In this paper, landing characteristic analysis of lunar lander considering lunar regolith and topography is performed. The status of landing stability of the lunar lander is classified into stable landing, conditionally stable landing due to sliding, and unstable landing due to tip-over. In particular, the quasi-static tip-over equation is derived considering the phenomena of lowering the center of gravity and extension of footpad interval of the landing gear. These results are compared with finite element analysis results using a commercial software ABAQUS and its validity and accuracy are verified. The verified finite element model is used for examining the tendency of various environmental variables such as landing conditions, friction coefficient, lateral speed and slope of the ground.
Also, a coarse lunar soil model is developed using discrete element method and compared its computed physical properties with the actual lunar soil for its validation. The surface of the actual moon consists of numerous craters and rocks of various sizes, and it is covered with fine dry soil which seriously affects the landing stability of the lunar lander. Therefore, in consideration of the environment of the lunar regolith, the lunar soil model is generated using the discrete element method. To validate the coarse model of lunar soil, the indentation test and the direct shear test are performed to check the physical properties(indentation depth, cohesion stress, internal friction angle). To examine the performance of the proposed model, the landing analysis of finite element model of the lunar lander is performed on a rigid surface and two soil models. The impact load delivered to the strut of the lander is compared according to three ground conditions.
A single-leg landing gear drop test is conducted to develop a high-precision analytical model of the lunar lander. The impact load and acceleration delivered to the lander body are measured. Using this data, precise calibration is performed of the existing model of the lander. Finally, landing stability evaluation of lunar lander is performed considering lunar topography and regolith.