Exploration of direct transfer opportunities and loitering strategies for lunar surface access

The Lunar Gateway will be staged in the southern (Formula presented) Near-Rectilinear Halo Orbit (NRHO) with a 9:2 resonance with the lunar synodic period. This lunar space station, proposed by NASA, will serve as a two-way staging point for lunar surface missions. Thus, low-cost two-impulse transfers from the Gateway’s planned orbit for lunar surface access are developed. Two strategies are explored for access to any lunar surface location. The first strategy introduces direct transfers, which delivers the spacecraft to the desired access point with a second maneuver for low lunar orbit (LLO) insertion. The second strategy utilizes the lowest-cost direct transfer developed in the first strategy to get to any surface access point, then utilizes a second maneuver and loitering to reach its terminal access point. All transfers in a transfer family lie on a characteristic surface, comparing the costs or transfer times to the accessed lunar surface location. Strategies are applied to several problems, including finding the best departure point off the Gateway orbit for each access point and determining the accessibility of the lunar surface given a fixed amount of fuel.