Terminal sliding mode control for landing on asteroids based on double power reaching law

In the declining stage of soft landing on asteroid, there are many problems in control system of probe such as low convergence speed, long convergence time and severe chattering. A terminal sliding mode control method based on double power reaching law is proposed in this paper. On the basis of conventional reaching law analysis, combined with nonlinear, weak gravitational field characteristics, control schemes in this paper proposes double power reaching law and adopts the terminal sliding mode control method. The controller can weaken the chattering, improve system stability and convergence rate, so that the system can make status tracking error converges fast to zero in the limited time. It has a fast speed either away from or approach to the sliding surface. Simulation results show that the proposed control method achieve fast convergence of the system state in a finite time and strong robustness to disturbances, and eliminates the presence of control chattering. Also, the proposed control law can ensure a smooth landing to the specified descent height, and ultimately secure a soft landing.