A J-2X engine is test fired for the final time on the A-1 test stand at NASA’s Stennis Space Center. The 330-second test was the last in a series of gimbal, or pivot, tests on the engine. Credit: NASA

Aerojet Rocketdyne wrapped up ground tests on the hydrogen-fueled J-2X upper stage that was once to be paired with NASA’s Space Launch System, but which the agency decided in 2013 to mothball instead.

In a June 26 press release, Aerojet Rocketdyne announced the J-2X testing program was complete. The Sacramento, California-based company built four J-2X ground-test engines that racked up a cumulative five hours of hot-fire tests at the A-1 test stand at NASA’s Stennis Space Center in Mississippi and “demonstrated full power operation for twice [the engine’s] designed life service,” according to the press release.

The J-2X generates about 294,000 pounds of thrust in a vacuum and was being developed under a $1.5 billion contract awarded to Pratt and Whitney Rocketdyne in 2007 for the since-canceled Constellation program. Aerojet parent Gencorp acquired Pratt and Whitney Rocketdyne in 2012.

The J-2X, derived from the Apollo-era J-2 that powered the second and third stages of the Saturn 5 rocket, was conceived as the upper stage engine for the Ares 1 crew rocket and Ares 5 cargo launcher that were canceled along with Constellation in 2010.

The Space Launch System NASA is now building with a mix of Ares designs and space shuttle hardware will use a Boeing-designed Interim Cryogenic Propulsion Stage, powered by a single Aerojet Rocketdyne RL-10 engine, as an upper stage for its first two missions. The first two SLS launches will send the Orion crew capsule to the same distant lunar retrograde orbit to which NASA may redirect a small asteroid for astronauts to visit. The inaugural SLS launch will take place in either 2017 or 2018, NASA spokesman Rachel Kraft said in a June 23 email. The second is scheduled for 2021 and will be the first crewed SLS launch.

For later SLS missions, Boeing Space Exploration of Houston, which will build the SLS core and upper stages, has proposed a so-called Exploration Upper Stage that would comprise multiple hydrogen-fueled RL-10 engines instead of a single J-2X. NASA has not formally given Boeing the go-ahead to begin building that proposed upper stage, although the agency and the company reached a handshake agreement on the general terms of the company’s SLS stages contract on April 15.

While J-2X development is now on indefinite hold, Aerojet Rocketdyne remains active on SLS. The rocket’s core stage will use four modified space shuttle main engines, or RS-25s. Hot-fire tests of the tweaked shuttle engines are set to begin at Stennis A-1 in “late July [or] early August,” Dan Dumbacher, NASA’s outgoing deputy associate administrator for exploration systems development, said June 11 at a Capitol Hill event hosted by the Space Transportation Association.

The modified RS-25 engines intended for SLS will use a new engine controller that Aerojet Rocketdyne successfully tested on the J-2X, Aerojet Rocketdyne said in its press release.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...