ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
/ Taking Spacecraft Commercial Practices TooFar ChuckLazansky" andScottChristiansen* Abstract Intheradically changing, commercially drivenspacecraft marketemphasis hasbeenplacedondrivingthe priceofcomponents toanabsolute minimum. Thispaperconsiders thequestion: Howdoesthepushfor simple, low-cost devices effecttheriskoffailureintheuseofthedevice? Starsys Research developed a paraffin-powered pinpuller fortheIridium®program. Thedesign wasverysuccessful initssimplicity, reliability, andlowcost.However, coststointegrate, operate, andcontrolthepinpuller onorbitwerehigher thanexpected asaresultofthedesign simplicity. Ultimately, theproblems wereaddressed andflight operation ofthemechanisms wassuccessful. Aftertheprogram, thepinpuller wasre-designed toaddress thelimitations oftheIridium device. The simplified control, integration, andground useofthenewpinpuller havewonwideappealdespite aslightly higherunitcost.Inretrospect, welearned someimportant lessons andpotential pitfallsinhigh-volume spacecraft component design. Thispaperwilldescribe thespecific problems encountered withtheIridiumpinpuller, andhowtheycame about.Howthoseproblems wereaddressed intheimproved designwillalsobepresented. Finally, a discussion ofhowthelessons ofIridiumhaveeffected ourdesignprocess willbeincluded. Introduction TheIridiumPro.qram In1994,Starsys Research wonacontract thatwouldtransform thecompany intoahigh-volume manufacturer ofspace-flight hardware. Starsys waschosen assupplier ofthehold-down andrelease mechanisms (HDRMs) fortheIridiumSatellite Constellation. Theprojectincluded designandqualification ofthehardware, followed byanaggressive delivery schedule ofweeklyshipments overthecourse of22 months. Thisdelivery schedule matched Iridium's planned production rateof1satellite perweekforthe 80spacecraft tobemanufactured. Inaddition totheHDRMhardware, adevicewasneeded tocageandrelease thegateway andcross-link antenna gimbals. AnHOPpinpuller concept wasselected asthemoststraightforward andcost-effective solution. Twelve (12)ofthepinpullers wererequired perspacecraft, andwithspares, over1000unitswere required fortheconstellation. Starsys wouldbeasupplier tothemanufacturer oftheantenna subsystems. Thepinpullers wouldbe shipped tothecustomer, installed intheantenna, tested, anddelivered totheprimecontractor for assembly intothespacecraft. Allofthedevelopment workwouldbedonewithourcustomer. Wedidnot workdirectly withtheend-user ofthespacecraft. Commercial Desiqn Approach Design forahigh-volume commercial application wasasignificant shiftforStarsys. Thetargetpricefor thepinpuller wasroughly $600perunit,withhalfthecostsestimated tocomefromparts,andhalffrom labor.Atthetime,typicalparaffin actuators werebuiltinlotsizesof5,atalmost 10timesthistargetcost. Thesheervolume ofhardware tobedelivered weekafterweekrequired thatStarsys takeaverydifferent approach tothedesign, assembly, andtestingofthepinpuller. Starsys Research Corporation, Boulder, CO Proceedings ofthe35thAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 275
Starsyswouldneedtobalancetwoverydifferentdesignapproaches. Onewashigh-reliability space-flight component design,withwhichwewereveryfamiliar.Theotherwasdesignforhigh-volume manufacturability, and"designtocost".Emphasiswasplacedonreducingcosts,minimizing partcount, andkeepingthedevicesimpletoavoidproductionproblemsandmaintaindeliveryschedule. Results Inbalancingthesedifferentapproaches, choicesweremadeinthedesignthathadsomeunexpected consequences. Onewasintheareaofon-orbitcontroloftheactuator.Thespacecraftdesignwasalready completewhentheactuatordesignbegan,sotheoptionsforcontrolwerelimitedtoasingletimedpower signaltooperatetheactuators.Assumptions weremadeduringthedesignphaseaboutthefeasibilityof thisapproach.Theassumptions werenotadequately