reaction control system
A reaction control system (abbreviated RCS) is a subsystem of a spacecraft. Its purpose is attitude control and steering. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow control of rotation (pitch, yaw, and roll). This is in contrast to a spacecraft's main engine, which is only capable of providing thrust in one direction, but is much more powerful.
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