ANALYSIS OF SMALL-TIME LOCAL CONTROLLABILITY OF SPACECRAFT ATTITUDE USING TWO CONTROL MOMENT GYROS

Small-time local controllability (STLC) of the combined dynamics comprising the spacecraft and two non-coaxially or coaxially arranged single-gimbal control moment gyros (CMGs) is investigated in sequence. Nonlinear controllability theory is used to shown that for the case of two non-coaxial CMGs, the combined dynamics are STLC at the equilibrium if and only if the two angular momentum vectors of two CMGs do not both lie along the same direction or in the plane spanned by two gimbal axis vectors. For the case of two coaxial CMGs, the combined dynamics are STLC at the equilibrium if the angular momentum vectors of two CMGs do not become collinear.