X-15 Flight 91

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Flight 91
Mission type Test flight
Operator US Air Force/NASA
Mission duration 11 minutes, 8.6 seconds
Distance travelled 543.4 kilometers (337.7 mi)
Apogee 107.96 kilometers (67.08 mi)
Spacecraft properties
Spacecraft X-15
Manufacturer North American
Launch mass 15,195 kilograms (33,499 lb)
Landing mass 6,260 kilograms (13,800 lb)
Dry mass 6,577 kilograms (14,500 lb)
Crew size 1
Members Joseph A. Walker
Start of mission
Launch date August 22, 1963, 18:05:57 (1963-08-22UTC18:05:57Z) UTC
Launch site NB-52A #52-003, Edwards
Dropped over Smith Ranch Dry Lake
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End of mission
Landing date August 22, 1963, 18:17:05 (1963-08-22UTC18:17:06Z) UTC
Landing site Rogers Dry Lake, Edwards
Joe Walker

X-15 Flight 91 was a 1963 American human spaceflight mission, and the second and final flight in the program to achieve sub-orbital spaceflight—a flight over 100 km in altitude—which was previously achieved during Flight 90 a month earlier. It was the highest flight of the X-15 program. It was the first flight of a reused spacecraft, as plane number three flew the previous sub-orbital flight on July 19. This mission was piloted by Joseph A. Walker on August 22, 1963, with the air-launch occurring from a modified Boeing B-52 Stratofortress support plane over Smith Ranch Dry Lake, Nevada, United States. Walker piloted the X-15 to an altitude of 107.96 km and remained weightless for approximately five minutes. The altitude was the highest manned flight by a spaceplane to that time and remained the record until the 1981 flight of Space Shuttle Columbia. Walker landed the X-15 about 12 minutes after it was launched, at Rogers Dry Lake, Edwards Airforce Base, in California. This was Walker's final X-15 flight.


Position Astronaut
Pilot Joseph A. Walker
Second spaceflight

Mission parameters

  • Mass: 15,195 kg fueled; 6,577 kg burnout; 6,260 kg landed
  • Maximum Altitude: 107.96 km
  • Range: 543.4 km
  • Burn time: 85.8 seconds
  • Mach: 5.58
  • Launch vehicle: NB-52A Bomber #003

Mission highlights

On this flight, Joe Walker became the first person to enter space twice. He had a maximum speed of 3,794 MPH and a maximum altitude of 354,200 feet. Second and final X-15 flight over 67 miles.[1] Unofficial altitude record set for class. Highest altitude achieved by X-15.[1] Last flight for Walker in X-15 program. Number 1 left RCS nozzle froze up. First flight with altitude predictor instrument (needed calibration).

The mission was flown by X-15 #3, serial 56-6672 on its 22nd flight.[1]

Launched by: NB-52A #003, Pilots Bement & Lewis. Takeoff: 17:09 UTC. Landing: 18:56 UTC.

Chase pilots: Wood, Dana, Gordon and Rogers.

The X-15 engine burned about 85 seconds. Near the end of the burn, acceleration built up to about 4 G (39 m/s²). Weightlessness lasted for 3 to 5 minutes. Re-entry heating warmed the exterior of the X-15 to 650°C in places. During pull-up after re-entry, acceleration built up to 5 G (49 m/s²) for 20 seconds. The entire flight was about 12 minutes from launch to landing.


  1. 1.0 1.1 1.2 Jenkins (2000), p. 119


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