A mission specialist, he was assistant to the director of NASA's Flight Crew Operations Branch before flying on the space shuttle Discovery in August 2001 on the mission that delivered the third resident crew to the International Space Station (ISS). His next flight to the ISS was postponed in 2004 following the 2003 Columbia space shuttle disaster. Forrester joined NASA's Johnson Space Center as an aerospace engineer in 1993 and was selected as an astronaut in 1996. He has logged 285 hours in space, with two space walks totalling 11 hours, 45 minutes. In June 2017 he became Chief of the Astronaut Office.