A thermal model for predicting the drilling temperature in deep lunar regolith exploration

Lunar drilling will work in an extreme environment and may lead to a high drilling temperature due to the poor heat dissipation approaches, with potentially devastating effects on the drill tool. This paper presents a mathematical thermal model for predicting the drilling temperature in lunar regolith exploration. The proposed model combines a unique heat balance equation for the system of the drill tool and the drilled cuttings. Modeling of the drill tool-cuttings system assumes an axial temperature distribution along the drill tool and one-dimensional transient heat transfer problem in a semi-infinite plane is employed to calculate the temperature. Geometric features of the drill tool, thermal and mechanical properties of the drill tool and lunar regolith, drilling parameters, and penetration force are taken into consideration in the model. The theoretical investigation addresses the significance of heat generation by the penetration force and heat dissipation by the drilled cuttings. Convolution is utilized to establish the heat transfer processes along the drill tool. Using the presented thermal model, a thermal property test bed was employed to simulate drilling in an evacuated lunar environment, and experimental and computational temperatures were compared in penetrating a lunar regolith simulant with different drilling parameters. Experimental results indicated that the theoretical model was effective in predicting the drilling temperature in sampling the lunar regolith simulant. (C) 2017 Elsevier Ltd. All rights reserved.