinthespectraofthe reflected light correspond to absorptions by some molecular groups. In the case of SuperCamthiskindofanalysiswillbedoneusingthreespectrometers:thevioletand visiblespectrometerintheSCBUandtheIRspectrometerthatispartoftheSCMU.This lastspectrometerconsistsonanacousto‐optictunablefilterthatsweepstheIRregion from1300to2600nm.focalizingthecollectedlightintoasinglephotodetector.InMars thecontinuouslightsourcewillbethesunlight,soitisimportanttocharacterizethe spectrumofthelightirradiatingthesamplebeforeanyabsorptionisproduced,andalso itisimportanttounderstandwhatismeasuringeachelementintheabsenceoflight, thedarkcurrent.Itcouldbealsousefultohavesampleswithawell‐knownreflectance toevaluatebetterthedifferencesinducedbytheilluminationlightsource.
82 So,theseare,tosummarize,therequirementstocalibratetheVISIRtechnique:tohave awhitesamplethatreflectsalmostallthespectraofthereceivedlight(inthemeasuring range),adarksamplethatabsorbsthereceivedlight,andthensomesampleswitha knownreflectancealongthespectrumofinterest.Sinceitisinterestingthewaythe calibrationsamplesabsorbornottheincidentlight,thesamplesshouldbedesignedin awaythatavoidanyspecularreflection,andofcourse,giventhe importance of performingcalibrationactivitiesbeforemeasurementsforthistechnique,thesamples needtobecleanofdustandothercontaminantsduringthemissiontime. Imagecalibration: RMI, as described before, will provide high magnification imagesoftheareaswere SuperCamwillperformthemeasurements.Thissupportofimagesgivescontextand morphologyinformationfromthetargetstobeanalyzedandthus,agoodcalibrationof thefocusingandthecolorbalanceisimportanttogetthebestpossibleimages. Foreveryopticalsystemdifferenteffectsmake thattheinputfromtheobjectplanedoesnot matchwiththeoutputattheimageplane.This happens when we stop considering the light and the telescope from a pure geometrical opticspointofview,andwestarttreatingthe lightasawave.Thesystem’saperturecutthe extentofthewavefrontsofthelightinducing diffraction,andmakingthateveninaperfect systemwithnoopticalaberrationstheobject doesn’t match its image, and that change is described in the Optical Transfer Function, OTF.Thisdirectlyseenintelescopeswherea starisobserveddifferentlyintheimageplanedependingonthepupilofthesystemand itssymmetryandaberrations,foranidealrefractivetelescopethistypicallyturnsthe star(apoint)intoadiffractionpatterncalledairydiscs.Tounderstandthistransfer functioncangiveusinformationofhowwellwearefocusingoursystemandthelimit resolutionthatcanbeachieved.Inthefigure2.32obtainedfromthemainarticleon Wikipediaitisshownhowthisfunctiondependsonthefocusingofthesystem: F IGURE 2.31: A STARIMAGEDBYATELESCOPE (W IKIPEDIA )
83 F IGURE 2.32: OTF VARIATIONWITHIMAGEQUALITY (W IKIPEDIA ) Tohaveperfectlycharacterizedourimagingsystem,alongwiththeOTF,weneedtotake intoaccounttheccdthatwillcollecttheimage,andthatimpliestocorrectlybalancethe whites, that depend on the fact that the illumination might not have a perfectly distributedintensityalongthespectrum,andtoadjustthecontrast. FortheSCCTthismeanstoprovideatypicalsetofRGBtargetstocalibratethethree colorchannels,whiteandblacktargetstoserveasreference,andthenintermediate grayscalestoadjustthecontrast.FortheOTFitisneededageometricpatternsimilar theoneshownbefore,wheredifferentspatialfrequenciesareprovidedandusedto optimizethefocusingofthesystemandobtainthetransferfunction,althoughinthis caseitcouldbebettertotalkofaModulationTransferFunction,whichisaparticular caseoftheOTFthatneglectsthephaseeffects. Organics: Itisoneofthemainscientificobjectivesofthemission,toevaluatethehabitabilityof Mars,pastandpresent,andlookforpossibletracesofmarkersthatcouldmeanthe presenceoforganicsorpastlifeonMars.Duringtheintroductionoftheenvironmental requirementsitwascommentedthatthesurfaceofMarsiscontinuouslyirradiatedwith theUVfromtheSun,anditseffectontheorganics.Thismeansthatitisnotexpectedto findcomplexorganicmoleculesinthesurfaceofMars,possibleorganicsthatappeared atsomemomentinthegeologicalpastofMarsmayhavebeendegradedintosimpler moleculesduetotheenvironment.Itistheninterestingtoknowasmuchaspossibleof thisdegradationprocess,seeifthedegradationoccursjustbythebreakoflongorganics chainsintosmallergroups,ortheappearanceofnewgroupsduetotheintroductionof oxidants,forexample.SinceLIBSisnotsensitivetothestructureofthesample,only Raman spectroscopy will have the ability to see these variations in Mars. So,
84 summarizingintoasciencerequirement,aspartofthecalibrationtargetthereshould beaorganicsampleprovidingdifferentmoleculargroupsandRamanbandsthatcanbe measured whiledegrading when exposed to martian environment, italsoneeds, of course,tobeagoodRamanscattererinordertohaveagoodsignaltobeanalyzed. Chemometricscalibration: Finally,theobjectiveofSCAMisnotonlytoprovideidentificationofthetargets,butto providemeasurementsoftheabundanceofcertainelementsormoleculargroups.In thecaseofLIBS,whilethepositionofthedifferentemissionlines that conform a spectrumcanbeconsideredfixed,therelationbetweenintensitiescanbeaffectedby matrix effects, environment, etc. To take everything into accountandimprovethe calculations based on the different spectral data that provided chemometric informationofthesample.Notonlyitisusefultocalibrateeachtechniqueindividually, buttohaveacrosscalibrationamongthedifferenttechniques.Inthefinalsectionof this work we will present an example of the power of data fusion techniques for chemometriccalculations,itisimportantthentobeabletocalibrateproperlyhowthe differentchemicalabundancesofdifferentelements,asseenbyLIBS,correspondto molecularabundancesasseenbyRaman,orrelateluminescencefromcertainelement withitsintensityinLIBSspectra. Tohavethiskindofcalibrationitisnecessarytocarrywiththeinstrumentasetof samplesofdifferentmineralspecieswithverywellknownchemicalcompositionthat canbeusedasreferenceforcalculations. Ofcourse,forthesesamplestobeusefulintermsofcalibrationitisimportantthatthey are homogeneous and the same measurement is obtained no matter where in the samplesweshoot.Giventhespotsizeoftheanalysisandthepointingaccuracy,wecan setthislimittobearound100micronsforSuperCam.Thismeansthatatascaleof100 microns the different samples need to be homogeneous in terms of elements distribution,andalsohomogeneousfromRamanpointofview.Thishomogeneityneeds tobecharacterized,asneedstobethefinalchemicalcompositionofthesamplesthat willflytoMars. 2.3.2.4 Summarytable Asasummary,amorecompletelistofrequirementstobemetbytheSCCTisincluded inthefollowingtables,accordingtothelevelorkindofrequirementsconsidered.Please notethatpartoftherequirementsareunderNonDisclosureAgreementswithNASA, someinformationispartoftheirknowhowanditisnotforpublicrelease,that’sthe reasonforsomegapsorundefinitions:
