Decision looms on when to introduce new SLS upper stage, Spaceflight Now
"Officials initially planned to power the upper stage with a J-2X engine, a modernized powerplant based on the J-2 engine designed in the Apollo era. But managers decided the J-2X, which had roots in the canceled Constellation moon program, was overpowered for the job and sidelined the engine after a series of hotfire ground tests. NASA spent more than $1.4 billion on the J-2X engine from 2006 through 2014, an agency spokesperson said."
Using Jedi Mind Tricks to Sell NASA's Next Big Rocket (2014), earlier post
"The initial plan was to launch EM-1 with an upper stage composed of a modified Boeing Delta IV upper stage i.e. the Interim Cryogenic Propulsion Stage (ICPS). After trying this for several years, and spending $400 million or so, NASA realized that this was not going to work. So they are going to ask Boeing to deliver a standard Delta IV upper stage and use that. NASA then wants to commence work on a 4 engine Exploration Upper Stage (EUS) that will only be used a few times."
NASA Set for New Round Of J-2X Testing at Stennis Space Center, (2013) earlier post
"NASA's progress toward a return to deep space missions continues with a new round of upcoming tests on the next-generation J-2X rocket engine, which will help power the agency's Space Launch System (SLS) to new destinations in the solar system."
"We found that NASA's Upper Stage Engine (USE) Element Manager, located at Marshall Space Flight Center in Alabama, reviewed the J-2X rocket propulsion testing options and selected the A-3 test stand to be built at Stennis without the required formal reviews or recommendations of the NRPTA, or NASA's RPTMB."
"Similar to the OIG's conclusions 5 years ago, the OIG found that NASA failed to follow its internal policies or its agreement with the DOD when it decided to spend approximately $352 million to refurbish and test the SLS core stage on the B-2 test stand at Stennis."
NASA Has No Clear Use for the J-2X That It Once Needed, earlier post