Lunar-Gravity-Assist Transfer Design to Earth-Moon Collinear Libration Points Under Ephemeris Model

Orbits around the Earth-Moon collinear libration points are valuable for deep space exploration, cislunar communication, and space situational awareness. However, designing low-energy transfer trajectories to these orbits remains challenging. Most existing methods typically focus on a single orbit type and rely on the circular restricted three-body problem (CRTBP) or planar bicircular model (PBCM), but these are not directly applicable when orbit data is provided in the ephemeris model. Therefore, there is a need for a design method for transfers to collinear Lagrange point orbits (LPOs) under the ephemeris model. This paper introduces a novel approach for lunar gravity-assist transfers to these orbits, demonstrating high efficiency and robustness. The method begins by applying velocity perturbations to the target orbit, followed by backward integration to the perilune. A tangential maneuver is then introduced to ensure the trajectory reaches the Moon’s sphere of influence (SOI). Using a continuation approach, the transfer maneuver is initially optimized at the SOI, with the distance to the Moon gradually reduced and the maneuver optimized at each step until it aligns with the perilune distance. This method is applicable to a wide range of orbits, including Lyapunov, Halo, and Vertical orbits around the collinear libration points.