Comparison of Different Attitude Control Schemes 87-2391 for Large Communications Satellites

A comparative study of the robustness of various spacecraft body at t i tude control systems with structural flexibility is presented in this paper. The control systems examined are: (a) 3-Reaction Wheels (b) Body-fixed momentum wheel with offset thrusters (c) Skewed body-fixed momentum wheels with offset thrusters and (d) Body-fixed momentum wheel with two reaction wheels. For the size of large spacecraft considered in this paper, all these systems a re shown to result in satisfactory performance. In order to exhibit their relative merits, the presence of severe structural interaction had to be introduced. Comparison was then made in terms of stability, which is affected by non-colocation of actuators and sensors. Performance borne out of the nonlinear simulation with both the large flexible spacecraft and dummy unstable interacting low structural mode is illustrated. This la t ter study shows that a system with single body-fixed momentum ?heel along pitch axis and two reaction wheels oriented along roll and yaw axes, is the most robust.