Terminal sliding mode control of a lunar lander with electric propulsion

This paper presents an attitude control method based on electric propulsion systems for the lunar lander that considers the important characteristics of nonlinearity and uncertainty of lunar soft landing maneuvers with large attitudes. The attitude control law is designed according to the terminal sliding mode variable structure control method. A soft lunar landing utilizing the proposed control method is simulated, and the results show that this attitude control system demonstrates superior global robustness, consumes less propellant, and can achieve higher precision than a conventional chemical propulsion-based control system. For a lunar lander with a pulse plasma thruster as the propulsion system, the attitude control precision of the system is 0.002 degrees when the attitude control force is 0.1 Newtons. When a conventional chemical, not electric, propulsion thruster is used, if the attitude control force decreases by one order of magnitude, then the control precision of the lunar lander decreases 10-fold. This study demonstrates that a terminal sliding mode variable structure control method combined with low level thrust electric propulsion can improve the precision of lunar soft landings.