85 REQ.TEXT Evaluation Thenot‐to‐exceedenvelopeforSuperCamcomponentsshallbeasshownon theappropriateSuperCaminterfacedefinitionsagreedwithJPL Demonstration Inspection Thenot‐to‐exceedvalueforSuperCamCalibrationTargetmassis0.27Kg Test TheaccommodationofSuperCamlasercalibrationtargets(LIBS&Raman), shouldmakethemviewablebySuperCamMast‐Unit,atadistancebetween 1.5and1.7m(goalis1.56mtocomparewithChemCam). ThepassivesamplesusedforVISIRandimagingshouldbeplacedinawaythat ensuresthatnoshadowingofotherhardwareontheRover’sdeckcanshadow them during operation time. Note: for the laser targets only, there is no requirement on shadows. Rationale: This distance is important to keep MSL heritage and to avoid exclusionzones/distances,wherethelasercannotbefired. Demonstration Inspection Allenclosedspacesshallhaveventpathsforreleasingentrappedairduring launchandforrepressurizingduringMarsentry. Demonstration Inspection SCCTfunctionalperformanceshallbeverifiedbeforeandafterenvironmental testing. Demonstration M2020 instruments which are sensitive to plume heating and/or contamination shall be designed or protected against such heating and contamination. This is due to the Sky Crane rockets, that couldimpactor contaminatetheSCCTduringlanding. Analysis Due to the wide range of latitudes covered in the initial definition of the mission(beforesettingalandingsite)andthelargediurnalswingsofMars surfacetemperatures,theSCCTwillneedtofacetemperaturesgoingfrom‐ 130ºCto80ºCduringitsoperationonMars Test DuringtheMarssurfacemissionphase,theSCCTshallbedesignedtomaintain temperaturesasrequiredwhenexposedtotheSurfaceSolarFluxesandthis shouldbedonepassively. DESIGN SCCTshallbedesignedtomaintaintemperatures,asrequiredwhenexposed totheMarsdiurnalnear‐surfaceandgroundtemperatureprofiles,andagain, thisshouldbedonepassively. Analysis Test The SCCT shall be designed to maintain temperatures as required when exposedtotheskytemperaturesofMars.Thisshouldbedonepassively. Analysis Test TheSCCTshallbetestedintheappropriatethermalenvironmentfordesign verificationaccordingtotheparameters,levels,andmarginsagreedwithJPL Inspection
86 REQ.TEXT Evaluation TheProjectspecifiesthetypeoftesttoberun(ie.Qual,PForFA).Thetest mediumandpressureshallbeasrequiredbyJPL. Inspection Assemblies subjected to thermal testing shall demonstrate performance withinspecificationoverallmissionoperationalmodesduringthecoldandhot temperature extremes and during transitions between thermal states. Test Hierarchy TheSCCTshallbedesignedforthefollowingMarsatmosphericcomposition. BaseduponVikingLandermeasurements,themolefractionsofgasesinthe Mars atmosphere are approximately: 0.955 ± 0.0065 CO2 0.027 ± 0.003 N2 0.016 ± 0.003Ar 0.0015 ± 0.005O2 0.0007CO 2.5ppmNe 0.3ppmKr 0.08ppmXe Inspection The SCCT shall be designed to operate and/or survive, as required per applicable Functional Requirements, over possible atmospheric pressure valuesitcouldface. Hierarchy TheSCCTshallbedesignedtowithstandatheatmosphericpressuredecay rate associated with the launch and also designed to withstand the Mars descentrepressurizationrate. Analysis TheSCCTshallbedesignedtooperateasrequiredperapplicableFunctional RequirementsduringandafterexposuretosustainedwindsrequiredbyJPL Analysis TheSCCTshallbedesignedtosurviveafterexposuretosustainedwindsas requiredbyJPL Analysis TheSCCTshallbedesignedtosurviveafterexposuretowindgustsasrequired byJPL Analysis The SCCT shall be designed to mitigate the effects of dust contamination duringMarsdescentandsurfaceoperations. Analysis Itshallbeshownbyanalysis(ortest)thattheperformanceoftheassembly will not be impaired by this deposition of dust over the required M2020 missionlifetime. Analysis
87 REQ.TEXT Evaluation TheSCCTshallbedesignedforormitigateforthesurvivabilityforaMarsdust stormcondition. Hierarchy The random vibration design and test requirements for assemblies are specifiedbyJPL.Thesespectrashallbeappliedineachofthreeorthogonal axesatthemountinginterfaceoftheassembly.TheDesign/Qualexposure timeis2minutesperaxis,PFandFAexposureis1minuteperaxis. Test Theassembliesshallbetestedtotherandomvibrationzonerequirementsof JPL,andmaybeforcelimitedtoreduceover‐testathardmountedresonance frequencies. Test Assemblies to be mounted onto/within the M2020 spacecraft shallbe designedtowithstandthepyrotechnicshockenvironment. Test Asaminimum,allmaterialsusedintheconstructionofinstrumentsshallbe non‐sheddingandlowoutgassingwithaTotalMassLoss(TML)of<1.0%anda Collected Volatile Condensable Material (CVCM) of <0.1% as tested in accordancewithASTME595“StandardTestMethodforTotalMassLoss andCollectedVolatileCondensableMaterialsfromOutgassinginaVacuum Environment Inspection The Outgassing Rate Measurement should meet ECSS requirements: 1.) Assume temperature causes no damage to hardware. 2.)Thetimeperiodforthebakeoutphasedoesnotbeginuntilthespecified temperatureandchamberpressureof5.0E‐5Torrarereached.Certification atthespecifiedcertificationtemperaturemaybeattemptedafter50hoursof thermal‐vacuumconditioningatthebakeouttemperature. Analysis Inspection SCCTExteriorCleanlinessRequirementsatLastAccess: CalibrationTarget:Molecular=100ng/cm^2;Particulate=L300 Analysis Inspection Thebakeoutoperationsandoutgassingmeasurementsshouldbedoneatthe specifiedpressure.Outgassingratesshallbedemonstratedtobelessthanthe maximumrateslistedpriortohardwaredelivery.JPLwithmeasuretheglobal outgassingrateafterdelivery. Analysis Inspection
