Quantifying Gas Leak Rates through Regolith Feed Columns in Vacuum

Abstract

All in situ resource utilization regolith reactor systems that aim to extract gases or vapors must maintain a seal along the flow path of the regolith from the inlet hopper to where extracted gases or vapors are generated. Using a column of regolith at the inlet has been proposed as an alternative to systems that use a series of mechanical valves to reduce mass and complexity. Different vertical regolith simulant plug diameters and heights were tested under vacuum with dry nitrogen to observe leak rates and approximate steady-state pressure gradient equilibria, demonstrating a linear relationship between column height and resulting leak rate. The effect of absolute ambient pressure was also studied by repeating tests at incremental pressures ranging from 10−5 up to 760 Torr to corroborate ambient tests from previous work. Pressure decay rates decreased up to 27-fold under vacuum when compared to equal differentials relative to ambient pressure, demonstrating the importance of vacuum testing for regolith seal systems. Disrupted regolith simulant was found to exhibit higher leak rates than pristine, as-poured simulant, indicating the need to consider the impact of recovery from depressurization events. Both GRC-1 and OB-1 lunar regolith simulants were used to demonstrate seal sensitivity to regolith mechanical properties.