A cryogenic rocket engine is a rocket engine which utilizes a cryogenic fuel or oxidizer that implies fuel and oxidizer are liquefied gases stored at low temperatures. These engines were important factors for ultimate success to reach the Moon by the Saturn V rocket.
American and Soviet engineers discovered that rocket engines require high mass flow rate of fuel and oxidizer to generate a thrust in which oxygen and low molecular weight hydrocarbons used as fuel and oxidizer pair. Both are in gaseous state at room temperature and pressure. If propellants stored as pressurized gases then the size and mass of fuel tanks decrease efficiency of rocket to obtained the mass flow rate.
The combination of liquid hydrogen (LH2) fuel and liquid oxygen (LOX) oxidizer is widely used which are cheaply and easily available. It has the highest entropy released by combustion if burned.
Conclusion:
This Cryogenic Rocket Engine Hydrogen Fuel System project concludes that the cryopumps are turbo pumps which are powered through gas turbines differentiated into a bypass flow configuration or main flow configuration.
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