He flew on the Atlantis flight in April 2002 to the International Space Station, making two space walks to prepare the station for future space walks. In February 2008 he returned to the ISS, where he helped deliver the European Columbus science laboratory. In July 2011 he flew to the ISS aboard the final space shuttle mission, which was the smallest crew (four persons) since April 1983. He has logged over 566 days in space and over 36 hours of space walks. Walheim was a flight controller and operations engineer at NASA's Johnson Space Center from 1986 to 1989. He was selected as an astronaut in 1996 and remains active.