The development of a new type of deep-sea vehicle sporting unique technologies and innovative methods to strike a balanace between size, weight, materials cost and functionality has made it possible to routinely reach the bottom of the ocean.
Last month, the Woods Hole Oceanographic Institution (WHOI) announced the successful dive of a new type of deep-sea robotic vehicle called Nereus to the deepest part of the world’s ocean. Nereus reached a depth of 10,902 meters (6.8 miles) last May 31, 2009, at the Challenger Deep in the Mariana Trench in the western Pacific Ocean.
The Nereus engineering team knew that, to reach maximum depths, they needed to develop a new type of deep-sea vehicle. The greatest challenge was developing a tethering system that would not snap under its own weight. To solve this challenge, the team adapted fiber-optic technology developed by the Navy’s Space and Naval Warfare Systems Center Pacific (SSC Pacific) to carry real-time video and other data between the Nereus and the surface crew.
Andy Bowen, a WHOI engineer that led the efforts to developed Nereus, spoke about the new technology in the cable that links it to the ship in an interview with Oceanus, the organization’s magazine and website:
“The tether is a specially designed glass fiber that allows the transmission of digital information, we can transmit video signals and data from sensors up from Nereus, and then we send commands down to Nereus to “turn left,” “go up,” “move your arm,” “pick up this object” — those types of things as, unlike on land, there are no digital signals in the ocean. Outside the glass fiber is a very thin layer of plastic that protects the fiber from contact with seawater or air. All of that is about the diameter of a human hair.
Nereus has its own batteries onboard to provide power, and it can swim back to the ship on its own. So we can dispense with the copper for power and the steel for strength, and use only a light optical fiber cable to allow bi-directional passage of information to and from the vehicle.”
Another weight-saving advance of the vehicle is its use of ceramic spheres for flotation, rather than the much heavier traditional syntactic foam, which only withstands pressures of depth of about 6,000 meters.
Don Peters, one of the five engineers who developed Nereus, spoke about the development of this new floating device in an interview with Oceanus:
“Ceramics, when compressed, have about fives times the strength of steel, but weigh about a third as much. They are a relatively inexpensive raw material.
In looking at the options, we were aware of a fellow named Jerry Stachiw, who had done by far the most experimental work developing ceramic pressure housings for the Navy. It turned out that he had also been looking into making seamless ceramic spheres for flotation.
Then we became aware that a company called DeepSea Power & Light had already done a lot of work testing and verifying 3½-inch ceramic spheres for a use in the oil-production industry.
This material is very strong when you push on it, but it’s also very brittle and capable of breaking. The external pressure we’re putting the sphere under is completely uniform—from the water around it. The spheres are as circular in all directions as can be manufactured, and that geometry distributes the load uniformly in all directions along the skin of the sphere. So even though the spheres are about the thickness of a tortilla chip, about 50/1,000ths of an inch thick, they can handle a lot of compression.”
Each of Nereus’s two hulls contains approximately 800 of the ~9-centimeter (3.5-inch) hollow spheres.
WHOI engineers also modified a hydraulically operated robotic manipulator arm to operate under intense pressure and make effective use of the vehicle’s limited battery power.
With its tandem hull design, Nereus weighs nearly 3 tons in air and is about 4.25 meters (14 feet) long and approximately 2.3 meters (nearly 8 feet) wide. It is powered by more than 4,000 lithium-ion batteries.
Funding to develop Nereus was provided by the National Science Foundation, the Office of Naval Research, the National Oceanic and Atmospheric Administration, the Russell Family Foundation, and WHOI.
To read the full interview with Andy Bowen visit “Miles Under the Sea, Hanging on by Hair-Thin Fiber” and with Ron Peter visit “Floating without Imploding”
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC