Joseph Albert "Joe" Walker (February 20, 1921 – June 8, 1966), flew the first two spaceplane flights, in 1963, becoming the seventh American astronaut. Walker was a Captain in the United States Air Force, an American World War II pilot, an experimental physicist, a test pilot with NASA, and a member of the U.S. Air Force Man In Space Soonest spaceflight program. In 1963, he made two X-15 experimental rocket aircraft flights beyond the altitude of —the Kármán line which marks the boundary of outer space and qualified Walker as an astronaut under both the rules of the U.S. Air Force and of the Fédération Aéronautique Internationale (FAI).