Joseph A. Walker - X-15 astronaut (NASA)

Joseph Albert Walker (20 February 1921 - 8 June 1966) was an American military test pilot; in 1963, he made two X-15 flights past the 100 kilometer edge of space, the only spaceplane flights past that threshold made until SpaceShipOne in 2004. These flights qualified him as an astronaut under both U.S. Air Force and Fédération Aéronautique Internationale rules. Joe Walker was the first person to enter space twice.

Born in Washington, Pennsylvania, Walker earned a degree in physics from Washington and Jefferson College before entering the United States Army Air Force. He flew P-38 aircraft in World War II.

After World War II, Walker spent 21 years working as a test pilot. In 1960, he made the first test flight of the X-15 aircraft; Walker would go on to fly the X-15 24 times, including the only two flights of the X-15 to exceed 100 kilometers in altitude, Flight 90 (19 July 1963; 106 km) and Flight 91 (22 August 1963; 108 km).

One of the first Fellows of the Society of Experimental Test Pilots, Walker was killed on June 8, 1966, in a collision between his F-104 chase plane and an XB-70. Walker was married and had four children.