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North American X-15

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"X-15" redirects here. For other uses, see X-15 (disambiguation).

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The North American X-15 rocket plane was part of the USAF/NASA/USN X-series of experimental aircraft, including also the Bell X-1. The X-15 set numerous speed and altitude records in the early 1960s, reaching the edge of space and bringing back valuable data that was used in the design of later aircraft and spacecraft. It could be considered the first manned suborbital spacecraft ever flown.[citation needed]

During the X-15 program, 13 flights (by eight pilots) met the USAF's criteria for a spaceflight by passing an altitude of 50 miles (80 km) and the pilots were accordingly awarded astronaut status by the USAF. Three X-15 pilots also qualified to receive NASA astronaut wings.[1][2]

Some respected aerospace researchers have placed the threshold of space at lower altitudes than the USAF and NASA, so many X-15 pilots could also be considered as astronauts. The "aeropause" region, where space-equivalent conditions are first encountered, starts at an altitude of 19 miles (30 km) above the Earth. Many X-15 pilots traveled through, and far above, the aeropause.

Out of all the X-15 missions, two flights (by the same pilot) also qualified for the international FAI definition of a spaceflight by passing the 62.1 mile (100 km) mark.

Design and development

X-15 just after release.
X-15 touching down on its skids. Compare jettisoned lower ventral fin with color picture, top.

The original Request for Proposals was issued for the airframe 30 December 1954, and for the rocket engine on 4 February 1955. North American received the airframe contract in November 1955, and Reaction Motors contracted in 1956 to build the engines.

As with many of the X-aircraft, the X-15 was designed to be carried aloft under the wing of a B-52. The fuselage was long and cylindrical, with fairings towards the rear giving it a flattened look, and it had thick wedge-shaped dorsal and ventral fins. Parts of the fuselage were made of a heat-resistant nickel-based alloy (Inconel-X 750). The retractable landing gear consisted of a nose wheel and two skids — to provide sufficient clearance part of the ventral fin had to be jettisoned before landing. The two XLR-11 rocket engines of the initial model X-15A delivered 36 kN (8,000 lbf) of thrust; the "real" engine that came later was a single XLR-99 that delivered 254 kN (57,000 lbf) at sea level, and 311 kN (70,000 lbf) at peak altitude.

Prior to 1958, USAF and NACA (later NASA) officials discussed an orbital X-15, called the "X-15B", to be launched into space atop a Navajo missile. The idea was scrapped after NASA was formed out of NACA and Project Mercury was approved for manned orbital spaceflight. By 1959, the X-20 Dyna-Soar space-glider program became the USAF's preferred means to launch a military manned spacecraft into orbit. The X-20 program was cancelled in the early 1960s.

The first X-15 flight was an unpowered test made by Scott Crossfield on 8 June 1959, who followed up with the first powered flight on 17 September. The first flight with the XLR-99 was on 15 November 1960.

Operational history

Three X-15s were built in all, and they made a total of 199 test flights, the last one on 24 October 1968. Plans were made for a 200th X-15 flight to be launched over Smith Ranch, Nevada. It was scheduled for 21 November 1968 with William J. Knight as the pilot. Various technical and weather delays caused the planned launch to slip at least six times until late December, 1968. Finally after a cancellation on 20 December 1968 due to weather, it was decided there would not be a 200th flight. The X-15 ground crew de-mated the aircraft from the NB-52A, and prepared it for indefinite storage. X-15 #1 was sent to the National Air and Space Museum in Washington, DC. X-15 #2 is on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. X-15 #3, 56-6672, was destroyed in a crash on 15 November 1967.

Twelve test pilots flew the plane, including Neil Armstrong, later the first man on the Moon, and Joe Engle, who went on to command Space Shuttle missions.

In July and August 1963, pilot Joe Walker crossed the 100 km altitude mark twice, becoming the first person to enter space twice.

Air Force Test pilot Major Michael J. Adams was killed on 15 November 1967 when his X-15-3 began to spin on descent and then disintegrated when the acceleration reached 15 g (147 m/s²), scattering wreckage over 50 square miles. On 8 June 2004 a memorial monument was erected at the location of cockpit crash site near Randsburg, California. Maj. Adams was posthumously awarded astronaut wings for his last flight in the X-15-3, which had attained an altitude of 266,000 feet (81.1 km). In 1991, Adams' name was added to the Astronaut Memorial at the Kennedy Space Center in Florida.

