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A reduced gravity aircraft is a type of fixed-wing aircraft that provides brief near-weightless environments for training astronauts, conducting research and making gravity-free movie shots. Versions of such airplanes, officially nicknamed Weightless Wonders,〔(NASA "Weightless Wonder" )〕 were operated by the NASA Reduced Gravity Research Program. The unofficial nickname "vomit comet" became popular among those who experienced their operation.〔http://www.nasa.gov/audience/forstudents/brainbites/nonflash/bb_home_vomitcomet.html〕 == Operating principles == The aircraft gives its occupants the sensation of weightlessness by following an elliptic flight path relative to the center of the Earth.〔William Tyrrell Thomson, Introduction to Space Dynamics, Dover 1986. p. 91.〕 While following this path, the aircraft and its payload are in free fall at certain points of its flight path. The aircraft is used in this way to demonstrate to astronauts what it is like to orbit the Earth. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness. Initially, the aircraft climbs with a pitch angle of 45 degrees using engine thrust and elevator controls. The sensation of weightlessness is achieved by reducing thrust and lowering the nose to maintain a neutral, or "straight and level" configuration (0 degree angle of attack). Weightlessness begins while ascending and lasts all the way "up-and-over the hump", until the craft reaches a downward pitch angle of 30 degrees. At this point, the craft is pointed downward at high speed, and must begin to pull back into the nose-up attitude to repeat the maneuver. The forces are then roughly twice that of gravity on the way down, at the bottom, and up again. This lasts all the way until the aircraft is again halfway up its upward trajectory, and the pilot again reduces the thrust and lowers the nose. This aircraft is used to train astronauts in zero-g maneuvers, giving them about 25 seconds of weightlessness out of 65 seconds of flight in each parabola. During such training the airplane typically flies about 40–60 parabolic maneuvers. In about two thirds of the passengers, these flights produce nausea due to airsickness, giving the plane its nickname "vomit comet". 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「Reduced gravity aircraft」の詳細全文を読む スポンサード リンク
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