To Explore the Deepest Ocean, Nereus Past and Nereus Future Have One Thing in Common

An artist's concept of old Nereus, part human and part marine creature

"Old" Nereus

Pop Quiz for those who have not read the headline! Which Nereus changes its shape—the old and wise mythological Greek god of the sea, or the new Nereus, under development to explore 35,000 feet (11,000 meters) deep--to the very bottom of the ocean where no other exploration or research vehicle can reach?

In Greek mythology, “Nereus" was a god of the sea with power to foretell the future, but he would not answer questions unless he was caught and to avoid that he would change his shape.

The new Nereus will be a next-generation ocean exploration system, and it is very much in the business of changing its shape.

For years remotely operated vehicles (ROVs) have used armored cables to connect ship-based operators to complex undersea vehicles. In recent decades a new class of robots, autonomous underwater vehicles (AUVs) have cut the cord.

Views of Nereus as an untethered AUV and a tethered ROV

"New" Nereus in both AUV and ROV modes. Credit: Jack Cook, Woods Hole Oceanographic Institution

The new Nereus exhibits something of a split personality in that it can be a tethered ROV, or an untethered programmed AUV. In its basic AUV mode it is much like other AUVs. It accepts mission programming and executes the mission on its own without operator feedback. It then returns to the ship and offers up its data to the waiting scientists. But then it can change modes. By adding a ROV module, additional lights, cameras and sampling tools are added to the vehicle, and it operates at the end of a wire connected to a “pilot” who controls the vehicle using a joystick on the research vessel.

So, the new Nereus is a hybrid ROV—an HROV—a novel combination of technologies yielding a new class of undersea systems, able to change as mission requirements change. The old Nereus would be proud.

What does it all mean? No existing undersea research vehicle, manned or robotic, can operate below 21,000 feet (6,500 meters). After sea trials to 19,500 feet (6,000 meters) in the Fall of 2007, and when Nereus becomes operational at 11,000 meters in the Spring of 2008, it will reign supreme in the bottom 14, 500 feet (4,500 meters) of the ocean. NOAA’s Ocean Exploration program hopes to host the HROV on its new ship, the Okeanos Explorer, for a voyage back to the seafloor in 2008.

Among other missions, the new Nereus will use a wide variety of new technology to take sensors, lights, cameras and a manipulator arm to the deepest ocean areas—to the bottom of trenches formed where one tectonic plate is subducted under another. Plate pressures, when suddenly released in those areas, have produced undersea earthquakes, landslides and tsunamis, and Nereus will be a valuable new tool to survey and sample those deep areas.

The $6 million HROV is being developed by engineers at the Woods Hole Oceanographic Institution (WHOI) Deep Submergence Lab who are using the best of 21st century technology to develop this new tool to bring science to the depths. Major funding is from the National Science Foundation with additional funds from NOAA’s Office of Ocean Exploration and Undersea Research Program. The HROV is also funded by the Navy, and its Space and Naval Warfare Systems Command laboratory in San Diego is adapting Navy technology in wire guidance for use with Nereus.

Matt Heintz holding a sample of fiber optic cable 1/32 of an inch thick.

Matt Heintz holding a sample of fiber optic cable 1/32 of an inch thick. Credit: Tom Kleindinst, Woods Hole Oceanographic Institution

The small fiber tether is a big part of the hybrid’s operation in the ROV mode, and it’s a great example of how Nereus will employ advanced technology. Other deep-sea ROV’s require sizable shipboard winches and large reels spooled with heavy armored wire, and the shipboard support system can be the size of a large motor home. The micro-thin fiber optic tether that trails out as far as 25 miles to Nereus, fits in a box the size of a small microwave oven. With this reduction in size and weight, Nereus may be deployed on smaller vessels including those without Dynamic Positioning, a satellite-based ship’s positioning system that is critical to safe operation of traditional heavy ROVs.

Nereus’ tether is so thin that a 9-pound bass would exceed its breaking load, so Nereus is programmed to operate as an AUV when separated from its ROV tether. Andy Bowen, WHOI’s Project Manager for Nereus, is confident about the hybrid’s ability to find its way home.

“The vehicle knows where it is and tracks its progress underwater through acoustic and inertial navigation systems,” he said. “It will find its way back to the ship, or to wherever it’s programmed to surface.” Asked why there is twenty five miles of fiber optic tether when the ocean is only seven miles deep, Bowen explained, “One good reason is that Nereus is expected to operate in the ROV mode laterally, especially under ice in the Polar regions.”

Other technology advances will run deep with Nereus. It will include the first use of high-performance ceramics for full ocean depth flotation, achieving an estimated 40 percent weight savings over more traditional syntactic foam material. To protect electrical components at depth, Nereus will also use high performance ceramic materials, resulting in a 60 percent weight savings over traditional titanium. Advanced and lightweight imaging and lighting are also part of the vehicle’s design. All these advancements make the HROV smaller and lighter, and thus able to travel further underwater. For power in both the ROV and AUV modes, Nereus will use small cells such as those found in laptop computers, but 2,000 cells will need to be bundled for the HROV to power its four thruster engines and its onboard compliment of sensors and systems. Nereus will have power to operate for 36 hours as an AUV, and between 20 and 24 hours tethered.

Only two humans have been to the deepest part of the ocean—nearly seven miles below the surface at Challenger Deep in the Mariana Trench. In 1960, they spent just 20 minutes on the seafloor in the Navy’s Trieste submersible, and no person has been that deep since. Trieste is now a museum piece, and it was never replaced. Later, scientists could hope to work with the Japanese robotic system Kaiko. This was the only tool in the world capable of reaching the very bottom of the ocean. Sadly this system was lost in an operational incident in the face of rough seas.

“This HROV is very exciting technology,” said Barbara Moore, Director of NOAA’s Undersea Research Program. “It will provide capability to take our national science program to the deepest ocean for the first time since Trieste made its historic dive more than 45 years ago.” At a depth of more than 35,000 feet, Challenger Deep is as deep as the height at which jets fly, and it is a mile deeper than Mt. Everest is high.

Despite decades of progress exploring our ocean planet, our ocean frontier remains essentially unexplored. With new technology and operational flexibility such as found in Nereus, we will significantly enhance our ability to better understand our largely unknown ocean and its inhabitants, perhaps including old Nereus.

To Explore the Deepest Ocean, Nereus Past and Nereus Future Have One Thing in Common—Change!