Gas permeability of BP-1 lunar regolith simulant at sub-atmospheric pressures

Abstract

The risks to lunar surface assets from high-velocity regolith ejecta particle streams have significant implications for the sustainable human exploration of the lunar surface. Such regolith can result from lander engine plume-surface interactions. Consequently, the gas permeability of lunar regolith must be understood for precise plume surface interaction ejecta acceleration models. Motivated by these risks, and with the goal of supplying future plume surface interaction models with improved input parameters, the objective of this study is to understand the gas permeability of lunar regolith simulant BP-1 at sub-atmospheric pressures while considering density and moisture content variations. The Regolith Gas Permeability Tester (REGAPT) presented here is a purpose built transparent permeameter that allows the flow of gas to be controlled through the BP-1 once the whole system has reached pressures below 130 Pa. Results from REGAPT demonstrate a range in BP-1 gas permeability from $0.4\times 10^{-13}{m}^2$ to $1.9\times 10^{-13}{m}^2$. Higher densities and lower porosities reduce permeability as expected. Outgassing from residual moisture in BP-1 is found to bias gas permeability measurements. It is therefore important to carefully control the moisture content of lunar regolith simulants in experimental studies that involve gas flow, such as those investigating the effects of plume surface interactions.