Investigation on in-situ water ice recovery considering energy efficiency at the lunar south pole

Abstract It is of great significance to realize the in-situ utilization of lunar water ice for the establishment and sustainable operation of the future lunar base. Considering the location of water ice in the lunar polar regions, based on the in-situ thermal mining method, an integrated approach for the water ice recovery was established. The evolution characteristics of average temperature of the icy soil and water vapor collection rate with the mining time were analyzed. The optimal mining temperature for the recovery of water ice was studied. The energy efficiency under various arrangement densities of heating elements was assessed with the optimal number of heating elements determined. The results show that as the mining time increases, for different target mining temperatures, the average temperature of the icy soil rapidly rise at first, and then tend to stabilize. The water vapor collection rates at different target mining temperatures vary greatly due to the difference in saturated vapor pressure of water ice. At high mining temperatures, the sublimation coefficient also significantly affects the process of water vapor collection. The water vapor collection rate with sublimation coefficient being unity is up to 36% larger than that with non-constant sublimation coefficient for the lunar soil under investigation within four earth weeks at the target mining temperature of 240 K. In addition, the increase of the mining temperature increases the water vapor collection rate, and at the same time, the water vapor pressure in the capture tent also increases, which may lead to the instability of the water ice production system. Combining with water vapor collection rate and change rate of water vapor pressure in the capture tent, the temperature of 220 K is obtained as the optimal target mining temperature. Furthermore, for the lunar soil in this work, the energy efficiencies for water ice production with seven and nine heating elements are same, and greater than that with five heating elements. Considering the energy efficiency, the minimum number of heating elements could be determined.