Thermal environment of the Chang?E-5 landing site and its effect on the external temperature of the lander

The thermal environment of the lunar surface is extremely important to the thermal design of the lander, the placement of the detection instruments, and the interpretation of scientific exploration data. Clarifying the source and intensity of radiation on the outer surface of the lander is the key to its thermal management. In this paper, we first reported continuous temperature records over a 47.2 h period from five thermal couple sensors mounted on the auxiliary pillars of the landing gear of Chang'E-5 (CE-5). The recorded temperatures varied from a relatively small range of 245.68-272.52 K at the beginning to a considerably wider range of 284.86-369.76 K at the end of the recording period. To analyze the obtained CE-5 temperature records, we first developed a lunar surface thermal environment model with a layered regolith and temperature-dependent thermal physical properties. The model calculated that the ambient temperature of the CE-5 landing site over the sensor recording period increased from 341.40 to 356.15 K. The calculated temperature was comparable to the estimates based on the in-situ spectral measurement, whereas it was systematically 6-12 K higher than Diviner thermal infrared brightness temperature. We further developed a heat conduction model of the sensor-mounted auxiliary pillar and considered the surface temperature and the pillar geometry with respect to the Sun's and the Earth's orbital parameters. By introducing an impact factor F and via trial and error, we fitted the five CE-5 lunar temperature records with the RMESs of 0.72, 2.14, 0.53, 1.35, and 3.36 K, respectively. Our analysis showed that the lunar surface thermal environment has a significant effect on the temperatures of both the shaded and sunny sides of the lunar lander. The environmental impact on the shaded side even exceeds that on the sunny side during the CE-5 recording period. The results of this paper are of great significance to both the theoretical research on the mechanism of the lunar thermal environment and the engineering applications in the thermal management design of a lunar lander, site selection of a lunar exploration mission, and temperature-related data interpretations, such as in-situ spectral data analysis.