checkedout,andwewerewellintotheproduction phasewhenitbecameclearthattheproposedcontrolschemewouldnotwork.Itrequiredasignificant effortandre-programming ofsoftwaretoarriveataworkablecontrolmethod. Anotherresultoftheaggressive designapproachwasanactuatorthatwaslessuser-friendly, andmore pronetodamageatthehandsofunskilledoperators.Normally,afteroperation,aresettoolre-extendsthe pintoitsproperstartposition.Itwaspossiblefortheactuatorpintobepulledouttoofar(e.g.,byhand) duringgroundreset.Oncethishappens,therearsealsareun-seatedfromtheirbore.Theactuatorwillnot pressurize, andthepinwillnotpull.Sincetheresetprocessisfairlystraightforward, webelievedproper trainingandprocesscontrolscouldpreventthis. Resettingtheunitintheactualspacecraftproductionenvironment, however,wasmoredifficultthanwe envisioned duringthedesignphase.Asaresult,fiveunitsonthefirstspacecraftwereunknowingly overextendedpriortoflight,anddidnotactuateon-orbit.Fortunately, thesignalcouldbere-routedandthe disabled antenna didnotcompromise thesystem. Theproblem wascorrected through improved procedures andre-training, andnootheractuators weredamaged. AfterIridium, animproved version ofthepinpuller wasdeveloped fortheOrbview program. Thenew designaddressed eachoftheweaknesses oftheIridium design. Forexample, itcontained aninternal, redundant power-interrupt feature making itveryeasytointegrate andcontrol. Thesuccess oftherevised pinpuller hasgivenperspective onwhatistrulymeantbysimple, robust, andcost-effective design. Ithas ledustore-examine theIridium process andwonder ifthedesignteamhadtakencommercial spacecraft practices toofar. Paraffin Actuators andtheIridiumDesi,qn Aparaffin actuator isarelatively simpledevicecompared tomanyotherspacecraft components. Itutilizes thethermal expansion ofparaffin todowork.Paraffin iscontained insideasealed chamber, whichis typically heated byaKapton-film resistance heater. Oncetheparaffin reaches itsmelting point,itexpands approximately 15%,creating hydraulic pressure insidethedevice. Thispressure istranslated intolinear motionoftheoutputshaft.Pressure continues toincrease aslongastheheating iscontinued, soturning poweroffuponcompletion ofthestrokeisnecessary toprevent damage duetoexcess heatand pressure. Ifpowerisnotturnedoff,component partswilldegrade, outgas, andultimately, sealfailurewill occur.Somestandard HOPdesigns areshowninFigures 1and2. Figure1.IH-5055-type HOPactuator 276
Figure 2.EH-3525 Hermetically Sealed HOPActuator Acrosssection oftheIddium pinpuller design isshowninFigure3.Thebody,orpressure vessel, is titanium withakapton heaterapplied tothesurface. Thetitanium pinhasVitono-ringsealsateachend. Thelargerdiameter oftherearsealscreates anetretraction forceontheshaftwhentheparaffin chamber pressurizes. ATorlonmounting flangeprovides themechanical interface, andgoodthermal isolation so thataspacerisnotnecessary. Figure3.Iridium Pinpuller, extended position 277
1-pLhL -/" II IIII II I Ir--I__" .L-- _E,_, _-- LI:jJTZ',b FErFL, L[ Figure4.Iridium Pinpuller, retracted position Theelectrical interface issimplya2-wiretwisted, shielded pairforpowertotheheater. Theactuator is covered withahigh-emissivity Flexible Optical Surface Reflector (FOSR) thermal controlfilmtoprovide marginagainst self-actuation duetosolarexposure. Control Strategy: AnOver-Constrained Design DesignConstraints Onorbit,onlyasingleoperation ofthepinpuller wasrequired torelease thegimbals. Thepinpuller needed torelease ashearloadofupto445N(100Ibf),overatemperature rangeof-65°Cto+70°C, givena variable inputvoltage of22VDCto36VDC.Forground testing, aresettoolprovided byStarsys wouldbe usedtore-extend thepinforthenextoperation. Options forcontrolling theactuator wereverylimitedduetotheexisting designofthegimbals. Theslip ringsinthegimbals onlyallowed foratwo-wire connection toeachactuator fortheheater. Nowireswere available forshutoff