Length: 12.5"
WingSpan: 5.5"
Code: NC09132

The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design. It currently holds the world record for the fastest speed ever reached by a manned aircraft.

During the X-15 program, 13 of the flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80.47 km 264,000 ft), thus qualifying the pilots for astronaut status. The USAF pilots qualified for USAF astronaut wings, while the civilian pilots also qualified for NASA astronaut wings.

Of all the X-15 missions, two flights (by the same pilot) qualified as space flights, per the international (Federation Aeronautique Internationale) definition of a spaceflight by exceeding a 100 kilometer (62.137 mi, 328,084 ft) altitude.

The X-15 was based on a concept study from Walter Dornberger for the NACA for a hypersonic research aircraft.  The requests for proposal were published on 30 December 1954 for the airframe and on 4 February 1955 for the rocket engine. The X-15 was built by two manufacturers: North American Aviation was contracted for the airframe in November 1955, and Reaction Motors was contracted for building the engines in 1956.

The first X-15 flight was an unpowered test flight by Scott Crossfield, on 8 June 1959; he also piloted the first powered flight, on 17 September 1959, with his first XLR-99 flight on 15 November 1960.

Like most X-series aircraft, the X-15 was designed to be carried aloft, under the wing of a B-52 bomber plane. The X-15 fuselage was long and cylindrical, with rear fairings that flattened its appearance, and thick, dorsal and ventral wedge-fin stabilizers. Parts of the fuselage were heat-resistant nickel alloy (Inconel-X 750). The retractable landing gear comprised a nose-wheel carriage and two rear skis. The skis did not extend beyond the ventral fin, which required the pilot to jettison the lower fin (fitted with a parachute) just before landing. The two XLR-11 rocket engines for the initial X-15A model delivered 16,000 lbf (71 kN) of total thrust; the main engine (installed later) was a single XLR-99 rocket engine delivering 57,000 lbf (250 kN) at sea level, and 70,000 lbf (310 kN) at peak altitude.

Before 1958, USAF and NACA, (later NASA), officials discussed an orbital X-15 spacecraft — the X-15B — for launching to outer space atop an SM-64 Navajo missile, that was cancelled when the NACA became the NASA, and Project Mercury was approved. By 1959, the X-20 Dyna-Soar space-glider program became the USAF's preferred means for launching military manned-spacecraft into orbit; the program was cancelled in the early 1960s.