Chrysler / Douglas Saturn IB

The Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration (NASA) for the Apollo program. It uprated the Saturn I by replacing the S-IV second stage, with the S-IVB. The S-IB first stage also increased the S-I baseline's thrust from 1,500,000 to 1,600,000 pounds-force and propellant load by 3.1%. This increased the Saturn I's low Earth orbit payload capability from 20,000 to 46,000 pounds, enough for early flight tests of a half-fueled Apollo command and service module (CSM) or a fully fueled Apollo Lunar Module (LM), before the larger Saturn V needed for lunar flight was ready.