Modelling of Optical Inter-Satellite Link Terminals for Operational Real-Time Simulations of LEO Constellations

Kurzfassung

In recent years, the growing demand for fast and widespread global connectivity, as well as Earth Observation (EO) and Positioning, Navigation, and Timing (PNT) services, has driven the development of satellite constellations such as Starlink, OneWeb, and Project Kuiper, leading to new challenges for the aerospace industry. At the same time Free Space Optical (FSO), communication has gained prominence due to its low power consumption and mass, scalable bandwidth, unregulated spectrum, and rapid deployment and redeployment capabilities, making it well suited for inter-satellite links. Despite all its advantages, optical communication presents several limitations and open challenges. Establishing a link requires precise pointing and continuous tracking, making the network highly dynamic and sensitive to small satellite movements. For this reason, the development of a constellation simulator becomes even more crucial for the design of Optical Inter-Satellite Links (O-ISLs) constellations. This paper presents a detailed spacecraft-level simulation of O-ISLs within the NASA Operational Simulator for Small Satellites (NOS3). It evaluates the impact of optical-terminal operations on satellite power consumption and attitude control in a Low Earth Orbit (LEO) constellation. By incorporating flight software, satellite subsystem models, ground control systems, and an environment simulator, NOS3 provides a unified framework for testing satellite operations. An optical-terminal component is integrated into the satellite model to analyze these system-level effects. The approach is then extended to four terminals per satellite, covering in-plane (forward and backward) and cross-track links to adjacent orbital planes. The power consumption of the Pointing Acquisition and Tracking (PAT) processes, Attitude and Orbit Control System (AOCS) maneuvers, and data transmission are estimated, and their impact on the satellite's overall power budget is assessed. Finally, given the multiple movements of the optical terminals required to establish and maintain the links, the resulting torques on the satellite's overall attitude can be determined, allowing evaluation of the operational impact of O-ISLs on connectivity within the constellation.