RF-Assisted Uncertainty Cone Reduction in Free-Space Optical Inter-Satellite Links

One of the space communications industry’s current focuses is developing high-throughput communication terminals for satellite-to-satellite communication links. Optical inter-satellite links provide high data rates, long-range, and robustness against interferences, and they do not require frequency licensing as radiofrequency communication systems. Nevertheless, as the uncertain location of the receiver is comprised in an area larger than that illuminated by the transmitting laser, the pointing accuracy is a critical element in the success of the optical link establishment and maintenance, requiring a pointing, acquisition, and tracking mechanism. The acquisition process is the most time-consuming of the pointing processes, limiting the time available to send data, especially in highly dynamic networks. This paper focuses on reducing the acquisition time by reducing the initial satellite position uncertainty. To this end, a hybrid system that combines RF and optical technologies in a single communication module is proposed. Whereas the control plane is managed via the RF link to exchange more precise global navigation data, the optical link corresponds to the data plane in which payload data is exchanged. The pointing between two satellites is simulated to analyze its behavior, considering the error of cumulative orbital propagation data and global navigation satellite system data. This work also analyzes the cumulative error produced by the propagation of the TLEs over time. Finally, the results show how a system that relies on the exchange of global navigation satellite system positioning data achieves up to 99.45% better-pointing accuracy than a system that bases positioning data on TLE propagation.