Constructing Earth-Moon Data Relay System: Trajectory Design of Ballistic Lunar Transfer for Nano Spacecraft

The lunar south pole region is expected to be an active area for future exploration, as a lunar base is planned to be constructed in the Artemis program. However, communication with the Earth is difficult in the lunar south pole region, thus data relay by spacecraft is indispensable. Against this background, the Space Robotics Laboratory (SRL) at Tohoku University has been developing a 6U CubeSat to relay data between a lunar rover and a ground station. The spacecraft is expected to be released from Lunar Orbital Platform-Gateway (Gateway) and inserted into a lunar orbit for communication with the lunar south pole region. Nevertheless, the spacecraft's propulsive power is limited due to its 6U CubeSat size (l00x200x300 mm), so it is required to take a trajectory that reduces transition energy. In this study, a ballistic lunar transfer using solar perturbation, called Weak Stability Boundary (WSB) trajectory, is used to decrease the transition cost. In this paper, we describe the results of the analysis and design of the WSB trajectory and the conditions necessary to insert the nano spacecraft into lunar orbit under limited propulsion capability.