A first data transmission test, using the laser link (SILEX) between ARTEMIS and SPOT-4, was realized on Nov. 21, 2001 (with ARTEMIS in parking orbit) on four consecutive SPOT-4 orbits for contact periods between four and 20 minutes each. The SILEX terminal on-board ARTEMIS activated its optical beacon to scan the area where SPOT was expected to be. When contact was made, SPOT-4 responded by sending its own laser beam to ARTEMIS. On receiving the SPOT-4 beam, ARTEMIS stopped scanning and the optical link was maintained for a pre-programmed period lasting from 4 to 20 minutes. Data rates of 50 Mbit/s were reached transmitting test data from SPOT-4 via ARTEMIS to the ground. An extremely low bit error rate of the data stream was confirmed (better than 10-9) at ESA's test station in Redu (Belgium) and the SPOT 4 receive station in Toulouse, France. On Nov. 30, 2001, the first-ever transmission of an image by laser link took place from one S/C to another.
