Saturn S-IVB

The S-IVB was the third stage of the Saturn V and the second stage of the Saturn IB launch vehicles. Douglas Aircraft Company built it around a single J-2 rocket engine burning liquid hydrogen with liquid oxygen, and it appears among the products listed for McDonnell Douglas. On lunar missions it fired twice, first to place the spacecraft in Earth orbit after the second stage cut off and then to send it toward the Moon. It evolved from the S-IV stage of the Saturn I. Douglas built two versions, a 200 series for the Saturn IB and a 500 series with a flared interstage for the larger Saturn V, twelve and sixteen flight stages respectively. A surplus tank became the hull of Skylab, the first American space station, and from Apollo 13 onward spent stages were crashed into the Moon to give seismic measurements.