Sensor Fusion for Autonomous Orbit Determination and Time Synchronization in Lunar Orbit

As interest in lunar exploration grows, establishing infrastructure for communication and Positioning, Navigation, and Timing (PNT) services has become a priority. Space agencies have developed LunaNet, a network of networks architecture to deliver these services. Several systems, such as NASA's Lunar Communications Relay and Navigation Systems (LCRNS), ESA's Moonlight, and JAXA's Lunar Navigation Satellite System, which consist of small satellite constellations, have been proposed within LunaNet to provide PNT services on the Moon. However, it is challenging for current autonomous Orbit Determination and Time Synchronization (ODTS) methods to meet the stringent performance requirements required for PNT services on the Moon. This work reviews multiple autonomous ODTS solutions, including the use of GNSS signals, Inter-Satellite Links (ISLs), and Optical Navigation (OpNav) techniques to better understand the limitations of individual sensors and how they can be combined to improve state estimation accuracy. We propose and analyze a sensor fusion approach that integrates OpNav methods, such as horizon and crater matching, with radio-based techniques, such as GNSS and ISL measurements, to enhance state estimation accuracy.