The S-IVB must satisfy two different sets of vehicle constraints: 1) as a second stage for the Saturn IB launch vehicle, and 2) as a third stage with restart capability for the Saturn V launch vehicle. A comparison between these missions is presented. Since upper stages generally contribute more kinetic energy to the payload, they are more critical than lower stages from a performance tradeoff aspect. Initially, space launch vehicles were single-burn devices, with mission times measured in minutes. The current S-IVB mission time encompasses more than 6–1/2 hours, a significant portion of which is in a near-zero g environment. This operational requirement imposes severe demands on stage design. The resulting problem areas are identified, and their solutions are described.
The primary and secondary technical objectives of stage missions are discussed in general. Specific emphasis is placed upon the LH2 experiment investigating orbital propellant management, which will be flown on the SA-203 vehicle of Saturn IB. Compatibility between the stage, GSE, and facilities are discussed. The general influences of program costs and schedules are examined.