Operational Simulation of Optical Inter-Satellite Links in LEO Constellations

Kurzfassung

Optical Inter-Satellite Links (O-ISL) are gaining increased adoption, due to their advantages over standard radio communications in terms of achievable bandwidth and virtually non-existent band interference issues. These benefits are crucial for LEO constellations serving diverse sectors such as disaster management, financial services, law enforcement and intelligence services, which all have a demand for reduced data latency and timeliness of actionable information. For this reason, large constellations foresee the use of or are starting to employ O-ISLs at least for in space communication links. One of the challenges in adopting O-ISLs is the management of the network in space and the data routing within the constellation. This paper focuses on the development of an operational simulator for OISLs in LEO constellations using NASA Operational Simulator for Small Satellites (NOS3). The goal is to present the integration and employment of an O-ISL subsystem model into the simulator to examine the operational impact. NOS3 provides a simulation engine for CubeSat and small satellite missions, which integrates the flight software, satellite subsystem models, ground control software and environment simulator to create a realistic platform for testing satellite operations. Multiple instances of NOS3 have been deployed to simulate a constellation and an O-ISL subsystem has been integrated on each satellite of the constellation. A single orbital plane of a Walker Delta constellation consisting of 8U CubeSats is implemented. The O-ISL are modelled as 1U optical heads with a 1-degree field of view and are mounted on the ram and wake direction of the CubeSat, enabling it to establish intra-planar links with adjacent satellites in the forward and backward positions within the same orbital plane. Operating O-ISLs necessitates precise pointing and tracking mechanisms due to the narrow beamwidth of laser communications. Accurate knowledge of satellite position and attitude is critical. Communication establishment combines GPS-derived satellite positions with the propagation of other satellite orbits using periodically updated two-line elements. Once the link is established, multiple operational scenarios are simulated. These include real-time data sharing, where satellites can transfer data, telemetry or commands within the orbital ring. Another scenario involves data relay to ground stations, where the satellite acquiring actionable information over an area of interest but without ground station coverage can relay the data via the optical links within the constellation to a satellite with ground station access, ensuring the data latency is minimized. The simulation environment evaluates the resilience of the intra-planar O-ISL network under dynamic conditions, assessing both the effectiveness of attitude adjustments in maintaining link integrity and the system’s ability to meet stringent latency requirements for time-sensitive operations. This paper also discusses the lessons learned from introducing a new subsystem model into the NOS3 engine, the challenges that need to be addressed when doing so, and the fidelity achievable with NOS3 as an operational simulator.