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''Nereus'' was a hybrid unmanned autonomous underwater vehicle (HROV, a type of remotely operated underwater vehicle) built by the Woods Hole Oceanographic Institution (WHOI). Constructed as a research vehicle to operate at depths of up to , it was designed to explore Challenger Deep, the deepest surveyed point in the global ocean. ''Nereus'', named for Greek sea titan Nereus (who has a man's torso and a fish-tail) through a nationwide contest of high school and college students, began its deep sea voyage to Challenger Deep in May 2009 and reached the bottom on May 31, 2009. On this dive the ''Nereus'' reached a depth of , making the ''Nereus'' the world's second-deepest-diving vehicle in operation at the time, and the first since 1998 to explore the Mariana Trench, the deepest part of the ocean known.〔〔 On 10 May 2014, ''Nereus'' was lost while exploring the Kermadec Trench at a depth of . Communications were cut off at around 2 p.m. local time, and debris retrieved later revealed that it imploded due to high pressure. ==Hybrid design== Being a hybrid ROV means that the vehicle could operate untethered or tethered with a thin optic fiber cable and operated by pilots aboard the ship. The latter enabled it to make deep dives while being highly maneuverable.〔 〕 The optic fiber tether has the approximate diameter of a human hair, and can bear only . It is made up of a thin layer of plastic surrounding a slender glass fiber core. The vehicle carried approximately of cable wound in two small canisters that play out the fiber as the vehicle descends. This slim tether is smaller, lighter, and more cost effective than cable.〔 ''Nereus'' weighed approximately 3 tons in air and was about 4.25 meters (14 feet) long and 2.3 meters (8 feet) wide. Approximately 2,000 lithium-ion batteries provided its power. The vehicle made use of precisely designed ceramic spheres rather than the much heavier syntactic foam that is typically used for submersible vehicles. Each hull contained between 700 and 800 9-cm (3.5-inch) hollow spheres that were specifically designed to handle intense pressure. ''Nereus'' had a lightweight robotic manipulator arm to conduct the sample collecting that operates hydraulically and was able to perform under intense pressure.〔 〕 As an alternative to the tether, the ''Nereus'' could be switched to a free-swimming mode and operated as an autonomous vehicle to survey the ocean floor.〔 (【引用サイトリンク】title=Hybrid remotely operated vehicle 'Nereus' reaches deepest part of the ocean ) 〕 In designing the vehicle, the design team relied on previous experience in developing autonomous underwater vehicles (AUVs) and tethered robots to build a hybrid vehicle that could both fly like an aircraft to explore large areas of the ocean floor, but would be easily converted into a remotely operated vehicle (ROV) able to hover over the small areas to conduct experiments or collect samples of rocks and sea life.〔 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「Nereus (underwater vehicle)」の詳細全文を読む スポンサード リンク
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