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A reaction control system (RCS) is a spacecraft system that uses thrusters to provide attitude control, and sometimes translation. Use of diverted engine thrust to provide stable attitude control of a short-or-vertical takeoff and landing aircraft, below conventional winged flight speeds, such as the Harrier "jump jet", may also be referred to as a reaction control system. An RCS 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 (roll, pitch, and yaw). RCS systems often use combinations of large and small (vernier) thrusters, to allow different levels of response. Spacecraft reaction control systems are used: * for attitude control during re-entry; * for stationkeeping in orbit; * for close maneuvering during docking procedures; * for control of orientation, or 'pointing the nose' of the craft; * as a backup means of deorbiting; * as ullage motors to prime the fuel system for a main engine burn. Because spacecraft only contain a finite amount of fuel and there is little chance to refill them, some alternative reaction control systems have been developed so that fuel can be conserved. For stationkeeping, some spacecraft (particularly those in geosynchronous orbit) use high-specific-impulse engines such as arcjets, ion thrusters, or Hall effect thrusters. To control orientation, a few spacecraft, including the ISS, use momentum wheels which spin to control rotational rates on the vehicle. ==Location of thrusters on spacecraft== The Mercury space capsule and Gemini re-entry module both used groupings of nozzles to provide attitude control. The thrusters were located off their center of gravity, thus providing a torque to rotate the capsule. The Gemini capsule was also capable of adjusting its re-entry course by rolling, which directed its off-center lifting force. 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 manned spacecraft with translation as well as rotation capability. In-orbit attitude control was acheved by firing pairs of eight thrusters located around the circumference of its adapter module at the extreme aft end. Lateral translation control was provided by four thrusters around the circumference at the forward end of the adaptor module (close to the spacecraft's center of mass). Two forward-pointing thrusters at the same location, provided aft translation, and two thrusters located in the aft end of the adapter module provided forward thrust, which could be used to change the craft's orbit. The Apollo Command Module had a set of twelve hypergolic thrusters for attitude control, and directional re-entry control similar to Gemini. The Apollo Service Module and 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 centers of gravity, 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reaction control system」の詳細全文を読む スポンサード リンク
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