Illumination and regolith temperature at China’s next candidate lunar landing site Shackleton crater

Abstract

This study focuses on the illumination and temperature at China’s next lunar candidate landing site Shackleton crater. We used the NASA’s SPICE system to evaluate the terrain obscuration effect on real-time illumination; the resulting illumination map resembles previous studies, validating the methodologies used in our study. In addition, we estimated an accumulated illumination map for the period of likely rover movement. The map indicates the illuminated inner wall of the Shackleton crater is close to 27% of the whole, meaning that the rover will likely receive solar radiation during its movement. Using the real-time illumination and the distributed 1-D thermal diffusion model, we continuously evaluated the regolith temperature for more than 20 years to stabilize the temperature, and selected the temperature of the end time as the initial value used in a thermal study set for July 20, 2023 and May 8, 2027. Our results indicate the temperature in the permanent shadow region remains nearly constant, thus validating the stability of our estimated initial temperature. Our results also indicate that the surface temperature is more sensitive to transient illumination, but the subsurface temperature is more likely to be associated with the accumulated illumination. This difference indirectly implies that the conductivity of the lunar regolith is inefficient. The locations receiving more solar radiation show a temperature larger than the threshold (∼112 K) of ice stability. The permanently shadowed regions can be as cold as 25 K, and such extreme coldness is a hazard to the rover. There are suitable temperature locations which have a warm surface but cold subsurface to preserve water ice. To further ensure normal rover movement, we provided a map of suitable temperature sites and found that these locations exist not only in the Shackleton crater’s inner wall, but also outside the crater. We suggested four trade-off sampling sites with suitable temperatures and gradual slopes.