Reaction Control System
A system of small thrusters used for attitude control and small trajectory adjustments on spacecraft and launch vehicle upper stages.
Explanation
A reaction control system (RCS) uses small thrusters, typically burning hydrazine or a hypergolic bipropellant, to produce precise low-thrust maneuvers. RCS thrusters are used for three-axis attitude control (pitch, yaw, roll), station keeping, docking approach, propellant settling, and small delta-v corrections. They are distinct from reaction wheels, which provide finer control but cannot change the spacecraft's net momentum. RCS thrusters are valued for their ability to produce both torque and translation from a single system. Most spacecraft carry multiple RCS thrusters arranged around the body for full six-degree-of-freedom control. The International Space Station uses large RCS thrusters for reboost and attitude control. RCS propellant is often the limiting factor for mission life once the primary propulsion system is exhausted.
Why It Matters
RCS provides the maneuvering capability that separates a passive satellite from an actively controlled spacecraft. Without it, satellites cannot maintain orientation, avoid collisions, or perform orbital adjustments.
Concept Map
How Reaction Control System connects to other glossary terms:
Frequently Asked Questions
How are RCS thrusters different from main engines?
RCS thrusters produce much lower thrust (typically 1-100 N) and are designed for precision and frequent firing, unlike main engines which produce high thrust for major burns.
What propellant do RCS thrusters use?
Most use hydrazine or hypergolic bipropellants (nitrogen tetroxide and hydrazine derivatives). Some modern systems use cold gas or green propellants.
Sources
Last updated: July 1, 2026