Differential GNSS for ranging and synchronization between lunar orbiters: Impact of large baselines and relative dynamics

As lunar exploration progresses, autonomous spacecraft navigation is becoming critical. Global Navigation Satellite System (GNSS) signals provide a valuable alternative to traditional ground-based systems, offering real-time navigation for lunar orbiters. NASA’s LuGRE initiative recently demonstrated GNSS signals reception at 432,384 km from Earth, proving its feasibility despite challenges such as low power levels and poor geometry. These limitations justify the need for augmentation strategies to extend GNSS usability in the Space Service Volume (SSV) and potentially support future lunar navigation systems. This study investigates cooperation between lunar orbiters via Differential GNSS (DGNSS) where missions are assumed to exchange pseudorange and Doppler measurements to estimate their Inter-Spacecraft Ranges (ISR). A key challenge is the asynchronous nature of pseudorange data caused by clock biases because of the large dynamics characterizing such scenario. Therefore, this work provides an assessment of a time-extrapolation technique used to mitigate these offsets and then evaluates its impact on the ISR estimation process using simulated data. The findings provide insights into DGNSS as a potential augmentation solution, supporting the roadmap towards a robust lunar navigation architecture