Humanoid robots are expected to operate in unstructured environments where foot-soil interaction strongly affects mobility. This work develops a simulation framework that couples multibody dynamics with deformable terrain models to study locomotion under such conditions. We compare two approaches: the Discrete Element Method (DEM), which provides particle-level accuracy at high computational cost, and the Soil Contact Model (SCM), an empirical formulation calibrated through DEM-based virtual bevameter tests. Through a progression of experiments–from single-foot validation to full-robot walking, climbing, running, and jumping–we show that SCM predicts foot-soil forces and joint loads with accuracy sufficient for motion planning, while achieving near real-time efficiency. DEM, while more computationally demanding, remains essential for analyzing extreme maneuvers involving rapid soil deformation. Together, these results highlight a pathway for scalable, high-fidelity simulation of humanoid locomotion in granular environments, with direct implications for planetary exploration, disaster response, and other field robotics applications.

Recently, there has been a surge of international interest in extraterrestrial exploration targeting the Moon, Mars, the moons of Mars, and various asteroids. This contribution discusses how current state-of-the-art Earth-based testing for designing rovers and landers for these missions currently leads to overly optimistic conclusions about the behavior of these devices upon deployment on the targeted celestial bodies. The key misconception is that gravitational offset is necessary during the terramechanics testing of rover and lander prototypes on Earth. The body of evidence supporting our argument is tied to a small number of studies conducted during parabolic flights and insights derived from newly revised scaling laws. We argue that what has prevented the community from fully diagnosing the problem at hand is the absence of effective physics-based models capable of simulating terramechanics under low gravity conditions. We developed such a physics-based simulator and utilized it to gauge the mobility of early prototypes of the Volatiles Investigating Polar Exploration Rover (VIPER). This contribution discusses the results generated by this simulator, how they correlate with physical test results from the NASA-Glenn SLOPE lab, and the fallacy of the gravitational offset in rover and lander testing. The simulator, which is open-sourced and publicly available, supports trafficability analysis and facilitates principled studies into in-situ resource utilization activities like digging, bulldozing, and berming in low gravity environments.