Vacuum effects on the angle of repose of lunar soil simulants: Experimental insights

Understanding the behaviour of lunar regolith under space-relevant conditions is essential for future in situ resource utilisation (ISRU) and surface operations. One of the key properties that govern regolith mobility and stability is the angle of repose. This study investigates the influence of vacuum conditions on the static and dynamic angles of repose of a mare-type lunar soil simulant. Two complementary measurement methods were employed: a rotating drum setup for dynamic angles, and a fixed funnel system for static angles, both adapted for operation inside a high-vacuum chamber ( 8 × 1 0 − 4 Torr). Statistical analyses revealed that vacuum exposure significantly altered both the static and dynamic repose angles when compared to atmospheric and post-vacuum conditions. The dynamic angle remained more stable across varying rotational speeds under vacuum, while the static angle consistently decreased, likely due to the removal of residual moisture and changes in interparticle cohesion. Degassing effects were visually confirmed during pump-down, suggesting internal structural changes within the granular bed. Additionally, platform geometry was found to influence the static angle of repose. These results demonstrate that vacuum conditions have a statistically significant and repeatable impact on regolith behaviour. The findings underscore the need to incorporate vacuum testing in terrestrial simulations of lunar operations and suggest that dynamic repose measurements may be more suitable for microgravity adaptation due to their robustness and simplicity. • Vacuum conditions alter the parameters of lunar regolith simulant. • Both static and dynamic angles of repose vary under vacuum, atmospheric, and post-vacuum conditions. • Degassing during pump-down alters the morphology of regolith piles.