Trajectory design for rendezvous in lunar Distant Retrograde Orbit

This paper describes solutions to the lunar Distant Retrograde Orbit (DRO) rendezvous in terms of trajectory and launch window design. Our study is motivated by the future potential to construct a new space station or fuel refilling ports in the Earth-Moon neighborhood. A DRO, which has a long-term stability, is a possible candidate for the orbit in which such habitable structures are located. Since these structures have to rendezvous with visiting vehicles from Low Earth Orbit (LEO), it is valuable to investigate rendezvous technology in DROs. Our current study is focused on designing rendezvous trajectories which require reasonable operational cost, such as delta-v and flight time. Launch window analysis derived from trajectory design is also within the scope of this paper. We applied a three-impulse transfer with retrograde powered lunar gravity assist, and examined the total delta-v and flight time required to transfer from LEO to various phase points in a certain DRO. The results showed how a certain region where the ΔV cost is low exists, and the flight time varies considerably according to the rendezvous point. We proposed an applicable launch window with these features in mind. We also conducted a case study to evaluate delta-v and the flight time required for rendezvous after the visiting vehicle is inserted into the DRO at a certain distance from the station. The result showed the potential to widen the option to rendezvous. In our study, trajectories are computed using Systems Tool Kit (STK) / Astrogator software module. Unlike a Circular Restricted Three-Body Problem (CRTBP) model, STK/Astrogator employs various force models and accurately integrates trajectories, which enables more realistic operation scenarios to be discussed.