Analysis of Small Satellite-Based Lunar Navigation Service Availability and Accuracy on the Surface and in Low Orbit

There has been an increased interest in the Moon recently, not just for its own exploration, but as a gateway for searching other planets as well as the deep space. To facilitate future exploration endeavors on Moon, Lunar Communications Relay and Navigation Systems (LCRNS) are proposed that will enable Position, Navigation, and Timing (PNT), along with other functionalities. This paper focuses on the Lunar Navigation Services (LNS), achieving full coverage using a lunar relay constellation. Five satellite constellation consisting of four satellites in Elliptical Lunar Frozen (ELF) orbits and one in a circular orbit around the equator are assessed for their availability. Assuming the integrity criteria having been met, satellite-receiver relative geometry can provide good indication of LNS availability. Also, for accurate PNT on the lunar surface, a lunar time must be devised, considering the limited capability for Earth-based ground stations. The LNS was analyzed for availability on the lunar surface, especially focusing on the South Pole region. A fully operational LCRNS will enable complex surface and near-surface operations, including Search and Rescue (SAR), situational awareness, and safe lunar descent enabling soft-landing, especially in the undulating lunar terrain.