Thermal rockets use an inert propellant, heated by electricity ( electrothermal propulsion) or a nuclear reactor ( nuclear thermal rocket).Ĭhemical rockets are powered by exothermic reduction-oxidation chemical reactions of the propellant: Here, "rocket" is used as an abbreviation for "rocket engine". Rocket engines become more efficient at high speeds, due to the Oberth effect. The ideal exhaust is hydrogen, the lightest of all elements, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket vehicles carry their own oxidiser, unlike most combustion engines, so rocket engines can be used in a vacuum to propel spacecraft and ballistic missiles.Ĭompared to other types of jet engine, rocket engines are the lightest and have the highest thrust, but are the least propellant-efficient (they have the lowest specific impulse). Vehicles propelled by rocket engines are commonly called rockets. Most rocket engines use the combustion of reactive chemicals to supply the necessary energy, but non-combusting forms such as cold gas thrusters and nuclear thermal rockets also exist. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordance with Newton's third law. RS-68 being tested at NASA's Stennis Space Center Viking 5C rocket engine used on Ariane 1 through Ariane 4Ī rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. For reaction engines not possessing a de Laval nozzle, see Reaction engine. For rocket-propelled vehicles, see Rocket. This article is about a type of reaction engine.
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