Paper presented at ISTVS 2025 | 55th Conference of the International Society for Terrain-Vehicle Systems https://doi.org/10.56884/5A0PXCI7
Authors: James Hurrell, Keisuke Takehana, Kentaro Uno, Kazuya Yoshida
Keywords: Terramechanics; Single-wheel test; Lunar rover; Grouser wheel; Lunar regolith simulant; Reduced gravity
Abstract:
Purpose: The impact of gravity and use of gravity offload on rover tractive performance is evaluated and compared between Earth and lunar environments. Single-wheel experiments and discrete element method (DEM) simulations of a micro-rover wheel modelled on the Rashid-1 rover designed for the Emirates lunar mission are conducted. The wheel's interaction with Toyoura sand and FJS-1 lunar regolith simulant is studied. Consideration is made for why the use of gravity offloading has been prominent and other options that are available.
Methods: Slip conditions, traction coefficient and grouser pitch for single-wheel experiments are measured for a range of fixed slip values at the expected rover load of 24.5 N at a nominal 0.02 m/s, termed a low-speed regime. Single-wheel simulations have been previously verified by comparison with experimental results. Lunar simulations can predict lunar gravity performance.
Results: Wheel performance regarding traction coefficient and tractive efficiency under lunar gravity matches that under Earth gravity. Traction performance in tractive force and resistive torque is reduced by the ratio of Earth to lunar gravity, 1/6, for the same mass. Earth gravity results for 4.1 N are understood to over-predict the traction coefficient compared to lunar conditions. Using load matching of 24.5 N in lunar gravity reduces performance.
Conclusion: Gravity offloading is unsuitable. Depending on the aspect desired to study the influence of gravity on the rover, consideration should be made to use either Earth conditions, granular scaling laws, or a full-scale reduction of the rover. This may change with a transition to high-speed wheel motion.
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