Enhanced GNSS-based Positioning in space exploiting Inter-Spacecraft Cooperation

The momentum taken by the space sector in the exploration of our Moon pushes private and governmental actors to intensify their efforts for launching missions to our natural satellite. In this context, novel infrastructures and techniques are being studied and experimented to reach an increased autonomy of the positioning and navigation services in the cislunar volume. Research performed in the past years have proved that Global Navigation Satellite System (GNSS) Space Service Volume could be further extended to the cislunar volume. Furthermore, both the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) have revealed their plans to design a lunar satellite system for both navigation and communications purposes. With that said, the present research revisits the concept of GNSS-Cooperative Positioning (GNSS-CP) already proven successful in the frame of terrestrial applications for space missions. The implementation of the GNSS-CP solution for space would leverage on the presence of GNSS receivers and communication links to improve the performance of the spacecraft navigation solution while implementing a non-invasive solution, hence reducing the Size, Weight and Power of the navigation sub-system. In order to demonstrate the potential benefits of GNSS-CP in space, we consider in this paper the following case scenario: The Lunar Pathfinder and Volatile and Mineralogy Mapping Orbiter (VMMO) mission. This work simulates the fusion of their respective GNSS pseudorange measurements to compute the Inter-Spacecraft Range (ISR). The reception of Galileo E5a, GPS L5, and S-Band signals are simulated. S-band signals are generated by one lunar satellite as planned by the ESA Moonlight initiative for the Lunar Communication and Navigation System (LCNS) vision. This preliminary analysis proves to be promising as a naive Least Mean Squares (LMS) estimator used on Weighted Double Differences between pseudorange observables results in an estimated distance between Pathfinder and VMMO usable to further improve the position solution of those missions.