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. 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). Walker was the chief project pilot for the X-3 program. Walker reportedly considered the X-3 to be the worst airplane that he ever flew. In addition to research aircraft, Walker flew many chase planes during test flights of other aircraft, and he also flew in programs that involved the North American F-100 Super Sabre, McDonnell F-101 Voodoo, Convair F-102 Delta Dagger, Lockheed F-104 Starfighter and Boeing B-47 Stratojet. X-15 program In 1958, Walker was one of the pilots selected for the U.S. Air Force's Man In Space Soonest (MISS) project, but that project never came to fruition. That same year, NACA became the National Aeronautics and Space Administration (NASA), and in 1960, Walker became the first NASA pilot to fly the X-15, and the second X-15 pilot, following Scott Crossfield, the manufacturer's test pilot. On his first X-15 flight, Walker did not realize how much power its rocket engines had, and he was crushed backward into the pilot's seat, screaming, "Oh, my God!". Then, a flight controller jokingly replied "Yes? You called?" Walker would go on to fly the X-15 25 times, including the only two flights that exceeded in altitude, Flight 90 (on July 19, 1963: ) and Flight 91 (on August 22, 1963: ). Walker was the first American civilian to make any spaceflight, and the second civilian overall, preceded only by the Soviet Union's cosmonaut, Valentina Tereshkova one month earlier. Flights 90 and 91 made Walker the first human to make multiple spaceflights according to the FAI definition of greater than 100 km (62 mi). Flight 77 on January 17, 1963 also qualified Walker as an astronaut, according to the US Department of Defense definition of greater than 50 mi (80 km). Walker flew at his highest speed in the X-15A-1: (Mach 5.92) during Flight 59 on June 27, 1962 (the fastest flight in any of the three X-15s was about (Mach 6.7) during Flight 188 flown by William J. Knight on October 3, 1967). LLRV program Walker also became