ARTEMIS and SPOT-4
ARTEMIS and SPOT-4 were two European satellites that established an 830 nm intersatellite link as part of an ESA/CNES mission. Unlike many technical demonstrations, the optical link was used throughout the lifetime of the two satellites and was operated for a total of 230 hours to exchange telemetry and sensor data. This was the first demonstration of imagery transmission between two satellites over an optical communications link.
More information on SPOT-4 can be found on the Earth Observation Mission website .