Op#csforAXISWilliamW.Zhang

NASAGoddardSpaceFlightCenter

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NextGenera#onX-rayOp#csTeam

2

K.D.Allgood1,M.P.Biskach1,J.Bonafede1,K.W.Chan2,M.Hlinka1,J.D.Kearney1,L.D.Kolos,J.R.Mazzarella1,R.S.

McClelland1,H.Mori2,A.Numata1,T.Okajima,L.G.Olsen,R.E.Riveros2,T.T.Saha,M.V.Sharpe1,P.M.Solly1,W.W.Zhang

NASAGoddardSpaceFlightCenter1S6ngerGhaffarianTechnologies,Inc.

2UniversityofMaryland,Bal6moreCounty

J.M.Carter,J.A.Gaskin,W.D.Jones,J.J.Kolodziejczak,S.L.O’DellNASAMarshallSpaceFlightCenter

WilliamW.ZhangAXISWorkshop

KeyFeaturesofAXISOp#cs

•  Highangularresolu#on– 0.5”HPDonaxis,similartoChandra’s– CanbebeVer,butatexpenseofFOV

•  Largefieldofview(FOV)– 15arc-mindiameterwith0.5”PSF– Cf.4arc-minsofChandra-ACIS-I

•  Largeeffec#vearea– 10XChandra’sat1keV– 15XChandra’sat10keV

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Eff.Areavs.Energy(op#csonly)

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AXIS

Chandra

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Effec#veAreaRa#ovs.Energy

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PSFvs.Off-axisAngle

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Chandra

AXIS

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Op#csTopLevelErrorBudget

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ContributiontoHPD(") Notes

Axialfigure(sag) 0.1 ShownasofJune2017Axialfigure(otherthansag) 0.2 ShownasofJune2017Focus(roundness,coneangleanditsvariation)

0.2 Probablycanbeshownby2018

Coating(distortiontoaxialfigureandfocus)

0.1 Difficulttoassessduetoinssuficientdata.

Alignment 0.1 By2019

Bonding 0.2 Difficulttoassess.Emphasisofworkincomingyears.Tallestpole!!!

0.1 Canbedonerelativelyeasily.0.1 Needtobelookedat.0.1 ShownbyanalysisasofJune2017.0.1 ShownbyanalysisasofJune2017.0.4 RSSofallabovenumbers.0.3 TimoSaha'sdesignmemo.

0.5 RSSofabovetwonumbers.

MirrorAssemblyFabricationTotal

MirrorAssemblyOn-OrbitPerformanceMirrorAssemblyOpticalDesignTotal

ParameterorProcess

MirrorSegment

Integrationofsegmentstometa-shells

Integrationofmeta-shellstoassemblyLaunchshift

ThermalgradientsGravityrelease

WilliamW.ZhangAXISWorkshop

OutlineofPresenta#on•  Op#caldesign

–  Fundamentalgeometryandphysics– AXISmirrordesign

•  Technology–  Substratefabrica`on–  Coa`ng– Alignmentandbonding

•  Engineering–  Structural,thermal,andop`calperformance

•  MakingthecasetotheDecadal–  Casefortechnicalreadiness–  Caseforcostandschedule

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Op#calDesign

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GeometryandPhysics(1/2)

•  X-raysreflectonlyatgrazingangles– Grazinganglesdecreasewithenergy– àFieldofviewdecreaseswithenergy

•  AnX-raytelescopeisreallya“lightbucket”– Manyconcentricshells– X-raysfromdifferentshellsaddincoherently

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GeometryandPhysics(2/2)•  Diffrac#onlimitsareaweightedaverageofmanyshells– Eachshell’sdiffrac`onlimitispropor`onaltof/(H*r*E),wherefisfocallength,Hshelllength,rshellradius,andEx-rayenergy

– Eachshell’seffec`veareaispropor`onaltoH*r*R2(E,r/f),Risreflec`vityanddependsonEandr/f.

