an auxiliary rocket engine mounted on an aircraft or missile and used to boost acceleration during launch. Booster rockets have operating times substantially shorter than that of the main engine and high ratios of thrust to the launch weight of the vehicle (for booster rockets on missiles). Solid-propellant rocket engines with up to several tens of kilonewtons of thrust and operating times up to several seconds are usually used as booster rockets; liquid-propellant rocket engines are also used, but rarely. Booster rockets are used for airplanes, high-altitude research rockets, and winged rockets. The engines of the first stages of launch vehicles are often called booster rockets if they are constructed in unit with later stages.