Gerhard Thiele commenced astronaut basic training in 1988 at the German Aerospace Center (DLR) and was assigned to the D2 Spacelab mission two years later. He served as backup payload specialist for this 1993 mission from the DLR Control Center at Oberpfaffenhofen. In 1995 he was appointed Director of the DLR Crew Training Center (CTC).
Thiele travelled into space for the first time on 11 February 2000: Shuttle mission STS-99 had the task of gathering radar data for the first three-dimensional digital atlas of the Earth's surface; it was also known as the Shuttle Radar Topography Mission (SRTM). Mapping commenced less than 12 hours after launch.