ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Conclusions Theresultsofthesetwoflextests,aswellasothersperformed priortothesetests,haveproventhatthe mechanical discontinuities inthecablesobserved intheBAwereaninherentdesignfeatureintheold cablesratherthanduetoanovertest. Coldwelding, whichcausesthesediscontinuities, hasproventobe dependent onanumberoffactors,including therateandtravelthatthecablesareflexed.However, changing thesetwofactorswillnotpreventcoldweldingintheoldcables. Lookingathowthetraveleffectscoldwelding, theresultssuggestthatacombination ofsmallandlarge angleflexuresdevelops thediscontinuities fasterthaneithermotionbythemselves. Duringthedither/slew test,thesmallanglemotionsdeveloped coldweldingofthebraidandfoilfasterthanthelargeangle motions, inpartbecause therelativemotionofthetwocomponents waslargeenoughtocreatetheclean surfaces neededforcoldweldingyetsmallenoughnottobreakupthesebonds,allowingthemto strengthen. Then,theadditionoftheslewsflexedthecoldweldedcablesenoughtocreatethehingepoints. Thus,thedither/slew test,whichbetterrepresents theactuallifetestthanslewingalone,hasproventhatold cablesarepronetoRF-degrading mechanical discontinuities whensubjected toflexinginavacuum environment. Although changing therateofmotiondidnotpreventtheRFfailuresduetocoldwelding, theredidseemto besomedependence onwhenthecoldweldingoccurred. Thisdependence canbeattributed tothe duration ofthecontactbetween thewirebraidandthefoil.Astherateofmotionisdecreased, thetimethe wirebraidandfoilareinintimatecontactincreases, formingstronger coldwelds.However, morerigorous flextestingisrequired tobetterunderstand thisratedependence. Ultimately, theresultsofthisextensive investigation intotheRFfailuresresulted inthedecision torefurbish theBAwithdifferent coaxialcables.CableswiththePTFEbarrierbetween thewirebraidandfoilwere selected asthereplacement, duetotheirsimilarity totheolddesign. Lessons Learned Certainly, thelessonslearnedfromthisfailurearevaluable toanymechanism engineer whomustcontend withflexingofcoaxialcableinaspaceenvironment. Duetothewidespread useofcoaxialcabletotransmit RFsignalsinlow-loss/high frequency applications, coldweldingisacommon spacecraft mechanism design consideration. Furthermore, theselessonsextendbeyondcoaxialcabletoanycableconstruction where similarmetalsareincontact. Also,theimportance oflifetestingfullyconfigured spacecraft mechanisms isdemonstrated bythis example. Often,lifetestsareperformed ondrivemodules (consisting ofmotors,bearings, gears,etc.)only, assuming thatothercomponents suchascablesarestablethroughout thelifeoftheunit.Butwhen sensitive components areinvolved, unexpected observations aresometimes encountered. Although theBA faileditslifetest,thepurposeofalifetest,toidentifypotentially missionthreatening conditions, wasfulfilled Successfully. Acknowledgements Theauthorwouldliketothankthemembers oftheBAteamfortheirhardworkanddedication. Special thankstoKathyDaceyandRaymond Liufortheirperseverance andsupport. Also,Iwouldliketothank MarkCarrollforpersuading metowritethispaperandhelpingitthroughtheapproval stagewhile1was exploring Europe. 274
