Autonomous Navigation For Moon Missions: A Realistic Performance Assessment, Considering Earth GNSS Signals And LCNS Constellation

Lunar exploration is going to have a central role in the future of space industry. A large number of missions, both scientifically and economically oriented, are planned for the next decade, many of which are consolidated and structured within international agencies, such as the ESA/SSTL Lunar Pathfinder and NASA Artemis program. This opens the door to the exploration of new technologies and techniques for missions to the moon, with the objective of improving autonomy and robustness, while reducing the costs. The use of weak-GNSS signals to navigate spacecraft in cislunar space has been investigated in several publications, bringing the advantage of being less expensive and based on already existing infrastructure, allowing to improve accuracy, robustness and autonomy. ESA is planning to demonstrate this technology as part of the Lunar Pathfinder mission. Despite the tremendous advantages brought by the use of GNSS signals in lunar orbit, this concept has some limitations, for example it cannot serve users on the far side of the Moon and the service for users experiencing Moon occultation would be compromised. Within the Moonlight initiative, ESA is currently working to define a Lunar Communication and Navigation Service (LCNS), which aims to provide advanced communication and navigation services, covering the limitations of Earth GNSS and improving further the navigation performances in cis-lunar space. This paper presents the outcome of a research aimed to perform a representative end-to-end assessment of what are realistic navigation performance achievable by an autonomous GNSS navigation system for two Moon mission scenarios. In addition, preliminary performances using a potential LCNS constellation are assessed, together with Earth GNSS or standalone. The test campaign shows the performances of two different key scenarios: Lunar Pathfinder and Low Lunar Frozen Orbit (LLFO). For the Lunar Pathfinder, it resulted that Earth-GNSS signals can be successfully utilized to reach satisfactory navigation performance: positioning errors as low as 50 meters 3D Root Mean Square (RMS) were obtained using Earth GNSS signal alone, with a slight improvement introduced by LCNS constellation. For the LLFO, the usability of Earth GNSS signal is heavily compromised by the scenario inherent characteristics. In these case, the introduction of the LCNS constellation significantly improves navigation performance, allowing to obtain results similar to the Lunar Pathfinder. This work has been performed as part of the ESA activity NAVISP-EL1-023 “Earth-Moon Navigation: System Study and development of a high-sensitive spaceborne receiver”.