Multiple Simultaneous Optical Links for Space-Based Platforms

Abstract

Space-based Free Space Optical Communications (FSOC), or lasercom, offers key advantages over Radio Frequency (RF) communications in bandwidth, Size, Weight, and Power savings, and unregulated spectrum. Theoretical and demonstrated lasercom systems have shown higher data rates for similar or equal SWaP compared to their RF counterparts. New space-based network architectures, such as the broadband constellations currently being deployed by SpaceX and Telesat, among others, leverage optical intersatellite links to increase total system throughput and reduce the number of ground stations which lowers the overall system costs. Beyond LEO, the Artemis program infrastructure includes an optical communication relay between the Orion capsule and Earth, with eventual plans to expand to lunar orbiters for continuous surface coverage. Despite the performance advantages and increasing adoption across applications, state-of-the-art RF communication systems currently outperform lasercom systems in part because of optical communication systems’ inability to support multiple simultaneous links. Techniques such as frequency reuse, access methods, and dynamic beam forming enable RF communication systems to work around bandwidth limitations and establish simultaneous links with other nodes within a network (e.g., multiple ground stations, user terminals, etc). This work looks at extending this capability to laser communication systems, evaluates the technology required to support multiple simultaneous optical links, and quantifies the impact of multi-user lasercom within a network configuration. We develop a model to simulate the performance of such a system and verify it against existing models and data. The model is then applied to a LEO and deep-space network scenario which analyzes different access methods, network configurations, and terminal technologies such as fiber amplifiers versus photonic integrated circuits. We perform trade studies to identify the limitations and constraints of the proposed approach. We then make architecture recommendations for each scenario based on key performance parameters. For example, we find for the LEO case, a swarm of four, 6U cubesats can achieve a total system throughput of 12 Gbps with wavelength division multiple access in a mesh network configuration. Additionally, by using a photonic-based transceiver instead of a fiber-based one, an additional ~2.5X savings to mass can be achieved.