Nereus: WHOI’s Hybrid Deep-Sea Vehicle

Engineers at Woods Hole Oceanographic Institution have been working with Nereus a unique vehicle that can reach depths over 6 miles deep. The $8 million dollar vehicle was developed to withstand crushing pressure; about 1,000 times the pressure exerted at sea level. Nereus is a combination of two different types of vehicles. It can operate as a Remotely Operated Vehicle (ROV) or as an Autonomous Underwater Vehicle or (AUV). While operating as an AUV the vehicle can cover large areas of the seafloor while mapping the areas with cameras, sensors, and sonar. It can also be converted to an ROV onboard the ship so that pilots can hover over an area to get images or collect samples. Because of the vehicles smaller size it can be launched from smaller vessels that are less costly to operate. One of the challenges the engineers faced was in creating an ROV tether that could reach the depth capable by Nereus. Traditional robotic systems use heavy, steel-reinforced cables containing copper wires to power the vehicle and optical fibers to transmit information between the ship and the vehicle. Such a cable, extended to reach the seafloor in the Mariana Trench, would snap under its own weight. To solve this challenge, the Nereus team adapted fiber-optic technology developed by the Navy’s Space and Naval Warfare Systems Center Pacific to carry real-time video and other data between Nereus and the surface crew. The tether is composed of a glass fiber core with a very thin protective jacket of plastic. It is about as wide as a human hair, weighs less than a kilogram, and will break if a force of only 4 kilograms (8.8 pounds) is applied. As Nereus descends, it spools out up to 40 kilometers (25 miles) of micro-fiber tether from two canisters the size of large coffee cans. If the fiber breaks the vehicle turns into an AUV and returns back to the ship. Nereus has successfully made it to the deepest part of the ocean in the Mariana Trench known as the Challenger Deep, which is approximately 36,000 feet deep.