Propellant Requirements
Several different fuel/oxidiser combinations have been used in heavy lift launch vehicles. The earliest ones were simply liquid hydrogen and liquid oxygen, which, when combined, release a very significant amount of energy, and whose only combustion byproducts are heat and water vapor. This approach was used for the main engines of the Space Shuttle and for the upper stages of the Saturn V, and is still used for the main engines on some HLLVs, such as the Ariane 5 and Delta IV. It is also often used for upper-stage motors, due to its high specific impulse.
Other propellant options include those used by solid-fuel rockets, combinations of various liquid fuels such as RP-1 and liquid oxygen as used in the Atlas 5 first stage or in both the main and upper stages of the Falcon Heavy, and hypergolic propellants, such as unsymmetrical dimethyl hydrazine and nitrogen tetroxide, used in the Proton rocket.
Read more about this topic: Heavy Lift Launch Vehicle