Snapshot Tracking of GNSS Signals in Space: A Case Study at Lunar Distances

The latest space missions have unveiled GNSS usability for distances greater than 187 000 km from the Earth’s surface. The actual availability and usability of GNSS signals beyond such an altitude are still questionable, and experimental evidence still lacks. The Lunar GNSS Receiver Experiment (LuGRE) is a joint NASA-Italian Space Agency (ASI) payload aiming at demonstrating GNSS-based positioning, navigation, and timing through its trajectory towards the Moon. After the launch in 2024, the payload will receive multi-frequency Global Positioning System (GPS) and Galileo signals across the different mission phases, and will conduct onboard and ground-based scientific experiments. Besides positioning and raw GNSS observables, the LuGRE payload will deliver snapshots of GNSS digital signal samples. Such snapshots will be at the core of a set of science investigations, and require the development of a post-processing unit being operated within the LuGRE ground segment throughout the mission. In this paper, we present an analysis that aims at identifying a minimum snapshot duration suitable for a successful, post-processing tracking of the recorded signal along the Moon transfer orbit and on the Moon surface. The processing of realistic mission-related signals has been performed to tune the receiver architecture and investigate the tracking performance in the LuGRE framework. Subsequently, a statistical analysis of the tracking lock conditions has been carried out leveraging a Monte Carlo approach to characterize the performance for different settings of the receiver front-end.