Thermophysical properties of lunar regolith simulant LHS-1 and ice sublimation kinetics in its mixtures with frozen water

Abstract

A recently developed lunar regolith simulant LHS-1 is used currently to advance the technologies for water extraction from icy regolith in the polar regions of the Moon. However, thermophysical properties of LHS-1 at low temperatures have not been studied yet, which hinders the development of these technologies. It is also unclear whether experimental data on the rate of ice sublimation in LHS-1/ice mixtures can be applied to the actual icy regolith of the Moon. In the present paper, the specific heats and thermal diffusivities of LHS-1 and its finer version LHS-1D were studied at low temperatures using differential scanning calorimetry and laser flash analysis. The thermal diffusivities of LHS-1 and LHS-1D have been measured in the temperature range of 148−300 K in a helium environment at pressures of about 90 kPa and less than 1 Pa. The reduced pressure decreased the thermal diffusivity by several times owing to the decreased role of helium in the heat transfer during the test. The thermal diffusivity also decreased with increasing temperature and decreasing particle size. The specific heats of dry simulants have been measured in the temperature range of 110−320 K. The obtained values are close to the specific heats of the Apollo regolith samples at the same temperatures. The specific heats of LHS-1 and LHS-1D, mixed with water, have been measured in the temperature range of 110−340 K. The theoretically expected increase in specific heat due to the addition of 3 − 5 wt % ice was within the experimental error. The ice sublimation rates in LHS-1/ice and LHS-1D/ice mixtures have been measured at temperatures of 240, 247, and 258 K at pressure of 4 Pa. The sublimation rate decreases with time for all samples, which may be associated with increasing vapor pressure over the subliming surface as the sublimation front propagates downward. The analysis of the obtained data has shown that the area of the subliming surface is much less than the surface area of the simulant particles. This should be taken into account when the results of experiments with simulant/ice mixtures are applied to the actual icy regolith on the Moon.