The Saturn IB (also known as the uprated Saturn I) 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 (90000 lbf, 43,380,000 lb-sec total impulse), with the S-IVB (200000 lbf, 96,000,000 lb-sec