GNSS Inter-User Ranging for Lunar Orbiters Flying the Spaceborne Navimoon Receiver

In 2024, a pivotal moment in space navigation occurs as a GNSS receiver journeys to the Moon, marking its inaugural lunar deployment to showcase GNSS navigation feasibility at lunar altitudes. However, the challenge of increasing Dilution Of Precision with greater distance from GNSS constellations remains a significant barrier to the effective use of GNSS in space. Consequently, achieving the requisite accuracy for reliable autonomous GNSS navigation at lunar distances is uncertain. As an enabler of potential collaborative navigation paradigms relying on GNSS measurements, this study proposes a GNSS-based inter-user baseline estimation technique, previously effective in terrestrial scenarios, and analyzes different methodologies to achieve unbiased baseline estimation in space navigation. This solution primarily benefits from the fact that it is non-invasive and solely based on the availability of a communication link between the cooperating space users. The present work shows the application of the estimation of the baseline length between a lunar CubeSat mission, VMMO, and the communication relay Lunar Pathfinder mission. Most notably, this is performed using real GNSS measurements generated by an actual Engineering Model of the NaviMoon receiver in the ESA/ESTEC Radio Nav-igation Laboratory, while being fed by GNSS signals emulated by a radio-frequency constellation simulator.