Thrusters (spacecraft)
Thruster is a propulsive device used by spacecraft for station keeping, altitude control, in the reaction control system, or long-duration, low-thrust acceleration. A vernier engine or gimbal engine is a particular case used on launch vehicles where a secondary rocket or other high thrust device is used to control the attitude of the rocket while the primary thrust engine (generally also a rocket engine) is fixed to the rocket and supplies the principal amount of thrust. Some devices that are used or proposed to use as thrusters are: