Nonsingular terminal sliding mode control for approach to non-cooperative target

The problem of final approach to a non-cooperative tumbling target was researched. The relative orbit and attitude dynamics model with arbitrary eccentrics was established. Then, the system's external disturbance, model uncertainty and the system nonlinear term were expressed as total disturbance. Based on the theory of extended state observer (ESO), ESO was designed to estimate the total disturbance. Furthermore, by applying the nonsingular terminal sliding mode control method, the nonsingular terminal sliding mode control law was designed, which just needs the relative position and attitude measurement information. The stability of the control law was demonstrated via a Lyapunov analysis. The designed controller is model independent, which overcomes the problem of unknown dynamics parameters and can track the desired trajectory in finite time. The numerical simulation shows the effectiveness of the controller.