The second X-15A was rebuilt after a landing accident. It was lengthened by about 2.4 ft (0.74 m), received a pair of auxiliary fuel tanks slung under the fuselage, and was given a heat-resistant surface treatment, the result being called the X-15A-2. It first flew 28 June 1964, and eventually reached a speed of 7,274 km/h (4,520 mph or 2,021 m/s).

The altitudes attained by the X-15 remained unsurpassed by any piloted aircraft except the Space Shuttle until the third spaceflight of SpaceShipOne in 2004. The speeds and altitudes have, also, frequently been exceeded by unpiloted air-launched rockets, such as the Pegasus rocket which has carried several satellites all the way into orbit. The widely reported record achieved by the diminutive X-43A scramjet testbed on 16 November 2004 of nearly Mach 10 (6,600 mph or 10,620 km/h or 2.95 km/s) at 95,000 ft (29 km) is only a record for an air-breathing jet engine.

Five main aircraft were involved in the X-15 program: The three X-15s and two B-52 carrier aircraft.

  • 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 October 1969)
  • NB-52B - 52-008 (retired November 2004)

Specifications (X-15)

General characteristics

  • Crew: one

Performance

Record flights

Highest flights

In the United States 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) or more. However the FAI set the limit of space at 100 km. Thirteen X-15 flights went higher than 50 miles (80 km) and two of these reached over 60 miles.

X-15 flights higher than 50 miles (80 km)
Flight Date Top speed Altitude Pilot
Flight 62 17 July 1962 3,831 mph 59.6 miles Robert M. White
Flight 77 17 January 1963 3,677 mph 51.4 miles Joe Walker
Flight 87 27 June 1963 3,425 mph 53.9 miles Robert Rushworth
Flight 90 19 July 1963 3,710 mph 65.8 miles Joe Walker
Flight 91 22 August 1963 3,794 mph 67.0 miles Joe Walker
Flight 138 29 June 1965 3,431 mph 53.1 miles Joseph H. Engle
Flight 143 10 August 1965 3,549 mph 51.3 miles Joseph H. Engle
Flight 150 28 September 1965 3,731 mph 55.9 miles John B. McKay
Flight 153 14 October 1965 3,554 mph 50.4 miles Joseph H. Engle
Flight 174 1 November 1966 3,750 mph 58.1 miles Bill Dana
Flight 190 17 October 1967 3,856 mph 53.1 miles Pete Knight
Flight 191 15 November 1967 3,569 mph 50.3 miles Michael J. Adams†
Flight 197 21 August 1968 3,443 mph 50.6 miles Bill Dana

† fatal

Fastest flights

X-15 ten fastest flights
Flight Date Top Speed Altitude Pilot
Flight 45 9 November 1961 4,092 mph 19.2 miles Robert M. White
Flight 59 27 June 1962 4,104 mph 23.4 miles Joe Walker
Flight 64 26 July 1962 3,989 mph 18.7 miles Neil Armstrong
Flight 86 25 June 1963 3,910 mph 21.7 miles Joe Walker
Flight 89 18 July 1963 3,925 mph 19.8 miles Robert Rushworth
Flight 97 5 December 1963 4,017 mph 19.1 miles Robert Rushworth
Flight 105 29 April 1964 3,905 mph 19.2 miles Robert Rushworth
Flight 137 22 June 1965 3,938 mph 29.5 miles John B. McKay
Flight 175 18 November 1966 4,250 mph 18.7 miles Pete Knight
Flight 188 3 October 1967 4,519 mph 36.3 miles Pete Knight

X-15 Pilots

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
Robert M. White†† U.S. Air Force 16 1 0 6.04 4,092 59.6

† Killed on X-15 Flight 191.

†† Capt Iven Kincheloe had been selected in September 1957, as the Air Force's project test pilot for the X-15 Program (with Capt Bob White as his alternate) but was killed the following year in an F-104 crash before the X-15 ever flew.

* This pilot crossed the 60 mile mark during the X-15 program.

** These two pilots crossed the 60 mile mark after leaving the X-15 program, Armstrong in Gemini and Apollo and Engle in the Shuttle program.


References

Notes
  1. ^ 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.
  2. ^ NASA Press Release, NASA astronaut wings award ceremony, August 23, 2005
Bibliography

See also

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

Aircraft of comparable role, configuration, and era

Related lists

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