Nereus (underwater vehicle)

Being a hybrid ROV means that the vehicle could operate untethered or tethered with a thin optical fiber cable and operated by pilots aboard the ship. The latter enabled it to make deep dives while being highly maneuverable. The optical 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 pay out the fiber as the vehicle descends. This slim tether is smaller, lighter, and more cost-effective than cable. 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. In designing the vehicle, the design team led by Andy Bowen at the Woods Hole Oceanographic Institution relied on previous experience in developing autonomous underwater vehicles (AUVs) and tethered robots to build a hybrid ROV that could both fly like an aircraft to explore large areas of the ocean floor, but would be easily converted to able to hover over the small areas to conduct experiments or collect samples of rocks and sea life. ==Deepest dive==

in the Mariana Trench The Challenger Deep is located in the Western Pacific Ocean near the island of Guam in the Mariana Trench, the deepest known part of an ocean on Earth, and the deepest known location on Earth. The May 2009 dive by the Nereus achieved a depth of , making it the world's deepest-diving vehicle then in operation, and the first since 1998 to explore the Mariana Trench. Nereus is the third vehicle in the world to reach the bottom of the Pacific Ocean's Challenger Deep. The first was the crewed Bathyscaphe Trieste, which carried U.S. Navy Lieutenant Don Walsh and Swiss engineer Jacques Piccard and made the voyage on 23 January 1960. The Nereus dive aimed for the same spot. On 24 March 1995 a Japanese robotic deep-sea probe called Kaikō made the first uncrewed trip to the Challenger Deep. Once at the bottom, Nereus collected liquid and rock specimens. Patricia Fryer, co-chief scientist of the expedition, said the following about the samples. "We want to know how all of this relates to subduction around the globe, changes in the chemistry of the ocean in general and, therefore, potential effects those changes may have on ocean-atmosphere interactions and things like global climate change." ==Loss==

On 10 May 2014, at around 2 p.m. local time, Nereus was lost while conducting a dive at in depth in the Kermadec Trench, believed to be caused by extreme pressure at up to . Nereus was sent to complete the first systematic study of a deep-ocean trench as part of the NSF-sponsored Hadal Ecosystems Study (HADES) project under chief scientist Timothy Shank, a WHOI biologist who also helped conceive the vehicle. It was being controlled from the Research Vessel Thomas G. Thompson. Thirty days into the forty-day mission, about seven hours into a nine-hour dive, communications with Nereus were lost. When standard emergency recovery protocols were unsuccessful, the team initiated a search near the dive site. They then spotted several pieces of debris on the surface nearby later identified to be parts of Nereus, indicating a catastrophic implosion. The ship's crew recovered the debris to confirm its identity and to discover more information about the nature of the failure. Despite this, WHOI Director of Research Larry Madin stated that WHOI will continue to develop, build, and operate more underwater research craft for oceanographic exploration. ==References==