Landing Behavior Analysis of Lunar Probe Based on Drop Tests and RFT in a Vacuum

This letter addresses the influences of footpad shape and ground condition on the motion behavior of a lander in a vacuum. To evaluate the influences, we first developed a drop test apparatus that can conduct repeated drop tests in the vacuum chamber. The footpad drop tests were then conducted with various shaped footpads on different surface conditions. Subsequently, the motion behavior of the footpads in a vacuum was modeled, based on the resistance force theory (RFT) and its penetration characteristics were numerically analyzed. The usefulness of the RFT based model was discussed along with the experimental results. Finally, drop tests were conducted using a four-legged lander to comprehensively analyze its landing behaviors. From the footpad drop tests and numerical analysis based on the RFT, we confirmed the following: (1) the force acting on the footpad is enhanced, and the penetration depth is reduced in a vacuum, (2) the force and kinetic energy conversion rate are smallest for the curved footpad, and (3) an increase in the ground density had a relatively small impact on the penetration depth of the footpads in a vacuum. Furthermore, the drop tests using the lander model confirmed that even if some of the lander's footpads land on regolith simulant with different densities, this does not lead to postural imbalance or turnover of the lander in a vacuum.