A booster, also known as a booster rocket, is the name given to any of three different components of a launch vehicle: (1) A stage of a launch system (see staging) used to provide an initial thrust greater than the total liftoff weight. (2) A rocket engine, either solid- or liquid-fueled, which assists the normal propulsive system or sustainer engine of a rocket or aeronautical vehicle in some phase of its flight. (3) A rocket used to set a launch vehicle in motion before another engine takes over. A booster assembly is a structure that supports one or more booster rockets.