The North American X-15 rocket-powered aircraft was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, NASA, and the USN. 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 (Fédération Aéronautique Internationale) definition of a spaceflight by exceeding a 100 kilometer (62.137 mi, 328,084 ft) altitude.

Engines & fuel

The X-15 had a long fuselage with short stubby wings and an unusual tail configuration. A Reaction Motors Inc XLR99 rocket engine generating of thrust powered the aircraft. This engine used ammonia and liquid oxygen for propellant and hydrogen peroxide to drive the high-speed turbopump that pumped fuel into the engine. This rocket could be throttled like an airplane engine and was the first such throttleable engine that was "man-rated" or declared safe to operate with a human aboard. Early flights used two Reaction Motors XLR11 engines.

Design and development

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 of total thrust; the main engine (installed later) was a single XLR-99 rocket engine delivering at sea level, and 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.

Operational history

Three X-15s were built, flying 199 test flights, the last on 24 October 1968. Twelve test pilots flew the X-15; among them were Neil Armstrong (first man on the moon) and Joe Engle (a space shuttle commander). In July and August 1963, pilot Joe Walker crossed the 100 km altitude mark, joining the NASA astronauts and Soviet Cosmonauts as the only men to have crossed the barrier into outer space (Alan Shepard was the first American in space, reaching 187 km during suborbital flight, while Soviet Yuri Gagarin was the first human being in space, reaching 327 km in apogee of his orbital flight) and becoming the first to exceed this threshold twice.

U.S. Air Force Test pilot Major Michael J. Adams was killed on 15 November 1967 in X-15 Flight 191 when his craft (X-15-3) entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his craft's flight control system operated the control surfaces to their limits, the craft's acceleration built to 15 g vertical and 8 g lateral. The airframe broke apart at 60,000 ft altitude, scattering the craft's wreckage for 50 square miles. On 8 June 2004, a monument was erected at the cockpit's locale, near Randsburg, California. Major Adams was posthumously awarded Air Force astronaut wings for his final flight in craft X-15-3, which had reached 266,000 ft (81.1 km, 50.4 mi.) of altitude. In 1991, his name was added to the Astronaut Memorial.



The second X-15A was rebuilt after a landing accident. It was lengthened , a pair of auxiliary fuel tanks attached under the fuselage, and a heat-resistant surface treatment applied. Re-named the X-15A-2, it first flew on 28 June 1964, reaching 7,274 km/h (4,520 mph, 2,021 m/s).

The altitudes attained by the X-15 aircraft do not match that of Alan Shephard's 1961 NASA space capsule flight nor subsequent NASA space capsules and space shuttle flights. However, the X-15 flights did reign supreme among rocket-powered aircraft until the third spaceflight of Space Ship One in 2004.

Five aircraft were the X-15 program: three X-15s, two B-52 bombers:

• X-15A-1 - 56-6670, 82 powered flights
• X-15A-2 - 56-6671, 53 powered flights
• X-15A-3 - 56-6672, 64 powered flights
• NB-52A - 52-003 (retired in October 1969)
• NB-52B - 52-008 (retired in November 2004)

A 200th flight over Nevada was slated for 21 November 1968, piloted by William J. Knight. Technical problems and bad weather delayed the flight six times, and on 20 December 1968, the 200th flight was finally cancelled. The X-15 was unfastened from the wing of bomber NB-52A, and prepared for indefinite storage.

Gallery

Current Static Displays

• X-15-1 (s/n 56-6670) is on display in the National Air and Space Museum "Milestones of Flight" gallery, Washington, D.C.
• X-15-2A (s/n 56-6671) is at the National Museum of the United States Air Force, at Wright-Patterson Air Force Base, near Dayton, Ohio. It was retired to the Museum in October 1969. The aircraft is displayed in the Museum's Research & Development Hangar alongside other "X-planes", including the Bell X-1 and X-3 Stiletto.
• X-15-3 (s/n 56-6672) was destroyed. Parts have been recovered at the crash site as late as the 1990s.

Mock-ups:

• Dryden Flight Research Center, Edwards AFB, CA (painted with s/n 56-6672)
• Pima Air Museum, Tucson, Arizona (painted with s/n 56-6671)
• Evergreen Aviation Museum, McMinnville, Oregon (painted with s/n 56-6671). This is the only known full-scale wooden mock-up of the X-15, and it is displayed along with one of the rocket motors.

Stratofortress Motherships:

• NB-52A (s/n 52-003) is at the Pima Air Museum, Tucson, Arizona - launched the X-15 #1 thirty times, the X-15#2 eleven times, and the X-15#3 thirty-one times (as well as the M2-F2 four times, the HL-10 eleven times and the X-24A twice).
• NB-52B (s/n 52-008) is at the Dryden Flight Research Center, Edwards AFB, CA - Launched the majority of X-15 flights.

Specifications (X-15)

Record flights

Highest flights

There are two definitions of how high a person must go to be referred to as an astronaut. The USAF decided to award astronaut wings to anyone who achieved an altitude of 50 miles (80.47 km) or more. However the FAI set the limit of space at 100 km. Thirteen X-15 flights went higher than 50 miles (80.47 km) and two of these reached over 62.137 miles (100 km).

