X-15
Role	Experimental high-speed rocket-powered research aircraft
Manufacturer	North American Aviation
First flight	8 June 1959
Introduction	17 September 1959
Retired	December 1970
Primary users	United States Air Force NASA
Number built	3

An X-15A2, with sealed ablative coating, external fuel tanks, and ramjet dummy test, on this upgraded model. (dropped by a B-52)

The North American X-15 was a rocket-powered aircraft operated by the United States Air Force and the National Aeronautics and Space Administration (NASA) as part of the X-plane series of experimental aircraft. 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. As of 2012^[update], the X-15 holds the official world record for the fastest speed ever reached by a manned rocket-powered aircraft.^[1]

During the X-15 program, 13 different flights by eight pilots met the USAF spaceflight criterion by exceeding the altitude of 50 miles (80 km) thus qualifying the pilots for astronaut status. The USAF pilots qualified for USAF astronaut wings, while the civilian pilots were awarded NASA astronaut wings in 2005, 35 years after the last X-15 flight.^[2][3]

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 100 kilometers (62.1 mi, 328,084 ft) in altitude.

Design and development[link]

The X-15 was based on a concept study from Walter Dornberger for the NACA for a hypersonic research aircraft.^[4] 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.

Like many X- series aircraft, the X-15 was designed to be carried aloft, under the wing of a NASA B-52 mother ship, the Balls 8. Release took place at an altitude of about 8.5 miles (13.7 km) and a speed of about 805 kilometers per hour (500 mph).^[5] 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).^[4] 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.

Cockpit and pilot systems[link]

An X-15 after being dropped

The X-15 was a research aircraft, and there were changes to it over the course of the program and between the different airframes. The X-15 had to be operated under several different situations including the time attached to a carrier aircraft, drop, main engine start and acceleration, a ballistic flight into thin air/space, re-entry into thicker air, and an unpowered glide to landing. Alternatively, if the main engine was not started the pilot needed to go directly to a landing. The main rocket engine only operated for a relatively short part of the flight, but was capable of boosting the X-15 to its high-speeds and altitudes. Without the main engine on, the X-15's instruments and control surfaces remained functional, but the plane could not maintain altitude.

Because the X-15 also had to be controlled in a region where there was too little air for aerodynamic surfaces, it had a reaction control system (RCS) that used rocket thrusters.^[6] There were two different X-15 pilot controls setups: one type basically used three joysticks, and another type used one joystick.^[7]

The X-15 type with multiple control sticks for the pilot, included a traditional rudder and stick, and another joystick on the left which gave commands to the reaction control system.^[8] A third joystick on the right side was used during high G maneuvers to augment the center stick.^[8] In addition to pilot input the X-15 "Stability Augmentation System" (SAS) gave extra inputs to the aerodynamic controls to help the pilot maintain control.^[8] The reaction control system could be operated in two modes: manual and automatic.^[7] The automatic mode used a feature called "Reaction Augmentation System" (RAS) that helped stabilize the vehicle during high altitudes.^[7] The RAS was typically used for around three minutes of a X-15 flight before being automatically turned off.^[7]

The other setup used the MH-96 flight control system which allowed one joystick in place of three and simplified pilot inputs.^[9] The MH-96 could automatically blend aerodynamic and rocket controls depending on how effective each system was at controlling the X-15.^[9]

Among the many other controls, were the rocket engine throttle and a control for ejecting the bottom tail fin.^[8] Another feature of the cockpit were heated windows to prevent icing, and a forward headrest for periods of high de-acceleration.^[8]

The X-15 had an ejection seat that allowed ejection at speeds up to Mach 4 and/or 120,000 feet (~36.6 km) altitude, although it was not used during the program.^[8] In the event of ejection, the seat had deployable fins which were used until it reached a safer speed/altitude, where it could deploy its main parachute.^[8] Pilots wore a pressure suit, which could be pressurized with nitrogen gas.^[8] Above 35,000 ft (~10.7 km) altitude, the cockpit was pressurized to 3.5 psi (0.24 atm) with nitrogen gas, and oxygen for breathing was fed separately to the pilot.^[8]

Engines and fuel[link]