88 REQ.TEXT Evaluation SCCTExteriorCleanlinessRequirementsatDelivery: CalibrationTarget:Molecular=100ng/cm^2;Particulate=L300 Analysis Inspection SCCT’s external surface average bioburden density shall not exceed 300 spores/m2. Demonstration The SCCT shall be compatible with PP microbial reduction processing (e.g. alcoholwiping,HMR,etc)andbioassayverification(waterdampenedswabor wipe). Inspection TheSCCThardwareshallbecleanedwithisopropylalcohol(orethanol)prior toassembly. Inspection The SCCT shall incorporate multiple microbiological samplings at different stagesoftheassemblyprocess. Inspection The SCCT Ground Support Equipment (GSE) shall also be cleaned with isopropylalcoholpriortoenteringacleanroomfacility/bench.Thecleaning leveloftheGSEshallbeperformedtothesamestringentlevelsthattheflight hardware. Inspection TheSCCTteamshallapplyplanetaryprotectionrequirementstoanypotential flighthardware(e.g.qualification,proto‐flight,flightspare)orhardwarethat maybeprocessedalongwithflighthardware. Inspection TheSCCTteamshallconductPPcleaningandmicrobialreductiononground support equipment and hardware used for integration and environmental testing. Inspection TheSCCTteamshalluseaClass100K/ISOClass8orbettercleanroomfacility orcleanbenchtoassemblemajorpiecepartsandsub‐assemblies,perform functionaltesting,finalintegration,andcontinuedtesting.Variousparameter specifications permitted for burden estimates where bioassays are not feasiblecanalsoeliminatetheneedforabioassay. Inspection AllmicrobiologicalsamplingandassaysfortheSCCTshallbecarriedoutby certifiedpersonnel. Inspection The SCCT team shall package and transport flight hardware to minimize biologicalandorganiccontamination. Inspection TheSCCTteamshallidentifyanyPPhandlingconstraintsaspartofthePDR, CDR,andHRCR/IDRpackages. Inspection
89 REQ.TEXT Evaluation The SCCT team shall provide an organic materials inventory of bulk constituentswiththeassociatedmassforalllaunchedhardware. Inspection A minimum of 20 calibration targets shall be implemented for LIBS. They should be representative of major rock units, following recommendations of the SuperCam calibration group. Design One 10X10 mrad FOV Ti target shall be used for spectral calibration with LIBS. Design A minimum of 2 calibration targets shall be implemented for Raman. They should be representative of 2 mineralogies, following recommendations of the SuperCam calibration group. Design There shall be a geometric target to measure resolution and modulation transfert function (MTF) of the imaging capability. Design There shall be 3 RGB targets for white balance of the imaging capability. Magnets will be used to minimize dust over >= 1 mrad. Design Two targets (white > 95% (TBC) and dark < 5% (TBC)) shall be used to monitor the radiometric and spectral calibrations of the VisIR capability. Magnets will be used to minimize dust over ≥ 1 mrad. Design EachindividualLIBScalibrationtargetshallbeabletoaccommodate>100 analysesof50lasershotseach. Inspection Test EachindividualLIBScalibrationtargetshallhaveanangularextentof?5mrad asviewedfromtheMU Inspection Twotargets(white>95%(TBC)anddark<5%(TBC))shallbeusedtomonitor theradiometricandspectralcalibrationsoftheVisIRcapability.Magnetswill beusedtominimizedustover?1mrad. Inspection OnetargetshallbeusedfortheRamaninvestigationwavelengthandintensity calibration.Itsangularextentshallbelargerthan2mrad. Inspection AtleastonetargetshalluseamagnettocollectdustforLIBSanalysis. Inspection SeveraltargetsshallbeusedfortheRMIinvestigation,tocheckforresolution, theRGBscale,andGreyscale. Inspection AtleastonetargetshallbeusedforthecalibrationoftheIRcapability.Its angularextentshallbelargerthan2mrad.Itwilluseamagnettominimize dust. Inspection SeveraltargetsshallbeusedfortheRamaninvestigationTheirangularextent shallbelargerthan2mrad. Inspection Threetargetsshallconsistofsamplesoftheplagioclase‐feldsparfamily,being closetotheend‐membersalbite,anorthite,andorthoclase. Inspection
96 TheSCAMinstrumentisahighheritageinstrumentinheritingcome components or designsolutionsfromChemcam.InthecaseofChemCamCT,thematerialsusedforthe target were ceramics, and some of them showed cracks after landing. As an improvementandlessonlearned,thebaselineistouseflashsinteringtomanufacture the samples to be included in the SCCT, what should provide a better mechanical performance,thisinadditiontoasmallersizeofthetargetsshouldprovideahigher reliability than ChemCam’s targets. Anyway, the fact of having at least 20 different samples from 20 different materials, passing through sintering presented some challenges: - Fromthemechanicalpointofview:Thebehaviorofthesamplesisunknown,and theamountthatwasavailablemadeitnotfeasibletoperformafullcharacterization oftheirproperties.Thislimitedtheaccuracyofsimulationsandanalysis. - Fromthethermalpointofview:Differentmaterialspresentedalso different thermalbehaviors,thisneededtobetakenintoaccountwhendesigningtheSCCT, thethermomechanicaldesignneededtoadapttoagreatvarietyofmaterials. - ThefinalsamplesincludedintheSCCTwerenottotallydefineduntilastageofthe projectfarpassedCriticalDesignReview,whenafinaldesignwasalreadyclosed. Thisimpliedthatseveralcandidatesneededtobetakenintoaccount,morethan reallyneeded,andthedesignneededtobereliableforanypossiblecombinationof thesecandidates. - Gluedmaterials.Gluingisalwaysarisk,especiallywhenhappeninginhardware goingthroughhightemperatures,asinDHMR.TheSCCThasgluingproceduresin themagnet‐samplestackofthepassivesamples,andinthegeometrictargetsand thediamond. - Highgshockzone.TheSCCTisincludedin3.5gzone,thismeansthatneededtobe qualifiedfor3500gpyroshocktest.Thiskindoftestcanbehardlysimulated,having animpactonthedevelopment,andisdifficulttobetested.Also,thepresenceof nonstandardmaterialsthatcouldbedamagedforhighgshockswasthemainrisk. ModelPhilosophy: AsforSCAMproject,fourmainmodelswereidentifiedasrequired: - SCCTCU(CalibrationUnit):thismodelconsistsonasetofcalibrationtargets,not limitedtothenumberthatcanfitintotheSCCTholder,andnotmountedinany supportingstructure.Thepurposeofthismodelistoserveastargetsforcalibration andfunctionaltestsforSCAM’sdevelopment. - SCCTEM(EngineeringModel):thisisanengineeringmodel.Themodelitselfneeds toberepresentativeoftheshape,envelope,weightandinterfaceoftheFM.This modelisnotintendedtoserveasSTM.TheRover’sEMmodelfunctionalitywillbe limited,sinceitwillhavenolaseron,whatmakesnotnecessarytoincludereal
