As America continued to chafe from the Soviet’s expanding space feats, Congress asked a fledgling NASA to develop a heavy launch vehicle to match the Soviet’s lifting capacity. They wanted a 1.5 million pound thrust rocket, and they wanted it quickly.
NASA officials turned to the team that had put our first satellite into orbit with a two month lead time, and since had orbited other heavier payloads with their Juno launch vehicle, based on the Army’s Jupiter IRBM—the Werner von Braun team at Marshall Spaceflight Center in Huntsville, AL. There was no existing military vehicle powerful enough to base such a booster on. Von Braun would have to design a new rocket. But the time constraints did not give him time to design and develop a completely new vehicle. He would have to use existing hardware and equipment.
The team already had a design in hand, developed under an Advanced Research Projects Agency (ARPA) contract. This contract was handed over to NASA. This would be the vehicle to test Apollo in Earth orbit.
The design used a Jupiter tank as a central structure. It was surrounded by eight lengthened Redstone tanks. The center tank and 
four of the Redstone tanks held LOX (Liquid Oxygen). The other four tanks held RP-1—very high grade kerosene. These would be mounted on a square thrust plate, and feed eight uprated Jupiter engines, each generating 188,000 pounds of thrust. For the new vehicle, these engines were given the new designation as H1s. The four outboard engines were gimbaled for steering.
This new booster would be bigger than anything that had been used up to that time. It would be 81 feet tall and 22 feet in diameter.
For the second stage, von Braun’s team turned to a new technology, being proven with the Atlas/Centaur vehicle—liquid hydrogen—LH2.
A rocket’s velocity is determined by two major factors—its mass ratio (MR) and the exhaust velocity of its propellants. Mass ratio is the difference in the mass of the rocket fully fueled, and its' mass when all the fuel and empty mass is discarded. That is why all space rockets are multi staged. As the lower stages are discarded, the mass ratio goes up.
The exhaust velocity of various propellant combinations varies widely. The LOX/RP-1 combination produces an exhaust velocity of about 7400 mph. LOX/LH2 produces an exhaust velocity of 15,000 mph. As the MR approaches 3, a rocket can reach the exhaust velocity of its propellants. If the MR exceeds 3, the rocket’s velocity can exceed the exhaust velocity of its propellants.
RP-1 is easy to store and handle. LOX had been in use since the V-2 days, so despite its -119 degree C (-182 F) temperature, its handling was no problem.
LH2 was another story. Its temperature is -252 C (-423 F). That is not too far above absolute zero (-273 C or -459 F—the temperature at which all molecular motion ceases). This made storage and handling difficult.
For the Centaur stage, which held some 17,000 lbs of LH2, these problems were minimized. For the new space launcher, now being called Saturn 1, and its second stage, now dubbed the S-1V, they would be maximized. The S-IV would hold 39,600 lbs of LH2. That required larger, well insulated storage tanks, and similarly constructed lines running to the launch pad.
There is another problem with LH2. It is highly flammable. The slightest spark can ignite it should the lines or a tank spring a leak which they did at one time during flight tests of the Saturn 1. And a hydrogen fire is virtually invisible because it burns so cleanly. In the case of the incident I noted, the fire was burning for several minutes before anyone knew there was a problem. We could not see any flames or indication of fire.
The storage tanks therefore had to be placed some distance from the pad, requiring long feeder lines to the pad. In the photo, the LH2 and LOX storage tanks are to the right.
The big S-IV stage was about 40 feet long and 18 feet in diameter. It was powered by six Centaur RL-10 engines, each producing 15,000 pounds of thrust.
In the original design, a Centaur was to be a third stage for satellite launches, but this configuration was never flown as the lunar program proceeded so quickly and budget cuts hit the Saturn program.