TheSeaWinds Scatterometer Antenna Subsystem ontheQuikScat Spacecraft BrianJ.Workman" andEricSchwartzbaum °" Abstract Intoday's environment of"Better, Faster, Cheaper", theabilitytoproduce reliable, flight-proven mechanisms formission criticalapplications ismoreimportant thanever.Suchamechanism was produced fortheQuikScat satellite. TheScatterometer Antenna Subsystem (SAS)isaspinmechanism thatcontinuously rotatesascatterometer antenna, andincludes thenecessary features (rotaryinterfaces, drives,launchlocks,etc)toallowcollection ofthescatterometry datathatwillinsuremission success. Thispaperwilldiscuss theevolution oftheSASfromitsdesignheritage ontheGGSPolarmission to qualification ontheADEOS IIsatellite tobeingakeyenabler fortherapiddevelopment oftheQuikScat Satellite. TheScatterometer Antenna Subsystem installed onthe QuikScat Satellite Copyright AviationWeekandSpaceTechnology, TheMcGraw-HillCompanies. Figure 1.TheSeaWinds Scatterometer Antenna Subsystem mounted onthenadirdeckofthe QuikScat spacecraft Introduction TheQuikScat spacecraft isthefirstobtained underanewNASAprogram forrapidspacecraft acquisition, andwascompleted injust12months. Designed toacquire global,all-weather, high-resolution measurements ofnear-surface windsovertheworld's oceans, thespacecraft hasbeeninthenews repeatedly foritsabilitytotrackandmeasure windspeeds associated withhurricanes andeventracking agianticeberg. Thespacecraft wasfeatured onthecoverofAviation Week&SpaceTechnology inMay of1999.QuikScat waslaunched inJuneof1999. _,Honeywell Inc.,Satellite Systems Operation, Glendale, AZ JetPropulsion Laboratory, California Institute ofTechnology, Pasadena, California Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-I2,2000 275
TheSeaWindsinstrumentflyingontheQuikScatSpacecraftanditsneartwinplannedforlaunchonthe ADEOSIIspacecraftarecomposedofthreemajorsubsystems. HoneywellSatelliteSystemsOperation (SSO)designed,built,andtestedtheScatterometer AntennaSubsystem, whichisshowninFigure1 mountedtotheQuikScatnadirdeck.TheSASincludesthespinmechanism, drivemotors,speedcontrol, dishantenna,andRFrotaryinterfaces. RaytheonprovidedtheScatterometer Electronics Subsystem (SES),whichgeneratestheradarpulsestransmitted totheoceanviatheantennaaswellasreceiving andprocessing theradarecho.TheSESandSASinterface viawaveguides. TheCommand andData Subsystem (CDS),whichprovides thecommand andtelemetry interface withthespacecraft, wasbuiltby theJetPropulsion Laboratory, whichalsointegrated thethreesubsystems intotheSeaWinds instrument. Thedeployment andspinmechanism portionoftheSAStracesitsheritage tothedespun platform mechanism onthePolarspacecraft oftheGlobalGeospace Science (GGS)program. Launched in February of1996,thePolarspacecraft hasflawlessly completed itsdesignlife,andoperation foranother fulllifetime iscurrently planned. Description Duetoitssizeandcomplexity, acomplete anddetailed description oftheScatterometer Antenna Subsystem isbeyond thescopeofthispaper. However, abriefdescription ofthemainmechanisms and components isusefulpriortodiscussion ofdesignevolution andlessons learned. TheSASisshowninFigure2.Overall heightincluding theantenna isapproximately 1.47meters(58 inches). Totalmassofthesubsystem isabout60kg.15esignlifeis4.5yearswithaplanned mission life of3years.TheSeaWinds SASconsists offourmajorsubassemblies: theAntenna Assembly (AA),the BaseStructure Assembly (BSA),theSpinActuator Assembly (SAA),andtheElectronics Assembly (EA). Thesemajorsubassemblies areidentified inFigure3.-.....__ Figure2.TheSeaWinds Scatterometer Antenna Subsystem Theantenna assembly isacarbongraphite composite dishantenna, onemeterindiameter, withapairof linearly polarized feedhornsthataresupported byatripodstrutarrangement. Thesefeedhorns alternately transmit andcollecttheRFradarpulsesgenerated bytheinstrument. Collected RFsignals 276
