Transfers between NRHOs and DROs in the Earth-Moon system

Abstract

The stable near rectilinear halo orbits (NRHOs) and distant retrograde orbits (DROs) are both considered as potential parking orbits for cis-lunar stations. Transfer orbits between NRHOs and DROs can promote the exploitation of their distinct advantages and be helpful for possible cooperations between cis-lunar stations in different kinds of orbits. By using the symmetry of the dynamics in the circular restricted three body problem (CR3BP), the transfers between NRHOs and DROs are investigated through the transfers from southern NRHOs to DROs, which are obtained by using a two-step approach, consisting of the search and optimization phases. Four NRHOs and three DROs, including those in previous studies and the 9:2 L2 NRHO considered as the nominal orbit for the Lunar Orbital Platform-Gateway (LOP-G), are considered in this study. Both the interior and exterior transfer orbits are found, and the exterior transfer orbits always have relatively low transfer costs. The transfer orbits with better performances than the best previous results are successfully constructed. In the cases of some transfers, the close lunar flyby has shown great advantages in changing the orbital plane and adjusting the velocity without fuel consumption. The comparison between transfer orbits to different DROs indicates that the dynamical structures have more significant effects on the transfer cost than the Jacobi energy. Then, some representative transfer orbits are refined in the high-fidelity ephemeris model for real mission scenarios. The comparisons between transfer orbits departing at different epochs indicate that the lunar orbit eccentricity has significant effects on the transfer time and cost, and some transfer orbits with specific epochs can have better performances than the nominal ones in the CR3BP. The results are of great significance for constructing connections between cis-lunar space stations, as well as for designing transport systems in the Earth-Moon system.