RT Journal Article SR Electronic T1 Satellite Ephemeris Parameterization Methods to Support Lunar Positioning, Navigation, and Timing Services JF NAVIGATION: Journal of the Institute of Navigation JO NAVIGATION FD Institute of Navigation SP navi.664 DO 10.33012/navi.664 VO 71 IS 4 A1 Cortinovis, Marta A1 Iiyama,, Keidai A1 Gao, Grace YR 2024 UL https://navi.ion.org/content/71/4/navi.664.abstract AB Plans to establish a satellite network around the Moon to support communication, position, navigation, and timing services are rapidly evolving. Satellites that are part of this system broadcast their ephemeris as finite parameters to lunar users for user state estimation. In this work, we investigate lunar satellite ephemeris design to identify the optimal parameterization to broadcast to a lunar user. The proposed framework directly approximates the lunar satellite position and velocity in the inertial frame and obtains the conversion parameters necessary for state representation in the lunar fixed frame. The framework leverages signal-in-space-error requirements as constraints in the parameterization process to guide the search for the best ephemeris parameter set. We evaluate the performance of our proposed framework for satellites in a low lunar orbit and an elliptical lunar frozen orbit. The performance of different methods is assessed based on the precision of the ephemeris prediction, fit interval, and message size. We showcase the ability of the developed framework to approximate satellite ephemeris for both orbits to the desired precision by adjusting the fit interval and the number of parameters to broadcast. In particular, we demonstrate that formulations with a standard polynomial basis and a Chebyshev polynomial basis produce feasible solutions for ephemeris approximation at varying epochs in orbits, abiding by signal-in-space-error requirements.