Microstructure of Icy Lunar Regolith Simulants

In order to develop technologies to use lunar ice as a resource, it is important to be able to produce representative analogs, or simulants, of icy lunar regolith. Unfortunately, previous work in this area has not been relevant to the lunar environment due to the practice of mixing liquid water with a regolith simulant before freezing. The lunar near subsurface cannot support liquid water due to very low temperatures and pressures, so water ice modification processes are limited to sublimation deposition. In this work, we investigate the microstructure of various icy lunar regolith simulants via micro-CT scans, including pressure sintered (PSS), thermally sintered (TSS), wet mixed, and unsintered. We show that the PSS and TSS samples are microstructurally most similar to each other and exhibit stark differences to the wet mix samples. We found that the presence of liquid water in the sample preparation process drastically altered the microstructure of the samples and identified key features differentiating the lunar-relevant sintering processes from the wet-mixed samples, including differences in total porosity, pore size, ice particle size, and degree of ice-regolith interconnection. These microstructural dissimilarities are caused in large part by the wetting and lubricating behaviors of liquid water. We conclude that because liquid water cannot exist in the lunar near subsurface and has been shown to behave fundamentally differently from sintered samples at the microstructural level, dry-mixed and sintered analogs should be used for lunar technology development, rather than wet-mixed analogs.