His space shuttle flights include two Microgravity Science Laboratory missions in April 1997 and July 1997, both aboard Columbia. In July 2001 he flew aboard Atlantis to install a new airlock module on the International Space Station, completing three space walks to do so. He has logged 43 days in space and more than 23 hours on four space walks. Gernhardt has been assigned to a future flight with an unknown date because of the 2003 Columbia space shuttle disaster. He worked independently on the development of new space-station tools until his selection as an astronaut in 1992.