Mission design for multi-target and multi-mode rendezvous missions to small bodies

Multi-target exploration to small bodies has the advantages of reducing mission cost and increasing scientific return. It will be widely used in the future small body exploration missions. This paper investigates the problem of perturbation sensitivity, complicated constraints and changeable thrust, which may be faced in the multi-target exploration mission. The Earth quasi-satellite sampling return and main-belt comet rendezvous missions are studied. First, based on the mission constraints, the mission design schedule and relevant constraints are given. Then, the multi-impulse asteroid sampling return trajectory is investigated in the elliptical three body model. Considering the gravitational perturbation of Earth, the integral trajectory design consist of Earth escape phase, interplanetary transfer phase, and Earth reentry phase is proposed. The trajectory design is divided into two parts. The optimal preliminary transfer opportunity is firstly searched in two-body problem and is transferred to the elliptical three body model. The differential correction scheme is applied to correct the error caused by Earth gravity perturbation. The trajectory for the Earth quasi-satellite 2016HO3 is designed. Finally, considering the engineering constraints, the first-order necessary condition of the changeable lowthrust trajectory are derived, where both the thrust and special impulse change with the distance to Sun. By introducing the B-plane parameters, the initial states determination under the constraint of the gravity assist is developed. Based on the homotopy method, the low-thrust optimal trajectory after Mars gravity assist to the main belt comet 133P are designed and compared with constant low thrust trajectory. The proposed multi-target exploration scheme and the orbit design method can provide a reference for future small bodies exploration missions in China.