RL10

There was a good, uh...

Remember at ISE, Jake, there was that RL-10 that had, like, the cutaways? I love a good cutaway.

Mm.

Yeah, yeah, yeah.

Built largely from existing rocket hardware, the Saturn I SI stage comprised eight propellant tanks from the PGM-11 Redstone ballistic missile, clustered around a single oxygen tank from the PGM-19 Jupiter missile, a configuration detractors amusingly dubbed Cluster's last stand.

This in turn was topped by an S-IV second stage with six Aerojet Rocketdyne RL-10 engines burning liquid hydrogen and oxygen which produced a maximum thrust of 400 kilonewtons or 90,000 pounds.

Together, these two stages were just powerful enough to loft a crewed Apollo CSM and LEM into low Earth orbit for a fraction of the price of a Saturn V launch.

A total of 10 Saturn I vehicles were launched from Cape Canaveral in Florida, starting with the SA-1 on October 27, 1961, and ending with the SA-10 on July 30, 1965.