 There was a large payload gap between the Saturn IB's low Earth orbit capacity and the Saturn V's capability.In the mid-1960s NASA's Marshall Space Flight Center (MSFC) initiated several studies to extend the capabilities of the Saturn family.NASA specified a LEO of , 28° inclination for payload calculations, and the studies examined a number of Modified Launch Vehicle (MLV) configurations based on the Saturn IB and Saturn V launch vehicles as well as Intermediate Payload (INT) launch vehicles based on modified Saturn V stages (MS-IC, MS-II, and MS-IVB).