telemetry, suchasalimitswitch. Afteractuation, propermovement oftheantenna stepper motors wouldindicate successful antenna deployment. However, thiscouldnotbeutilized to controlthepinpullers. Thebaseline designcalledforusingasingletimedpulseofpowertooperate the actuators underallconditions. Actuation timeisafunction ofhowlongittakesthedevicetoreachoperating temperature. Variations in starttemperature andbusvoltage strongly effectthetimerequired foractuation. Ideally, powerissupplied toaparaffin actuator onlyuntildeployment occurs, andthenitispromptly discontinued. Ifpowerisnot turnedoff,theactuator continues toheat,causing damage totheheater, andeventually leading toseal failure.Though theIridiumactuator wasonlyrequired tooperate onceonorbit,paraffin release fromthe actuator coulddamage thespacecraft's horizon sensors. Ontheotherhand,ifpowerisnotcontinued for longenough, theactuator maynotoperate underworstcaseconditions (lowtemperature andlow voltage). Iftemperature andvoltage areknown atthetimeofoperation, thenthecontrol problem isgreatly simplified. Thepinpuller canbecharacterized inground testing across theentirerangeofoperating 278
Aseriesoftestswasperformed inathermal-vacuum chamber todetermine survival times(andverify operation times)throughout thenarrowed temperature andvoltage range.Survival timewasdefined as thetimetosealextrusion andparaffin release, whichwasadiscrete, observable eventinthetest chamber. Survival timesforactuators withtheseal-gap discrepancy werealsodetermined, sincethefirst 15ship-sets werepotentially effected. Onceenough datapointshadbeencollected, thedatawasplotted asaseriesofcurves showing response timeasafunction ofpowerinput.Asurvival curve,showing survival timesfrom+65°Casafunction ofinputpower,wasadded.Theresulting plotisshowninFig.5. GMA/XI_ Laum_ I.m:kI_ms_ion Tines Ba_donQuid.TestVaiuas 14 16 10 20 22 24 "_ M 30 -_ I/V_qe, W_34 Figure5.Response timecurves (andestimated survivability line) Evenbeforethetestingwascomplete itwasclearthatasinglepower-on timewouldnotworkoverthe widerangeofoperating conditions. Thebestsolution tothiswasmeasuring busvoltage justpriorto operation on-orbit, andhavingthesystem software selectthepowerduration fromalook-up table.Itwas apparent toStarsys thatthiswasaconsiderable effortforthespacecraft company atthisstageinthe program. Nevertheless, avoltage feedback system andtablelook-up software wasputinplaceonall spacecraft. Intheunlikely eventofincomplete deployment ofoneoftheantenna, itwouldbepossible to manually powerindividual pairsofactuators. However, thiswouldhavebeenveryimpractical forlarge numbers ofactuators, andwasconsidered onlyasabackup plan.Thesummary ofthesolutions adopted: Summary ofSolution toActuator Control Problem 1)Voltage andtemperature rangenarrowed byearlierdeployment 2)Testing conducted tocharacterize actuator operation andsurvival 3)Busvoltage wasfedbackandusedtoselectapower-on time(basedontestresults) viaatable look-up incontrolsoftware. 4)Incaseofincomplete deployment, manual powering oftheactuators waspossible. 281
poweringofthedeviceswouldnothelp.Weworkedtosupporttheinvestigation withboththeantenna manufacturer andthespacecraftcompany. Justafewweekspriortothefirstlaunch,Starsyshadbeencontactedaboutdamagedpinpullersatboth theantenna andspacecraft facilities. Eachfacilityreturned aunittoStarsys forevaluation, though each wasalready awarethatthecauseofthedamage wasimproper operation. Duringtesting, oneunitwas powered forwellover5minutes whenthemaximum timeforground operation wassetat3minutes. This actuator hadobvious heatdamage, extruded sealmaterial, andhadlostparaffin. Another unithadbeen manually over-extended duringresetting. Apparently, theusershadattempted to"help"theresettoolby pullingonitwhilethepinwasextending. Thisdefeated thebuilt-instopincorporated intheresettool.Due tothecompact design, extending