LAUSR

Abstract To maximize the science return of asteroid exploration, multi-target asteroid missions are preferred. In this paper, the accessibility of asteroids in a mission, including both near-Earth asteroid (NEA) sample return and main-belt asteroid (MBA) rendezvous using gravity assists (GAs) is investigated. 1081 NEAs and 37 MBAs are chosen as candidates with given constraints. A Tisserand graph with modified tick marks is applied to give a straightforward and quick reference of the possible gravity-assist sequences. The patched conic method is adopted to compute the total velocity increments for six types of gravity-assist trajectories. The particle swarm optimization (PSO) algorithm is employed to minimize the total delta-V. To reduce the computational complexity of the optimization problem, only 50 optimal asteroid groups attained under the mission path of Earth-NEA-EGA1(the first Earth gravity assist)-MBA (ENEM) are reserved to be further optimized for the remaining other five trajectory paths. Feasible trajectory design results with launch dates between 2022 and 2028 are presented.