•  Off-axisPSFisweightedmeanofmanyshells– Eachshell’sbeingpropor`onaltotheta2*H/r,wherethetaisoff-axisangle

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Prac#calImplica#ons•  On-axisPSFconflictswithFOV

– Goodon-axisPSFdemandslongshells– Goodoff-axisPSFdemandsshortshells

•  DichotomyofSo]andHardX-raysforanearlydiffrac#on-limitedTelescope– SoiX-rays:pooron-axisPSFbecauseofdiffrac`on,butlargeFOVbecauseofgeometry

– HardX-rays:goodon-axisPSFbecauseofdiffrac`on,butsmallFOVbecauseofgeometryandbasicphysics

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AnExampleDesignforAXIS

Parameters ValuesFocallength(mm) 9,000

OuterDiameter(mm) 1,500

InnerDiameter(mm) 400

MirrorSegmentAxialLength(mm) 200

MirrorSegmentThickness(mm) 0.5(1.0)

UnobstructedFOV(arcmin) 15

Coa#ng iridium

No.ofshells 163

Diffrac#onlimits(arcsec90%dia.) 0.2@1keV

MassofMirrorAssembly(kg) ~500(~1,000)

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TakeawayMessages

•  AXIScanhaveeffec#veareas(op#cs+detector)–  >5,000cm2at1keV–  >1,000cm2at5keV

•  AXIS’sPSFandFOV– Moreorlessuniform0.5”HPDina15-armindia.FOV–  BeVerPSFon-axisatexpenseofoff-axisPSF.Forexample,0.1”on-axis,1.5”at6-arcminoff-axis

Underreasonableassump#ons:Focallength:9meters

Outerdiameter:1.5meterMirrorthickness:0.5mm

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Technology

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TheMeta-ShellParadigm

•  Eachmirrorsegmentisfabricated,qualified,andthenalignedbyandbondedtofourspacerswhichkinema`callyconstrainit.

•  Severalhundredmirrorsegmentsarealignedandbondedtoformameta-shell.

•  Adozenorsometa-shellsofdifferentdiametersformthefinalmirrorassembly

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MirrorSegment

Meta-shell

MirrorAssemblyWilliamW.ZhangAXISWorkshop

ThreeBasicElements•  SegmentorSubstrates

– Figurequality,includingmicro-roughness– Thicknessandmass

•  Coa#ng– Highreflectance– Nofiguredegrada`on

•  AlignmentandBonding– Loca`ngandorien`ngeachmirrorsegment– Keepingitthereforgood– Doingsowithoutcausingfiguredistor`on

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SubstrateFabrica#on•  Material:mono-crystallinesilicon

–  Freeofstress–  Lowdensity:2.35g/cm3

–  Highthermalconduc`vity:150Wm-1K-1–  Highelas`cmodulus:130–188Gpa–  Lowthermalexpansion:2.6ppm/K–  Commercialavailability–  Beststudiedandunderstoodmaterial

•  Fabrica#onprocess:polishing–  Grinding,lapping,slicing,acidetching,full-aperturepolishing,&sub-aperturepolishing,etc.

–  Bestpossiblefigureandfinishquality– Massproduc`onandrobo`cstominimizecost

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Fabrica#onSteps

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ConicalformgeneratedMonocrystallinesiliconblock Light-weightedsubstrate

Etchedsubstrate Polishedmirrorsubstrate TrimmedmirrorsubstrateWilliamW.ZhangAXISWorkshop

StatusofSubstrateFabrica#on

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ImagePerformancePredic#onofaPair

SiliconMirrors:0.44”HPD

SlopePowerSpectralDensity

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SubstrateFabrica#onSummary•  Canrealizeanyop#caldesign

– Wolter-I– Wolter-Schwarzschild–  Oranyother:equal-curvature,polynomial,etc.

•  CanmakesubstratesbegerthanChandra’s–  BeVermicro-roughnessàbeVer-behavingPSF–  Thicknessfrom0.5to1.5mm(cf.Chandra’s10-25mm)

•  Usenospecialorcustomequipment–  Allequipmentarecommercialofftheshelf.–  Alltoolingcanbemadeinordinarymachineshops.

•  Highthroughputandlowcost–  Fabrica`onprocessishighlyamenabletoautoma`on&massproduc`on

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Coa#ng•  Coa#ngisanessen#alpartofastrategytomeeteffec#vearearequirements– Agoodcoa`ngisanecessity,notanop`on

•  Noblemetalcoa#ng– Au:LowstressßàLowreflec`vity– Pt:MediumstressßàMediumreflec`vity–  Ir:HighstressßàHighreflec`vity

•  Otherpossibili#es– AniridiumlayerplusanovercoatofB4CorAl2O3

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Effectof15nmPtCoa#ng

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P-VSagchange54nmà0.32”inHPDchange

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Solu#onsbeingPursued

•  Balancefrontandback–  Inves`ga`ngPtcoa`ngnow–  IfsuccessfulwithPt,willinves`gateIr

•  Balancethin-filmstressonthefrontwithSiO2stressontheback–  Coa`ngstypicallyhavecompressivestress–  SiO2alsohascompressivestress.Itsgrowthcanbecontrolledtoanaccuracyof1nm.

