IN A WORLD WITHOUT CASTINGS


Would U.S. Astronauts Have Been First to Circle the Moon?


Te Apollo 8, which launched December 21,


1968, and orbited the moon on December 24, used an SPS service propulsion engine that featured some firsts in its design. “It was the first ablative thrust chamber of


any size to fly. Tere were no liners in it. It was a throat-gimbaled engine, and it was the first engine to fly with columbium in the nozzle,”said Clay Boyce, engineering manager of the Apollo Service Propulsion System (SPS) engine development. Te general configuration was 20,000 lbs. of thrust, with a chamber pressure of 100 psi and specific impulse (Isp) of 314.5. Te 100-lb., 2-ft.-sq. propellant valve was a


complex casting with significant machining, and the team used the latest numerically controlled machine with multi-axis operations to speed production. Te fuel and oxidizer were in one valve assembly. “It worked very well because the two independent cast- ings had a cavity in between them. We had dual seals on each shaft where they went into the cavity/actuat- ing area, and that area was vented,” Boyce said.


Source: “Remembering the Giants—Apollo Rocket Propulsion Development,” edited by Steven C. Fisher and Shamim A Rahman, presented at the John C. Stennis Space Center, April 25, 2006, NASA.


May 2013 MODERN CASTING | 21


Photos courtesy of NASA


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