The idea behind submarines is stealth. Underwater warships and missiles are harder for the enemy to detect. But because they're propeller-driven, subs create a wake that can be spotted, especially by satellites. So the Navy is keen to develop unmanned subs that create little or no wake, and are also more maneuverable-propeller-- driven watercraft cannot exactly turn on a sand dollar. The best way to do that is to mimic fish, which wiggle through the water and create nary a surface ripple. Toward that goal, two professors of aerospace engineering at Texas A&M University-Othon Rediniotis and Dimitris Lagoudas-- are leading a team that's devised a prototype sub that shimmies through the water as smoothly as a hunting shark. To accomplish that feat, they use Shape Memory Alloy wires made from nickel and titanium that are filled with ethylene glycol (antifreeze). The wires are then alternately heated and cooled, causing them to expand and shrink, respectively. As the wires move, they move the sub's metal skeleton, causing it to flex like a fish. The sub's skin is a series of overlapping aluminum plates. The initial three-foot-long prototype used battery power to heat the wires, but batteries take up too much space. So the team is now working on using a fuel engine-probably running on propane-to supply the heat. Rediniotis says full-production subs could be as big as 20 feet in length. Possible military applications include underwater de-mining, intelligence gathering, and ocean mapping. The technology could potentially make smart torpedoes. There are no plans at present to make manned versions. The big problem would be "human comfort," Rediniotis says. Riding inside the belly of a fish could give the passenger a unique sea sickness. Even if the Navy doesn't want to use this technology, it may have a future as an amusement park ride.
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