In this paper, we investigate and model the motion behaviors in the atmosphere and vacuum of the landing gear of a lunar probe, which contacts the granular material covering the lunar surface. Drop and friction tests were conducted using the footpads of a lander on a lunar regolith simulant. In the drop tests, the footpads were dropped onto the simulant. The impact characteristics of the footpads were then analyzed. In the friction tests, footpads having varying shapes were slid onto the simulant. The sliding characteristics of the footpads were then evaluated. The drop tests showed that the simulant ejected by the footpad impact diminished, and the footpad penetration significantly decreased in the vacuum. The friction tests confirmed that the sinkage caused by the sliding of the footpad generally increased more in the vacuum than in the atmosphere. However, the difference in the sinkages can be negligible depending on the footpad shape. These findings enabled the deriving of fundamental models of landing gear and suggested guidelines for the design and development of landing gear.