MEMS技术在空间的应用(MEMSInSpace)

MEMSInSpaceSatellitesandspacecraftcouldlosetheirreputationforunreliabilityandhighcost,thankstosomeofthesmallestmachinesonEarth—oraboveitByStephenCassPosted2Jul2001|14:27GMTShare|Email|PrintPHOTO:ROBMAGIERIArtist'sconceptionofa1-kgsatellitebultwithmicroelectromechanicalsystems(MEMS).Thesatelliteindustrycouldexperienceitsbiggestrevolutionsinceitjoinedtheranksofcommerce,thankstosomeofthesmallestmachinesinexistence.Researchersareperformingexperimentsdesignedtoconvincetheaerospaceindustrythatmicroelectromechanicalsystems(MEMS)couldopenthedoortolow-cost,high-reliability,mass-producedsatellites.MEMScombineconventionalsemiconductorelectronicswithbeams,gears,levers,switches,accelerometers,diaphragms,microfluidicthrusters,andheatcontrollers,allofthemmicroscopicinsize[seeAQuickGlanceatMEMS].WecandoawholenewarrayofthingswithMEMSthatcannotbedoneanyotherway,saidHenryHelvajian,aseniorscientistwithAerospaceCorp.,anonprofitaerospaceresearchanddevelopmentorganizationinElSegundo,Calif.Allsatellitesrequireabasicsetofsubsystemstodousefulworkinorbit[seefigure].Apowersourceisone,typicallyasolarcellarraybackedupwithbatteries.Alsonecessaryareacommunicationssystemtoreceivecommandsandreturninformation,internalsensorstogaugethesatellite'sstate,andacontrolunittocoordinateallsubsystemactivities.Satelliteswithmorecomplexmissionswillalsorequiresystemstodeterminethespacecraft'sorientationandpositionandpropulsionsystemstocontrolboth.CommonSatelliteSystems:Allbutthesimplestsatellitesrequireacommonsetofsubsystems[orange].Morecomplexdesignsrequiremoresubsystems[blue].IfMEMS-basedsystemscanperformallthesetasks,thenmass-produced,lightweightsatellitesmayappearinorbit.IfallthefunctionsofthesesubsystemscanbeperformedbyMEMS,thenyoucouldstartthinkingoffabricatingsatellitesubsystemslikewemakeCMOSchipsforlaptops,saidHelvajian.SatellitescouldbeconstructedbystackingwaferscoveredwithMEMSandelectricalcomponents.Theresultwouldbea1-kg-classsatellite,orpicosat,thatcouldbemassproduced...youcouldputupaconstellationofhundredsoftheselittleguysinlowEarth-orbit[LEO]andget,say,incredibleweatherinformation,hecontinued.ThesamewassaidbyThomasGeorge,whosupervisestheMEMSTechnologyGroup,partoftheJetPropulsionLaboratory(JPL),inPasadena,Calif.Suchsatellites,havingnegligiblemass,size,andpowerconsumptionrequirements,canbeeasilypiggybackedonconventionalsatellitesorlaunchedusingsmallerandcheaperlaunchvehicles,hetoldIEEESpectrum.SomeoftheadvantagesofusingMEMS-basedsatelliteswerespelledoutbyErnestRobinson,adistinguishedengineeratAerospace.Lowlaunchcostsandhighresistancetoradiationandvibrationheadedthelist.ItcostsaboutUS$10000/kgtoputanobjectintoLEO.Clearly,smaller,lightersatelliteswillcostlesstolaunch.MEMS-basedsatellitesalsopromisetobecheapertodevelopandfabricatethanconventionalspacecraft.Robustnessisalsokey.Youcan'tupsetaMEMSswitchwithasinglecosmicrayimpact,butyoucanupsetasemiconductorswitchbydoingthat,Robinsonexplained.ThismeansthatMEMSaremuchmoreresistanttoradiationdamageandsowouldbeabletooperatecomfortablyinaveryhigh-radiationenvironmentsuchastheVanAllenbelts.TheVanAllenbeltsoccupyaregionofspacebetweenLEOandthecrowdedgeosynchronousorbit.Potentiallyavaluablepieceoforbitalrealestate,ithasremainedrelativelyunexploitedbecauseofthepracticalandeconomicdifficultiesofshieldingconventionalsatellitesfromhighdosesofradiation.Thenthere'sMEMSresistancetohighlevelsofvibrationandtheshockof,say,arocketlaunch.GeorgereferredtoademonstrationbyHoneywellCorp.,ofMorristown,N.J.,ofanimagingarrayofMEMS-basedbolometers(bolometersareusedtodetectinfraredandmicrowaveradiation).ThearraywastestedontheEarth'ssurfacebybeingshotfromahowitzer.Thoughsubjectedtoaccelerationsestimatedat20000timesgravitationalacceleration,thebolometersworkedperfectlyafterward.ThereasonMEMSdevicesstanduptothesekindsofforcessomuchbetterthanconventionallysizeddevicesisclear:themassofeachmovingcomponentisextremelysmall,sothatpotentiallydamaginginternalforcesbetweencomponentsarealsoverysmall.AnExtraPairofEyes:AMEMS-basedinspectorisasmallspacecraftcarriedaboardalargervessel.Ifthere'sanaccident,theinspectorcanbedispatchedonareconnaissancemission,communicatingwithitshostortheground.Whenitsmissionisover,theinspectorispropelledawaylestitbecomeahazarditself.Clickontheimagetoenlarge.AninspectoronboardAllthesame,thefirstapplicationofMEMS-basedminiaturespacecraftwillmostlikelynotbeasanindependentlong-livedsatelliteorsatelliteconstellation,butasashort-livedinspectordevice.Aninspectorwouldconsistofabattery,acontrolcomputer,asmallpropulsionunit,andsomeopticsorothersensors,suchasaninfrareddetector.Itwouldcommunicatewirelesslywithitsmothership[seefigure].Whenaspacecraftmalfunctions,agreatdealoftimeandenergyisspentdoingdetectiveworktofindoutwhathappenedandascertainitscurrentstate.Yetmuchofthiseffortcouldbeshort-circuitedifevenapictureortwoofthespacecraftwereavailabletogroundcontrollers,thankstoaninspector.InspectorscouldplayanimportantroleduringtheconstructionandoperationoftheInternationalSpaceStation.Suchalargestructureisboundtodegradeovertim