Editing Reaction control system (section)

{{short description|Spacecraft thrusters used to provide attitude control and translation}}
{{More citations needed|date=September 2014}}

[[File:LM RCS.jpg|thumb|right|Two of four Reaction Control System thruster quads on the [[Apollo Lunar Module]]]]
A '''reaction control system''' ('''RCS''') is a spacecraft system that uses [[Thrusters (spacecraft)|thrusters]] to provide [[Spacecraft attitude control|attitude control]]<!-- DO NOT CHANGE THIS TO "altitude control"!!! --> and [[translation (physics)|translation]]. Alternatively, [[reaction wheels]] can be used for attitude control, rather than RCS. Use of diverted engine thrust to provide stable attitude control of a [[V/STOL|short-or-vertical takeoff and landing aircraft]] below conventional winged flight speeds, such as with the [[Hawker Siddeley Harrier#Controls and handling|Harrier "jump jet"]], may also be referred to as a reaction control system.<ref>{{Cite web |title="What is RCS?" by NASA in a PDF file. |url=https://ntrs.nasa.gov/api/citations/20130010548/downloads/20130010548.pdf}}</ref>

Reaction control systems are 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]] ([[aircraft principal axes|roll, pitch, and yaw]]).<ref>{{cite web |title=REACTION CONTROL SYSTEM |url=https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-rcs.html#sts-rcs |website=science.ksc.nasa.gov}}</ref>

Reaction control systems often use combinations of large and small ([[vernier thruster|vernier]]) thrusters, to allow different levels of response.