Optimal near-perilune maneuvers in powered lunar flybys to distant retrograde orbits

Abstract

Powered Lunar Flyby (PLF) is an orbital transfer technique in which a maneuver is performed during a lunar gravity assist to reduce mission fuel consumption. However, the commonly adopted strategy in PLF involves applying an impulsive thrust along the direction of velocity at the perilune. This paper examines the efficiency of this conventional perilune maneuver and investigates the optimal near-perilune maneuver by considering both the maneuver location and impulse direction as free variables. The analysis is conducted within the scenario of a spacecraft departing from a low Earth orbit (LEO) to rendezvous with a space station positioned in a lunar distant retrograde orbit (DRO) using a three-impulse trajectory optimization method. The main findings of this research include: (1) Far-side and near-side PLF trajectories are identified. For far-side PLFs, there exists a certain DRO phase angle under which the optimal maneuver position is at the perilune, while for near-side PLFs, the optimal maneuver is always not at the perilune. (2) The velocity increments for perilune and near-perilune maneuvers are similar when the DRO phase angle is near optimal, but can differ by up to 207 m/s when the phase angle deviates significantly from the optimal value. (3) In scenarios with a fixed transfer duration, not restricting the DRO insertion angle to the phase angle will help reduce the velocity increment. The results provide strategic guidance for the optimization of PLF maneuvers and valuable insights for reducing the fuel consumption in future practical missions.