Single-Satellite Lunar Navigation via Doppler Shift Observables for the NASA Endurance Mission

Set to launch in the 2030s, the NASA Endurance rover will explore and collect samples along a 2000 km traverse of the Moon’s South Pole-Aitken (SPA) impact basin. Precise geotagging of these samples will be critical to the mission’s science objectives, which aim to characterize the Solar System’s chronology and the Moon’s geological evolution. Concurrently, the Surrey Satellite Technology Ltd. (SSTL) will be launching the Lunar Pathfinder satellite to provide communication services to lunar surface users, including the Endurance rover. To enable precise absolute localization of the rover throughout its 2000 km traverse, we investigate the achievable position estimation by opportunistically leveraging the Doppler shift observables from the Lunar Pathfinder’s downlink communication signals with no navigation payload. With only one satellite available, we accumulate Doppler shift measurements over time while the rover is stationary and refine the rover’s position estimate through a weighted batch filter framework. In simulation, we model the effects of Doppler shift measurement uncertainty, which includes the frequency error of the rover’s clock as well as errors due to carrier tracking as a function of the carrier-to-noise ratio C/N0. The state estimation performance is evaluated at different key locations of the SPA basin under varying degrees of satellite ephemeris uncertainty and clock stability. With this framework of using Doppler shift as the only navigation observable, we find that the Lunar Pathfinder is, on average, able to opportunistically localize the Endurance rover with sub-10-m accuracy within two orbital periods of the Lunar Pathfinder. To the best of the author’s knowledge, this paper is the first to examine lunar localization using a single satellite that is not equipped with a navigation payload.