Thornton, William Edgar (1929– )

US scientist-astronaut and physician. He flew on the space shuttle Challenger in August 1983 and April 1985, studying the effects of weightlessness on the human body on the first flight, and on monkeys and rodents on the second (the first animal payload in a crewed flight). He developed the treadmill used for in-flight exercise on shuttles. He served with the US Air Force, working in space medicine research, before being selected as a scientist-astronaut in 1967. He left NASA in 1994.