“…our building’s shaking here. Our building’s shaking! Oh it’s terrific, the building’s shaking! This big blast window is shaking! We’re holding it with our hands! Look at that rocket go into the clouds at 3000 feet!…you can see it…you can see it…oh the roar is terrific!…” Walter Cronkite – Apollo 4 launch.
The key to high-energy stages was to use liquid hydrogen as the fuel. Liquid hydrogen fuel appealed to rocket designers because of its high specific impulse, which is a basic measure of rocket performance. Specific Impulse is the impulse delivered per unit of propellant consumed. You might think of it as the efficiency of the rocket. Compared to an RP-1 (kerosene) fueled engine of similar size, liquid hydrogen fuel could increase the specific impulse or efficiency of an engine by 40 percent. The combination of hydrogen and oxygen for propellants made the moon shot feasible.
After viewing the Apollo spaceport being built in Florida, President Kennedy flew on to Huntsville, Alabama. There, during a tour of Marshall and a briefing on the Saturn V and the lunar-rendezvous mission by von Braun, Jerome Wiesner interrupted Von Braun in front of reporters, saying, “No, that’s no good.” Webb immediately defended von Braun and lunar-orbit rendezvous. The adversaries engaged in a heated exchange until the President stopped them, stating that the matter was still subject to final review.
“I would like to reiterate once more that it is absolutely mandatory that we arrive at a definite mode decision within the next few weeks. . . . If we do not make a clear-cut decision on the mode very soon, our chances of accomplishing the first lunar expedition in this decade will fade away rapidly.” Wernher Von Braun June 7, 1962.