97 samples.However,itshouldserveforpointingandaccuracytesting.Asthisisnota STM,thereisnotneedtobeflight‐likeintermsofcoatingsorpaints,whicharethe onlythermal‐controlmeasuresofthetarget.ThismodelisdeliverabletoJPL. - SCCTEQM(EngineeringandQualificationModel):thequalificationmodelneedsto beabsolutelyrepresentativeoftheflightmodel.Nodifferencesinenvelopeorsize (fartherthanmanufacturingtolerances)willbeallowed.Also,thecoating,surface finishingandpaintneedtobeascloseaspossible.Thesetofsamplestobeincluded inthismodelneedstobealsoflight‐like.Anychangesanddifferencesbetweenthis model and FM should be addressed through change notes and be taken into account if they could invalidate qualification campaign. This model is not a deliverable. - SCCTFM(FlightModel):thismodelincludesthefinalsetofsamplesprovidedbythe scienceteam.NeedstofulfilalltherequirementsapplicabletotheSCCT,withthe exception of those related to the qualification tests campaign. This model is deliverabletoJPLandistheonethatwillflytoMars. - SCCTFS(FlightSpare):atwinmodeloftheFM.Theidea,giventhekindofhardware, istomanufactureFMandFStogether,sosameprocesses,materials or workmanshipareassuredtoremainthesamebetweenFMandFS.Thismodelisto bekeptunderproject’scustodycleanandreadytodeliveruponJPLrequest. Given the mentioned constrains and risks, it was also found advisable by SCCT developmentteamthemanufacturingofanEngineeringTestingUnit(ETU).Toperform themostconcerningenvironmentaltest,whichistheshocktest,onaflight‐likemodel. Forthismodelthemass,themechanicaldesignandtheinterfaceneedtoremainthe sameasSCCTFM.ItshouldbeabletoaccommodatethesamesamplesastheSCCTFM andbeabletogounderpyroshocktesting.Thismodelisnotadeliverable. Developmentpathandmodeldetails: F IGURE 2.33 SCCT DEVELOPMENTPATH
98 Firstmilestonetobeaccomplishedwasthedefinitionofagoodsetofcandidatesforthe samplestobeimplementedintheFM.Thenumberofcandidatesneededtobehigher thantheneededsamplesfortheFM,inordertohavebackupoptionsifasampledidn’t survivethetestingcampaign,andalsotoprovideavarietyofcandidatestothescience teamtodecidethebestfittingsettoJezeromineralogy.Dueto requirements of homogeneity,thesamplesforallthemodelsweremanufacturedtogetherinsetsofat leastsixreplicates(CU,Development,qualification,FM,FSandsciencebackup).Onefull setofthesecandidatesistobedeliveredtoLANLasSCCT‐CU. Oncethepossiblecandidatesweremanufactured,apreliminarywasintegratedintothe SCCT‐ETUforshocktesting.Thistestservedtoevaluatetheperformance of the mechanicaldesignandthedifferentsamplesagainstpyroshcok. SCCT‐ETU: Thismodelneededtoimplementthefollowingfeatures: - Needstoaccommodatefivepassivesamplesintheirflightconfiguration. - Needstobeabletoaccommodateatleast23mineralsamplesinflight configuration. - ElementssuchastheGeometricplateorTiplatecanbesubstitutedbydummies. - Nameplatecanbealsosubstitutedbyadummy. - GeneralenvelopeofthemodelneedstorepresentativeofFMasshouldbethe mass. - RoverinterfaceneedstobethesameofFM. - MaterialsoftheholderstructuralpartsneedtobethesameofFM. - FastenerswillbesimilartothoseintendedforFM,astheyhavetoprovidesimilar fixation. - Surfacefinishing,coatings,paintsorcleanlinessarenotneededtoberepresentative oftheflightconfiguration. SCCT‐EM: TakingadvantageofthepartsmanufacturedfortheSCCT‐ETUandETU2integration, oncethismodelisnolongerneeded,ETUcanberefurbishedintotheSCCT‐EM,asa cost‐saving measure. TheSCCT‐EM is intended to beimplemented intheRoverEM model,modelwithlimitedfunctionality,andtherefore,representativityoftheEMisalso limited.HerearethefeaturestobeprovidedbySCCT‐EM: - Needstoaccommodatefivepassivesamplesordummies. - Needstoaccommodate23sampledummies. - Tiplatecanbesubstitutedbyadummy. - Flight‐likegeometrictargetisrequired. - Nameplatetoidentifythemodel. - GeneralenvelopeofthemodelneedstorepresentativeofFMasshouldbethemass uptoa20%uncertaintyinthemass.
99 - RoverinterfaceneedstobethesameofFM. - MaterialsoftheholderstructuralpartsneedtobethesameofFM. - FastenerswillbesimilartothoseintendedforFM,astheyhavetoprovidesimilar fixation. - Surfacefinishing,coatings,paintsorcleanlinessarenotneededtobeflight‐like. - NoremovebeforeflightcoverorotherGSEneedstobeprovided. F IGURE 2.38 F LOWCHARTFORTHEFINALDESIGN . SCCT‐EQM This model should be absolutely representative of the flying model and serves to validatethedesignandtoverifythedesigncapabilitytosurvivethequalificationlevels. Forthatpurposethedesign,envelopeandmassneedtobeequal,withinmargins,to thoseoftheFM.ShouldanychangeneedtobeimplementedbetweenEQMandFM, changenoteshouldbeissuedandtheimpactofthischangeinthequalificationneeds tobeaddressed. Alltheprocessesandmaterialsneedtobeflight‐like,andthemodel isintendedas rehearsalandtestingofCC&PPplans.Allthesamplesandplateelementsneededtobe likethoseoftheFM.Exceptionally,smalldifferencesinnotstructural/scienceelements werealloweduponagreementwiththeproject. ThismodelservedtodemonstratethatthedesignwassolidenoughtobesenttoMars, soitwasafterthequalificationcampaignthatthemanufacturingofSCCTFMandFSwas authorized,followingsamemanufacturingprocedures,mechanicalpartsandproviders used in the EQM. This model is not a deliverable. The details on the qualification campaignareshowedinalatersection.