areconductedthroughtwocompositeWR75waveguidesattachedtooneofthesupportstruts.The waveguidesinterfacetoadualchannelrotaryjointhousedwithintheSAAandmountedtotheantenna plate,whichinterfaceswiththeantennapedestal.Thecompositeantennaassemblyisbondedtoa titaniummountingring(forthermalisolationbetweentheAAandSAA)thatfacilitatesattachment tothe SAA. Antenna Assembly (AA) SpinActu; Assembly (SAA) Base Assembly (BSA)y_A) Figure 3.Majorsubassemblies oftheScatterometer Antenna Subsystem TheBSAprovides thestructural interface between thesPacecraft, theSAA,andtheEA.Itconsists ofa hollowaluminum cylinder approximately 48cm(19in)indiameter onathermally isolating titanium base ring.TheSAAmatestotheUppermounting flangeoftheBSAwithitslowerportionextending downinto thecylinder. Mounting pointsonthesideofthecylinder provide forattachment oftheEA.Interfaces are provided forconnecting tothewaveguiderunsthataremounted tothespacecraft nadirdeckandextend totheSES.Twobulkhead connectors atthebottomoftheBSAprovide forelectrical connection tothe pyrotechnic initiators ontheSAA.Twowhiterectangles ofthermal paintlocated atselectlocations onthe outside oftheBSAactaspassive thermal radiators. Theremainder ofthesurface oftheBSAiscovered withamultilayer insulation (MLI)thermal blanket. Aswillbediscussed inthe"Design Evolution" section, theoutside oftheBSAprovided mounting locations forthelateraddition ofthe"survival" heaters that werenecessary foradaptation ofthedesignforoperation ontheQuikScat mission. TheSAAistheheartoftheSeaWinds instrument. Thisassembly houses themotors, bearing system, encoder, launchlockandrelease mechanism, andheaters. Thesecomponents areshowninFigure4. 277
Redundant powerconditioning, motorcontrol,andbridgedrivercircuitcardassemblies arelocated aroundthecircumference oftheSAAasshowninFigure4.TheseelectronicstraceheritagetotheGGS program.TheSAAhastwobrushlessDCmotorsthatareoffsetslightlytohelpreducecoggingtorque. Theredundant,24-polebrushlesswye-wound motorsarecontinuously commutated. AdualchannelRF rotaryjointprovidestherotaryinterfacebetweenthewaveguidesoftheantennaandthoseintheBSA. Duplex Bearing J Assembly Launch Retention / Release /_ Diaphragms \m A_ m \ LSimplexAssemblyBearing_I ,,i¢/V-Band ?-- DualBrushless  DCMotors Encoder Assembly  SAAElectronics Simplex Preload Diaphragm Figure 4.Cutaway viewoftheSpinActuator Assembly The15-bitincremental opticalencoder produces 32,768pulsesperrevolution withanend-of-life incremental accuracy ofapproximately 10arcseconds. Thesepulses, alongwithaonce-per-revolution indexpulseprovide antenna azimuth position totheCDS,criticalforground signalprocessing and inferring oftheoceanwindvectors. Theopticalencoder alsoproduces twoanalogoutputs, onesineand onecosineatt2pulsesperrevolution usedintheSAAelectronics forcommutation ofthedrivemotors. Theopticalencoder iselectrically redundant, usingseparate pick-off stations foreachchannel. Encoder electronics arepackaged onfoursemicircular cardslocated underneath thedisk. Pointing kn0Wiedgeand Stability arecriticalrequi?emen{s oftheSAS.Antenna boresight pointing knowledge accuracy-is criticalforobtaining th-e-re-q-uiredwind vectoraCcurac_,i Eievaiion afig]ecalibration uncertainty i_.clud_es_all uncertainties inthemeasurement ofbeamang!efromtheelectrical boresight to anopticalreference cubeontheBSAandmustbelessthan0.15degree. Totalazimuth uncertainty also includes uncertainties relatedtotheencoder andcommand signalprocessing. Azimuth uncertainty must belessthan0.20degree. Post-launch beamanglestability effectsincludethermal distortion, humidity, launchenvironment, rotation, gravity, life,andothertime-varying, on-orbit effects. Therequirements for elevation andazimuth beamanglestability arelessthanorequalto0.15degree and0.25degree, respectively. Therequired highprecision pointing andstability requirements aremaintained through employment ofclosetolerance interference fits.SASelevation andazimuth pointing stabilities as 278