theshaftonly1.27mm(0.050in)beyond itszero-point canunseatthe rearseals.Oncethishappens, theactuator iscompromised. Iftheoperator pushes theshaftbackin, thereisariskoftearingthesealonthebody'sinterior corner. Ifthesealremains unseated, thenatthe nextoperation, theactuator willnotfullypressurize, andparaffin willescape. Itquickly became clearthatthereasontheactuators didnotdeploytheantenna wasthattheyhadbeen resetimproperly orotherwise damaged ontheground. Paraffin wasfoundonthefloorwherethe spacecraft wasassembled asevidence ofeitherover-extension orover-powering oftheunits.Atthis point,ourinvolvement intheinvestigation wasnolongernecessary andwefounditdifficult togetfurther information fromthespacecraft company. Sources indicated tousthattraining difficulties andworkforce turnover wereissuesattheintegration facility. Nevertheless, theproblem wasaddressed bymore thorough training oftheoperators. Aninspection ofthepinposition wasaddedfollowing actuator reset,to verifyproperextension. Thissolvedtheproblem, andnootherinstances ofimproper resetoccurred. The partially disabled spacecraft didnotadversely effecttheoverallfunctioning ofthesatellite network. The communication signalswerere-routed toothersatellites tocompensate. Boththeantenna contractor andthespacecraft manufacturer experienced difficulties inground operations including excess powerduration andimproper resetting. Though theprocedures wereclearandwell known, themagnitude oftheproject andthemanypeopleinvolved created manyopportunities forerror. Design decisions whichsimplified thedevicelefttoolittlemargin forerroringround operations. The actuator wasproneto"human factors", andthoughitshowed betterthan"four-nines" reliability onpaper,it wasreduced to5failures in1000inactualuseduetobeingdamaged priortoflight. Figure6.TheImproved Design (TypeSP-5025 pinpuller) 283
Improved Design ofaPinpuller Desi,qnImprovements Theprimary goalofthedesign improvement wastocreateadevicewhichwasnotonlyeasytooperate andresetontheground, butalsosimpleinitscontrolrequirements. Though thepinpuller wascompletely re-designed, itsbasicstructure isverysimilartotheoriginal design. Thekeyfeature oftheimproved designisitsabilitytodiscontinue powerafterretraction iscomplete. This isachieved through theCircuitInterrupts (CIs),whichisahigh-reliability switching mechanism attherear oftheactuator. Thecontacts areheldnormally closedwitharelatively highpre-load (13to89N[3to20 Ibf]).Whenthepinisfullyretracted itreaches thecontact, overcomes thepre-load, andopenstheCI circuit.Iftheheaterpowerisroutedthrough thiscircuit,thepoweris"interrupted". Theactuator willbegin tocool,andthepinre-extends slightlyduetotheCIpre-load, closingtheCI.Powerwillcycleonandoffat asafelevelinthismanner untiltheexternal powersupplyisturnedoff.TwoCIsareusedineachactuator forfullredundancy. TheCIwires(2pairs)arenotinternally connected totheheaters, sotheend-user can choose thefinalwiringconfiguration. Withtwoindependent heater-circuits andtwoCI-circuits, therearea varietyofwiringchoices tosupport manydifferent controlphilosophies. Forexample, theCIscanbewired in-series withtheheaters, ortheycanbeusedseparately fortelemetry, oranycombination ofthetwo. TheCIsgreatly simplify on-orbit control. Iftheheaters andCIsarewiredin-series, thecontroller simply needstosupplyafixed-duration powersignalthatisatleastaslongastheworstcaseresponse time,plus margin. Ontheground, operators neednotbeconcerned aboutover-powering duringtheresetoperation. Powercanbeapplied untiltheCIschange state,andthentheresettoolisapplied. Powercanbelefton indefinitely without causing damage. Across-section oftheimproved deviceisshownbelow. Figure7.Cross-Section, Improved Design Thedifficulties resetting theIridiumpinpuller werealsoaddressed intheimproved design. Over-extension ofthepinwassolvedwiththeaddition ofahardstopfeature tolimitextension andsetthezero-position of thepin.Theresettoolitselfwasredesigned tobeeasiertouse,requiring lesshand-strength fromthe user. Changes werealsomadetoimprove themanufacturability ofthedevice. Forexample, theIridiumpinpuller hadthemounting flangemadefromTorlon4203L. Itshighstrength andgoodthermal insulation properties madeitagoodchoiceforthemounting interface. However, itisalsohygroscopic andsubject to 284
