Hydrogen Is Working and It’s Much Cheaper Than We Thought

[OKIsItJustMe]

8. It’s difficult to say which comparison is valid or invalid, it’s a matter of priorities

Last edited Thu Aug 18, 2016, 12:04 PM - Edit history (1)

The Saturn V used kerosene “RP-1” in its first stage, and (liquid) hydrogen “LH₂” in its upper stages.

Why? Well, different priorities:


http://history.nasa.gov/SP-4206/ch6.htm

…

The upper stages of such a vehicle were critical to the eventual success of the mission-especially the top stage, which inserted the payload into the final, stabilized orbit. Douglas engineers were emphatic. "The overall performance of the end-stage has greater influence than the primary stages. The Saturn V launch vehicle for the lunar mission requires 50 pounds (23 kilograms) of booster weight at liftoff for each pound of payload injected into a translunar trajectory," they explained. "Without high-energy upper stages this factor would be significantly greater." The key to these high-energy stages was liquid hydrogen as the fuel. An engineer from Douglas, the eventual contractor of the S-IV and the S-IVB, summed up the significance of the decision to use liquid hydrogen. "The combination of hydrogen and oxygen for propellants made the moon shot feasible," he declared. "Its use in upper stages results in a significant increase in performance over the propellant combinations of oxygen and kerosene then in use in first-stage boosters."

…

http://history.nasa.gov/SP-4206/ch7.htm

…

When the contract to build the biggest stage of the Saturn V, the S-IC first stage, was awarded to Boeing on 15 December 1961, general outlines of the first-stage booster were already fairly well delineated. The main configuration of the S-IC had already been established by MSFC, including the decision to use RP-1, as opposed to the LH₂ fuel used in the upper stages. Although LH₂ promised greater power, some quick figuring indicated that it would not work for the first stage booster.

Liquid hydrogen was only one half as dense as kerosene. This density ratio indicated that, for the necessary propellant, an LH₂ tank design would require a far larger tank volume than required for RP-1. The size would create unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became the fuel. …

For the upper stages, the higher energy/mass ratio of hydrogen made it the winner. For the first stage, the higher energy/volume ratio of RP-1 made it the better choice.

The fundamental laws of physics remain the same today.