•  Polishafigureerrorinthesubstratethatwillcanceldistor#oncausedbycoa#ngstress,iftheeffectofcoa#ngstressishighlyrepeatable&stable.

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ApproachtoAlignment&Bonding

•  Usekinema#cmounttominimize/eliminatedistor`ontomirrorsegments

•  Usefiniteelementanalysistoop`mizeloca`onsofsupports

•  Useepoxyasadhesiveonly,notasafillerofanyspacethatisnotpreciselycontrolled

•  Usegravity,themostrepeatableforce,asthenes`ngforce

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MinimalConstraints•  Threespacersorpostsfullydeterminetheorienta#onofaflatmirror:–  pitch,yaw,&xbygravity–  roll,y,andzbyfric`on

•  Fourspacersorpostsfullydeterminetheorienta#onofanX-raymirror:–  pitch,yaw,x,andybygravity–  zandrollbyfric`on

•  Usevibra#onofop#malfrequencyandamplitudetoovercomefric#on

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ProofofConcept

•  Placementrepeatability–  Thesamemirrorfromplacementtoplacement–  Fromonemirrortoanotherofthesameprescrip`on–  Stabilityoverlongperiodsof`me:~10hours

•  Precisionmachiningofposts–  Currentprecisionat25nm,limitedbymetrology–  Enablessub-arcsecondmirrroralignment

•  Bondingmirrorwithepoxy–  Preservesalignment:noindica`onofalignmentshii–  Preservesfigure:onlylocalizeddistor`onsduetoepoxycurestress

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ProofofConceptModule

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AccomplishedasofMay2017Singlepairofmirrorsaligned,bonded,andX-raytested.

ExpectedtobeaccomplishedbyDecember2017Mul`plepairsofmirrorsaligned,bonded,andX-raytested.

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X-rayTestResult

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Engineering:Structural,Thermal,&Systems

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Meta-ShellApproach•  Meta-shellintegratesmanyfourspacer

mountedsegments–  Interlockinglayersofmirrorsegments

bondedontoacentralstructuralshell(silicon)

–  Mirrorsarecan`leveredoffstructuralshellsimilartoNuSTAR

–  Brick-likebuildupspreadstheload•  Oncecomplete,meta-shellissimilartoa

fullshellwithanorderofmagnitudemorecollec#ngarea–  Structurallys`ff(allsilicon)–  Rota`onallysymmetric–  Insensi`veto`lt–  LeverageChandraandXMM-Newton

heritage•  Integratedonaprecisionairbearing

–  Createsanop`calaxisreference–  PostheightsdeterminedbyHartmanntest–  Bondedindistor`on0.05”HPD(gravity

releaseerror) 31WilliamW.ZhangAXISWorkshop

MirrorAssembly•  Mul#pleconcentricmeta-shellsco-

alignedandmountedintoacarrierstructure–  SimilartoChandra(CAP)andXMM-

Newton(Spider)–  Aluminumstructure(orCFRP)–  Co-alignandbondmeta-shellsusing

Chandratechniques(CDAwithretro-reflec`ngflat)

–  Chandra-likeflexuremountallowsformechanicalisola`on

•  Heatedstray-light/thermalbafflesintegraltocarrierstructure(Aluminum)

•  MountwithinInterfaceRingthatprovidesinterfacetotelescope/spacecra](Aluminum)

•  Un-heatedthermalbaffles(G10)

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Meta-shell #1 Meta-shell #15

Carrier structure

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StructuralAnalysis

•  Analysisandtestshowweakpointisinnermostbond

•  Bondstressisdeterminedby:–  Bond/spacerdiameter–  Numberofsegmentsaroundthecircumference,i.e.,numberofbondsperlayer

–  Numberoflayers•  Mathema#cmodelofbondstress

developed–  Determinesfeasiblemeta-shelldesigns

–  VerifiedbydetailFEAandcoupontests

•  Determinis#cmethodtoderiveallmeta-shelldesignparameters

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PrototypeEnvironmentalTes#ng

