Projection matrix approach for design of IPACS of spacecraft with VSCMGs

The steering law of variable speed control moment gyros (VSCMGs) used in integrated power/attitude control system (IPACS) is studied. The dynamical equations of a rigid spacecraft with VSCMGs were established. An attitude control law which guarantees asymptotic stability was designed by Lyapunov theory. On the analysis of the VSCMGs' dynamics a steering law is designed by projection matrix. In the steering law the commanded torque was decomposed into two sub-torques, one of which is produced by the control moment gyro (CMG) mode, and the other by the reaction wheel (RW) mode. The CMC mode is valid even when VSCMGs are in the singular configuration and thus abates the load of the RW mode. The steering law demands at least three VSCMGs for IPACS. It is proved the steering law can solve the singularity of IPACS effectively. Simulation validates the feasibility of the scheme.