100 SCCT‐FMandFS Thesemodelsarethefinaldesign,aftervalidationandinagreementwithscienceteam, thatismanufacturedtobesenttoMars.WhiletheFMwasdeliveredtoJPLafterthe acceptance campaign to verify workmanship, the Flight Spare remains in clean environmentwaitingforfinalactionsandacceptancecampaignincaseitisrequiredby JPL.Thisisacommonmeasureinspaceprojectnottoriskthelaunchincaseanunlucky eventmakestheFMnotabletobeflight. Thepathtoafinaldesign Aftertheintroductionofthemodelphilosophyandthedevelopmentplanfollowedto gettothefinal,flight,model,Iwantedtointroduceanarrativeofthedifferentevents andadvancesmadeinaccordancetothisplan,nowwithdates. AftertheannouncementoftheinclusionofSuperCam inthe payload ofMars2020 Rover,theteaminSpainwasset.BetweenthedateontheannouncementandtheDelta PDR,heldinValladolidinFeb.2016,wherethepreliminarydesignwasevaluatedbythe project,alltheworkdoneuntilthatmomentwasrelatedtodevelopmentofdifferent modelsandconceptsthatcouldbeworthyevaluating. PrePDR: F IGURE 2.39 C HEM C AM ' S C ALIBRATION T ARGET BeforethePDRwasheld,aconceptdesignbasedonChemCam’scalibrationtargetwas thebaseline.Inthisconceptdesignjust20mineralsampleswereincluded,alongwith aspectralonwhitetargetfortheIR.Thecolorcalibrationandgrayscalewasinitially plannedtobedoneusingaplate.Regardingthefixationofthesamplesinplace,itwas donebymeansofamanufacturedscrewedlidandtheloadwasappliedbyaspring washer.Thismodelhadseveralissuestomeetalltherequirements.
101 FIGURE2.40SCCTCONCEPTBEFOREPDR(AVS) Tostart,northespectralonorthecolorplatehadanymeasuretopreventthedeposition ofdust.Also,thefixationmechanismforthesampleswasconsideredarisky,although itwaslaterkeptduringPDR. Inthisconceptthemainconcernwasthethreadofthesamplescrew.Thelidwastoo thin,whatrequiredthethreadofthescrewtobeextrathin.Thiscoulshavebeena potentialissueduringintegrationifatanypointthelidwasdamaged. ThedifferentBelleville,orspringwasher,wereintroducedtoabsorbvibrations,shocks, andmanufacturetolerancesofthesamples. PDRlevel: ThePDR,standingforPreliminaryDesignReview, served as the first opportunity for the whole SCCT development team to be together. This milestone meant a great boost to the project, with several detailschangingtowardsamoredefinedmodelthat couldmemanufactured. The first change was the need to prevent dust depositiononselectedsamples.Thiswasaddressed using a development similar to the one used in MastCam’scalibrationtarget,thatwasalsobasedon themagneticexperimentsonboardtheMER.Thisconsistontheinclusionofamagnetic ringaroundthesamplesthatwillmaketheferromagneticdustonMarstofollowthe FIGURE2.41SCCTSAMPLEFIXATION INITIALCONCEPT
102 fieldlines.Thisleavesasmallareainthecenterofthesamplewherejustnon‐magnetic dustcoulddeposit. Thesample‐stackisassembledusingadhesive.Themagnetswereselectedtobethe same MastCam used and MastCam Z was planning to use, so the heritage and experience with these elements minimized risks. These magnets are delicate SaCo magnets that are manufactured bysintering.Bythemselvestheyare a brittle componentthatrequiresofthesampleandthebondingwithittohaveacertainlevel ofstructuralresistance. AnotherchangeintroducedduringthePDRwasachangeinthekindofsamplestobe usedforthecolorbalance,andtheVISIRspectroscopy.Theusualsamplesthatareused insimilaraplicationsonearth,theSpectralon TM forexample,areusuallybasedonPTFE, a polymer know to have a bad endurance against UV radiation. This material was selectedtobechanged,andthecolorsamplesalsochangedfromaplatetoadapttothe magneticdustremovalsystem. Finally,somethingthatbackthenwasstillondiscussion,theheliscout,introduceda concern in the project. The antenna used to communicate with the helicopter was placedonapositionoftheroverdeckthat,undersomeorientationatcertaintimesof theday,couldcastashadowoverthereflectancestandards.Thiswasidentifiedasan operationalriskanddiscussionsanditerationsbetweenSuperCamteamandJPLstarted sothiscouldbesolved.Thedifferentoptionsevaluatedduringtheseiterationshadtheir impactinthedevelopmentoftheSCCT. Theproject,antthedevelopmentteamoftheSCCTgainedmomentumthankstothis meeting,andbecause of that thismeetingshouldbemarkedasamilestoneinthe historyofSCCT.InthepreviousmeetingsbeforetheformalPDRthedefinitionofthe samplesandtheholderevolvedquickly,andinparallelanalysiswereprovidedonthese latestevolutionsofthedesign.Asaresult,agooddesignforthelevelofdefinition requiredatPDRlevelwasachieved. F IGURE 2.42 A) C ROSS SECTION OF THE SAMPLE ‐ MAGNET STACK . B) T EST SHOWING HOW FERROMAGNETICDUSTAVOIDSTHECENTEROFTHESAMPLE . 10
103 PreCDR: Atthismomentoftheprojectoneofthemaindriversinthechangesanddifferent evolutionssufferedbytheSCCTwasthepossiblechangeintheaccommodationonthe rover,andamajorconcernregardingtheshockleveltobeappliedtotheSCCT. Also,anewelementthatwasn’tatagooddefinitionlevelatPDRwastheRemoveBefore FlycoveroftheSCCT.ThiselementisintendedtoprotecttheSCCTduringtransportation andhandling,andalso,oneitismountedontherover,topreventitfromscratchesor impactsduringATLOactivities.Thiselementisnotintendedthenasacontamination controlelement.TheSCCTisnotexpectedloleavecontrolledenvironmentsatanytime. ThedesignofthiselementanditsfixationtotheSCCTisalsoanelementthatchanged atdifferentmomentsoftheprojectandintroducedsmallchangesintheSCCTdesign. ThesamplesusedforVISIRcalibrationchanged,fromjustwhiteandblacksamplesusing themagneticdustremovalsystem,andaseparatedcolorplate,todedicate5slotsto haveRGBandwhiteanddarkreflectancestandardsprotectedbythemagnet,witha separatedgeometrictarget. Asmentionedbefore,thepartsoftheSCCTthatsufferedmorechanges and reevaluationswerethoserelatedtotheprotectionagainstshocks.Thepossiblechange intheaccommodationoftheSCCTtoahighershockzonegaveaincreaseinthemass budgetfortheSCCT.Attisstagethefixationsystemchangedseveraltimes,andalsothe designoftheSCCT.OneoptionconsideredwastosplittheSCCTintotwoholders,with thesamplesaffectedbyshadowinginaseparated,smaller,dedicatedholder,andthe restoofthesamplesinamodelsimilartotheonedesignedatPDR.Otheroptionwasto prescindtheindividuallidsandusejustonebackcovertofixthesamplesinplace. Differentoptionshaddifferentadvantagesanddisadvantages.Attheend,afewextra grams allowed a redesign of the holes and fixation lids, changing also the shock
104 absorbingmeasurementsthatnowallowedtheSCCTtodealbetterwithdifferentsizes ofthesamples.ThisisthefinalmodelpresentedatCDR. FIGURE2.43MAINREDESIGNSOFTHESCCTBETWEENINITIALCONCEPTANDEQM(AVS/UVA)
