For now, the Navy is mostly developing AUVs as mine hunters. Long-term, though, they're expected to do more than take the man out of the minefield. AUVs will map currents and the ocean bottom to help manned subs and ships navigate safely. They'll be sent secretly to the coastlines of hostile countries to monitor enemy actions and report back via satellite. They will act as beacons, enabling other underwater devices to keep their bearings without surfacing for a GPS signal. And they will determine when an enemy sub is nearby, follow, and, if necessary, blow it up. "They increase the reach of Navy systems," says Tom Swean, head of the Ocean Engineering and Marine Systems Program at the Office of Naval Research in Arlington, Virginia. "There may come a time, thanks to AUVs, when very few people are involved in violent action."
TODAY: HUNTING MINES
Today's Navy is a blue-water force -- its strengths are in the depths, not the shallows -- but it's preparing for a brown-water fight. Seventy-four percent of Persian Gulf waters are shallower than 180 feet. And in what the Navy terms very shallow water -- from about 40 feet to the 10-foot depths where waves begin to break -- mines pose an especially acute threat. There, where ships and manned subs can't venture, the Navy traditionally relies on dolphins to find and mark mines, and on human divers to set charges nearby, then swim away before they explode. The work is painstakingly slow and dangerous.
That's why military planners would love to send in a team of AUVs instead. The AUVs in the Navy Seals' tests are programmed before being dropped into the water. Each vehicle dedicates itself to a discrete portion of the harbor, covering it in a series of parallel runs -- a tactic called "mowing the grass." Scanning 150 feet in each direction with sonar, the robot subs note the location of all mine-like objects. To keep their bearings, they continually send signals to two transponders that the Seals have dropped in the water at predetermined locations. (The subs are programmed to know where the transponders are, so by assessing how long it takes for their signals to bounce back, they ascertain their own location.) After a few hours, when the robot subs have covered the entire harbor, they gather at an appointed place to be retrieved.
The AUV used in this operation is the Remus (Remote Environmental Monitoring Unit System), originally developed in 1994 at the Woods Hole Oceanographic Institute for non-military survey work. The institute's commercial spin-off, Hydroid Inc., now produces special versions for military use.
The Remus is 63 inches long and 7.5 inches in diameter. It can stay out for up to 22 hours and specializes in depths of 10 to 40 feet, making it ideal for the shallows of the Gulf. The Navy teams several Remuses together in a system known as Sculpin. Each vehicle can be packed in a metal case that weighs just under 150 pounds, the FedEx maximum for rapid commercial delivery: Sculpin's handlers travel lighter than most camera crews. For now the Sculpin system is designed only to detect mines; human divers would handle detonation.
The Battlespace Preparation AUV (BPAUV), being developed for the Navy by Bluefin Robotics in Cambridge, Massachusetts, operates in the next depth zone, between 40 and several hundred feet. Ten feet long, 21 inches in diameter and weighing about 500 pounds, the BPAUV is no minnow. But Scott Willcox, chief technology officer at Bluefin, says a smaller, more manageable version is in the works. Both the BPAUV and the Remus use side-scanning sonar devices to search for mines buried on or beneath the ocean floor. Transducers on the vehicles' sides dispatch a thin beam of sound waves that extends out like a fan for 150 feet.
Acoustic sensors work best for the job because coastal waters are often turbid, according to Doug Blaha of Marine Sonic Technology in White Marsh, Virginia, which manufactures the Remus's sidescan sonar. "If you walk into a smoke-filled room, you may not be able to see someone across the room," Blaha says, "but you can certainly hear him."
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.