"We can operate one of these for a year and across whole ocean basins," says Eriksen.
Driven By Heat
Since one of the greatest limitations of the gliders is the finite amount of energy stored in the on-board batteries, Webb Research in East Falmouth, Mass., has a glider of a slightly different design.
The company's Slocum Glider operates on a similar principle to the Seaglider. But instead of electric pumps to move the oil, its AUV uses a complex system that involves a proprietary, temperature-sensitive material.
Like the Seaglider, oil is pushed into a balloon inside the Slocum Glider's hull. As the oil fills the balloon, it also displaces a specially developed liquid out of the glider's hull the glider into external tubes.
As the glider slips lower into colder ocean water, the liquid contracts into a solid form, pulling more oil into the balloon and sinking the glider lower.
Once it reaches a certain depth, the glider's computer turns a valve, allowing a tank of compressed nitrogen gas to expand and force the oil out of the balloon. The now-buoyant glider rises to the surface, where warmer waters cause the solid material to expand back to liquid form. As the material expands, it fills the empty balloon and compressed the nitrogen tank and prepares the glider for a repeat sinking performance.
Clayton Jones, a project engineer at Webb Research, says that since the propulsion engine is driven by the heat of the ocean, the range and endurance of its AUV is greatly increased.
"You're saving the battery energy for the sensors, navigation and communication equipment," says Jones. "A thermal glider will run for like four years."
Silent Spy Service for the Navy?
In addition to long range and endurance, the researcher says the gliders will be cheap in comparison to traditional research ships. The scientists say each hand-built prototype cost around $50,000 to $75,000 to build — a figure that could possibly be made even lower if a commercial venture undertook production.
But both teams admit that their gliders still need to be extensively tested — especially in deep, open waters. The Seaglider is currently undergoing such trials just off Cape Flattery in Washington. And Webb Research plans for open sea tests of the Slocum Glider sometime in January.
In addition to their own research, the Navy will get into the deep sea act as well. Thomas Swean, Jr., team leader for ocean engineering and marine systems section of the Office of Naval Research says both gliders will be part of a larger Navy exercise next September.
Swean says that the Navy is interested in the gliders' abilities to collect and monitor ocean conditions — capabilities that would be useful in naval conflicts. Collecting information about the waters off a hostile shore would help sailors tune their ships' sonar systems for optimal performance, for example.
What's more, "The gliders almost make zero noise," says Swean. And that would make them ideal underwater spies that could be used to help land special forces troops in advance of any sea-based invasion.
If next year's open water tests go well, Swean says it's possible that the Navy could be using underwater gliders within two or three years.