Strap V-Block Separation NutCoilSpring Catcher Housings (6) i_ _,/Separation Nut Figure5.Pyrotechnically released V-Band launch lockmechanism Thermal controlisprovided bytheappropriate selection ofradiator sizeand heaterpowerl TheSAA contains thermostatically controlled "replacement" heaters thatarepowered onwhentheelectronics are notinordertomaintain temperatures attheoperational level."Supplemental" heaters (also thermostatically controlled) maintain electronics andbearing temperatures whentheInstrument isin operation. Inaddition, theQuikScat version oftheSeaWinds instrument addsexternally mounted "survival" heaters thatwerenecessary toaccommodate differences between theQuikScat andADEOS II electrical bus.TheQuikScat survival heaters arepowered onbythespacecraft automatically insurvival orlaunchmodes. Thermal isolation between theSAAandAAismaintained byvirtueofthetitanium antenna mounting plate,minimized physical contact withthetitanium shaft,andaskirtofaluminum thermal shields mounted around thecircumference ofthebaseoftheantenna plate.Thisthermal skirtis isolated fromthetitanium antenna platebyphenolic spacers andscreens thetitanium interface minimizing radiative heattransfer todeepspace. Thermal isolation between theSASandthespacecraft ismaintained byuseofareduced contact areabetween thespacecraft andthetitanium ringthatmakes upthelowerportionoftheBSA.t 280
flightunitortheengineering unitinspiteofthefactthatallwerefromthesamelotandtheengineering unitwassignificantly exercised duringqualification testing. Whentheoriginal strapdrawing wasgenerated andthestrapswerefabricated fortheheritage GGS application, themosteconomical waytomanufacture thestrapswastohavethemstamped fromasheet andthenformed onmandrels totheirfinalshape. Bythetimeprocurement oftheSeaWinds strapswas initiated, advances inmanufacturing techniques allowed numerically controlled lasercuttingtobecome muchmoreeconomical because thetoolingrequired forstamping wasnolongerneeded. Unfortunately, andunknown tothestrapvendor, thislesscommon titanium alloyissusceptible toembrittlement from localized heating. Honeywell SSO'sfailureanalysis laboratory performed afailureanalysis onthepart. Investigation byscanning electron microscopy, microhardness testing, microstructure examination, and chemistry analysis revealed aheataffected zonecontaining recastlayersandrecrystallized alpharich grainsnearthefracture origin. Secondary cracking wasalsodetected atthesamelocation. Figure6isaphotograph ofthefractured web.Thewebis7.37mm(0.29inch)inwidthandistheupper oftwowebsthatwraparound theright(separation nut)trunnion. "Up"istotherightinthisviewandthe fracture initiation pointisidentified bythearrow. Acloseupviewofthefracture surface isshowninthe scanning electron micrograph ofFigure7.Itshowsthecrackinitiation siteintherecastlayers(marked withanarrow)andthealpha-rich grain(marked withadoublearrow). Boththerecastlayerandthealpha richgrainarepronetobeingbrittle.Theremaining areaexhibits thecharacteristic features ofatypical ductilefracture. Figure9represents theupperfracture section showninFigure7witharrow,viewed in thelongitudinal direction afterpolishing away0.41mm(0.016inch)fromtheoutside surface andetched withareagent. Thedistinctive whiteanddarkareasindicate theheat-affected zonewherephase transformation andmicrostructural changes inthemetalhaveoccurred. Thetypicalmacroetched appearance ofthistitanium alloycanbeobserved ontherightportionofthesection. Apre-production material coupon fromthesamelotwassubjected tothesameprocesses tosimulate theproduction experience ofthefailedstrap,anditwasverified thattheseembrittled areaswerecaused bylocalized overheating duetothelasercutting. Thesolution