Team SPAWAR's fiber-optic technology helps Nereus reach deepest part of the ocean.
The unique hybrid-vehicle design of Nereus makes it ideally suited to explore the ocean's last frontiers. The unmanned vehicle is remotely operated by pilots aboard a surface ship via a lightweight, micro-thin, fiber-optic tether that allows Nereus to dive deep and be highly maneuverable.
The tethering system presented one of the greatest challenges in developing a cost-effective remotely operated vehicle (ROV) capable of reaching these depths. Traditional robotic systems use steel-reinforced cables containing copper wires to power the vehicle and optical fibers to enable information to be passed between the ship and the vehicle. If such a cable were used to reach the seafloor in the Mariana Trench, it would snap under its own weight.
Solving the Challenge
To solve the challenge, the Nereus team adapted fiber-optic technology developed by SSC Pacific to carry real-time video and other data between the Nereus and the surface crew. Similar in diameter to a human hair and with a breaking strength of only 4 kilograms (8.8 pounds), the tether is composed of glass fiber core with a very thin protective jacket of plastic.
Nereus brings approximately 40 kilometers (25 miles) of cable in two canisters the size of large coffee cans that spool out the fiber as needed. By using this very slender tether, instead of a large cable, the team was able to decrease the size, weight, complexity and cost of the vehicle.
To reach the trench, Nereus dove nearly twice as deep as research submarines are capable of and had to withstand pressures 1,000 times of that at Earth's surface--crushing forces similar to those on the surface of Venus. Only two other vehicles have succeeded in reaching the trench: the U.S. Navy-built bathyscaphe Trieste, which carried Jacques Piccard and Don Walsh there in 1960, and the Japanese-built robot Kaiko, which made three unmanned expeditions to the trench between 1995 and 1998.
Neither of these is presently available to the scientific community. Trieste was retired in 1966, and Kaiko was lost at sea in 2003.
The Nereus engineering team knew that to reach these depths, a tethered robot using traditional technologies would be prohibitively expensive to build and operate. So they used unique technologies and innovative methods to strike a balance between size, weight, materials cost and functionality. Building on previous experience in developing tethered robots and autonomous underwater vehicles (AUVs), the team fused the two approaches together to develop a hybrid vehicle that could fly like an aircraft to survey and map broad areas and then be converted at sea into a tethered ROV that can hover like a helicopter near the seafloor to conduct experiments or to collect biological or rock samples under real-time human control.
The present trials of Nereus are being conducted in this tethered ROV mode of operation. Nereus can also be switched into a free-swimming, autonomous vehicle.
Reaching the bottom
On its dive to the Challenger Deep, Nereus spent more than 10 hours on the bottom, sending live video back to the ship through its fiber-optic tether and collecting geological and biological samples with its manipulator arm. It also placed a marker on the seafloor signed by those aboard the surface ship.
"We couldn't be prouder of the stunning accomplishments of this dedicated and talented team," said Susan Avery, president and director of Woods Hole Oceanographic Institution.
"With this engineering trial successfully behind us, we're eager for Nereus to become widely used to explore the most inaccessible reaches of the ocean. With no part of the deep seafloor beyond our reach, it's exciting to think of the discoveries that await."
The dive makes Nereus the world's deepest-diving vehicle and the first vehicle to explore the Mariana Trench since 1998.
For more information, go to the SPAWAR Web site: http://enterprise.spawar.navy.mil/.
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|Date:||Jul 1, 2009|
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