Ephemeris Design for Lunar Navigation Satellites

With Marta Cortinovis, Prof.Gao (Stanford University)

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.

Related Publication:

Satellite Ephemeris Approximation Methods to Support Lunar Positioning, Navigation, and Timing Services, ION GNSS+ 2023, 2023 Best Presentation of the Session [Paper] [Slides] [Video]