Fault tolerant control of spacecraft in the presence of sensor bias

We develop a stable scheme for bias estimation in the case of attitude tracking. The scheme is based on the design of nonlinear observers for unknown bias identification and state estimation. In the case of gyro bias, our nonlinear observer design, based on the quaternion dynamics, leads to an error model and adjustment laws that result in guaranteed convergence of the unknown bias estimates to their true values. We demonstrate that our scheme results in a stable overall system, and achieves highly accurate pointing in the presence of unknown sensor bias. The properties of the proposed scheme are evaluated through simulations using a generic spacecraft model.