Dynamics and control of proximity operations for asteroid exploration mission

In asteroid exploration mission, the spacecraft needs to execute a series of proximity operations such as approaching, accompany flying, orbiting and hovering, which are the premise and key points to achieve asteroid sample return. Based on the concept of Chinese future asteroid exploration missions, this paper studies the dynamics and control of the proximity operation. First, considering the path and line-of-sight angle constraint, the sliding guidance law is used to design the multi-impulse approaching trajectory. A reconstruction iterative strategy is proposed for the perturbation effect including the irregular shaped gravity, solar radiation pressure, and three-body perturbations. Second, in order to obtain the preliminary physical characteristics of the asteroid, the accompany orbit and slow hyperbolic flybys are designed. The equation of the relative distance and velocity of the accompany orbit is established and the families of accompany orbits with different offsets and sizes are discussed. The spin rate and preliminary shape model of the asteroid can be established during the accompany phase. Then, by slow-flybys, the mass and coefficients of the gravity field of the asteroid can be obtained. The relation between flyby velocity, flyby distance, and flyby duration are found to achieve the global mapping of the asteroid. Several kinds of slow-flyby trajectory are presented. Finally, a self-adaptive control law is designed and proved to achieve the stable hovering at any point or region near the asteroid against varies perturbations and model uncertainty. Based on the control law, the fixed-point hovering and local region hovering are investigated respectively, which can be utilized to precise local exploration and imaging. The simulation results of asteroid 2016 HO3 verify the feasibility of the proposed method. The study can provide a reference for Chinese future asteroid exploration missions.