Method for Thermal Modeling and Volatile Measurement of Lunar Regolith

The opportunity of in situ resource utilization (ISRU) within lunar permanently shaded regions (PSRs) prompts the need for characterizing sources for excavation. The percussive heated cone penetrometer (PHCP) is an instrument being developed, through a Lunar Surface Technology Research (LuSTR) grant at Michigan Technological University (MTU) in the Planetary Surface Technology Development Lab (PSTDL), which will be able to determine the distribution of water-bearing regolith and other volatiles in PSRs. This paper explains the methodology and preliminary results of thermal profiling as well as the development of a thermal model for the PHCP that can identify the presence of volatiles in the surrounding terrain. The evaporation of various volatiles can be detected by recording the temperature as a function of time of the material surrounding the hot penetrometer and comparing the results to a dry reference material. An initial reference test setup with dry F-80 silica sand was used to determine the size of the heat-affected zone at various power levels. In two additional test series, water was then added to these sand samples to account to provide moisture levels of 5% and 10% water by weight. Temperature curves obtained from wet sand samples show plateaus due to the latent heat of vaporization, indicating the presence of water. Tests with dry, wet, and frozen lunar regolith simulant samples were then performed to refine the PHCP thermal model to provide a closer resemblance to lunar material thermal behavior. The data sets from the thermal mapping and modeling will inform the design and manufacturing of the cone penetrometer for the LuSTR project.