The X-15 was the last in a line of manned rocket-powered research airplanes built during the 1950s to explore ever-faster and higher flight regimes. Nineteen years before Space Shuttle, the X-15 showed it was possible to fly into, and out of, space. Launched from the wing of a modified B-52 bomber, the ship rocketed higher and faster than any manned aircraft of the time. There had never been anything like the X-15; it had a million-horsepower engine and could fly twice as fast as a rifle bullet. In the joint X-15 hypersonic research program that NASA conducted with the Air Force, the Navy, and North American Aviation the aircraft flew over a period of nearly 10 years and set unofficial speed and altitude records, in a program to investigate all aspects of piloted hypersonic flight. Information gained from the highly successful X-15 program contributed to the development of the Mercury, Gemini, and Apollo piloted spaceflight programs as well as the Space Shuttle program.
