Summary:Apossible methodofcontrolling andmomentum-storage elements. Inthe develop criteria foradequate small-signal theattitude ofsatellites andspacevehicleslatter casegasjetsaregenerally usedto performance.

ycontrol torques andtostore highvalues of A high-capacity reaction-wheel systemis Pertinent Dynamics angular monmentum) canextendtheap- defined asonecapable ofdeveloping large plicability ofreaction-wheel control to vehicular rates[oftheorderof1rad/ Consider thedefinition oftermsshown include deep-space missions. Theproblemssec(radian persecond) ]andlarge vehic-inFig.1.Theaxesshownarerigid spaceencountered inthedesign ofsuchsystems aremainly thosewhicharise fromcross-ularaccelerations (oftheorder of0.1rad/ craftaxes.Hz isthetotalangular coupling oftorques amongtheprincipal sec2). Thiscontrasts withtypical sys- momentumcomponent along theithaxis, axesandfromcomponent nonlinearities. tems,currently underconsideration for andOjistheinertial rateofthejthaxis A design fora 3-axis control system,earthsatellites, whichhavemaximum (i.e., thequantitv measured by a rate inwhichcontrol torques abouteachaxis slewing rateS andaccelerations ofapproxi-gyroaboutthejthaxis).Thenettorque arederived solelv fromangular information s measured aboutthesameaxis, ispresented. mately10-2rad/sec and10-3rad/sec2 T, (T=iT+±jT2+kT3) on thevehicle Thesystem isdesigned forniaximum ob- respectively. High-capacity reaction-equals therateofchangeofangular tainable rates ofseveral degrees persecond.wheelsystems maybepreferable toother momentum. System stability andboundsontheniagni-methodsofattitude control incertain tudesoftheinteraxial disturbances are .r . . r T H investigated analytically froma linearized T2 = at2 + H1t3 -H301( model.Nonlinear effects areinvestigated 1.If a gas-jet systemisusedexclusively L2i.LZ LHA- H162j bymeansofdigital computersimulation fa . . r .. ~~~~~~for stablization on a longvoyage,a proandanexperimental model. hibitively large supply ofpropellant may Hiconsists, generallv, ofthree additive berequired. Reaction-wheel control over- terms: comesthisproblemsince, intheabsence ofexternal torques, theenergyrequire-H =hi+Iii+gi (2) THE current trend toward sophisticated mentsofthesystemcanbecontinually spacevehicles necessitates, among supplied bysolar batteries. Moreover, the where other requirements, methods forefficient judicious exploitation of solar' pressure attitude control. Present attitude-con- through solar vaties caneliminate theneed hi=aangular momentumofreaction wheel attol systudems used in earthsatellitesand formomentum-dumping propellant, ifthe abouttheithaxis