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.

It exceeded its design specifications of 4,000 miles per hour and altitudes up to 50 miles.

On Aug. 22, 1963, NASA pilot Joseph Walker piloted the craft to a record altitude of 354,200 feet, slightly over 67 miles.

On June 27, 1962, Walker attained a record speed of 4,104 miles per hour with a Mach number of 6.00, at 123,700 feet. On Dec. 5, 1963, Maj. Robert A. Rushworth attained a higher Mach number -- 6.06 -- but at the slower speed of 4,018 mph and an altitude of 101,800 feet.