X-15 flights higher than

Flight	Date	Top speed	Altitude	Pilot
Flight 62	17 July 1962			Robert M. White
Flight 77	17 January 1963			Joe Walker
Flight 87	27 June 1963			Robert Rushworth
Flight 90	19 July 1963			Joe Walker
Flight 91	22 August 1963			Joe Walker
Flight 138	29 June 1965			Joseph H. Engle
Flight 143	10 August 1965			Joseph H. Engle
Flight 150	28 September 1965			John B. McKay
Flight 153	14 October 1965			Joseph H. Engle
Flight 174	1 November 1966			Bill Dana
Flight 190	17 October 1967			Pete Knight
Flight 191	15 November 1967			Michael J. Adams†
Flight 197	21 August 1968			Bill Dana

Fastest flights

X-15 10 fastest flights

Flight	Date	Top Speed	Altitude	Pilot
Flight 45	9 November 1961			Robert M. White
Flight 59	27 June 1962			Joe Walker
Flight 64	26 July 1962			Neil Armstrong
Flight 86	25 June 1963			Joe Walker
Flight 89	18 July 1963			Robert Rushworth
Flight 97	5 December 1963			Robert Rushworth
Flight 105	29 April 1964			Robert Rushworth
Flight 137	22 June 1965			John B. McKay
Flight 175	18 November 1966			Pete Knight
Flight 188	3 October 1967			Pete Knight

X-15 pilots

X-15 pilots and their achievements during the program
Pilot	Organization	Total Flights	USAF space flights	FAI space flights	Max Mach	Max speed (mph)	Max altitude (miles)
Michael J. Adams†	U.S. Air Force	7	1	0	5.59	3,822	50.3
Neil Armstrong	NASA	7	0	0	5.74	3,989	39.2
Scott Crossfield	North American Aviation	14	0	0	2.97	1,959	15.3
Bill Dana	NASA	16	2	0	5.53	3,897	58.1
Joseph H. Engle	U.S. Air Force	16	3	0	5.71	3,887	53.1
Pete Knight	U.S. Air Force	16	1	0	6.70	4,519	53.1
John B. McKay	NASA	29	1	0	5.65	3,863	55.9
Forrest S. Petersen	U.S. Navy	5	0	0	5.3	3,600	19.2
Robert A. Rushworth	U.S. Air Force	34	1	0	6.06	4,017	53.9
Milt Thompson	NASA	14	0	0	5.48	3,723	40.5
Joe Walker	U.S. Air Force	25	3	2	5.92	4,104	67.0
Robert M. White*	U.S. Air Force	16	1	0	6.04	4,092	59.6
† Killed * White was backup for Captain Iven Kincheloe

See also

References

Notes

1. "Aerospaceweb.org | Aircraft Museum X-15". Aerospaceweb.org, 24 November 2008.
2. Jenkins, Dennis R. Space Shuttle: The History of the National Space Transportation System: The First 100 Missions, 3rd edition. Stillwater, Minnesota: Voyageur Press, 2001. ISBN 0-9633974-5-1.
3. "NASA astronaut wings award ceremony". NASA Press Release, 23 August 2005.
4. Käsmann 1999, p. 105.
5. X-15A Crash site
6. United States Air Force Museum 1975, p. 73.

Bibliography

• American X-Vehicles: An Inventory X-1 to X-50, SP-2000-4531 - June 2003; NASA online PDF Monograph
• Flight experience with shock impingement and interference heating on the X-15-2 research airplane 1968 - NASA (PDF format)
• Godwin, Robert, ed. X-15: The NASA Mission Reports. Burlington, Ontario: Apogee Books, 2001. ISBN 1-896522-65-3.
• Hallion, Dr. Richard P. "Saga of the Rocket Ships." AirEnthusiast Six March-June 1978. Bromley, Kent, UK: Pilot Press Ltd., 1978.
• Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane - NASA report (PDF format)
• Käsmann, Ferdinand C.W. "Die schnellsten Jets der Welt". Weltrekord-Flugzeuge [World Speed Record Aircraft] (in German). Kolpingring, Germany: Aviatic Verlag, 1999. ISBN 3-925505-26-1.
• Thermal protection system X-15A-2 Design report 1968 - NASA report (PDF format)
• Thompson, Milton O. and Neil Armstrong. At the Edge of Space: The X-15 Flight Program. Washington, DC: Smithsonian Institution Press, 1992. ISBN 1-56098-107-5.
• Tregaskis, Richard. X-15 Diary: The Story of America's First Space Ship. Lincoln, Nebraska: iUniverse.com, 2000. ISBN 0-595-00250-1.
• United States Air Force Museum Guidebook. Wright-Patterson AFB, Ohio: Air Force Museum Foundation, 1975.
• X-15 research results with a selected bibliography - NASA report (PDF format)

External links

• NASA's X-15 website
• X-15 Research Results With a Selected Bibliography (NASA SP-60, 1965)
• "Transiting from Air to Space: The North American X-15" (1998)
• "Proceedings of the X-15 First Flight 30th Anniversary Celebration, 8 June 1989"
• (PDF) Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane (NASA SP-2000-4518, 2000)
• A Field Guide to American Spacecraft - Locations of X-15 aircraft
• unofficial X-15 website
• X-15 Research Results (1964)
• X-15 photos at Dryden
• Encyclopedia Astronautica's X-15 chronology
• Major Michael Adams Monument
• X15 site in French, with detailed flight reports
• Aerospace Legacy Foundation
• X-15, X-15A-2 • Dimensional references, plans and images (Primary source: NASA Technical Reports)
• Fly the X-15 in Flight Simulator.
• Interview with Neil Armstrong about his experience in the X-15