Navigation Performance of Low Lunar Orbit Satellites Using a Lunar Radio Navigation Satellite System

Exploring the Moon is the next long-term target for space agencies in the coming decade depicted by the Moonlight program from the European Space Agency (ESA) which envisions the creation of a dedicated Lunar Communication and Navigation Service (LCNS) infrastructure. The purpose is to entail the installation of the human presence on the moon and support the long-term, sustainable, human presence on Earth’s natural satellite. The proposed LCNS constellation aims to support the lunar activities in the cislunar space, including landing, and surface operations. At an international level, ESA and NASA worked on the definition of an interoperability framework for communication and navigation services in cislunar space, leading to the definition of the LunaNet Interoperability Specification [NASA & ESA, 2022]. LunaNet defines multiple services, among which is a GNSS-like concept called Lunar Augmented Navigation Service (LANS). It is expected that multiple institutional and commercial programmes will adhere to LunaNet, allowing the creation of a network of nodes interoperable with each other. However, at least in the initial phase of systems deployment, the number of visible satellites for a cislunar user will be limited. This limitation can be mitigated by adopting sensor fusion techniques and other navigation techniques. This contribution investigates the achievable performances for a user in Low Lunar Orbit (LLO) using a constellation of satellites as an example of such a Lunar Communication and Navigation Service (LCNS). Realistic Orbit Determination and Time Synchronisation (ODTS) for the lunar constellation are simulated to be as representative as possible of the expected performances. The user navigation algorithm implements an accurate dynamical model by means of an extended Kalman filter, allowing it to compensate for the gaps in satellite visibility. Three types of low lunar orbits (LLO) (polar orbit, equatorial orbit and 45°inclined) are simulated to cover different scenarios. Position accuracy below 100m at 2sigma and a velocity determination accuracy below 1 m/s at 2sigma are achievable in real-time on-board.