A Three-Dimensional SPH Simulation of Lander Footpad Impact on a Lunar Regolith Bed

Landing spacecraft experience significant impact forces during landing, resulting in large deformation and failure in the soil surface, which severely affects landing safety and stability. This paper establishes a smoothed particle hydrodynamics (SPH) model based on the theory of soil elastoplastic constitutive relations to describe the process of a lander’s footpad impacting lunar regolith vertically. The model can provide engineering indices such as impact load and penetration depth, and illustrate the large deformation and crater characteristics of the regolith. A detailed analysis of the response of the footpad and lunar regolith during landing reveals that the process can be broadly divided into two stages of rapid penetration and oscillatory attenuation. Furthermore, there are significant similarities in the landing process under different landing velocities and footpad masses. The research investigates the large deformation and crater characteristics of the lunar regolith bed. The results demonstrate two failure modes in the regolith. Under the impact of a footpad with a smaller mass, the final failure surface of the regolith exhibits a bowl-shaped profile with a uniformly open mouth. In contrast, under the impact of a footpad with a larger mass, the final failure surface of the regolith presents an urn-shaped profile with a large abdomen and a small opening. However, the impact craters in both scenarios show a bowl-like distribution. In cases of high-velocity impacts, the impact crater exhibits obvious blocky spalling on its sides. The SPH model developed in this study can be applied to predict the large deformation and failure response of lunar soil under the impact of rigid structures as well as the impact load and penetration depth. It effectively predicts the dynamic response of the landing process, which is expected to provide a reference for engineering design.