Op#csforAXISWilliamW.Zhang
NASAGoddardSpaceFlightCenter
1WilliamW.ZhangAXISWorkshop
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.
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Acknowledgements
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