Failure-accommodating control of large flexible spacecraft

This paper considers the problem of designing failure-accommodating controllers for large flexible spacecraft when there are sector-type nonlinearities in the loops. It is proved that an LQG-type controller can be made failure tolerant by inserting appropriate gains in the actuator paths and state estimator residual paths. For the state feedback case, when the actuators are saturating type, it is proved that there exists a finite region of attraction, which is invariant in the presence of these gains. Another class of controllers, which employs collocated sensors and actuators is presented, and is shown to have excellent failure-accommodation properties in addition to its robustness properties.