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A New Deep-Sea Robot Called Sentry Autonomous underwater vehicle completes its first scientific mission |
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| Enlarge ImageCrew members bring Sentry back on board the ship during its inaugural test cruise in August 2008. The vehicle 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 this first cruise, it surveyed about 20.5 square miles (53 square kilometers) of seafloor.
(Photo by Dan Fornari, Woods Hole Oceanographic Institution) |
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| Enlarge ImageTowCam, a towed underwater camera system also operated by WHOI, worked in tandem with Sentry during vehicle's first trip to sea. Sentry mapped the seafloor while TowCam took images.
(Photo by Dan Fornari, Woods Hole Oceanographic Institution) |
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| Enlarge ImageThe TowCam underwater camera system took these photos of rocks and
crabs on the seafloor. The images will be correlated with seafloor maps
constructed with sonar data collected by Sentry.
(Photo courtesy of Dan Fornari, Woods Hole Oceanographic Institution) |
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| Enlarge ImageOn Sentry's first scientific mission, Dana Yoerger woke up after
a stressful 24-hour period of work to find that his shipboard
colleagues playfully painted a grin on the vehicle. (Does it resemble
Yoerger's own smile? You decide).
(Photo by Dana Yoerger, Woods Hole Oceanographic Institution) |
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| Enlarge ImageWHOI engineer Dana Yoerger will join Sentry on at least three expeditions planned for 2009: in the Gulf of Mexico; to study undersea oil seeps off Santa Barbara, Calif.; and to map a chain of active underwater volcanoes at the Carlsberg Ridge in the Indian Ocean.
(Photo by Tom Kleindinst, Woods Hole Oceanographic Institution) |
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Related Links |
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» TowCam
A towed underwater camera system operated by WHOI researchers
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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), completed 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, which revolutionized deep-sea exploration by
expanding scientists’ reach into the deep.
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 pre-programmed
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 engineer 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.
Sentry's unconventional shape
“As expected on its maiden voyage, Sentry had some
'teething' problems,” said John Delaney, a University of Washington
(UW) 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.”
While Sentry mapped, WHOI geologist Dan Fornari and
biologist Erich Horgan simultaneously used a towed underwater camera
system called TowCam to obtain visuals that can be married with the
maps.
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 keep moving in one direction.
A busy summer ahead
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 this first cruise, Sentry
collected as many as 60 million individual soundings of seafloor depths
in a single dive. It surveyed about 20.5 square miles (53 square
kilometers) of seafloor. Engineers adjusted a balky navigation system
and are now investigating the use of new propellers that could improve
the vehicle's speed (about 2 miles per hour) and range.
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. Beginning in June, researchers plan to use Sentry
on at least three expeditions: to explore deep-sea corals in the Gulf
of Mexico; to study undersea oil seeps off Santa Barbara, Calif.; and
to map a chain of active underwater volcanoes at the Carlsberg Ridge in
the Indian Ocean.
“I’m pleased that we have all these interested scientists and lots of interesting problems they want to tackle using Sentry,” Yoerger said. As for Sentry’s progenitor, ABE, Yoerger joked: “He’s going out to stud.”
—Amy E. Nevala and Lonny Lippsett
Funding for the development of Sentry was provided by the
Ocean Sciences Division of 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; by the Arizona State
University; and by the UW School of Oceanography.
Posted: March 19, 2009 [top] |
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