The international interest in the Moon is rising again and several countries are launching projects to explore the Moon. As part of the Moonlight Programme, the European Space Agency (ESA) is developing Lunar Communication and Navigation System (LCNS) services with its industrial partners. In parallel, ESA is collaborating with North American Space Agency (NASA) and Japan Aerospace Exploration Agency (JAXA) to define the LunaNet interoperability specification. Among others, this specification will define the GNSS-like Augmented Forward Signal (AFS), for which the data component will send clock and ephemeris data of the LCNS satellites, which is essential for a Position, Navigation and Timing (PNT) system.
On Earth, the Global Navigation Satellite Systems (GNSS), such as Galileo, provide high precision positioning globally with a constellation of satellites. One of the key aspects of these systems is the navigation message conveying the satellite position and velocity to the user in a way that keeps the validity and accuracy as good as possible. The accuracy of the navigation message depends on the orbit model, the fitting algorithm, and the binary representation. For example, for the Galileo satellite the representation is provided by a set of 16 parameters.
The Moon orbits, specifically the Elliptical Lunar Frozen Orbits (ELFO), are quite different compared to the GNSS Medium Earth Orbits (MEO). The Kepler orbit parameters representation is different and the orbit is subjected to different perturbations.
This paper will present a novel orbit model for the LCNS that can support ELFOs. The paper will introduce the ELFO dynamics, the state-of-the-art on lunar orbit models and the problem of designing a model that can cope with these orbits. The paper will compare different models for ELFO to show the performance of the new model in terms of accuracy and number of bits (required to broadcast the information).