Stability Analysis of a Flexible Spacecraft with a Sampled-Data Attitude Sensor

The pitch attitude control system for a flexible communications satellite is analyzed using sampled-data techniques. The sampling arises mainly from the use of discrete-time attitude measurement rather than from the digital controller implementation. It is found that Nyquist techniques lead to a relatively simple stability analysis that models the multirate sampling process with considerable fidelity, eliminating guesswork associated with equivalent delays. Controller modifications that improve stability are arrived at by this route. Finally, flexiblemode frequency and damping are varied to evaluate their influence on stability. There seems to exist a critical frequency at which stability margins are very small. Increasing the damping, predictably, improves matters.