Heavy lift launch vehicle
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A Heavy Lift Launch Vehicle, or HLV / HLLV, is an Orbital Launch Vehicle capable of lifting between 20,000 to 50,000kg to LEO.  The current Heavy-Lift Launch vehicles in service are the Ariane 5 in its ES variant and the United Launch Alliance Delta IV Heavy.
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[clarification needed] 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 V first stage and hypergolic propellants, such as unsymmetrical dimethylhydrazine and nitrogen tetroxide, used in the Proton rocket.
- NASA Space Technology Roadmaps - Launch Propulsion Systems, p.11: "Small: 0-2t payloads, Medium: 2-20t payloads, Heavy: 20-50t payloads, Super Heavy: >50t payloads"
- Mallove, Eugene F. and Matloff, Gregory L. The Starflight Handbook: A Pioneer's Guide to Interstellar Travel, Wiley. ISBN 0-471-61912-4.