Mechanical Properties of Icy Mars Regolith Simulant: Assessment of a Potential ISRU Feedstock

Abstract

Recent data on near-surface water availability at Mars, along with ongoing research on the low-temperature and in situ behavior of fresh water and sea ices, has been employed to identify feasible engineering approaches for capturing water as a Mars ISRU feedstock. Acknowledging the need to minimize biological contamination, we have proposed extracting water from Mars regolith fines as a very conservative feedstock harvesting approach that is relatively insensitive to fixed base site selection. Relatively pure water ice can be found in the polar regions of Mars, and data from the Phoenix lander site suggest that veins of pure water ice or brine ice may be accessible near the surface at other locations, permitting drilling or sawing chunks of those feedstock ice materials, and the hardware systems to extract those materials have been defined for other applications. Mars permafrost feedstock was the focus of this investigation because it appears to be the least understood, and could be present near the surface at desirable mid-latitude landing sites. JSC Mars-1A, Mars regolith simulant has been employed as a surrogate solid matrix in order to anticipate the flexural strength and modulus of elasticity of Martian permafrost for consideration as a potential ISRU feedstock. Test specimens were produced containing distilled water ice mass fractions ranging from 15 to 35 %. Testing showed that water mass fractions less than 20 % lacked sufficient cohesion, when frozen, to produce a rigid sample, whereas water concentrations greater than 35 % produced non-homogeneous water pockets or puddles. Sample preparation was based on ASTM testing procedures, and an effort was made to avoid uncontrolled water contamination and to minimize adsorbed gases on the simulant particles, prior to adding distilled water. After the regolith simulant was combined with the desired mass of distilled water, and mixed to assure homogeneity, 43 rectangular bar-shaped, three-point bend test samples 25.4 mm wide by 12.7 mm thick by 101.6 mm long (1 x 0.5 x 4 inches) were produced. The test articles, created in individual molds were frozen above slabs of dry ice, inside a freezer, attempting to approximate rapid permafrost formation in a carbon dioxide-rich atmosphere at Mars-like temperatures. Triplicate sample sets were produced containing distilled water mass fractions of 20, 25, 30 and 35 percent, to permit testing to failure at test temperatures of 133 K, 210 K, and 253 K. An additional test specimen set, consisting of 35% water and 2 % sodium chloride salt, by mass, was prepared in a cursory attempt to investigate the possible influence of frozen brine systems on the mechanical behavior of Martian permafrost. Our experiments indicate that the bending strength of Martian permafrost will be less than 10 MPa, and it should be possible to harvest liter-size permafrost feedstock blocks by sawing 10 cm-deep grooves into exposed permafrost, then breaking off and recovering the resulting material.