The 212-foot core stage rocket, along
with a pair of solid rocket boosters, and
the Orion crew module largely make up
the Space Launch System (SLS), which NASA is
counting on for its Artemis program’s 2026 return
to the moon—a feat the agency last accomplished
with Apollo 17 in 1972.
Despite the decades between manned lunar
launches, the SLS relies on a workhorse from the
shuttle program. Mounted at the bottom of the core
stage are four RS-25 engines—formerly called the
Space Shuttle Main Engine (SSME)—supplied by
Aerojet Rocketdyne. Originally designed in the
1970s, the engines are seasoned, upgraded veter-
ans, with 25 previous space shuttle flights among
them. Among the four engines mounted to the SLS
are numbers 2045 and 2060, both used on July 8,
2011, to launch the shuttle’s final mission, STS-135.
Doug Bradley was at Kennedy Space Center
during that launch, working as a chief engineer for
Rocketdyne. “I’ve been to many flights, but it was
different for 135,” Bradley says. “It was electric. It
was a very emotional flight.”
The retirement of the space shuttle left Rock-
etdyne with a backlog of 16 engines, which the»
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54 May/June 2022
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