Normal force on the asteroid regolith generated by the impact of lander footpad

The landing of a probe on the surface of an asteroid can produce a stable operating platform and obtain vital data describing the mechanical response of the asteroid material. The fine-grained regolith area on the asteroid surface is essential in cushioning the probe from impact energy and in avoiding the risk raised by the large protruding rocks during the landing of the probe. Models incorporating macro forces explaining the interaction between the landing terminal of the probe and the regolith on the asteroid surface conclusively reflect the mechanical process and characteristics of the interaction, making them particularly suitable to analyze and control the landing process of the probe. In this paper, we study the macro normal force of the interaction between the footpad of a legged probe and the regolith on the asteroid surface with particular attention paid to the mathematical expression of the force model and the contribution of the most essential soil parameters. The ultimate bearing theory of soil mechanics is extended to discuss the mathematical model of the macro normal force on the asteroid regolith in a micro-gravity environment undergoing different damage modes. Subsequently, a series of discrete element method simulations are implemented to verify the normal force model and to analyze its characteristics under the influence of landing impact. On the basis, the effect modes of several most essential soil parameters of soil porosity, particle size and cohesive strength are revealed through a robust regression analysis of the simulation data. Next, the correlation coefficients of the effects of soil parameters on the macro normal force are researched. The model of macro normal force established in this paper can be used to facilitate an effective performance analysis in the development of the landing-cushioning mechanism of the probe, as well as to conclude a reference for the most essential soil properties parameters of the asteroid regolith via the inverse solution of the interaction data recorded in actual landing missions.