Propulsion Glossary

A component that injects and ignites additional fuel in the exhaust stream downstream of the turbine to produce extra thrust, commonly used in military jet engines.

A rocket propulsion system that uses two separate propellants, a fuel and an oxidizer, which are mixed and burned in the combustion chamber.

The ratio of the mass of air flowing through the bypass duct to the mass of air flowing through the engine core in a turbofan engine.

The pressure of combustion gases inside a rocket engine's combustion chamber, a key parameter affecting engine performance.

A simple propulsion device that expels a stored, pressurized inert gas through a nozzle to produce small amounts of thrust, often used for attitude control.

The section of a gas turbine engine that increases the pressure of incoming air before it enters the combustion chamber.

A nozzle shape that first narrows (convergent) then widens (divergent), used to accelerate exhaust gases from subsonic to supersonic velocities.

The total change in velocity that a propulsion system can impart to a spacecraft, used as the fundamental metric in mission planning.

The speed at which propellant gases exit the nozzle of a rocket engine, directly related to specific impulse and thrust.

A pivoting mount that allows a rocket engine nozzle to be tilted to change the direction of thrust, providing vehicle steering.

The shape of the internal bore of a solid rocket propellant grain, which determines how the burning surface area and thus thrust change over time.

Speeds greater than Mach 5, at which aerodynamic heating and real-gas effects become dominant design considerations.

An electric propulsion device that creates thrust by ionizing a propellant and accelerating the ions with an electric field to very high velocities.

The ratio of a rocket's total mass at ignition (wet mass) to its mass after all propellant has been consumed (dry mass).

A single chemical propellant that decomposes exothermically when passed over a catalyst, producing hot gas for thrust without a separate oxidizer.

A propulsion concept where a nuclear reactor heats a working fluid (typically hydrogen) to generate high-temperature exhaust for thrust.

A chemical substance that provides oxygen or another electron acceptor for combustion of the fuel in a propulsion system.

Any material ejected from a propulsion system to produce thrust, including chemical fuels, inert gases, and ionized particles.

A method of cooling rocket engine components by circulating one of the cryogenic propellants through channels in the chamber and nozzle walls before injection.

A supersonic combustion ramjet engine designed for hypersonic flight in which air flows through the engine at supersonic speeds throughout.

A propulsion technology that uses the momentum of photons from sunlight reflected off a large thin surface to generate continuous thrust without propellant.

The total impulse delivered per unit weight of propellant consumed, measured in seconds. The standard metric for comparing propulsion system efficiency.

The division of a launch vehicle into separate sections that are jettisoned sequentially to shed empty mass and improve the remaining mass ratio.

The ability to change the direction of the thrust force produced by a propulsion system, typically by gimbaling the engine or using secondary injection.

A high-speed turbine-driven pump that feeds liquid propellants into a rocket engine's combustion chamber at the required high pressures.