Terminal sliding mode control of attitude synchronization for autonomous docking to a tumbling satellite

In order to solve the attitude synchronization control problem of an on-orbit servicing spacecraft autonomously docking to a tumbling satellite with the unknown bounded disturbances and system uncertainties, a fast terminal sliding mode control law is presented in this paper. The most important contribution of this paper is to design an attitude synchronization control law, which will be realized by the terminal sliding mode control method, for a servicing spacecraft autonomously docking to a freely tumbling satellite in space. First of all, the model of relative attitude dynamics is derived from the attitude dynamics of servicing spacecraft and tumbling satellite. Then, the relative attitude dynamic model is converted to the normal formation to apply the control method of fast terminal sliding mode. Furthermore, a fast terminal sliding mode control law for attitude synchronization is designed based on the normal formation of relative attitude dynamic model. During the design process of the control law, the measurement errors and parameter variations are also considered. Finally, several numerical simulations are conducted to verify the designed attitude synchronization control law, and the results verified the effectiveness of the designed control law. Moreover, it´s robustness to the unknown bounded disturbances, system uncertainties and measurement errors has also been demonstrated.