October 07, 2013
Credit: International Aeronautical Federation
The upper-stage J-2X engine, once considered the pacing item for the next U.S. human-rated rocket, will be mothballed after development testing wraps up next year because it will not push humans toward Mars for years.
Conceived as a way to use Apollo-era technology to hasten development of a replacement for the space shuttle, the J-2X is emblematic of a long series of funding-related setbacks that have slowed exploration work to a snail's pace. Just last week, the U.S. government shutdown forced NASA to terminate a three-day workshop on its planned asteroid-redirect mission, which also was devised as a way to stretch exploration dollars.
Unveiled in NASA's budget plan for the fiscal year that began Oct. 1, the asteroid mission faced an uphill fight in Congress before the agency ran out of appropriated funds at the start of the new fiscal year. But even the heavy-lift Space Launch System (SLS), which Congress forced the Obama administration to start developing in 2010, is straggling.
While NASA is actively seeking other missions for the SLS in the planetary science and military arenas, most human flights it has in sight probably can be accomplished with an upper stage powered by the RL-10 engine instead of the J-2X.
“The J-2X for certain [design reference missions] is somewhat overpowered,” Todd May, NASA's SLS program manager, told Aviation Week in Beijing at the 64th International Astronautical Congress, where spacefaring nations gathered to discuss their latest plans for space exploration.
An upgrade of the Saturn V upper-stage engine, the all-cryogenic J-2X generates 294,000 lb. 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 powerplant for the SLS upper stages that will be needed before that far-off flight.
Congress ordered an SLS able to lift 130 metric tons to low Earth orbit (LEO), which is a generally accepted requirement for launching a Mars mission. But for missions to the Moon, where a lot of Mars-precursor shakeout cruises are being planned, a 105-ton SLS is probably sufficient, according to Steve Creech, May's deputy, who is responsible for finding other applications for the big new rocket.