Robust pointing control of spacecraft with large appendages

Pointing control design for flexible spacecraft with large appendages such as the Tracking and Data Relay Satellite (TDRS H, I, and J) requires special attention. In particular, the loop interaction effects and plant configuration variations must be considered. The classical single-loop stability margin may no longer guarantee robustness due to loop coupling especially when the control loops interact with low flexible modes. This paper addresses a practical design procedure wherein the above-mentioned issues are adequately accommodated. Two designs are proposed, one with the classical method and the other with the H_∞ method. Examples from the TDRS H, I, and J are used to illustrate the technique