Contact Plan Optimization and Distributed State Estimation for Delay Tolerant Satellite Networks

Future deep space exploration, particularly the upcoming lunar missions, stands to benefit significantly from networks of small satellites, given their cost-effective communication and monitoring capabilities. However, challenges like frequent network partitions, high communication delays, and the demand for onboard orbit determination (OD) and time synchronization present obstacles for these satellite networks. One of the key problems in this context is how to schedule satellite communications and generate a contact plan. This paper presents an integrative solution that combines navigation and communications performance for contact plan optimization. Additionally, we propose a novel two-way inter-satellite link (ISL) scheme to acquire range and differential clock bias estimates that take into account rapid inter-satellite range shifts and signal propagation delays. Building on these, a distributed orbit and clock bias estimation algorithm is introduced, which emphasizes the use of batch processing to improve orbit observability. Performance metrics are validated through a simulation of a lunar navigation constellation, assessing OD error, time synchronization error, and inter-satellite communication delay. The combined insights and proposals presented, especially in terms of navigation and communications performance tradeoffs, offer promising avenues to enhance the operability and efficiency of small satellite networks.