SILEX optical interorbit link experiment

The implementation of communication links between a low earth-orbiting satellite and a geostationary one, or between two geostationary satellites, will lead to significant improvements in the performance of space communication systems. Optical technology is attractive for these applications when high-data-rate communication is required. The European Space Agency (ESA) has therefore instigated an in-orbit demonstration project known as SILEX (semiconductor laser intersatellite link experiment) using a pre-operational link between the French SPOT-4 low earth orbit satellite and the ESA Advanced Relay and Technology Mission Satellite (ARTEMIS). Such an optical communication system brings some new and challenging requirements. In particular, the communication beam, which has a divergence of around 6 urad, must achieve and maintain a very demanding pointing accuracy in the presence of both host satellite vibration and relative satellite motion. This paper provides an overview of the SILEX project and describes a novel pointing mechanism.