Toward the Age in Cislunar Communication: An AoI-Optimal Multi-Relay Constellation With Heterogeneous Orbits

With the proliferation of massive explorations on Lunar Far-side Surface (LFS), deployments of scientific infrastructures have drawn substantial attention with the aids of relay satellites for the moon, i.e., China's 'Queqiao', which allows real-time reporting for current status information from the landing equipment and space vehicles. Without suitable constellation with well-designed scheduling scheme, it would be very difficult to get timely information if depending only on single Halo relay satellite due to large coverage gap and limited energy budget for the communication links. In this paper, we design a hybrid circular-Halo orbital multi-relay constellation system for the LFS communication by minimizing the average per-device Age of Information (AoI) of users on the earth. In particular, we develop an age-optimal scheduling strategy with constellation design for accessing different relay satellite of constellation by solving a Constrained Markov Decision Process (CMDP) optimization problem to significantly reduce the average coverage gap in LFS area. Simulation results show that the average per-device AoI of the proposed scheduling algorithm with the well-designed constellation could achieve 16.20% less in time than that of single Halo satellite relay system compared with typical algorithms.