Characterizing transient thermal interactions between lunar regolith and surface spacecraft

We present a new method, its development, implementation, and verification, for calculating the transient thermal interaction between lunar regolith and moving spacecraft travelling across the surface of the Moon. Regolith temperatures can be determined for lunar landscapes as defined by laser altimeter remote sensing data refined with local crater and boulder models. The purpose of this approach is to enable more detailed, dynamic thermal analyses of mobile systems on the lunar surface rather than relying on worst case, boundary condition design approaches typically used for spacecraft thermal engineering. This new simulation method is based on integrating models that represent small and large scale landscapes; reproduce regolith and boulder temperatures on the Moon; define the position of the Sun; and perform ray tracing to determine infrared and solar heat fluxes between passing objects and the surface. The thermal model of the lunar regolith enhances established models with a slope- and depth-dependent density. The simulation results were verified against remote sensing data obtained from the Diviner Lunar Radiometer Experiment of the Lunar Reconnaissance Orbiter (LRO) and from other sources cited in the literature. The verification results for isolated regolith surface patches showed a deviation from established models of about ±3-6 K (±1-6%) during lunar day, and lunar night. For real landscapes such as Crater Calippus and Crater Marius A, the deviation is less than ±15 K (±10%) compared to remote sensing data for the majority of measured data points. Only in regions with presumed different regolith material properties, such as steep slopes or depressions, or in regions with a low resolution on the topographic map, were the deviations up to 100 K (60%). From the results, empirical equations were derived, which can be used for worst case calculations or to calculate initial temperatures for more elaborate time marching numerical models. The proposed new method could be further enhanced to address scientific questions by incorporating more detailed regolith and boulder models, or be used as-is to evaluate the dynamic thermal envelope of moving spacecraft.