Joseph Albert Walker (February 20, 1921 – June 8, 1966) (Capt, USAF) was an American World War II pilot, experimental physicist, NASA test pilot, and astronaut who was the first person to fly an airplane to space. He was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the Air Force and NASA.

In 1961, Walker became the first human in the mesosphere when piloting Flight 35, and in 1963, Walker made three flights above 50 miles, thereby qualifying as an astronaut according to the United States definition of the boundary of space. The latter two, X-15 Flights 90 and 91, also surpassed the Kármán line, the internationally accepted boundary of 100 kilometers (62.14 miles). Making the latter flights immediately after the completion of the Mercury and Vostok programs, Walker became the first person to fly to space twice. He was the only X-15 pilot to fly above 100 km during the program.

Walker died in a group formation accident on June 8, 1966.

Born in Washington, Pennsylvania, Walker graduated from Trinity High School in 1938. He earned his Bachelor of Arts degree in physics from Washington and Jefferson College in 1942, before entering the United States Army Air Forces. He was married and had four children.

During World War II, Walker flew the Lockheed P-38 Lightning fighter and F-5A Lightning photo aircraft (a modified P-38) on weather reconnaissance flights. Walker earned the Distinguished Flying Cross once, awarded by General Nathan Twining in July 1944, and the Air Medal with seven oak leaf clusters.^{[citation needed]}

After World War II, Walker separated from the Army Air Forces and joined the National Advisory Committee for Aeronautics (NACA) Aircraft Engine Research Laboratory in Cleveland, Ohio, as an experimental physicist. While in Cleveland, Walker became a test pilot, and he conducted icing research in flight, as well as in the NACA icing wind tunnel. He transferred to the High-Speed Flight Research Station in Edwards, California, in 1951.^{[citation needed]}

Walker served for 15 years at the Edwards Flight Research Facility – now called the Neil A. Armstrong Flight Research Center. By the mid-1950s, he was a Chief Research Pilot. Walker worked on several pioneering research projects. He flew in three versions of the Bell X-1: the X-1#2 (two flights, first on August 27, 1951), X-1A (one flight), X-1E (21 flights). When Walker attempted a second flight in the X-1A on August 8, 1955, the rocket aircraft was damaged in an explosion just before being launched from the JTB-29A mothership. Walker was unhurt, though, and he climbed back into the mothership with the X-1A subsequently jettisoned.^{[citation needed]}

Other research aircraft that he flew were the Douglas D-558-I Skystreak #3 (14 flights), Douglas D-558-II Skyrocket #2 (three flights), D-558-II #3 (two flights), Douglas X-3 Stiletto (20 flights), Northrop X-4 Bantam (two flights), and Bell X-5 (78 flights).^{[citation needed]}