The 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 (flight dynamics, pitch, yaw, and roll). This is contrast to a spacecraft's main engine, which is only capable of providing thrust in one direction, but is much more powerful.
RCS systems often use combinations of large and smaller thrusters, to allow different levels of response from the combination.
Reaction control systems are used:
* for attitude control during re-entry
* for stationkeeping in orbit
* for close space rendezvous/maneuvering during docking procedures
* for control of orientation, or 'pointing the nose' of the craft
* as a backup means of de-orbiting
The reaction control thrusters are the standard thrusters used by the Federation for low-velocity propulsion, station-keeping and maneuvering control in space.