Rocket engine

A reaction engine that produces thrust by ejecting propellant, often without relying on surrounding air. Its exhaust carries momentum in the direction opposite the vehicle’s motion.

Rocket propulsion: Propulsion produced by ejecting mass to generate an equal and opposite reaction force. The general principle explains how an engine’s exhaust creates thrust.
Chemical rocket: A rocket that obtains exhaust energy from chemical reactions between propellants. Chemical engines are the most common high-thrust rocket engines.
Rocket stage: A separable section of a launch vehicle containing propulsion and other systems for part of a flight. Stages discard spent engines and tanks to reduce mass during ascent.
Gas-generator cycle: A rocket-engine cycle that burns some propellant in a separate turbine-driven generator and discards its exhaust. It powers turbopumps with a relatively simple cycle but sacrifices some propellant efficiency.
Specific impulse: A measure of rocket-propellant efficiency, expressed as thrust per unit weight flow. It compares how effectively different engines turn propellant into thrust.
Liquid-propellant rocket: A rocket engine that feeds liquid fuel and oxidizer into a combustion chamber. Its valves and feed system allow thrust control and, in some designs, restart.
Upper stage: The final powered stage of a launch vehicle, used to place payloads into their intended orbits or trajectories. Its engine often needs long burns and reliable restart in space.
Staged combustion cycle: A rocket-engine cycle that routes turbine-driving preburner gases into the main combustion chamber. Unlike gas-generator engines, it uses turbine exhaust rather than discarding it.
Nozzle: A shaped passage that controls and accelerates fluid flow, often converting pressure into directed velocity. Its geometry determines how exhaust expands and how much thrust the engine produces.
Solid-propellant rocket: A rocket motor whose fuel and oxidizer are mixed into a solid grain that burns after ignition. Its simple construction contrasts with engines that pump liquid propellants.

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