105 CDRlevel: AtCDR,anothertypicalimportantmilestoneIspaceengineering,theSCCTdesignhad evolved significantly. The mode, at CDR had incorporated several changes and suggestions from the mechanical team. The most important was the change in the fixationsystemofthesamples. TheinitialconceptthatusedindividualscrewedlidsandBellevillewashersneededto change.Firstreasonwastheinadaptabilityofthepreloadingspringstoawidemarginin manufacturingtolerances.Again,theusageofseveralkindsofsamples,manufactured withanewprocess(sintering),madedifficulttoestimatethemanufacturingtolerances achievableinthefinalmachiningofthesamples.Oncethesamplesweremanufactured thedifferencesamongthemwereinthesameorderofthelengthoftheBellevillespring loaded,meaningthatusingthesamedesignforallthesamplesonesamplecouldreceive excessiveloads,increasingtheprobabilityofdamages,whileothersamplecouldreceive almostnone,beinglooseintotheslot.Also,thiskindoffixationsystemwastoostiff, meaningabetterpropagationoftheshockwaveduringthepyroshockevent.Bothissues were solved by the introduction of different element, a wavespring, with a greater operative length that implies a better adaptability to different sizes while better absorbingshocks. Anotherchangeimplementedwasthelidstofixthesampleinplace.Thescrewedlidsin theinitialconcept,thesamesystemChemCamused,wasidentified as risk during assembly.Thethreadlineofthisindividualscrewswasverythin,thematerial,although ishard,couldbedamagedduringassembly,andinthatcasethedamagedpartcouldbe themainholderbody.Thefinalsolutionimplementwasanindividuallidthatwasfixed tothemainbodybymeansoftwoscrewsfasteningagainstaninsertthatprotectedthe holder,allowedseveraloperationsoffasteningandunfasteningwithoutrisk,andalso providedthelockingsolutionitself. Minorchangeincludedwasfourthreadedholesineachcornerofthemainbodytoallow thefixationoffiducialelementsthatwillallowJPLtocorrectlyalignandpositionthe SCCTaccordingtotherequirements. Afinalelementthatwasalsobetterdefined,althoughnotshowed,wastheRBFcover. Atthatmomentitwasfixedtothestructureusingdedicatedthreadedholesinthemain structure. DuringCDRanalysiswereshowed,alongwithabetterdefinitionofthesamplesthat wouldbeincludedinthefinalFMmodel.Again,oneoftheconcernsattheprojectlevel wastheperformanceagainstshocks.AsaresultadevelopmenttestusingJPLfacilities wasencouraged.
112 F IGURE 2.48 S KETCHOF SCCT EQM Thewholeframeismadeofaluminum7075,analuminumalloywithzincofwideusein aeronauticsforitsstrengthandlowdensity.Unfortunatelythiskindofalloyhasalimited resistancetocorrosion,reasonwhy(inaccordancewithECSSstandard)allthe7075 partswerecoatedwithachromaticconversiontreatment. EachsamplewasmountedintheSCCTwiththepreviouslydescribedwavespringandlid design.TodimensiontheholesintheSCCTamaterialwiththefarthestthermalbehavior totheT7075wasselected,inthiscasePTFE,sothesamplesslotscouldstillhousethe samples under the worst case of thermal expansion or contraction given the huge ThermalExpansionCoefficientmismatch.Asforthetemperatures,theworstcasewas selected,coveringarangefrom‐135ºCto115ºC. Forgeneralsimulationsanaveragesamplewasselected,withamassof1.61gramsin thecaseofmineralsamples,and4.22forthepassivesamplesincludingmagnet.This estimationwaskeptfordesignpurposesandalsoforthecalculationthemassbudget, anditisimportanttoremarkthatthewholemassofthesampleswasconsidered(and infactitwas)tobelessthan60grams,whatlessthana25%oftheplannedmassfor thewholeSCCT,numberthatpictureshowthewholemainbodyframedominatedthe mechanicalbehavioroftheSCCT.
113 InformationregardingtheFEManalysisoftheSCCTcanbefoundinthereportfromAVS: AVS‐SCCT‐ANA‐0002andrequesteduponapprovalbyUVAandAVS.Generalconclusion ofthisreportmatcheswiththepreviousstatement.Thealuminumstructuredominates thefrequencyresponseofthewholesystem,withalocalmodein1724.3Hzwithan associatedmassfractionof68.38%. DifferentloadswereevaluatedinthepreviousFEManalysisreport,showingthatthe finaldesignoftheSCCTcouldmeet,withmargin,thedynamicsloadsrequiredbythe project.Otherloadswereconsideredas: - Winds loads: given the low density of the martian atmosphere, the calculationsshowedthatforspeedsupto100m/stheforceappliedbythe windscouldbeneglected.Thefollowingexpressionwasused: 𝐹𝜌𝑉𝐶𝐴 2 Wherethedensityoftheatmosphereismultipliedbythesquareofthe windspeed,thedragcoefficientandtheareaexposedinthedirectionof thewind.FortheSCCTthisforcewas0.28N - Thermalloads:aswascommentedbefore,thegreatestthermalexpansion mismatchhappensinthesamplesandthatwassolvedbydesign.Other stressesforthemismatchesbetweenthealuminaofthegeometrictarget andthebracket,ortheTitaniumplateandthemainbodystructurewere analyzedandconsideredsafe.Rocketplumeswerealsoevaluatedandtheir effectwasfoundnotariskfortheintegrityoftheSCCT. Contaminationconsiderations: Anotherelementthatwasevaluatedintermsofanalysisisthecontamination.There weresomeconcernsregardingthepossibleimpactofcontaminationintheSCCTtargets thatcouldimpactthecalibrationmeasurements.Fortheestimatedcontaminationthat couldbereceivedbytheSCCTthefollowingtableshowssomeestimatesperactivity, withtheglobalamount:
114 TABLE2‐9CONTAMINATIONPREDELIVERY Stage Particlecont. (mm2/m2) Molecularcont. (g/cm2) IntegrationISO‐4 0.4 5.48E‐10 thermaltest 20 5.00E‐08 mechanicaltest 14 1.10E‐10 storage30daysISO‐5(bagged) 1 3.29E‐09 Finallevel 35 5.39E‐08 ValuesfarfromtheL300requirementforparticulate,and0.1microgramsperosquare centimeterformolecular. Anotherconsiderationshouldbetakenintoaccountwhenevaluatingcontamination sourcesthatcouldappearaftertheassemblyanddelivery: - AlltheactivitiesprevioustothelaunchwillbedoneinanISO8environmentor better.Contaminationratesperyearintheseenvironmentsareshown in the followingtable: TABLE2‐10CONTAMINATIONPERYEARINCLEANROOMS Environment ISO5 ISO6 ISO7 ISO8 Molecular contamination per year (g/cm2) 1*10-7 1*10 -7 2*10 -7 2*10 -7 Particulate surface contamination per day (mm2/m2/24h) 2 10 52 275 - Foranycontaminationsourceprevioustothelanding(rocketplumes,degassingof nearpartsinvacuum),wheredustwouldbethemainconcern,theamountthat couldbeabsorbedbythesamplesshouldbeminimumandsuperficial.Inthecase ofLIBS,asageneralprocedure,thefirst5shotsarediscardedandcleanthesample, sonocontaminationshouldaffecttheLIBSmeasurement.ForRaman,giventhatis a standoff Raman system, the contamination level should be veryhightobe detectedbythistechniqueorVISIR. As a result, possible contamination was evaluated and found not concerning if the cleaningproceduresandcontaminationcontrolplansarefollowedproperly.