X-15 tail with XLR-99

Early flights used two Reaction Motors XLR11 engines. Later flights were undertaken with a single Reaction Motors Inc XLR99 rocket engine generating 57,000 pounds-force (250 kN) of thrust that powered the aircraft. This engine used ammonia and liquid oxygen for propellant and hydrogen peroxide to drive the high-speed turbopump that delivered fuel to the engine.^[6] It could burn 15,000 pounds (6804 kg) of fuel in 80 seconds.^[6] The XLR99s could be throttled, and were the first such controllable engines that were man-rated.^{[disputed – discuss]}

The XLR11 used ethyl alcohol and liquid oxygen, and the XLR99 used ammonia and liquid oxygen as fuel. The X-15 reaction control system (RCS), for maneuvering in low-pressure/density environment, used hydrogen peroxide as a monopropellant.^[7] More specifically, it was high-test peroxide, which decomposes into water and oxygen in the presence of a catalyst, and can give an I_SP of 140 seconds.^[10] The HTP also fueled a turbopump for the main engines and auxiliary power units (APUs).^[6] Additional tanks for helium and liquid nitrogen performed other functions, for example the fuselage interior was purged with helium gas and the liquid nitrogen was used as coolant for various systems.^[6]

Wedge tail and hypersonic stability[link]

The X-15 had a thick wedge tail for stability at hypersonic speeds.^[11] However, this produced a lot of drag at slower speeds.^[11] In fact, the blunt end of the X-15 could produce as much drag as an entire F-104 Starfighter.^[11]

A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds. A vertical-tail area equal to 60 percent of the wing area was required to give the X-15 adequate directional stability.

— Wendell H. Stillwell, X-15 Research Results (SP-60)

Additionally, stability at hypersonic speeds was aided by side panels that could extend out from the tail to further increase area, and these panels doubled as air-brakes.^[11]

Operational history[link]

In the first 50 years of human spaceflight the X-15 became the world's first operational spaceplane, reaching space in 1962/1963 (depending upon Kármán line classification [ US / FAI ]). It was followed by the Space Shuttle, the Buran, SpaceShipOne, and the Boeing X-37. Of these only the X-15 and SpaceShipOne launched from a mother ship.

Altitudes attained by X-15 aircraft do not match those of Alan Shepard's and Virgil Grissom's Project Mercury space capsules in 1961, nor of any other manned spacecraft. However, the X-15 ranks supreme among manned rocket-powered aircraft, becoming the world's first operational spaceplane in the early 1960s.

Before 1958, USAF and NACA officials discussed an orbital X-15 spaceplane, the X-15B that would launch into outer space from atop an SM-64 Navajo missile. This was canceled when the NACA later became NASA and NASA adopted Project Mercury instead.

By 1959, the Boeing X-20 Dyna-Soar space-glider program became the USAF's preferred means for launching military manned spacecraft into orbit; however, this program was canceled in the early 1960s before an operational vehicle could be built.^[2] Various configurations of the Navajo were considered, and another proposal proposed a Titan I stage.^[12]

Three X-15s were built, flying 199 test flights, the last on 24 October 1968.

The first X-15 flight was an unpowered test flight by Scott Crossfield, on 8 June 1959. Crossfield also piloted the first powered flight, on 17 September 1959, and his first flight with the XLR-99 rocket engine on 15 November 1960. Twelve test pilots flew the X-15. Among these were Neil Armstrong, later a NASA astronaut, and Joseph H. Engle, later a commander of NASA Space Shuttle test flights.

In a 1962 proposal, NASA considered using the B-52/X-15 as a launch platform for a Blue Scout rocket to place satellites up to 150 pounds into orbit.^[12][13]

In July and August 1963, pilot Joseph A. Walker exceeded 100 km in altitude, joining NASA astronauts and Soviet cosmonauts as the first human beings to cross that line on their way to outer space. The USAF awarded astronaut wings to anyone achieving an altitude of 50 miles (80 km) (80.5 km), while the FAI set the limit of space at 100 kilometers (62.1 mi).

On 15 November 1967, U.S. Air Force test pilot Major Michael J. Adams was killed during X-15 Flight 191 when the (X-15-3) entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his aircraft's flight control system operated the control surfaces to their limits, acceleration built to 15 g vertical and 8.0 g lateral. The airframe broke apart at 60,000 ft (18,000 m) altitude, scattering the X-15's wreckage for 50 square miles (130 km²). On 8 June 2004, a monument was erected at the cockpit's locale, near Randsburg, California.^[14] Major Adams was posthumously awarded Air Force astronaut wings for his final flight in X-15-3, which had reached and altitude of 81.1 km (50.4 mi, 266,000 ft). In 1991, Adams's name was added to the Astronaut Memorial.

