January/February 2008

Untethered in the Deep

Autonomous underwater vehicles advance--not to mention stop, turn, and hover.

By Greg Mone

Credit: Christopher Harting

The two-meter-long robotic submarine Odyssey IV could easily be mistaken for a half-finished undergrad project. Although its electronic innards and motors are in place, its body is a work in progress--a stainless-steel frame with a few chunks of foam tacked on for flotation. Some pool floats holding a temporary power cable are attached to the top. But once the vehicle is lowered into the water, it acquires a sudden grace, coasting forward, stopping to hover in place, and executing perfect turns. For now it's merely cruising the 25-yard Alumni Pool in Building 57, but soon, the finished version could be exploring some of Earth's most remote underwater destinations.

Odyssey IV is on its way to becoming the newest addition to the family of autonomous underwater vehicles, or AUVs, that have been conceived, designed, and built through the MIT Sea Grant College Program since 1988. Thanks to great advances in mechanical design and programming, these independent and--by submarine standards--inexpensive swimming robots have explored the depths of the Antarctic ocean, searched for ancient shipwrecks off the coast of Greece (see "Excavating the Deep," May 2003), scoured underwater minefields, and even inspected the hulls of ships. And MIT researchers are convinced that these recent successes are just the beginning,

In the mid-1980s, Chryssostomos Chryssostomidis, now director of the program, grew frustrated with the technology used for deep-sea exploration. The top robotic submarines of the day were remote-operated vehicles, or ROVs, controlled via cables by engineers on large surface ships. The size of the surface ships, and of their crews, made the subs expensive to deploy, and the cables, which also provided the subs with power, limited their range and maneuverability. "The tether was a nuisance," says ­Chryssostomidis, who looks and sounds like a Greek fishing captain. "So we asked ourselves, 'Could we make it tetherless?' "

This wasn't a simple problem. Getting rid of the tether meant that the sub needed to be independent. Radio waves don't travel well through water, so there was no way for scientists to wirelessly pilot the vehicles from the surface. The robots would have to steer themselves.

Inspired by his computer science colleagues' continual efforts to push their field in new directions, Chryssostomidis decided to try to do the same with subs. He challenged his students to build, for less than $100,000, a robotic submarine that could dive to 6,000 meters (ROVs with tethers couldn't go deeper than 1,000 meters). He also wanted it to be light enough for two undergrads of average strength to carry it down to the Charles River for testing.

In 1992, led by research engineer James ­Bellingham, PhD '88, who now runs the AUV program at the Monterey Bay Aquarium Research Institute, the students produced Odyssey I, a robot that met Chryssostomidis's main requirements. Well, almost. It could dive twice as deep as its remotely operated brethren, and it weighed just one-sixth as much. But it cost closer to $140,000, and a typical pair of physics majors probably wouldn't have been able to lug it more than a few feet. "It needed two very strong undergraduates to carry it," Chryssostomidis jokes. (In fact, students used a cart to get it to the river.)