Active fault tolerant control system for a high accuracy planet-image and stellar-pointing satellite

This paper focuses on the problem of nonlinear fault detection, diagnosis, and fault tolerant control for a satellite model through the construction of disturbance decoupled adaptive filters designed via the nonlinear geometric approach. Each filter of the bank is sensitive to all but one fault, and decoupled from aerodynamic disturbances. In order to fulfil the requirements of the proposed mission, the disturbance decoupling represents the key point, since the aerodynamic model is often uncertain. To the authors' knowledge, this is the first work presenting the solution of the aerodynamic disturbance decoupling problem. The controller reconfiguration logic exploits a further control loop depending on the on-line estimate of the fault signals. Simulations results for the case of a nonlinear satellite model with aerodynamic, gravitational, magnetic, and solar pressure disturbances are presented with reference to a pointing mission. The suggested approach allows to achieve better performances with respect to control schemes simply designed to be robust with respect to the considered disturbance contributions.