AN INVERSE-FREE TECHNIQUE FOR ATTITUDE-CONTROL OF SPACECRAFT USING CMGS

This paper presents a technique for CMG-based attitude control of spac ecraft that does not require calculating the pseudo-inverse of the CMG Jacobian matrix. In order to obtain a steering law, the transpose of the Jacobian matrix is used rather than its pseudo-inverse. The transp ose-based method alleviates some of the problems inherent in the exist ing steering laws that use the pseudo-inverse, such as high gimbal rat es near singularities. The proposed method provides viable rates for t he CMGs even when the gimbals pass through a singular configuration. T he validity of the steering law is demonstrated using Liapunov's stabi lity theorem, and it is shown that the method provides superior result s when compared with conventional steering laws that use the pseudo-in verse of the CMG Jacobian Matrix. In addition, the redundant feature o f the 4-gimbal CMG system is exploited to force the gimbals to attain certain specified angles while the spacecraft's attitude is being cont rolled. This is done by adding appropriate null motion to the CMGs. Th e specified angles for the gimbals can be arbitrary as long as their n et momentum is consistent with the requirements of the spacecraft. (C) 1997 Elsevier Science Ltd.