The X-15 rocket research airplane was built by the Los Angeles (Calif.) Division of North American Aviation for the U.S. Air Force, the U.S. Navy, and the National Aeronautics and Space Administration. The airplane was designed to conduct research experiments during actual flight conditions beyond the Earth's atmosphere and to obtain knowledge of aerodynamic heating, re-entry conditions, acceleration and deceleration forces, and reactions of man to weightlessness. A B-52 mothership air-launched the X-15.