115 Forthedust,however,thegreatestconcernisthatsomesamplesneededforimaging orthesampleusedforRamancouldbecoveredbydust,resultinginanopacityofthe samples. It was already described how the magnetic dust removalsystemis implementedincriticalsamplestocopewiththisrisk. F IGURE 2.49 M AGNETICFIELDLINESFROMTHEMAGNETSAROUNDTHEPASSIVESAMPLES (NBI) Figure2.49showshowaferromagneticdustparticlewouldfollowthefieldlinesandbe depositedfarfromthecenterofthesample,leavinga4mmdiametercleararea inthecenter. Inadditiontothisdustcountermeasures,thewholeSCCTwillbetilted,limitingthe amountofdustthatwillbedepositedonit.Inthefollowingpicture,Fig2.49Bfrom Curiosity’sroverdeckafter1197Solsitcanbeseenhowwhiletheflatroverdeckis coveredbydust,ChemCam’scalibrationtargetremainsclean. F IGURE 2.49B C URIOSITY ' S R OVERDECKAFTER 1197 S OLS (JPL). ThistiltedpositionoftheSCCTclearlycontributestokeepitclean. Thefollowingexpression,morerelatedtosolarpanels,relatesthedustdepositionrate onageneralsurfaceatacertaintiltangle,intheworstcasescenario: r=(0.0072)(cosTilt.)/sol=0.0046/solfor50ºtilt.
116 So,accordingtothepreviousexpression,andconsideringr=1foratotalcoverageofthe samples,itwilltake217.39solstoreachthetotalcoverageofthesamples,intheworst casescenario. Thisworstcasescenarioisfarfromtherealitythatcanbeseeninthepicturesfrom Curiosity,andaccountsforanextraordinarydustactivityonunprotectedhardware.This calculationscanbethenevaluatedwiththeeffectofthemagneticdustremovalsystem. ConsideringthedatafromPhoenix’smagneticexperimentsinwhichthedustsettling ratewas18timeshigherinthedirtyareaofthemagnetswhencomparedtotheclean area(Drube, 2009), and assuming that this is related to the amount ofdustthatis ferromagnetic and is effectively affected by the magnet ring, if considering the effectivityofthesystemtoreducethedepositionrateinafactor10inthecentralarea, thismeansthatthetotalcoverageoftheprotectedareainthecenterofthesamples wouldhappenafter2173sols,farfromthe670missionsolsofnominalmission,andit givesanideaofhowprotectedthesesamplesare. Othercountermeasureswereintroducedtoprotectallsamples,astheinclusionofa chamferinthelipoftheholderontop,thatlimitsthethicknessofdustthatcanbe accumulatedinthisinterface.Again,asageneralapproach,theLIBStargetswillbe cleanedbylaser,andsamplessurroundingLIBSsampleswillbealsocleanedbythislase shots. Finalconclusion: Asfarascanbeevaluatedbyanalysis,thedesignissolidenough and meet all the requirements. Plans and simulations were done to make sure the SCCT will endure duringitsoperationtime.Otherfactorsneededtobeevaluatedbytest. Aswasdiscussedbefore,thetestsdoneonthemodeltobedeliveredforitsassemblyin therover,theacceptancetests,areonlydonetoverifyworkmanship,reasonwhythey weren’tincludedinthepresentwork.Integrationandtestingofthedifferentmodels DifferenttestsandinspectionshavebeenplannedtoverifythattheSCCTcomplieswith the endurance, interface and functional requirements for this element. Different inspectionpointswereidentified,someofthemdirectresponsibilityofUVAandothers MandatoryInspectionPoints(MIPS)thataredoneinaccordance,andifdesiredwith concurrence,ofJPL. Ingeneral,UValedandchairedmostoftheinspections,withtheexceptionofincoming inspections of material that were carried out by AVS. For several inspections and measurementsUVacounted withtheexpertiseandhelpofINTA.Dependingofthe model,theAITflowisasfollows:
117 C HART 2‐1 ETU/EM AIT FLOWCHART
118 C HART 2‐2 EQM AIT FLOWCHART
119
120 C HART 2‐3 FM/S PARE AIT FLOWCHART
121 Asaremarkregardingtheflowcharts,theSCCTunitbakeoutwasdecoupledfromthe contamination witnesses bakeout in order to subject the SCCT unit to the DHMR temperaturesbeforethequalificationtests.Thiswasn’tthecasefortheFM. Isauthor’sunderstandingthatthequalificationcampaign,thetestsdoneontheEQM, servedtodemonstratethattheSCCTcouldfacetheenvironmentalthreatsassociated withthemission.Forthisresondetailsonthecampaignandresultsareshowninthe followingsection. 2.3.5.2 Qualificationandtests ThequalificationcampaignoftheSCCTwasagreedwithJPL,andincludedseveraltests thatcanbeseparatedintotwodifferentgroups:dynamicstestsandthermaltests. 2.3.5.2.1 Dynamicstests ForthedynamicteststheSCCTwasfirstlymountedonavibrationtable.Inthistable threetestsweredone,twoaspartofthequalificationcampaign, and one done repeatedlyasverification. Forverificationofthehardware,sinesurveysaredoneatdifferentmomentsofthetests lookingforvariationinthemodesthatcouldmeanthatsomethingisbroken,orloose. Additionally,beforethedynamicstest,athermalvacuumat115ºCfor120hourswas doneonthehardware.Thisinducedthethermalstressingluesbeforedynamicstesting andallowedtoassestheenduranceofthebondingline. ASpartofthequalificationcampaignthen,twodifferenttestsweredone,quasistatic loads,QSL,andRandomVibration. Afterthevibrationtests,theSCCTEQMwasmountedontheshockstabletoreceivetwo 3500 g shocks (the levels were lowered by JPL between developmenttestsand qualification)ineachaxis.
