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A vernier thruster is a thruster used on a spacecraft for attitude control. It may be a smaller thrust motor than main attitude control motors,〔 or a small control thruster relative to the main propulsion motors,〔 or may be simply a small thruster of the reaction control system. Vernier thrusters are used for fine adjustments to the attitude or velocity of a spacecraft. Vernier thrusters are used when spacecraft control requirements, such as maneuvering during docking with other spacecraft, dictate a wide range of different thrust levels for attitude or velocity control. On space vehicles with two sizes of attitude control thrusters, the main ACS (Attitude Control System) thrusters are used for larger movements, while the verniers are reserved for smaller adjustments. As an alternative, larger thrusters fired for very short durations, or pulses, may be fired instead. Thus, by having a large pulse for a short amount of time, the same vernier end result is reached as when pulsing a much smaller jet for a longer period of time. ==Implementations== One type of vernier thruster is a smaller rocket engine used for attitude control in conjunction with a larger spacecraft propulsion engine. These were used on early Atlas missiles. Due to their weight and the extra plumbing required for their operation, vernier rockets are seldom used in new designs.〔 (【引用サイトリンク】title=Rocket Control: Examples of Controls )〕 However, the R-7 rocket family, with over seventeen hundred successful launches to date, is based on Vernier rocket design solution. The Space Shuttle reaction control system had six vernier engines or thrusters.〔 〕 During STS-130 commander Zamka and pilot Terry Virts used the space shuttle ''Endeavours vernier thrusters to reboost the International Space Station to its correct altitude. 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「vernier thruster」の詳細全文を読む スポンサード リンク
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