In this paper, a continuous globally stable tracking control algorithm is proposed for aspacecraft in the presence of unknown actuator failure,controlinputsaturation,uncertaintyininertialmatrixand externaldisturbances.Thedesignmethodisbasedonvariablestructurecontrolandhasthefollowing properties: (1)fastandaccurateresponseinthepresenceofboundeddisturbances;(2)robusttothe partial lossofactuatoreffectiveness;(3)explicitconsiderationofcontrolinputsaturation;and(4)robust to uncertaintyininertialmatrix.Incontrasttotraditionalfault-tolerantcontrolmethods,theproposed controller doesnotrequireknowledgeoftheactuatorfaultsandisimplementedwithoutexplicitfault detection andisolationprocesses.Intheproposedcontrollerasingleparameterisadjusteddynamically in suchawaythatitispossibletoprovethatbothattitudeandangularvelocityerrorswilltendtozero asymptotically.ThestabilityproofisbasedonaLyapunovanalysisandthepropertiesofthesingularity free quaternionrepresentationofspacecraftdynamics.Resultsofnumericalsimulationsstatethatthe proposed controllerissuccessfulinachievinghighattitudeperformanceinthepresenceofexternal disturbances, actuatorfailures,andcontrolinputsaturation.

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