Aviation Week reports that the new upper stage J-2X engine will be mothballed next year after engineers complete its development and not put into use until NASA is ready to send humans to Mars, which probably won’t be until the late 2020’s at the earliest.
The engine, which NASA has spent $1.2 billion developing since 2007, is overpowered for the precursor human mission to asteroids and the moon the agency is likely to do in the interim.
An upgrade of the Saturn V upper-stage engine, the all-cryogenic J-2X generates 294,000 lb. of thrust with its gas-generator cycle. While it almost certainly will be needed to send men and women to Mars, the equally venerable RL-10 is beginning to look like a better power plant for the SLS upper stages that will be needed before that far-off mission.
One way to get to that capability would be with a “dual-use upper stage” carrying three or four RL-10s. All of them would ignite to get the payload — an Orion crew capsule, in-space habitat or lunar lander — into LEO, and then some subset of that number would fire for the trans-lunar injection to send the payload toward the Moon.
NASA hasn’t ruled out using the J-2X for that portion of the trip, but it could be faster to develop the dual-use stage than the originally planned SLS upper stage powered by the J-2X, and a cryogenic propulsion stage (CPS) for getting into lunar orbit.
“What we’ve looked at to try to save costs and accelerate mission capability [is] combining the functions of our upper stage and the CPS so that we just have to have one stage,” Creech says.
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