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An atmospheric satellite (US usage, abbreviated atmosat) or pseudo-satellite (British usage) is an unmanned aerial vehicle (UAV) that operates in the atmosphere at high altitudes for extended periods of time. Atmosats are generally powered by solar panel arrays and rechargeable batteries or fuel cells, though a balloon-based system is also under development. Atmospheric satellites are distinguished from low earth orbit satellites, which orbit above the atmosphere. ==Development history== The initial goals under the NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project were to demonstrate sustained flight at an altitude near 100,000 feet and flying non-stop for at least 24 hours, including at least 14 hours above 50,000 feet. The early development path of atmospheric satellites included the NASA Pathfinder (exceeding 50,000 feet in 1995), the Pathfinder Plus (80,000 feet in 1998), and the NASA Centurion which was modified into a prototype configuration for the NASA Helios (96,000 feet in 2001).〔 An Airbus/Qinetiq Zephyr clocked up a 14-day flight in the summer of 2010 and in 2014 a Zephyr 7 stayed up for 11 days in the short days of winter whilst carrying a small payload for the British Ministry of Defence. In 2014, the development goals of Titan Aerospace, purchased by Google,〔(【引用サイトリンク】publisher = ''The New York Times'' )〕 included operation at altitudes exceeding 60,000 feet for as long as five years.〔 ==Vehicle design and operation, and enabling technology== An atmospheric satellite may initially ascend at night under battery power, and reach altitude soon after dawn to allow solar panels to take advantage of a full day's sunlight. To enable nighttime operation and ensure endurance through consecutive 24-hour day/night cycles, in daylight hours solar panels charge batteries〔 or fuel cells〔 which subsequently power the vehicle during hours of darkness. A desired operating altitude is in the tropopause—at approximately 65,000 feet—where winds are generally less than 5 knots and clouds do not block sunlight. It is desirable in the United States to operate above 60,000 feet, above which the Federal Aviation Administration does not regulate the airspace.〔 ==Competing technologies== Atmospheric satellites are thought to be able to perform duties more economically and with more versatility than low earth orbit satellites,〔 which are less well suited for border security, maritime traffic monitoring, anti-piracy operations, disaster response, and agricultural observation.〔 The NASA and Titan Aerospace designs use propeller-driven aircraft, in contrast to Google's Project Loon which envisions using high-altitude balloons.〔〔(Google Buys Solar-Powered Drones to Expand Internet Access, Accessed April 22, 2014 )〕 ==Applications== Applications include atmospheric observation, weather monitoring, communications relay, oceanographic research, and earth imaging〔 as well as disaster recovery and Internet communication, with Facebook reportedly envisioning providing Internet access to the African continent with a fleet of 11,000 vehicles.〔 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「Atmospheric satellite」の詳細全文を読む スポンサード リンク
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