The engines are critical to NASA’s next plan for human spaceflight and illustrate an important principle guiding the design of the nation’s next booster: engineers are to use proven technology. The RS-25 engines, which performed almost flawlessly during 135 shuttle launches, are a gold standard for reliability and power that NASA wants to preserve.
Yet the last enhancement to the engines was made in the 1990s, and the new launch vehicle, uninspiredly named the Space Launch System, is expected to be the first one capable of sending humans beyond the moon. The contradiction between its design constraint and its ambitious mission puts engineers like McDaniel in a tough spot.
They are using space shuttle hardware for a vehicle tasked with a human spaceflight mission far more daunting than putting astronauts in orbit around Earth. But you won’t hear complaints at Stennis, where the engines are tested, or at Marshall Space Flight Center in Huntsville, Alabama, where the SLS program is managed.
“We had a school group in here one day to see the engines, and a girl raised her hand,” McDaniel recalls. “She said, ‘There are supposed to be 15 here but I only count 14.’ That’s the kind of person we want in this program, who doesn’t take things for granted.”
Little is taken for granted with the SLS, given the fate of its predecessor, the more imaginatively named Ares I rocket, which didn’t get very far. Ares made a single test launch in 2009 before the Obama administration cancelled the human exploration program, Constellation, which required a big new launch vehicle for missions to the moon. But the SLS borrows certain features from the Ares I rocket, including a new digital engine controller and the use of shuttle-era solid rocket boosters.
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