Launch from Cape Canaveral (KSC); landing on Cape Canaveral (KSC). The launch was scrubbed three times: On December 06, 1999 (technical problems), on December 16, 1999 (again technical problems) and on December 18, 1999 (weather).

STS-103 carried out the Hubble-Servicing-Mission 3A. Following two days in flight Hubble was captured successful in the first attempt.

The first EVA by Steven Smith and John Grunsfeld was performed on December 22, 1999 (8h 15m) in which three Rate Sensor Units with each two gyroscopes were replaced, because four gyroscopes had failed. They also opened valves on the NICMOS to purge nitrogen coolant from that instrument and installed Voltage/Temperature Improvement Kits.

The second EVA by Michael Foale and Claude Nicollier occured on December 23, 1999 (8h 10m). They replaced the outmoded DF-224-Computer and installed a new and better computer (20 times faster) and replaced a 500-pound fine guidance sensor.

The third and final EVA was conducted by Steven Smith and John Grunsfeld on December 24, 1999 (8h 8m) to replace a failed S-band transmitter and a Solid State Recorder. They also applied some new insulation on equipment bay doors to minimize degradation of the telescope's protective thermal coverings.

After that, on December 25, 1999, Hubble was deployed again.