Robots Down Under

Deep sea robots are increasingly important tools for scientists who want to explore some of Earth's most remote and hostile frontiers. Human scuba divers can descend safely only about 300 feet, or 100 meters. Yet the deepest parts of the ocean lie 11,000 meters below the surface. To explore greater depths, scientists in the 1960s began building small inhabited submersibles. Such vessels have been used to explore the R.M.S. Titanic's wreckage. But because such vehicles must carry their own fuel and air supplies, explorers are limited to eight to 12 hours per dive.

To overcome these limitations, engineers in the last 15 years have begun building uninhabited robotic vehicles that remain tethered to a research ship on the surface. Long cables feed power and instructions to the submersible and retrieve images and other data. These vehicles usually are equipped with video cameras to allow researchers to see what the vehicle "sees" in real time. They often possess robotic arms to collect artifacts, rocks and biological samples,

John Hopkins University doctoral student James Kinsey prepares to test the navigation and control systems that guide an underwater robot. Photo by Jay Van Rensselaer

"The deep ocean is a cold, dark, high-pressure, inhospitable environment, and this equipment must be able to operate reliably under these conditions," says Louis Whitcomb, associate professor in the Department of Mechanical Engineering at John Hopkins University, and director of a new underwater robotics research laboratory.

"Inhabited deep submersibles, such as the U.S. Deep Submergence Vehicle Alvin, remain the only way for humans to directly observe the benthic floor with their own eyes. Deep-diving submarines are ideal for many tasks, yet they have limited endurance. One advantage of an uninhabited submersible is that it can explore the deepest parts of the ocean 24 hours a day, seven days a week, under the remote control of science teams that are working around the clock aboard the mother ship."

Operating a robotic vehicle from a great distance poses certain challenges, however, and that's where Whitcomb's team comes in. "Our lab focuses on two key problems that occur in the design of remotely operated undersea vehicles: navigation and control," Whitcomb says. "One of the most difficult things about maneuvering an underwater vehicle is that you need to know where it is. What, precisely, is its position and orientation on our planet? To determine these things, we've developed a computer system that integrates signals from a dozen on-board sensors to compute the submersible's position and velocity." 

Based on this information, an operator on the surface can use a joystick to move the undersea robot in three dimensions. The control system developed by Whitcomb and his students also allows an operator to tell a computer precisely where the vehicle should be located; the software then automatically moves the vehicle to that point. At the new Johns Hopkins hydrodynamics lab, researchers are fine tuning this system by sending commands over a tether line to six electric thrusters mounted upon the test submersible. 

At sea, researchers on the surface can use this same system to carefully control a larger underwater robot's movements, instructing the vehicle to move in a precise grid pattern. This allows the sub to collect the images and sonar data needed to produce photographic and topographic maps of sections of the ocean's floor that contain interesting geological, biological or archaeological features. Whitcomb says his computer system also can direct a submersible to hover just 6 to 12 inches above the ocean floor, close enough to collect samples without disturbing ecologically sensitive surfaces. "With this system," he says, "we can control a vehicle's position to within a few centimeters and its heading to within a degree."

 Whitcomb supervises underwater robotics research at Johns Hopkins as director of the Dynamical Systems and Control Laboratory

Related Links:
Video of underwater robot
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