ADVANCES IN THE COUPLED DYNAMICS OF RIGID BODIES AND GRANULAR MEDIA FOR SMALL BODY CONTACT EXPLORATION

Contact exploration of small bodies is currently among the most challenging approaches in deep space exploration and constitutes one of the key technologies that must be mastered to advance China’s strategic goal of becoming a major space power. Such missions involve complex and highly dynamic interactions between probe and the non-spherical, particulate surfaces of small bodies. These bodies typically exhibit rubble-pile internal structures, with their surfaces covered by loosely bonded, gravel-sized particles that result in distinct granular behavior and mechanical unpredictability. Under extremely weak gravity, the interaction between the rigid probe structure and the granular medium shows multi-scale coupling, strong nonlinearity, and high sensitivity to disturbances, making the analysis and design of the contact process particularly difficult. Such rigid body-granular coupled dynamical problems fall beyond the applicable scope of traditional rigid body mechanics and conventional continuum mechanics, thereby posing entirely new challenges to the discipline of astrodynamics. In this context, this paper provides a comprehensive review of rigid body-granular coupled dynamics in small body contact exploration. Representative mission tasks are discussed, including landing, sampling, and impact, through which the key mechanical issues arising from probe-regolith interactions are identified and analyzed. Modeling approaches for characterizing the mechanical properties of small body surfaces are systematically summarized, ranging from rigid-elastic and plastic surface models to more sophisticated granular models. Particular emphasis is placed on the discrete element method, which has become the dominant tool for simulating granular surfaces. To accommodate different levels of fidelity in representing particle geometry and contact behavior, this review separately introduces spherical-particle models and non-spherical-particle models, with the latter further categorized according to the methods used to describe particle shape. Building upon these modeling strategies, analytical ideas and methodological frameworks for investigating rigid body-granular coupled dynamics are synthesized. Research progress on three representative categories of contact processes, namely quasi-static penetration, low-velocity impact, and high-velocity impact, is then systematically reviewed. Finally, future development trends in this field are discussed.