Abstract: Magnetorheological (MR) damper is applied to lunar landing system for shock absorption and vibration reduction. In consideration of the uncertain initial landing attitude angle of lunar lander and the unknown slope of lunar surface, a soft landing dynamic model is built. The mechanical property of MR damper is analyzed in view of the damping characteristics of MR fluid with highspeed and longstroke. The concept of safe angle scope is used to define the relationship between initial landing attitude angle and lunar slope, and a statejump algorithm is developed to realize semiactive control during soft landing. Compared with a certain type of passive lunar lander, the semiactive control is analyzed. Numerical results show that the safe angle scope of semiactive statejump control for MR is 0.977 4 times that of the perfect one, and 4.2 times that of the passive one when the allowable peak acceleration response does not exceed 8g. It is found that the relative standard deviation of the maximal acceleration variation is 0.59 times that of the passive one. Furthermore, when the initial landing attitude angle and lunar slope are very large, the attitude angle of lunar lander changes little, which ensures a smooth landing of the lunar lander.

Key words: semiactive control, MR damper, statejump, soft landing, lunar landing