Design and analysis of abort orbits for manned missions to the Earth-Moon libration points

A libration-point orbit (LPO) offers low-cost access to space and may be the destination of future manned missions. Usually, a lunar flyby is required for short-term LPO missions, thus the transfer trajectory from the Earth to LPO is composed of an Earth–Moon two-body leg and a Moon–LPO three-body leg. The abort orbit associated with the Earth–Moon two-body leg has been thoroughly studied. In this paper, the abort orbit of the Moon–LPO three-body leg is designed and analyzed. Along the Moon–LPO three-body leg, the abort orbits of direct, lunar-flyby, and low-energy return are designed and discussed separately. For the direct return, the abort orbits are obtained based on an initial Kepler solution with reentry constraint. For the lunar-flyby return, the abort orbits are designed by pseudostate theory. For the low-energy return, the abort orbits are further optimized by introducing nontransit/transit orbits and lunar flyby. In the Earth–Lissajous transfer scenario, three types of abort orbits for the Moon–LPO three-body leg are numerically designed. For the direct or lunar-flyby return case, the total impulse of abort orbits is greater than 0.9 km/s. This is a significant burden for manned mission planning. For the low-energy return, the minimum total impulses are 0.302 km/s and save 20–60% total impulse at the cost of a limited increase in flight time. This abort orbit employs a nontransit/transit orbit to return to the vicinity of the Moon and quickly return to Earth after applying a second maneuver at perilune. Finally, return windows and trajectory types of abort orbits are classified based on a reference trajectory.