EQUATOR-S was launched on December 2, 1997 into the Geostationary Transfer Orbit (200 km x 36000 km) on an Ariane 4 (44P). In the first phase of the mission the DLR ground station was supplemented by the NASA antennas in Australia, California and Spain. At the regular telemetry contact over Weilheim on 1 May 1998 it was discovered that EQUATOR-S did not send data anymore. This behavior was attributed to a failure of the redundant on-board processor which was active after the failure of the main processor on 17 December 1997. All attempts by GSOC to command and to reconfigure the spacecraft did not succeed. Mission operations were finally completed by the end of September 1998. However, the scientific data from EQUATOR-S led to new knowledge in the frame of the ISTP program.