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
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
design. It currently holds the world
record for the fastest speed ever reached by a manned
During the X-15 program, 13 of the flights (by eight pilots) met
the USAF spaceflight
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
) definition of a spaceflight by
exceeding a 100 kilometer (62.137 mi, 328,084 ft)
Engines & fuel
The X-15 had a long fuselage with short stubby wings and an unusual
tail configuration. A Reaction
Motors Inc XLR99
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
Design and development
X-15 just after release.
The X-15 was based on a concept study from Walter Dornberger
for the NACA for a
hypersonic research aircraft.The requests for
were published on 30 December 1954 for the airframe
and on 4 February 1955 for the rocket
. The X-15 was built by two manufacturers: North American Aviation
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
that flattened its
appearance, and thick, dorsal and ventral wedge-fin stabilizers.
Parts of the fuselage were heat-resistant nickel alloy
-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
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
— 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
became the USAF's preferred means for launching military
manned-spacecraft into orbit; the program was cancelled in the
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
(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
, while Soviet Yuri Gagarin
was the first human being in space, reaching 327 km in
of his orbital
flight) and becoming the first to exceed this threshold
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
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,
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
Bomber NB-52A (s/n 52-003), permanent
test variant, carrying an X-15, with mission markings; horizontal
X-15 craft silhouettes denote glide flights, diagonal silhouettes
denote powered flights.
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
, 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
Five aircraft were the X-15 program: three X-15s, two B-52
- X-15A-1 - 56-6670, 82 powered
- X-15A-2 - 56-6671, 53 powered
- X-15A-3 - 56-6672, 64 powered
- NB-52A - 52-003 (retired in October
- 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.
Current Static Displays
X-15 at the National Air and Space
- 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
- NB-52B (s/n 52-008) is at the Dryden Flight Research Center,
Edwards AFB, CA - Launched the majority of X-15 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
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
|X-15 pilots and their achievements during the
|Michael J. Adams†
||U.S. Air Force
||North American Aviation
|Joseph H. Engle
||U.S. Air Force
||U.S. Air Force
|John B. McKay
|Forrest S. Petersen
|Robert A. Rushworth
||U.S. Air Force
||U.S. Air Force
|Robert M. White*
||U.S. Air Force
|† Killed *
White was backup for Captain Iven
- "Aerospaceweb.org | Aircraft Museum X-15".
Aerospaceweb.org, 24 November 2008.
- 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
- "NASA astronaut wings award ceremony". NASA
Press Release, 23 August 2005.
- Käsmann 1999, p. 105.
- X-15A Crash site
- United States Air Force Museum 1975, p. 73.
- 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
- 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
- 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
- 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)