The Saturn S-IVB stage has a requirement for orbiting around the earth for up to 4.5 hours with approximately 60 percent of its initial propellant remaining at the end of the coast (prior to restart) . Extensive analyses must be performed to insure that this requirement is met. Both the maximum and minimum heat transfer rates are important because the maximum rates affect the hydrogen boiloff losses and thus the initial propellant loading requirements. The minimum rates are important because the boil off gases are used to maintain a minimum axial thrust level by venting the gases continuously through aft facing nozzles. This provides for a settling of the propellant throughout the orbital coast and alleviates the need for periodically venting the tank under zero gravity.
In April of 1960 the Douglas Aircraft Company was awarded a contract to develop the second and uppermost stage for the Saturn I space booster. In order to realize the high specific impulse available, this stage, called the S-IV, was to utilize liquid hydrogen and liquid oxygen as the propellants. After burn-out of the first stage, the S-IV Stage was to ignite its engines at an altitude of approximately 200,000 feet, burn for approximately 8 minutes, and inject a 20,000 lb spacecraft into a low earth orbit. This program represented Douglas's first major endeavor with liquid hydrogen. It was necessary to develop an insulation for the S-IV Stage that was capable of withstanding the thermal shock associated with loading, could provide adequate insulative properties to limit the flow of heat into the hydrogen, and was of minimum weight. This latter fact cannot be over emphasized because every extra pound of insulation is one less pound of available payload weight.