Rex Joseph Walheim (born October 10, 1962) is a retired United States Air Force officer, engineer and NASA astronaut. He flew three Space Shuttle missions, STS-110, STS-122, and STS-135. Walheim logged over 566 hours in space, including 36 hours and 23 minutes of spacewalk (EVA) time. He was assigned as mission specialist and flight engineer on STS-135, the final Space Shuttle mission.