•  Developedconserva#vepreliminaryrequirements–  Quasi-sta`cdesignloadsforIXOCLAwith2.0

MUF–  RandomloadsfromGEVS–  ShockloadsfromFalcon9

•  Can#leveredmassprototype–  Dummymasssimulateslayersofmirrors–  Singlesiliconsegmentwithfourspacerbonds–  Survivedrequiredrandomvibra`on–  Survivedrequiredshock(200g)–  Siliconisstrong(iftreatedproperly),has

gooddamping,andbondswell•  Meta-shellmechanicalmock-up

–  Aluminumandglassmeta-shell–  Bondedflexures–  3layers(54mirrors,432bonds)–  Survivedrequiredrandomvibra`on–  Survivedrequiredquasi-sta`cload(12.3g)

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500mm

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ThermalControl

•  FollowChandraapproach–  Op`csoperateat20°C(baseline,colderpossible)–  Heatlosttocoldspaceisreplacedbyheaters

surroundingtheop`calcavity–  Viewtocoldspaceislimitedbythermalbaffle

vanes(heatedandun-heated)•  DesignverifiedbypreliminaryStructural

ThermalOp#calPerformance(STOP)analysis–  Thermalmodelpredictstemperatures–  TemperaturesmappedtostructuralFEM–  Distor`onpredic`onsray-traced

•  LowCTEandhighthermalconduc#vityofsiliconresultinlowthermalsensi#vity–  Minimalgradientsoveramirrorsegment–  Currentresult0.16”HPD,roomforop`miza`on–  BestSTOPresultfromIXO6.6”HPDwithglass

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SummaryofEngineering•  Meta-shellapproach

–  Advantagesoffullshellop`csbutwithanorderofmagnitudemorecollec`ngarea

•  Preliminarystructural,thermal,andop#calanalysiscompletedtomaturethesystemdesign–  Shows0.5”missionisfeasible

•  Prototypeloadtes#ngdemonstratesthemeta-shellsarerobust

•  Developmentcon#nues:design,analysis,tes#ng

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MakingtheCasetotheDecadal

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NeedtoconvincetheDecadal!

•  Performance–  Effec`vearea– Angularresolu`on

•  Mass– Massismoney!– AXISmirrorassembly~500kg

•  Cost/Schedule–  Shouldbelessthan$160M+30%=$200MinRY$.(Cf.Chandra’sFY99$600Mfor1,500kgà$0.4M/kg).AXIS’smirrorisalso$0.4M/kg,butwithRY$.

– Mustbedoneinlessthan5years,preferablyin4years.

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BetweenNowandDecadal

•  Empiricallydemonstratethatmirrorsegmentsmee#ng(orclosetomee#ng)requirementscanbemade–  Repeatedly(highyield),–  Quickly(produc`onrate),and–  Costeffec`vely

•  Buildandtestsmallmirrormodules–  Basicalignment&bondingprocedureissound&efficient–  Theymeetperformanceandenvironmentalrequirements

•  Buildandtestreasonably-definedmeta-shells– Meet(orclosetomeet)bothperformanceandenvironmentaltests

–  ReachTRL-5by2020–  ShowaclearpathtoTRL-6oncetheobservatoryisdefinedwithsufficientfidelity

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MirrorAssemblyProduc#on(1/2)

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~15,000mirrorsegmentsà~6meta-shellsà1mirrorassembly

~2-3mirrorfabricatorsà~1-2meta-shellmakersà1integrator/testerDistributedproduc#onàCompe##onàCost/Scheduleriskreduc#on

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MirrorAssemblyProduc#on(2/2)

•  OneprimecontractorwithTBDsub-contractors–  Twotofourparallellinesofproduc`onofmirrorsubstrates

–  Twoparallellinesofmeta-shellconstruc`on– Onemirrorassemblyintegratorandtester(I&T)

•  Detailedproduc#onfacilityandschedule– Allneededinforma`oninhandformakingstep-by-steporblow-by-blowschedule

•  Detailedgrass-rootscostes#mate–  Produc`onandengineeringcostsunderstood– Managementcosttobees`matedbasedonpastexperience

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Thisworkhasbeenfunded

byNASAthrough

ROSES/SATandROSES/APRA.

42

Acknowledgements

WilliamW.ZhangAXISWorkshop