Saturn S-IV

The S-IV was the second stage of the Saturn I, the rocket NASA used for the early flights of its Apollo program. Douglas Aircraft Company built it, and it appears among the products listed for McDonnell Douglas, the company Douglas joined in 1967. The stage burned liquid hydrogen with liquid oxygen, held in tanks separated by a common bulkhead, and was powered by a cluster of six RL10A-3 engines that together gave about 400 kilonewtons of thrust. It was used for the early test flights of the Saturn I. Douglas later modified the design into the S-IVB, a similar but distinct stage that flew on the Saturn IB and the Saturn V, so the S-IV is the direct ancestor of the stage that later sent Apollo spacecraft toward the Moon.