Control Method of Soft Landing on Asteroid Based on the Optimal Sliding-mode Guidance Law

Landing an asteroid safely is an important link in the deep space exploration. A kind of soft landing guidance control law about terminal angular constraint is designed in this paper. This law is combining the optimal proportional guidance law and the sliding mode variable structure to control the speed and the direction. When the interference model is unknown in the system, the optimal sliding-mode guidance law can eliminate the steady oscillation of the line-of-sight rate and make sure it approaches to zero. The simulation results proved that, the guidance and control law designed in this paper can achieve the asteroid's landing angle and speed restriction, then perform the successfully soft landing on an asteroid's surface.