Reaction Control System

(From Memory Alpha)

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

RCS systems often used combinations of large and smaller thrusters, to allow different levels of response from the combination.

Reaction control systems were 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