128 F IGURE 2.58 I NITIALCYCLESINPHASE 2 Theteststoppedafterthecompletionofthisphase2tointroduceGN2gasupto6mbars ofpressure,andthenperformedthelastcycleatMarspressure. F IGURE 2.59 D ETAILOFTHELASTCYCLEAT M ARSPRESSURE
129 ShowingthatthetemperaturesrequiredbythetestproceduresagreedwithJPLwere reachedduringthewholetest. AfterthistesttheSCCTwasdeeplyinspectedshowingnosignalsoffatigue,ordamages ofanykind,withspecialattentiontothereflectancestandardsandthegeometricplate. FIGURE2.60EXAMPLEOFINSPECTIONBEFORE(LEFT)ANDAFTER(RIGHT)WITHAMAGNIFYINGGLASS. NODAMAGESWEREFOUND. Thefinalsteptoconsiderinthequalificationcampaignisthatduringthisrehearsalthe hardware is also compliant with the Contamination and PlanetaryProtection requirements. ContaminationwitnessesforPACandMOCwereinplaceduringthewholequalification process. Whenever the unit is uncovered, the witnesses were uncovered first. For bioburdenverification,swabassaysweredoneontheSCCTunit. PAC:Theparticulatecontamination wasmeasuredusingPFOsandwitnesses during integration,mechanicaltestsandTVACtests.Themeasuredvaluesarethefollowing: - Integration:26ppm - Mechanicaltests:11ppm - TVACtests:7ppm - Total:44ppm Given that the allowed PAC obscuration corresponding to the L300 requirement imposedfortheSCCTis329ppm,thePAClevelsarefoundinsidetherequirement. MOC:TheMOCwitnesswasuniqueduringthewholequalificationcampaign,including integrationandthequalificationtests.Themeasurementperformed(IR)afterthewhole qualificationwas4ng/cm2ofmolecularcontamination,whichismuchlowerthanthe allowed100ng/cm2.
130 Note:duringtheTVACtest,theMOCwitnesscouldnotbeplacedinsidethechamber. Thispointiscoveredinsection7.5,lessonslearned. BB: SeveralBBassaysareperformedalongtheprocess,allofthemproviding zero spores.Thismeansthatthetotalcontaminationistheminimumpossible(byprocess, 500spores/m2).GiventhetotalsurfaceoftheSCCT,thetotalnumberofsporesis160 spores/m2,whichalsocomplieswiththeallowed300spores/m2.Nevertheless,aDHMR isforeseentobecarriedoutontheFMbeforedelivery(fortheEQMitwasperformed beforethequal.testinginordertotesttheunitaftertheDHMR). 2.3.5.2.3 FinalInspections Visualinspectionsweredonebefore,duringandafterthequalificationtestcampaignon theSCCTunittoverifythephysicalintegrityoftheunit,aswellasitscleanlinessstatus. Inaddition,duringthedynamictests,low‐levelfrequencysurveyswereexecutedto verify the modal response of the unit. After the qualification campaign, a thorough inspectionincludingthedismountingofseveralsampleswasperformedtoverifythe internalstatusofthesamplesandmechanicalparts(e.g.wavesprings).Thefollowing picturesshowsomedetailsoftheinspections.Thesewerecarriedoutwithamagnifier fordetail. Afterintegration AfterDHMRanddynamicstests
131 AfterTVACtests The most critical tests are the dynamic tests. The detailed picturesofthesamples, beforeandafterthetestareshownbelow:
132 Thefinalinspectionincludeddismountingofseveralofthesamples.Nodamageswere foundinanyofthem,norinthewavespringsoranyothermechanicalpart(notevenon thesampleswithpre‐existingdamagesasforexamplesample5.1). Cyanmagnet(after) Sample5.1(after) 2.3.5.2.4 Incidencesandlessonslearned Asanexampleofthevalueofthequalificationcampaignalistoflessonslearnedis included.Theselessonsallowedtoimprovethedesign,integrationandtestingofthe FM,whatistherealcriticalmodeloftheSCCT. CCandPAINTINCIDENCESFOUNDDURINGTHEVIBRATIONANDSHOCKTESTSATCTA. 9‐13/4/2018: Acrylickaptonleftadhesiveresiduesintheglovesandwasthereforechangedforsilicon basedKapton.Intheendthisdemonstratedtobeabadidea,asitbondedtoowellto thepaintandremovedpartofthepaintononesideoftheSCCT LESSONLEARNED1:DonotusesiliconbasedKaptontape,evenifthelatterleaves residuesonthegloves. Aftervibrationtest,particlesweretrappedinthemagneticsamples.SCCTwasbagged, buttheIFscrewswerenotcovered,andthisistheprobablesourceofcontamination.
133 LESSONLEARNED2:UseKaptontocovertheIFscrews,orprepareabettersetupfor baggingtheFM. LESSONLEARNED3:toremoveparticles,firstblow,seconduseKapton,thendrywipe, thenIPAwetwipe. Afterthetests,thisdirtisswabbed/wipedtotrytoremoveit,withthefollowingresults.
134 Itcouldbeseenthatitwaspartiallyremoved.Nofurtherswabbingweredone,asthe paint seemed to be affected by the swabbing. Actually, using Kapton tape some powderedpaintwasremoved. Whenremovingthevibrationaccelerometerstogototheshockconfiguration,itwas observedthatsomeadhesivecontaminationisfoundonthepaint.Itisnotpossibleto removeitwithwipingortapeliftwithKapton. Alsointhecentralpart,someadhesiveisfound.Itispossibletocleanitwithswab.
135 LESSONLEARNED5:uselargerpadsofKaptontoplacetheaccelerometersontheFM model. However, it was noted that, after cleaning, some black spots that were not there appearedonthesurface,andageneraldecreaseofthepaintwasobserved‐>thismeans thatswabbingwithIPAremovesthepaintsurface,ascommentedbefore. AgeneraldirtyaspectoftheSCCTwasfoundafterthetests.After cleaning it was possibletorecoverthecleanlinessofthesurface,buttakingintoaccounttheprevious issueswiththepaint.
136
137 MOCwitnessplacementduringTVACtest DuringTVAC,theMOCwitnesscouldnotbeplacedinsidethechambertogetherwith theunit.ThiswascorrectedfortheFM,althoughtheimpactoftheTVACtestonthe MOCwasverylimited. 2.3.6.1.1 Finalconclusionsfromthequalificationcampaign TheQualificationofasystemisoneofthemostdemandingphasesinaspaceproject. AlthoughthemanufacturingandassemblyoftheFMisthefinalgoalandit’sthemost importantandpreciouspieceofhardware, EQMdemonstrates thatalltheprevious workdoneduringthedesignandanalysisstagewascorrect. TheSCCTEQMpassedsuccessfullythequalificationcampaigninthesummerof2018. WhatallowedthemanufactuturingoftheFMthatwasfinallydeliveredinspringofthe nextyear,2019. 2.3.6.2 TheFlightModelandfinalscheduleofthemilestonesaccomplished duringthiswork As a result of the lessons learned during the manufacturing and the qualification campaign of the SCCT, some small changes were introduced in this model. These