Editing Reaction control system (section)

==Location of thrusters on spacecraft==
[[File:Rcs-gemini.jpg|thumb|left|Gemini [[Orbit Attitude and Maneuvering System]], and Reentry (mislabeled "Reaction”<ref>{{Cite web |title=Project Gemini - A Chronology. Part 1 (B) |url=https://www.nasa.gov/history/SP-4002/p1b.htm |access-date=2024-08-27 |website=www.nasa.gov}}</ref>) Control System]]
The [[Project Mercury|Mercury]] [[space capsule]] and [[Project Gemini|Gemini]] reentry module both used groupings of nozzles to provide [[Spacecraft attitude control|attitude control]]. The thrusters were located off their [[center of mass]], thus providing a [[torque]] to rotate the capsule. The Gemini capsule was also capable of adjusting its reentry course by rolling, which directed its off-center lifting force.{{clarification needed |date=September 2022}} The Mercury thrusters used a [[hydrogen peroxide]] monopropellant which turned to steam when forced through a [[tungsten]] screen, and the Gemini thrusters used [[hypergolic]] [[mono-methyl hydrazine]] fuel oxidized with [[nitrogen tetroxide]].

The Gemini spacecraft was also equipped with a hypergolic [[Orbit Attitude and Maneuvering System]], which made it the first crewed spacecraft with [[translation (physics)|translation]] as well as rotation capability. In-orbit attitude control was achieved by firing pairs of eight {{convert|25|lbf|N|adj=on}} thrusters located around the circumference of its adapter module at the extreme aft end. Lateral translation control was provided by four {{convert|100|lbf|N|adj=on}} thrusters around the circumference at the forward end of the adaptor module (close to the spacecraft's center of mass). Two forward-pointing {{convert|85|lbf|N|adj=on}} thrusters at the same location, provided aft translation, and two {{convert|100|lbf|N|adj=on}} thrusters located in the aft end of the adapter module provided forward thrust, which could be used to change the craft's orbit. The Gemini reentry module also had a separate Reentry Control System of sixteen thrusters located at the base of its nose, to provide rotational control during reentry.

The [[Apollo command and service module|Apollo Command Module]] had a set of twelve hypergolic thrusters for attitude control, and directional reentry control similar to Gemini.

The Apollo [[Apollo command and service module|Service Module]] and [[Apollo Lunar Module|Lunar Module]] each had a set of sixteen [[R-4D]] hypergolic thrusters, grouped into external clusters of four, to provide both translation and attitude control. The clusters were located near the craft's average centers of mass, and were fired in pairs in opposite directions for attitude control.

A pair of translation thrusters are located at the rear of the Soyuz spacecraft; the counter-acting thrusters are similarly paired in the middle of the spacecraft (near the center of mass) pointing outwards and forward. These act in pairs to prevent the spacecraft from rotating. The thrusters for the lateral directions are mounted close to the center of mass of the spacecraft, in pairs as well.{{citation needed|date=March 2013}}

===Location of thrusters on spaceplanes===
[[File:Shuttle front RCS.jpg|thumb|250px|RCS thrusters on the nose of [[Space Shuttle Discovery|''Discovery'']], a [[Space Shuttle orbiter]].]]

The suborbital [[North American X-15|X-15]] and a companion training aero-spacecraft, the [[Lockheed NF-104A|NF-104 AST]], both intended to travel to an altitude that rendered their aerodynamic control surfaces unusable, established a convention for locations for thrusters on winged vehicles not intended to dock in space; that is, those that only have attitude control thrusters. Those for pitch and yaw are located in the nose, forward of the cockpit, and replace a standard radar system. Those for roll are located at the wingtips. The [[Boeing X-20 Dyna-Soar|X-20]], which would have gone into orbit, continued this pattern.

Unlike these, the [[Space Shuttle orbiter|Space Shuttle Orbiter]] had many more thrusters, which were required to control vehicle attitude in both orbital flight and during the early part of atmospheric entry, as well as carry out rendezvous and docking maneuvers in orbit. Shuttle thrusters were grouped in the nose of the vehicle and on each of the two aft [[Space Shuttle Orbital Maneuvering System|Orbital Maneuvering System]] pods. No nozzles interrupted the heat shield on the underside of the craft; instead, the nose RCS nozzles which control positive pitch were mounted on the side of the vehicle, and were canted downward. The downward-facing negative pitch thrusters were located in the [[Space Shuttle Orbital Maneuvering System|OMS]] pods mounted in the tail/afterbody.