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''Huygens'' was an atmospheric entry probe that landed successfully on Saturn's moon Titan in 2005. Built and operated by the European Space Agency (ESA), it was part of the ''Cassini–Huygens'' mission and became the first spacecraft ever to land on Titan. The probe was named after the Dutch 17th-century astronomer Christiaan Huygens,〔(【引用サイトリンク】url=http://saturn.jpl.nasa.gov/mission/introduction )〕 who discovered Titan in 1655. The combined ''Cassini–Huygens'' spacecraft was launched from Earth on October 15, 1997.〔 ''Huygens'' separated from the ''Cassini'' orbiter on December 25, 2004, and landed on Titan on January 14, 2005 near the Xanadu region.〔(【引用サイトリンク】url=http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/The_mission )〕 This was the first and, so far, only landing ever accomplished in the outer Solar System.〔(【引用サイトリンク】url=http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Cassini-Huygens_mission_facts )〕 It touched down on land, although the possibility that it would touch down in an ocean was also taken into account in its design. The probe was designed to gather data for a few hours in the atmosphere, and possibly a short time at the surface. It continued to send data for about 90 minutes after touchdown. It remains the most distant landing of any human-made craft. == Overview == ''Huygens'' was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory to the surface. When the mission was planned, it was not yet certain whether the landing site would be a mountain range, a flat plain, an ocean, or something else, and it was hoped that analysis of data from ''Cassini'' would help to answer these questions. Based on pictures taken by ''Cassini'' at 1,200 km above Titan, the landing site appeared to be a shoreline. Assuming the landing site could be non-solid, ''Huygens'' was designed to survive the impact, splash down on a liquid surface on Titan, and send back data for several minutes on the conditions. If that occurred it was expected to be the first time a human-made probe would land in an extraterrestrial ocean. The spacecraft had no more than three hours of battery life, most of which was planned to be used during the descent. Engineers expected to get at most only 30 minutes of data from the surface. The ''Huygens'' probe system consists of the 318 kg probe itself, which descended to Titan, and the probe support equipment (PSE), which remained attached to the orbiting spacecraft. ''Huygens'' The probe remained dormant throughout the 6.7-year interplanetary cruise, except for semiannual health checks.〔(【引用サイトリンク】url=http://huygensgcms.gsfc.nasa.gov/Mission.htm )〕 These checkouts followed preprogrammed descent scenario sequences as closely as possible, and the results were relayed to Earth for examination by system and payload experts. Prior to the probe's separation from the orbiter on December 25, 2004, a final health check was performed. The "coast" timer was loaded with the precise time necessary to turn on the probe systems (15 minutes before its encounter with Titan's atmosphere), then the probe detached from the orbiter and coasted in free space to Titan in 22 days with no systems active except for its wake-up timer. The main mission phase was a parachute descent through Titan's atmosphere. The batteries and all other resources were sized for a ''Huygens'' mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at least 3 additional minutes (and possibly a half hour or more) on Titan's surface. The probe's radio link was activated early in the descent phase, and the orbiter "listened" to the probe for the next 3 hours, including the descent phase, and the first thirty minutes after touchdown. Not long after the end of this three-hour communication window, ''Cassini'' Very large radio telescopes on Earth were also listening to ''Huygens'' The signal strength received on Earth from ''Huygens'' was comparable to that from the ''Galileo'' probe (the Jupiter atmospheric descent probe) as received by the VLA, and was therefore too weak to detect in real time because of the signal modulation by the (then) unknown telemetry. Instead, wide-band recordings of the probe signal were made throughout the three-hour descent. After the probe telemetry was finished being relayed from ''Cassini'' to Earth, the now-known data modulation was stripped off the recorded signal, leaving a pure carrier that could be integrated over several seconds to determine the probe frequency. It was expected that through analysis of the Doppler shifting of ''Huygens'' 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「Huygens (spacecraft)」の詳細全文を読む スポンサード リンク
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