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A CGI artist's impression of a J-2X.
Country of originUnited States
ManufacturerAerojet Rocketdyne
ApplicationUpper stage engine
Associated L/VBlock II Space Launch System (EDS)
StatusDevelopment halted
Liquid-fuel engine
PropellantLiquid oxygen / Liquid hydrogen
Mixture ratio5.5-4.5
CycleGas generator
Nozzle ratio92:1
Thrust (vac.)1,307 kN (294,000 lbf)
Thrust-to-weight ratio55.04
Isp (vac.)448 seconds (4.39 km/s)
Length4.7 metres (15 ft)
Diameter3 metres (9.8 ft)
Dry weight5,450 pounds (2,470 kg)

The J-2X is a liquid-fueled cryogenic rocket engine that was planned for use on the Ares rockets of NASA's Constellation program, and later the Space Launch System. Built in the United States by Aerojet Rocketdyne (formerly, Pratt & Whitney Rocketdyne), the J-2X burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,307 kN (294,000 lbf) of thrust in vacuum at a specific impulse (Isp) of 448 seconds (4.39 km/s).[2] The engine's mass is approximately 2,470 kg (5,450 Lb), significantly heavier than its predecessors.[2]

The J-2X was intended to be based on the J-2 used on the S-II and S-IVB stages of the Saturn rockets used during the Apollo program, but as required thrust for the Ares I increased due to weight problems it became a clean-sheet design. It entered development in 2007 as part of the cancelled Constellation program.[2] Originally planned for use on the upper stages of the Ares I and Ares V rockets, the J-2X was later intended for use in the Earth Departure Stage of the Block II Space Launch System, the successor to the Constellation program. The engine is intended to be more efficient and simpler to build than its J-2 ancestor, and cost less than the RS-25 Space Shuttle Main Engine.[1] Differences in the new engine include the removal of beryllium, a centrifugal turbo pump versus the axial turbo pump of the J-2, different chamber and nozzle expansion ratios, a channel-walled combustion chamber versus the tube-welded chamber of the J-2, a redesign of all the electronics, a gas generator and supersonic main injector based on the RS-68,[3] and the use of 21st-century joining techniques.[2][4]


On 16 July 2007 NASA officially announced the award to Pratt & Whitney Rocketdyne (PWR) of a $1.2 billion contract "for design, development, testing and evaluation of the J-2X engine",[5] and began construction of a new test stand for altitude testing of J-2X engines at Stennis Space Center on 23 August 2007.[6]

Component testing was undertaken between December 2007 and May 2008, with nine tests of heritage J-2 engine components at SSC in preparation for the design of the J-2X engine.[7] and on 8 September 2008 PWR announced successful testing of the initial J-2X gas generator design.[8] The completion of a second round of successful gas generator tests was announced on 21 September 2010.[9]

Starting in 2011, the full J-2X engine, derived from heritage and new designs, has undergone hot-fire tests.

  • June 2011: The first hot-fire test.[10]
  • November 2011: A test-firing lasting 499.97 seconds.[11]
  • June 2012: A test-firing lasting 1,150 seconds, during which the J-2X was throttled up and down.[12]
  • July 2012: A test-firing for 1,350 seconds (22½ minutes).[13]
  • December 2012: Final test-firing of Powerpack Assembly.[14]
  • Feb 2013: Testing of Engine 10002 begins on test stand A2 for 6 tests.[15]
  • June 2013: Engine 10002 moved to test stand A1 for 7 further tests.[16]
  • Sept 2013: Final test-firing of Engine 10002.[17]
  • Nov 2013: Testing of Engine 10003 begins.[16]

Program status[edit]

In October 2013, it was reported that work on the J-2X would pause following development testing in 2014, due to funding limitations, an expected delayed need for the engine's capabilities for piloted missions to Mars, and selection[18] of the RL10 powered Exploration Upper Stage for SLS.[19]

See also[edit]

Aerojet Rocketdyne J-2X Engine


  1. ^ a b "J-2X Engine". Aerojet Rocketdyne. Archived from the original on 12 January 2014. Retrieved 9 January 2014.
  2. ^ a b c d e Mark Wade (17 November 2011). "J-2X". Encyclopedia Astronautica. Archived from the original on 12 December 2011.
  3. ^ "The J-2X Upper Stage Engine: From Design to Hardware. Thomas Byrd, Deputy Manager, J-2X Upper Stage Engine Element Ares Projects Office Marshall Space Flight Center Huntsville, AL 35812" (PDF).
  4. ^ William D Greene (4 June 2012). "J-2X Extra: What's in a Name?". NASA.
  5. ^ "NASA Awards Upper Stage Engine Contract for Ares Rockets". NASA. 16 July 2007. Retrieved 17 July 2007.
  6. ^ "NASA's Stennis Space Center Marks New Chapter in Space Exploration". NASA. 23 August 2007.
  7. ^ "NASA Successfully Completes First Series of Ares Engine Tests". NASA. 8 May 2008.
  8. ^ "Pratt & Whitney Rocketdyne Completes Successful Test of J-2X Gas Generator". Pratt & Whitney Rocketdyne. 8 September 2008. Archived from the original on 9 August 2009.
  9. ^ "Pratt & Whitney Rocketdyne Completes Latest Round of Tests on J-2X Gas Generator" (Press release). Pratt & Whitney Rocketdyne. September 21, 2010.[permanent dead link]
  10. ^ Morring, Frank. "First J-2X Hot-Fire Test Could Come Next Week". Aviation Week. Retrieved 19 June 2011.[permanent dead link]
  11. ^ "NASA Test Fires Engine for Giant New Rocket". Space.com. 9 November 2011. Retrieved 26 February 2012.
  12. ^ "NASA Surpasses Test Facility Record with J-2X Powerpack Test". National Aeronautics and Space Administration. 8 June 2012. Retrieved 10 June 2012.
  13. ^ "A Summer of Records for Engine Testing". National Aeronautics and Space Administration. 26 June 2012. Retrieved 26 June 2012.
  14. ^ "Beating Heart of J-2X Engine Finishes Year of Successful Testing". National Aeronautics and Space Administration. 13 Dec 2012. Retrieved 14 Dec 2012.
  15. ^ "NASA Set for New Round Of J-2X Testing at Stennis Space Center". National Aeronautics and Space Administration. 11 Feb 2013. Retrieved 6 Feb 2014.
  16. ^ a b "J-2X Progress: November 2013 Update". National Aeronautics and Space Administration. 15 Nov 2013. Retrieved 6 Feb 2014.
  17. ^ "One Final Test for J-2X Engine No. 10002". National Aeronautics and Space Administration. 5 Sep 2013. Retrieved 6 Feb 2014.
  18. ^ Bergin, Chris. "NASA lines up Exploration Upper Stage workhorse for SLS". NASASpaceflight.com. Retrieved November 8, 2014.
  19. ^ "NASA's J-2X Engine To Be Mothballed After Testing". Aviation Week and Space Technology magazine. 4 Oct 2013. Retrieved 29 Oct 2013.