The second X-15A was rebuilt after a landing accident. It was lengthened 2.4 feet (0.73 m), a pair of auxiliary fuel tanks attached underneath its fuselage and wings, and a complete heat-resistant ablative coating was added. Renamed the X-15A-2, this plane first flew on 28 June 1964, reaching a maximum speed of 7,274 km/hr (4,520 m.p.h., 2,021 m/sec). in October 1967, flown by William "Pete" Knight of the U.S. Air Force.

NB-52B takes off with an X-15

Five aircraft were used duing the X-15 program: three X-15s planes and two B-52 Stratofortress 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 first scheduled for 21 November 1968, to be flown by William "Pete" Knight. Numerous technical problems and outbreaks of bad weather delayed this proposed flight six times, it was permanently canceled on 20 December 1968. This X-15 was detached from the B - 52 and then put into indefinite storage. This X - 15 was later donated to the museum at Wright Patterson Air Force Base for display.

• 

  NB-52A (s/n 52-003), permanent test variant, carrying an X-15, with mission markings; horizontal X-15 silhouettes denote glide flights, diagonal silhouettes denote powered flights.

• 

  X-15 just after release.

• 

  X-15 touching down on its skids, with the lower ventral fin jettisoned.

Current static displays[link]

X-15 at the National Air and Space Museum

• X-15-1 (AF Ser. No. 56-6670) is on display in the National Air and Space Museum "Milestones of Flight" gallery, Washington, D.C.
• X-15-2A (AF Ser. No. 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.^[15] The aircraft is displayed in the Museum's Research & Development Hangar alongside other "X-planes", including the Bell X-1B and Douglas X-3 Stiletto.
• X-15-3 (AF Ser. No. 56-6672) was destroyed during X-15 Flight 191. Parts from this aircraft have been recovered at the crash site as late as the 1990s.

Mock-ups[link]

• Dryden Flight Research Center, Edwards AFB, California, USA (painted with AF Ser. No. 56-6672)
• Pima Air Museum, Tucson, Arizona (painted with AF Ser. No. 56-6671)
• Evergreen Aviation Museum, McMinnville, Oregon (painted with AF Ser. No. 56-6672). A full-scale wooden mock-up of the X-15, it is displayed along with one of the rocket motors.

Stratofortress mother ships[link]

• NB-52A (AF Ser. No. 52-003) is displayed at the Pima Air and Space Museum adjacent to Davis-Monthan AFB in Tucson, Arizona. It launched the X-15-1 30 times, the X-15-2A, 11 times, and the X-15-3 31 times (as well as the M2-F2 four times, the HL-10 11 times and the X-24A twice).
• NB-52B (AF Ser. No. 52-008) is displayed at the Dryden Flight Research Center at Edwards AFB, California. It launched the majority of X-15 flights.

Record flights[link]

Highest flights[link]

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 km) (80.5 km) or more. However, the FAI set the limit of space at 100 kilometers (62.1 mi). Thirteen X-15 flights went higher than 50 miles (80 km) and two of these reached over 100 kilometers.

^† fatal

Fastest flights[link]

X-15 pilots[link]

Neil Armstrong and X-15

Specifications (X-15)[link]

Other configurations include the Reaction Motors XLR11 equipped X-15, and the long version.

General characteristics

• Crew: one
• Length: 50 ft 9 in (15.45 m)
• Wingspan: 22 ft 4 in (6.8 m)
• Height: 13 ft 6 in (4.12 m)
• Wing area: 200 ft² (18.6 m²)
• Empty weight: 14,600 lb (6,620 kg)
• Loaded weight: 34,000 lb (15,420 kg)
• Max. takeoff weight: 34,000 lb (15,420 kg)
• Powerplant: 1 × Thiokol XLR99-RM-2 liquid-fuel rocket engine, 70,400 lb_f at 30 km (313 kN)

Performance

• Maximum speed: Mach 6.72 (4,520 mph, 7,274 km/h)
• Range: 280 mi (450 km)
• Service ceiling: 67 mi (108 km, 354,330 ft)
• Rate of climb: 60,000 ft/min (18,288 m/min)
• Wing loading: 170 lb/ft² (829 kg/m²)
• Thrust/weight: 2.07

See also[link]

	United States Air Force portal
	Aviation portal
	Spaceflight portal

Aircraft of comparable role, configuration and era

• Bell X-2
• Douglas Skyrocket (D-558-2)
  

