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This study investigated the thermal problem of drilling into a lunar rock simulant. A thermal model involving radiation and heat transfer involved a geometry for drilling into the lunar rock simulant was established using discrete element method (DEM). Drilling experiments were performed in a vacuum to verify the model. Thermal simulations of drilling into the lunar rock simulant in a vacuum with and without lunar soil simulant were conducted, and very good agreement was observed between the simulation and experimental results. The simulation results showed that the lunar soil temperature during drilling in a vacuum simulant was much less than that of the lunar rock simulant, and lunar soil simulant had little effect on heat dissipation from the drilling tool. A drilling procedure intervention strategy for the thermal safety of drilling tools was investigated. It was found from the intervention process based on DEM that the temperatures of the drilling tool were within a safe range, and the time duration for heat dissipation was usually much longer than the time required for temperature increase. • A DEM thermal model for drilling into lunar rock simulant in a vacuum is established. • Lunar soil contributes little to heat dissipation from the drill in a vacuum. • The intervention strategy is proposed for thermal safety of the drill based on DEM. • Heat dissipation time is longer than that for temperature rise under intervention. [ABSTRACT FROM AUTHOR]

The bit and object thermal problem was investigated in this study with particular regard to the drilling of lunar soil simulant. The discrete element method (DEM) was used to establish a thermal model of the simulant that considered convection, radiation, and geometry. Parameter calibration of the DEM heat transfer model was undertaken, and drilling experiments were performed under normal pressure to verify the model. Thermal simulations of the drilling of the lunar soil simulant under normal pressure and in a vacuum were also conducted, and very good agreement was observed between the simulation and experimental results. The temperature rise of the lunar soil simulant was found to be much less during drilling in a vacuum compared to drilling under normal pressure for comparable temperatures of the drill bit. And in a vacuum, lunar soil simulant had little effect on heat dissipation from the drilling tool. [ABSTRACT FROM AUTHOR]