•Expectmorevariabilityinproduction processes withhighervolumes,multipleworkshifts,etc. Commercial spacecraftgetlesshighlevelattentionandscrutinythancustomspacecraft. ThelessonslearnedonIridiumhavehadaneffectonourapproach tonewdesigns. Weconsider issues suchaseaseofoperation andresetmorecarefully. Inshort,wedesignhardware todomoresotheuser hastodoless.Moreattention isgiventocontrolissues. Weworkwiththecustomer onthedetailsofthe controlsystem earlyinthedesignprocess. Wemakesurewehavedirectcontact withthefinaloperator of thespacecraft, andareavailable forsupport duringintegration andground testing. 286
->.."J/.i Design andDevelopment ofaMiniature Mechanisms Tool-kit forMicroSpacecraft CliffE.Willey', BrettHuettl", StuartW.Hill" Abstract Withthecontinued pushforsmaller, faster,andcheaper spacecraft comes anewerainmechanism design. Thedesiretodevelop "MicroSatellites", alongwithadvances intheprocessing andselection of materials, havecreated anabundance ofopportunities tominiaturize mechanisms. Simple designs with directapplications ofdeveloping technologies areidealfortheseminiature mechanisms. Thispaperwill focusonthedesign anddevelopment ofaminiature satellite "toolkit".TheJohnsHopkins University Applied Physics Laboratory (APL)andStarsys Research developed sixnewminiature mechanisms under aNASAAdvanced Technology Development Program. Themechanisms developed included aMicroand MiniSeparation Nut,aMiniRotaryActuator, aMiniBurnWireRelease, aMiniLinearActuator, andaMini Redundant Release Mechanism. Thispaperwilldiscuss theconcepts evaluated, designs chosen for fabrications, problems encountered duringdevelopment, achieved performance characteristics, and recommendations forfuturedevelopment. Introduction Micro-satellites inthe10-100 kgrangearebeingdeveloped forscientific, commercial andmilitary applications. Fortheirsize,thesespacecraft willhaveverysophisticated payloads andmissions. Thisis duetoadvances inminiaturization ofelectronics, RFsystems, sensors, andinstruments. TheJohns Hopkins University Applied Physics Laboratory isdeveloping manyleading edgetechnologies forawide variety ofmicro-sat applications. TheAPLmicro-spacecraft concept (Figure 1)provides amodularcustomizable busthatis3-axisstabilized, hasredundant IEEE1394databus,on-board instrument processing, andmakesuseofdevelopments inminiaturized electronics. NASA,military, andcommercial micro-satellite programs aremaking similaradvances withminiaturized payloads andelectronics. Highlyintegrated SIC electronics shown with covers removed Mass=30kgMiniaturizedInstrument Chip-on-Board Electronics MEMS Sensor Miniature Mechanisms Miniaturized StarCamera Miniaturized GPSReceiver Miniaturized RFSystem Figure1.JHU/APL Concept MicroSat JohnsHopkins University Applied Physics Laboratory, Laurel,MD Starsys Research Corporation, Boulder, CO Proceedings ofthe35thAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 287
