Enhancing Fast Transfer Launch Availability to the NRHO Using A Phasing Loop Approach

Artemis missions will require the launch of multiple Visiting Vehicles (VVs) to a Near Rectilinear Halo Orbit (NRHO) around the Moon and subsequent rendezvous with the Gateway space station. Launch availability is limited by the Delta-V (∆V) available on each VV, subject to the constraints of reaching the NRHO and conducting Rendezvous Proximity and Docking (RPOD) operations with the Gateway. A fast lunar transfer requires a launch that places the VV in a Trans-Lunar Injection (TLI) orbit that passes over the Lunar North Pole, followed by a gravity-assisted rotation of the VV’s orbit into the same plane as the NRHO. As the VV passes over the Lunar North Pole, it must execute a maneuver so that it will arrive in the NRHO at close enough proximity to the Gateway for RPOD to begin (References 1 and 2). The ∆V required for the VV varies significantly depending on the true anomaly of the Gateway within the NRHO at TLI. To minimize VV ∆V requirements, a phasing loop approach is proposed that will allow the VV to enter the NRHO orbit plane efficiently while also allowing a rendezvous with the Gateway that is insensitive to launch date. This paper will discuss the different types of phasing loops and how they vary with the position of the Gateway at VV mission start. As a motivating example, an analysis of the ∆V requirements for a Logistics Module (LM) mission spanning the 2028 launch year will also be discussed.