Sliding mode observer based attitude determination of spacecrafts without angular velocity measurement

An approach to restrain the influence of uncertain parameters and environmental disturbances on the precision of spacrcraft attitude estimation is presented. The approach is based on sliding mode observer (SMO) method. A three-order dynamic system is constructed by extending the uncertain parameters and environment disturbances as the state of the attitude dynamics which is small angle approximated and linearized. On this basis, an augmented sliding mode observer (ASMO) is designed to achieve the high precision of spacrcraft attitude angle and angular velocity estimation which only uses attitude angle as measurement. Compared with conventional SMO,the presented ASMO needs smaller switching gain as the uncertainty of the system is reduced. And the chattering phenomena in the sliding mode observer is alleviated in ASMO method. Also, the performances of augmented Kalman filter(AKF) are showed to be compared with ASMO. The simulation results show that ASMO is feasible.