Thermal Wadis in Support of Lunar Exploration: Concept Development and Utilization

Abstract

SummaryThermal wadis, engineered sources of heat, can be used to extend the life of lunar rovers by keeping them warm during the extreme cold of the lunar night. Thermal wadis can be manufactured by sintering or melting lunar regolith into a solid mass with more than two orders of magnitude higher thermal diffusivities compared to native regolith dust. Small simulant samples were sintered and melted in the electrical furnaces at different temperatures, different heating and cooling rates, various soaking times, under air, or in an argon atmosphere. The samples were analyzed with scanning electron microscopy and energy dispersive spectroscopy, X-ray diffraction, a laser-flash thermal diffusivity system, and the millimeter-wave system. The melting temperature of JSC-1AF simulant was ~50°C lower in an argon atmosphere compared to an air atmosphere. The flow of argon during sintering and melting resulted in a small mass loss of 0.04 to 0.1 wt% because of the volatization of alkali compounds. In contrast, the samples that were heat-treated under an air atmosphere gained from 0.012 to 0.31 wt% of the total weight. A significantly higher number of cavities were formed inside the samples melted under an argon atmosphere, possibly because of the evolution of oxygen bubbles from iron redox reactions. The calculated emissivity of JSCf-1AF simulant did not change much with temperature, varying between 0.8 and 0.95 at temperatures from 100 to 1200°C. The thermal diffusivities of raw regolith that was compressed under a pressure of 9 metric tons ranged from 0.0013 to 00011 in the 27 to 390°C temperature range. The thermal diffusivities of sintered and melted JSC-1AF simulant varied from 0.0028 to 0.0072 cm 2 /s with the maximum thermal diffusivities observed in the samples that were heated up 5°C/min from room temperature to 1150°C under argon or air. These thermal diffusivities are high enough for the rovers to survive the extreme cold of the Moon at the rim of the Shackleton Crater and allow them to operate for months (or years) as opposed to weeks on the lunar surface. Future investigations will be focused on a system that can efficiently construct a thermal wadi from the lunar mare regolith. Solar heating, microwave heating, or electrical resistance melting are considered.

Simultaneous measurement of temperature and emissivity of lunar regolith simulant using dual-channel millimeter-wave radiometry

“…The monolithic solid samples were then reheated from RT to 300 • C in air at 5 • C/min, while monitoring with the MMW instrument in order to obtain quantitative emissivity data below the sintering temperature of the sample (1050-1000 • C). 28 The low-temperature emissivity was not obtained for the powdered JSC-1AF sample from the first experiment, since the emissions scattered to the extent that a TRR signal was not obtained. Figure 2 shows the heating part of the experiment for the JSC-1AF powder samples.…”