Saturn IB

The Saturn IB was designed to fill the gap between the modest Redstone and Atlas rockets and the colossal Saturn V. While Saturn V was built to reach the Moon, the Saturn IB was optimized for missions to low Earth orbit, providing a more economical way to test Apollo hardware and later to service the Skylab space station.

The rocket''s first stage, designated S-IB, used eight H-1 engines burning RP-1 kerosene and liquid oxygen, producing 1.6 million pounds of thrust. Its second stage was the same S-IVB stage used as Saturn V''s third stage, powered by a single J-2 engine burning liquid hydrogen and liquid oxygen. This commonality reduced costs and simplified logistics across the Saturn program.

Saturn IB launched Apollo 7, the first crewed Apollo mission, on October 11, 1968, with astronauts Wally Schirra, Donn Eisele, and Walter Cunningham. The 11-day mission proved that the Apollo Command Module was spaceworthy after the extensive redesign that followed the Apollo 1 fire. The vehicle later carried all three Skylab crews to orbit in 1973-1974 and launched the Apollo spacecraft for the Apollo-Soyuz Test Project in 1975, the first international crewed space mission.