J-2X


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, the J-2X burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing of thrust in vacuum at a specific impulse of. The engine's mass is approximately 2,470 kg, significantly heavier than its predecessors.
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. 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 2 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 engine. 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, and the use of 21st-century joining techniques.

Testing

On 16 July 2007 NASA officially announced the award to Pratt & Whitney Rocketdyne of a $1.2 billion contract "for design, development, testing and evaluation of the J-2X engine", and began construction of a new test stand for altitude testing of J-2X engines at Stennis Space Center on 23 August 2007.
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. and on 8 September 2008 PWR announced successful testing of the initial J-2X gas generator design. The completion of a second round of successful gas generator tests was announced on 21 September 2010.
Starting in 2011, the full J-2X engine, derived from heritage and new designs, has undergone hot-fire tests.
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 of the RL10 powered Exploration Upper Stage for SLS.