The SOUT optical intersatellite communication terminal

Optical communications links between satellites promise to become an important element of future space infrastructure and are the subject of considerable development in Europe. Major advantages over conventional microwave links are low mass and power and smaller size leading to easier accommodation on the satellite. The Small Optical User Terminal (SOUT) is an optical communications package for interconnecting a low earth orbiting satellite to future optical data relay terminals and is the subject of an ESA development programme led by MMS (UK). The baseline terminal has a data rate of 2 Mbps over the return interorbit link and a mass of around 25 kg. The terminal configuration uses a unique combination of a periscopic coarse pointing assembly, refractive telescope, passive antivibration mount, combined acquisition and tracking sensor, and fibre coupled lasers and receivers. The paper discusses the design aspects for an asymmetric optical link based on the SOUT, covering link budgets, pointing, acquisition, and tracking and communications performance. Key SOUT subsystems are described and the structural and thermal configuration which allows these features to be combined in a compact unit is reported