totheproblem wastoreplace thestrapswithnewonesthathadbeencutbytheabrasive waterjetprocess. Thisprocess eliminates theheateffectcompletely. Thisconclusion wasverified by processing asample fromthepreproduction coupon, andissupported bypublished literature onthe abrasive waterjetprocess. Replacement strapswerefabricated usingthismethod andboththeQuikScat andADEOS IIflightunitshadtheirstrapsreplaced. Asanaddeddemonstration ofconfidence, thesenew strapswereprooftestedtolevelssignificantly inexcess ofthenominal tension range. Figure6.Aphotographic viewshowing thelocation ofthefractured web. Theinboard edgeofthewebisidentified withanarrow. 283
Figure 7.AScanning Electron Micrograph ofthefracture surface showing thecrackinitiation site inarecastlayer(single arrow)andthealpharichrecrystallized grain(double arrows). Figure 8.Amacrograph ofthefracture viewed longitudinally, showing theheat-affected-zone and recastlayeridentified withanarrowattheinboard edge. Because theoriginal manufacturing drawing forthestrapwasgenerated atatimewhenitwasknownthat thepartswouldbestamped, norestrictions regarding localized heating ofthepartwereincluded inthe notesonthedrawing. Engineering needstomaintain anunderstanding oftheprocesses usedduring manufacture ofparts,andneedtoremaincognizant duringtheprocurement process sotheybecome awareofchanges inthoseprocesses. Significant dropsinquotesfrommanufacturers tofabricate an established partshouldactasaflagtoinquireaboutanychanges inprocesses. CircuitCardStiffeners Onechannel oftheSAAelectronics onthefirstflightunitfailedtooperate afteraworkmanship vibration test.Investigation ofthefailureledtothediscovery thatthescrewholding downoneofthelarge inductors onthepowerconditioning cardshadnotbeentorqued. Thisinductor hadcomelooseand knocked anearbytransistor offthecard,disabling operation ofthatchannel. Theapparently obvious solution wastonotonlytorquetheseinductors down,buttoalsoaddasteptobondthemtothecircuit cardaswell.Thisseemed tosolvetheproblem astheunitpassed workmanship andacceptance level vibration atthesubsystem level.However, whenthesecond flightunitwithbonded inductors wasshaken duringitsacceptance test,afailureexhibiting thesamesymptoms asthefirstfailureoccurred. 284
References 1.)Aviation Week&SpaceTechnology, May17,1999.Aviation Week&SpaceTechnology isa publication ofTheMcGraw-Hill Companies, Inc. 2.)YingLiu,"Failure Analysis Report19406:V-Band Assembly", Honeywell Inc.,Satellite Systems Operation, Product Assurance Labs 3.)H.R.Phelps, "AWJCutting ofTitanium VentScreens fortheF-22Advanced Tactical Fighter", Lockheed MartinAeronautical Systems, Marietta Georgia 286
AntennaPointingMechanism forSteerableSpotBeamAntennas. Manfred Schmid* Abstract TheAntenna Pointing Mechanism (APM)wasdeveloped intheframeofaresearch anddevelopment program dedicated togeostationary Kabandcommunication antennas. Attheendofthedevelopment phase,anAPMqualification modelwasbuiltandsuccessfully tested. Oneofthemaindevelopment goalswastoestablish adesignnotonlyaccommodating thereference Kabandantenna, butfitfora rangeofpotential applications andantenna configurations atlowrecurring costs.Figure1showsthe Antenna Subsystem configuration thatformed thebasisfortheAPMdevelopment. Thispaperdiscusses thQchosen technical approach andmechanism features onthebasisoftheestablished requirements as wellaStheissuesencountered duringthedevelopment andtestphase. Introduction TheAntenna Pointing Mechanism developed byDSSisadevicetosteerspotbeamcommunication antennas. Itisacompact andself-standing unitwithsimpleinterfaces tothesatellite andalsotothe antenna. Theunittiltsacomplete antenna