Development of the J-2X started under the Bush administration’s Constellation program, which envisioned a human-rated launcher called the Ares I that used a shuttle-derived solid-fuel first stage, and an upper stage powered by the Saturn-heritage J-2X. At the beginning of the Constellation effort, the J-2X was considered the most time-consuming element of the Ares I, even though its Saturn heritage was chosen to minimize development complexity.
Now the engine has been built, using drawings and some hardware retained by NASA and Aerojet Rocketdyne, and is in development testing at Stennis Space Center in Mississippi. Those tests are scheduled to end next year, and after that work on the J-2X will halt “until we’re ready” to integrate the engine with an SLS upper stage, probably for the Mars mission, May says.
“Under constrained funding the number of simultaneous developments is limited, and that’s why we’ve essentially ended up with the architecture we did, because we only have the core to develop,” he says, referring to the SLS first stage. “And if you can do a dual-use upper stage you can actually get to a very capable rocket with only one more major development — not an upper stage and then a CPS.”