Related lists

• List of rocket planes
• List of X-15 flights
• List of space disasters
  

References[link]

Notes

Bibliography

External links[link]

Wikimedia Commons has media related to: North American X-15

NASA

• 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)
• Interview with Neil Armstrong about his experience in the X-15
• X-15 Hypersonic Research Program (12.15.09)
• X-15 photos at Dryden
• X-15 movies at Dryden
• Interactive X-15 portal by NASA (uses Macromedia Flash)

Non-NASA

• 1955 Report No. NA-55-221 X-15 Advanced Research Airplane Design Summary (North American's X-15 proposal)
• A film clip "X-15 Aloft. First Free Flight Of Manned Space Plane, 1959/06/11 (1959)" is available for free download at the Internet Archive [more]
• A film clip "X-15 Space Record. Plane Flown To 59-mile Mark, 1962/07/19 (1962)" is available for free download at the Internet Archive [more]
• A film clip "Space Triumph. Discoverer Capsule Recovered From Orbit , 1960/08/15 (1960)" is available for free download at the Internet Archive [more]
• A film clip "Nuclear Navy. First Polaris A-Sub Sails On Ocean Patrol, 1960/11/17 (1960)" is available for free download at the Internet Archive [more]
• The short film HISTORY OF THE AIR FORCE 1954 - 1964 -- FROM MISSILE DEVELOPMENT TO SPACE (1977) is available for free download at the Internet Archive [more]
• A Field Guide to American Spacecraft - Locations of X-15 aircraft
• unofficial X-15 website
• 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)
• X-15 at the Internet Movie Database

v t e United States human spaceflight programs Active ISS (joint) Previous X-15 (suborbital) Mercury Gemini Apollo Skylab Apollo-Soyuz (with USSR) Space Shuttle Shuttle-Mir (with Russia) Canceled MISS Orion (nuclear) Dyna-Soar Manned Orbiting Laboratory National Aero-Space Plane Space Station Freedom (now ISS) Orbital Space Plane Project Constellation

The Edge
Background information
Birth name	David Howell Evans
Born	(1961-08-08) 8 August 1961 (age 50) Barking, Essex, England, United Kingdom
Origin	County Dublin, Ireland
Genres	Rock, post-punk, alternative rock
Occupations	Musician, songwriter, activist
Instruments	Guitar, vocals, keyboards, piano, bass guitar
Years active	1976–present
Labels	Island, Mercury
Associated acts	U2, Passengers
Website	www.u2.com
Notable instruments
Gibson Explorer Fender Stratocaster Gibson Les Paul Fender Telecaster Gretsch Country Gentleman Gretsch White Falcon Rickenbacker 330/12

David Howell Evans (born 8 August 1961), more widely known by his stage name The Edge (or just Edge),^[1] is a musician best known as the guitarist, backing vocalist, and keyboardist of the Irish rock band U2. A member of the group since its inception, he has recorded 12 studio albums with the band and has released one solo record. As a guitarist, The Edge has crafted a minimalistic and textural style of playing. His use of a rhythmic delay effect yields a distinctive ambient, chiming sound that has become a signature of U2's music.

The Edge was born in England to a Welsh family, but was raised in Ireland after moving there as an infant. In 1976, at Mount Temple Comprehensive School, he formed U2 with his fellow students and his older brother Dik. Inspired by the ethos of punk rock and its basic arrangements, the group began to write its own material. They eventually became one of the most popular acts in popular music, with successful albums such as 1987's The Joshua Tree and 1991's Achtung Baby. Over the years, The Edge has experimented with various guitar effects and introduced influences from several genres of music into his own style, including American roots music, industrial music, and alternative rock. With U2, The Edge has also played keyboards, co-produced their 1993 record Zooropa, and occasionally contributed lyrics. The Edge met his second and current wife, Morleigh Steinberg, through her collaborations with the band.

As a member of U2 and as an individual, The Edge has campaigned for human rights and philanthropic causes. He co-founded Music Rising, a charity to support musicians affected by Hurricane Katrina. He has collaborated with U2 bandmate Bono on several projects, including songs for Roy Orbison and Tina Turner, and the soundtracks to the musical Spider-Man: Turn Off the Dark and the Royal Shakespeare Company's London stage adaptation of A Clockwork Orange. In 2011, Rolling Stone magazine placed him at number 38 on its list of "The 100 Greatest Guitarists of All Time".