Hybrid Lunar Satellite and Cooperative Surface Navigation: A Distributed Estimation Perspective

A large number of lunar surface missions is planned in the coming years. A key prerequisite for many missions is accurate and reliable position, navigation and timing (PNT). There are plans for lunar satellites operating under the frame of LunaNet, which should provide communications and PNT for orbit and surface users. Especially in an early phase, the number of satellites will be very limited. To ensure high availability and high accuracy, hybrid satellite navigation and cooperative radio navigation has been suggested. For cooperative radio navigation, radio signals exchanged among users on the lunar surface are used. The benefit of hybrid navigation for the moon has been shown by a theoretical study. How a hybrid navigation system could be implemented, especially considering the nature of the distributed system, has not been analyzed yet. With this paper, we introduce one centralized and three decentralized estimation algorithms for hybrid lunar satellite and cooperative surface radio navigation. We consider decentralized estimation algorithms based on broadcasting measurements, consensus, and equivalent ranging variance, representing different concepts of distributed estimation. Then, we evaluate all algorithms regarding the functional requirement accuracy and the non-functional requirements flexibility, scalability and robustness. We introduce a simulation framework to assess the performance of lunar surface navigation algorithms. Finally, we provide a comparison of the algorithms and discuss their strengths and weaknesses.