History of the X-15 program

The North American X-15 was a rocket-powered research aircraft that flew 199 times between 8 June 1959 and 24 October 1968. Dropped from a B-52 at about 45,000 ft, it set a speed mark of Mach 6.7 and an altitude mark of 354,200 ft, and it brought back data that fed Mercury, Gemini, Apollo and the Space Shuttle.

X-15 at a glance

Program

Joint NASA, US Air Force, US Navy and North American Aviation research program

Flights

199, by three aircraft (81, 53 and 65)

First flight

8 June 1959, an unpowered glide by Scott Crossfield

Last flight

24 October 1968, flown by Bill Dana

Pilots

12: five NASA, five Air Force, one Navy, one North American

Speed record

Mach 6.7 (4,520 mph), Pete Knight, 3 October 1967

Altitude record

354,200 ft (67.1 miles), Joe Walker, 22 August 1963

Launch

From an NB-52 at about 45,000 ft and more than 500 mph

Engine

Reaction Motors XLR99, up to 57,000 lbf of thrust

Research output

Data for more than 765 research reports

Why the X-15 was built

By the early 1950s rocket aircraft had passed the speed of sound, but almost nothing was known about flight at several times that speed. Engineers needed real answers on aerodynamic heating, stability and control at hypersonic speed, and on how an aircraft behaves as the air thins into space. A wind tunnel could not reproduce all of it. They needed a crewed aircraft that could fly there and come back.

The X-15 was that aircraft. Its flights showed that hypersonic boundary-layer flow is turbulent rather than smooth, and that heating and skin friction came in lower than theory predicted. It also carried 28 experiments, from astronomy to micrometeorite collection. Read the full story of how the program began.

Key milestones

A selection of the moments that defined the program. The full X-15 timeline has every milestone from 1952 to 2005.

1. June 1952 Program

   NACA recommends hypersonic research

   The NACA Committee on Aerodynamics recommends more research toward Mach 10 and altitudes of 12 to 50 miles. Preliminary studies of space flight research follow in September.

   Origins
2. December 1954 Program

   Joint program agreed

   The memorandum of understanding between NACA, the Air Force and the Navy is signed, and the Air Force invites contractors to compete for the design.

   Origins
3. 8 June 1959 Flight

   First flight: an unpowered glide

   Scott Crossfield flies airplane No. 1 on its first glide flight after release from the B-52.

   Flight profile
4. 17 September 1959 Flight

   First powered flight

   Crossfield makes the first powered flight in airplane No. 2, using the interim XLR11 engines.

   Aircraft
5. 15 November 1960 Flight

   First flight with the XLR99

   Crossfield flies airplane No. 2 with the XLR99, the throttleable engine that powers the remaining 175 flights.

   Aircraft
6. 9 November 1961 Record

   First flight to Mach 6

   Robert White takes the standard X-15 to Mach 6.04, the best speed it ever reached.

   Records
7. 17 July 1962 Record

   First flight above 300,000 ft

   Robert White flies flight 62 to 59.6 miles, the first X-15 flight above 300,000 ft and beyond the 50-mile line.

   Records
8. 22 August 1963 Record

   Altitude record: 354,200 ft

   Joe Walker flies flight 91 to 354,200 ft (67.1 miles), the highest altitude any X-15 reached.

   Records
9. 3 October 1967 Record

   Speed record: Mach 6.7

   Pete Knight flies the X-15A-2 on flight 188 to Mach 6.7 (4,520 mph), the fastest speed ever recorded by a crewed, powered aircraft.

   Records
10. 15 November 1967 Loss

    Flight 191 and the loss of Michael Adams

    X-15-3 breaks apart after a spin and an inverted dive. Michael Adams is killed. The aircraft is lost.

    Accidents
11. 24 October 1968 Flight

    Final flight

    Bill Dana flies the 199th and last X-15 mission.

    Accidents
12. 2005 Record

    Astronaut wings for three NASA pilots

    Bill Dana, Jack McKay (posthumously) and Joe Walker receive astronaut wings for flying above 50 miles.

    Records

Explore the X-15 story

• OriginsFrom a 1952 recommendation to a 1958 rollout.
• AircraftAirframes, Inconel X skin, the XLR99 engine and the X-15A-2.
• Flight profileDrop, burn, coast, re-entry, glide and landing, step by step.
• PilotsAll twelve pilots, their flights and what each is known for.
• RecordsMach 6.7, 354,200 ft and every first on the way there.
• AccidentsMud Lake 1962, flight 191 in 1967 and the final flight.
• LegacyReaction controls, heating data and the road to the Shuttle.
• TimelineEvery key milestone from 1952 to 2005, in order.
• FAQQuick answers: speed, altitude, pilots, engine and museums.

Fly it yourself

Project X-15 is a flight simulator of these flights. Hang under the B-52, drop, light the XLR99, climb toward the records above and land on the lakebed, with a step-by-step flight guide to coach you down. See how an actual flight worked in the flight profile, then take the controls.