maintainsthecollarintheproperpositiontorestrainthethreeNutSegments(6).TheSegmentRetainer Screw(3)isfurtherusedtoconstrainthepositionoftheNutSegments. Figure2.MiniSeparation NutAssembly WhenpowerJsapplied toheatthemechanism, theSMAsprings arewarmed andextend. Thisextension pushes theSpringWasher andcollarforward, whichallowstheNutSegments toseparate, releasing the screw(notshown). Afterpowerisdiscontinued andtheSMAsprings havebeenallowed tocool,thecollar mustbemanually resetbeforethescrewisinstalled. Forheating theMiniSep-Nut, aresistance wirewas attached around thebody. Characterization Testin,q andProblems Encountered Complete characterization testingwasnotperformed onthismechanism. Afterfabrication, assembly, and checkout, itwasdetermined thatthedesigncouldbeimproved toachieve asignificant reduction insize andmass.Thisleadtothedevelopment oftheMicroSeparation Nutoutlined below. MicroSeparation Nut Desi.qnApproach During theinitialdesign process, fourtypesofmaterials wereexamined toprovided mechanism actuation; paraffin, Ostalloy, SMAwire,andSMAsprings. TheSMAspringwaschosen asthemost favorable approach duetothehighstrokethatcouldbeachieved, thefairlyquickresponse time,andthe varietyofavailable shapes. AnSMAstripwasformed intoabandshapeanddepressed elliptically togrip thescrewinthedevice(Figure 3).Asthemechanism isheated, thespringexpands toitsoriginal band shapeandreleases thescrew.Thisspringconcept hasgoodstrokeandoutputforcetohandleavariety ofloading conditions onthescrewandisextremely compact. I------Compressed forlocking A/mfterheating andrelease Figure3.MicroSeparation NutSMABandSpring Operation ofthemechanism isverysimpleinordertobeminiaturized (Figure 4).Itisresetbyinserting thescrew(4)through theHousing (1)andpasttheinnerdiameter oftheSMAspring(3).TheCap(2) holdstheSMAspringproperly intheHousing. TheSMAspringisthenmanually compressed fromtwo sidesuntilitissecure around thescrew.Themechanism maynowbepreloaded andisreadytobe released. TheMicroSep-Nut isreleased simplybyapplying heattothehousing. AstheSMAspringis heated, itreturns toitscircular shape,releasing thescrew. 289
r_-r-''_ 1  ....3 I ......... 4 Figure4.MicroSeparation NutAssembly TheSMAsprings werefabricated from0.15-mm thickby2.2-mm wideribbonformed intoacircular shape (withtwocomplete turns). SincetheSMAsprings arenotpowered directly, allthematerials inthe mechanism aremetallic, primarily stainless steels,tobetterconduct theheattothesprings. Mostofthe components havebeenheattreated toincrease thehardness, duetothesmallsize. Characterization Testinq Initialtesting determined thevoltage required toheattheSMAtoitstransition temperature. Table2 showsthemaximum temperature reached witharangeofgiveninputvoltages. Tab5 InputVoltage (VDC)2.MicroSeparation Current(amps)NutMaxTemperature Power Maximum (Watts)Temp (oc) 0.5 0.06 0.03 29.1 1 0.11 0.11 34.7 1.5 0.16 0.24 52,7 2 0.22 0.44 68,2 2.5 0.26 0.65 88.0 Aftertheprototype unitwasfabricated, loadtestswereperformed todetermine theaffectontherelease timeandtemperature. Themaingoalwastodetermine themaximum loadthatcouldberestrained and released consistently. Thermal testing wasalsoperformed. Itwastakento-30°Candupto+40°Cand released withanominal loadof22N.Thereweresomeinconsistencies intheloadatlowtemperature. It isnotclearthecauseofthesevariations. Table3summarizes theresultsofthethermal testing. Table3.Thermal Testing, MicroSeparation TestTemp Ambient Release LoadRelease Time (°C) Load(N) (N) (sec) -30 22 18 65 41 22 27 16.8 39 22 31 16.1Nut Release Temp(°C) 64.4 72.6 62.8 Problems Encountered Finding aheaterforthismechanism wasdifficult. Thesmallsurface areaavailable ontheMicroSep-Nut makesithardtoattachastandard foiltrace-heating element. Traces wereusedfromalargerfoilheater andweresoldered together andattached tothebodywithasmallbandofshrinktube.Adiodewasused asanother heating approach. Aspowerwasapplied tothediodeiteventually providing enough heatto operate theSMAbandandrelease thescrew.Although itworked, thediodesizenearlydoubled the heightandmassoftheMicroSep-Nut. Toward theendoftheprogram, twosample custom heaters were delivered. Theheaters wereKapton laminate withfoiltracesconnected toleadwires.Unfortunately they weremadewithafairlylargeleadwire(26AWG).Theleadwiresizemadetheheaterstiffanddifficult to bendaround thediameter ofthehousing. Bothsample heaters ended upbeingdamage duringto installation. 29O