X-15 Flight 91

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Flight 91
Mission typeTest flight
OperatorUS Air Force/NASA
Mission duration11 minutes, 8.6 seconds
Distance travelled543.4 kilometers (337.7 mi)
Apogee107.96 kilometers (67.08 mi)
Spacecraft properties
ManufacturerNorth American
Launch mass15,195 kilograms (33,499 lb)
Landing mass6,260 kilograms (13,800 lb)
Dry mass6,577 kilograms (14,500 lb)
Crew size1
MembersJoseph A. Walker
Start of mission
Launch dateAugust 22, 1963, 18:05:57 (1963-08-22UTC18:05:57Z) UTC
Launch siteNB-52A #52-003, Edwards
Dropped over Smith Ranch Dry Lake
39°20′N 117°29′W / 39.333°N 117.483°W / 39.333; -117.483
End of mission
Landing dateAugust 22, 1963, 18:17:05 (1963-08-22UTC18:17:06Z) UTC
Landing siteRogers Dry Lake, Edwards
Joe Walker 

X-15 Flight 91 was an August 22, 1963 American crewed 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 by the same pilot, Joseph A. Walker. It was the highest flight of the X-15 program.

Flight 91 was the first flight of a reused spacecraft, as Walker had also flown plane number three on the previous sub-orbital spaceflight on July 19. The air-launch of Flight 91 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 crewed 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 (FAI-recognized) / Third (U.S.-recognized) and last 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 (6,106 km/h) 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 Russell 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. ^ a b c Jenkins (2000), p. 119


  • Goodwin, Robert (2000). X-15: the NASA mission reports, incorporating files from the USAF. Burlington, Ontario: Apogee Books. ISBN 1-896522-65-3.
  • Jenkins, Dennis R. (2000), Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane, NASA Technical Reports, NASA, hdl:2060/20000068530; Document ID: 20000068530
  • Price, A. B. (1968), Thermal protection system X-15A-2 Design Report, NASA Technical Reports, NASA, hdl:2060/19680016245; Document ID: 19680016245
  • Stillwell, W. H. (1965), X-15 research results with a selected bibliography, NASA Technical Reports, NASA, hdl:2060/19650010561; Document ID: 19650010561
  • Watts, Joe D. (1968), Flight experience with shock impingement and interference heating on the X-15-2 research airplane, NASA Technical Reports, NASA, hdl:2060/19920075739; Document ID: 19920075739