Another necessary area of improvement is in energy for propulsion. Currently, small AUVs like Remus can operate for up to 22 hours and larger ones like Seahorse for up to 72 hours, but military planners need vehicles that can stay out on their own for much longer. Devising better batteries for small AUVs and other power sources such as fuel cells for large ones is the key. To get an idea of how primitive current systems are: The Seahorse runs on 9,216 alkaline D cell batteries, the kind normally used in flashlights. For now that is the most efficient method, Head says, because D cells have higher energy density than currently available rechargeable batteries.
In an ideal world, Navy scientists would like to do much more. They want to build AUVs that have a salmon's sensitivity to water chemistry, and polymer skins that propel them the way an octopus is moved along by its rippling hide. And they would like their AUV sonars to be more like the dolphin's, whose broadband acoustic transmissions range from about 30 to 100,000 hertz. "A dolphin can detect a difference in an aluminum cylinder wall thickness of only 0.2 millimeters -- that's fantastic," says Patrick Moore, who runs SPAWAR's biosonar program.
THE FUTURE: ROBOTIC FIGHTERS
Perhaps the most futuristic element in the Navy's vision of wars to come -- called Manta for its rounded delta shape -- is taking form at the Naval Undersea Warfare Center Division at Newport, Rhode Island. Manta's mother ship would be a new kind of submarine, its hull clad in "smart skin" like a huge metal shark, its weapons mounted externally. Several 100-foot-long Mantas would be streamlined into depressions in this new sub's hull; while attached, they would be an integral part of the larger vessel. Once launched, however, they would be linked acoustically with the mother ship, extending her reach into canyons and shoals where a submarine can't follow.
Standing well offshore, the mother sub would deploy her giant AUVs to run reconnaissance patrols and in-shore surveys, to act as defensive pickets protecting the main force, to raid enemy ship and shore facilities with a submarine's full array of weaponry. But the Mantas would themselves be mother ships. Like stealthy Russian dolls, they would launch their own swarms of smaller AUVs and unmanned aerial drones. And, presumably, these smaller robots would be able to send out their own swarms of even smaller AUVs.
Toward this end, engineers at Newport have fashioned a one-third-scale Manta Test Vehicle. Shaped like a slightly overfed Concorde, the 8-ton vessel can make 10 knots, dive to 800 feet, and carry a variety of payloads. The craft began its at-sea trials in Narragansett Bay in 1999, and has since demonstrated such skills as deploying and communicating with smaller AUVs. Seen churning through the bay, the Manta Test Vehicle evokes images of the Loch Ness monster; but to undersea warriors, it looks more like the future. n
Carl Posey is a writer based in Alexandria, Virginia.single page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.