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A new deep-sea robot called Sentry completes first mission.

There's been a changing of the guard among deep-sea exploration vehicles.

Sentry, a new undersea robot built by engineers at Woods Hole Oceanographic Institution (WHOI), executed its first scientific mission last summer, scouting out sites for an undersea observatory network off the coast of Washington state. Sentry is the successor to ABE, the Autonomous Benthic Explorer, a pioneering free-swimming robot launched in 1995 that revolutionized deep-sea exploration by expanding scientists' reach.

Unlike human-occupied submersibles or vehicles connected by cables to surface ships, Sentry and ABE can survey wide swaths of undersea territory on dives lasting a day or more. The autonomous underwater vehicles, or AUVs, are preprogrammed to maintain a designated course but have enough decision-making capacity to avoid collisions with seafloor terrain. They are equipped with sonar to navigate and to map the seafloor and arrays of sensors that can measure water temperature and salinity, for example, or "sniff out" telltale chemicals that signal places and phenomena that scientists want to investigate.


AUVs can "work like bloodhounds," said WHOI scientist Dana Yoerger, who teamed with WHOI engineers Al Bradley and Barrie Walden to design both ABE and Sentry. "When they find something we're interested in, they can 'bark' and then return from the 'hunt.'" Or, as Sentry did on its premiere mission, it can make high-resolution maps of the seafloor.

"As expected on its maiden voyage, Sentry had some 'teething' problems," said John Delaney, a University of Washington oceanographer and the expedition's chief scientist. Nevertheless, "Sentry has given us a survey with great precision and resolution. These maps will help with the installation of the primary nodes of a networked observatory on the Juan de Fuca tectonic plate," he said.

"We were very pleased with Sentry's performance," Yoerger said. "We had tested the AUV as best we could before we got out here, but the steep terrain of the deep sea is quite a different matter. Our engineering team and our vehicle both performed very well under the stresses of putting a complex system into the ocean for the first time."

Sentry is not shaped like conventional AUVs, which resemble torpedoes. Delaney said it looks like "a flying bar of soap," albeit one that is 6 feet tall and bright yellow.

"Like a torpedo, Sentry has a streamlined body for low drag," Yoerger said. "But its shape gives it more stability while cruising through bottom currents."

The vehicle also has thrusters built into its foils, or wings, which are tiltable to give Sentry more maneuverability to start, stop, change directions, and "fly" in different ways, he said, including hovering like an underwater helicopter for close-up examinations. Traditional torpedo-shaped AUVs tend to move in only one direction. Sentry is designed to dive as deep as 5,000 meters (3.1 miles). It is powered by more than 1,000 lithium-ion batteries--similar to those used in laptop computers, though adapted for extreme pressures--which allow it to dive up to 20 hours. On future missions, Sentry can be equipped with other types of sensors, a digital camera, and a pump and filter system to draw in samples of tiny plankton.

As for Sentry's progenitor, ABE, Yoerger joked: "He's going out to stud."

Funding to develop Sentry was provided by the National Science Foundation (NSF), The Russell Family Foundation, the WHOI Deep Ocean Exploration Institute, the Comer Science and Education Foundation, and the WHOI Access to the Sea program. Funding for the August mapping cruise was provided by NSF through the Consortium for Ocean Leadership; the Arizona State University; and the University of Washington.
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Title Annotation:RESEARCH NEWS
Author:Nevala, Amy E.; Lippsett, Lonny
Geographic Code:1USA
Date:Oct 1, 2009
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