An Improved Adaptive Sliding Mode Control for Soft Landing on The Asteroid

This paper presents an improved adaptive sliding mode control method for soft Landing on the Asteroid, and addresses the problems of the unknown parameter of the upper bound of interference uncertainty and over-adaptation of switching gain. First, a three-dimensional dynamic model of asteroid probe, in which considering the interference uncertainty of the third-body gravitational perturbation and radiation pressure from the sun, is established in the fixed-body coordinate system. Second, an adaptive scheme is designed based on the degree of the system status deviating from the sliding surface to estimate the unknown parameter of the upper bound of system uncertainty, and the estimate value is used as the switch gain of sliding mode control to reduce the effects of uncertain dynamics. Besides, a monotone decreasing function is introduced in the sliding mode function to suppress the over-estimated value of the model-free interference which is resulted by system initial error. The stability of the closed-loop system is proved by using the Lyapunov theory. Finally, the simulation results of landing on the Eros are represented to illustrate the effectiveness of the proposed method.