orantenna dishonly,depending ontheapplication, withtwo rotational degrees offreedom. TheAPMprovides excellent pointing andperformance repeatability overa widetempeta_re rangeandwasalready testedinanopen-loop controlconfiguration. Theunitisableto accommodate ahigh-resolution encoder forclosed-loop position controlifrequired. Commercial subunitsandpartsmodified forspaceapplications areusedasfaraspossible. Subreflector Antenna StructureJ FeedandRadiatorMainReflector Figure 1:Steerable KaBandAntenna Reference Configuration *DaimlerChrysler Aerospace, Dornier Satellitensysteme GmbH(DSS),Friedrichshafen, Germany Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 287
BasicSetofRequirements Atthebeginning ofthedevelopment phase,abasicsetofdesign, performance andenvironmental requirements wasagreed uponandchosen asaworking basis. i,,, ,,, Desi_ln Requiremen!s '......... Number ofRotation Axes APMheight APMlength/width APMMassTable1: Value 2 150mm 360x360mm 6kg Antenna Masstobesupported 24kg 15kg-m2 Antenna Moltobesupported APMDesignLoads Storage Life Orbitlife Waveguide Routing Position Monitoring Ho'lddown andRelease Mechanisms Performance" Requirements' Pointing Range_ Pointing Velocity Pointing Accuracy / Repeatability StepResolution FirstSystem Eigenfrequencyinplane15g/outofplane 30g 7Years 15years possible torouteupto4 flexible Ku-orKa-band waveguides alongtheAPM provide I/Fforposition monitorin.q devices 2pyrotechnically activated HRMsDesi_ln Requirements Comments -massbudget hadtobeincreased from 5to6kgduetochange oftherequired antenna masstobesupported inthe courseoftheproject requirement waschanged from15kg to24kgduringtheproject at4rep,,ositionings /day potentiometers orencoders, depending onapplication. mounted totheantenna structure Table2: ValueI 10deghalfcone >5de9/minute +/-0.01 deg 0.002deg 50HzPerformance Requirements CommentsI111 achieved value+/-0.005deg atfullstepcommand i(antenna with24kgmassand15kgm" iMol,supported byAPMand2HRMs) Table3: Environmental Require..m.ent,s '..... SinusQual.Vibration Levels Random Qual.Levels Qualification Temperature Requirement l'ransportatio n'.T.emperature Humidity maxValue 12to15ginplane(x,y) 6to30goutofplane(z) 17grmsinplane(x,y) 20.5grinsourofplane(z) -40to+60°C +60°Cto-60°C 85%Environmental Recluirements _.. CommentsI Idepending onfrequency Goal+107°C to-110_C'was seton basisofthermal analysis resultsforan unprotected ApM relative 288
CardanFrame(1.1) IBaseAxis ISpringUnit(1.6) [Motor_'2.1) GearUnit(2.2) ISDindle Unit(2.3'1 Monitoring Switches (2.4) GimbalUnitBase Bracket(1.1) Figure 2:APMConfigurationi Antenna I/FFlange(1.2)I GimbalUnitFrame Bracket (1.1 (1.4)] Electrical I/F(3.1_] FlexibleWaveguide (4.1)I Table.4:MainAssemblies andSubassemblies Overview Assembly GimbalAssembly GimbalUnit/Cardan Frame Antenna IIFFlange Satellite IIFPlate Bearing Unit Potentiometer/Encoder I/F Sprin_lUnit Damper Unit LinearActuator Motor GearUnit SpindleUnit Monitorin_l Switches Electronics Electrical I/F Rx_TxPowerTransmission FlexibleWaveguideID-No. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2.1 2.2 2.3 2.4 3.1 4.1 changed fromtheassumptions of-40upto+60°Cmadeatthebeginning, tocalculated valuesreaching from-110"C upto+107°C foraworst-case orbit.Itwasfoundtobenotanadequate solution touseMLI ontheAPM,sincethemechanism hastoperform a2-axismotionleaving onlyaverysmallclearance underneath theantenna structure iftiltedtoanextreme position. Furthermore astronginterference with theHRMswasidentified, sothatforthefurtherdevelopment activities amechanism concept allowing to copewiththetemperature extremes hadtobeconsidered asabaseline. Basedonthesefacts,the 290