Abstract: With the constraints of atmosphere reentry interface parameters and the landingpoint location,a method was proposed for the preliminary design of the moon-to-earth trajectory with direct atmosphere reentry. The method included two stages of iteration loops. The inner loop made moon-center orbit and earthcenter orbit continuous at the boundary of the moon influence sphere. To solve the earthcenter orbit parameters meeting the reentry angle constrain, a method combined Lambert problem and Newton-Raphson method was adopted. The outer loop made the moon-to-earth trajectory meet the landing-point location constrain by adjusting the launch time. The analysis shows that four types of moon-to-earth trajectories meet atmosphere reentry interface parameters. The four trajectories are descent-descent trajectory, descentascent trjectory, ascentdescent trajectory and ascentascent trajectory. Then the characteristics of the transfer trajectories were analyzed, such as the perigee geocentric distance, the transfer orbit insertion point distribution, the reentry point distribution. Simulation results indicate that the preliminary design method is effective.

Key words: Sampling return, Orbit design, Moon-to-earth transfer trajectory, Atmospheric entry, Lunar probe