U.S. military will use new defense for mines

PANAMA CITY BEACH, Fla. (AP) — Mines that Iraq planted in the sea during the Persian Gulf War nearly split the cruiser USS Princeton in half and held an American amphibious assault force at bay.
Iraq, the Pentagon learned, was better at laying mines than the U.S. Navy was at clearing them.
That experience sent the Pentagon in search of a more effective defense and Navy researchers say they now have the answer, a collection of devices with relatives in medical technology that they call ALISS, for Advanced Lightweight Influence Sweep System.
“In mine warfare it’s a cat-and-mouse game,” said project manager Robert Buhl at the Navy’s Coastal Systems Station near this Florida Panhandle resort city. “They’ve got a countermeasure, and we’ve got a counter-countermeasure.”
ALISS uses a powerful superconducting magnet and a high-energy underwater noisemaker to fool “influence” mines into exploding at a safe distance. These are mines that sit on the sea bottom and explode when they detect the magnetic field or sound of a target floating overhead.
ALISS is already installed on a 32-foot ship for demonstrations, but until operational craft are built — possibly by 2005 — it’s being kept on standby and hasn’t been activated for the current confrontation with Iraq, Buhl said.
ALISS is designed to outwit even the most advanced mines by precisely mimicking the sound and magnetic signature of intended targets.
To mimic the magnetic signature of steel-hulled ships, the system uses a donut-shaped, five-foot-diameter superconducting magnet, similar to those in magnetic resonance imaging devices that allow doctors to peer into living human bodies.
“It’s simply an MRI system, only tweaked to do what we want,” Buhl said.
The most significant tweak is a new cooling system that uses a permanent supply of helium gas to cool the magnet, rather than costlier-to-maintain liquid helium.
Hospital MRIs use liquid helium that boils off and has to be replaced yearly, and that’s too often for the Navy, said Don Waltman, senior project engineer with the Naval Surface Warfare Center’s Carderock Division in Annapolis, Md. His unit and a contractor, General Atomics of San Diego, built the ALISS magnet.
“Especially if you are doing an operation in some remote area of the world, the Persian Gulf or something like that, supplying liquid helium to the fleet for minesweeping would be a very difficult task,” Waltman said.
Manufacturers are planning to apply the Navy’s technology to civilian MRIs, said Carderock project manager Joseph Tannenbaum.
ALISS’ acoustic system, which imitates the noise of passing warships, is a much more powerful adaptation of another medical technology, ultrasonic lithotripsy, which uses shock waves to disintegrate kidney stones. It was developed by the Coastal Systems Station with Hughes Aerospace in Mukilteo, Wash,, and Primex Physics International Co. of San Leandro, Calif.
ALISS uses three electrodes — each only an inch in diameter and a foot long — protruding beneath the hull of the minesweeper to discharge 30,000-watt electrical pulses, creating shock waves and a loud rat-a-tat noise in the water.
This technology has potential civilian uses in rock drilling, removing paint from large structures like bridges and in treating hazardous waste, said Anthony Bond, acoustics systems engineer at the Coastal Systems Station.
The ALISS demonstrator cost $1 million, and operational systems are expected to be less, Buhl said. So losing one wouldn’t be as serious as sinking a $25 million amphibious hovercraft or a warship costing $1 billion or more.
In addition, an ALISS boat could be operated by remote control.
“That keeps us from losing sailors,” Buhl said. “If we actually went to war you would not want anyone on this boat.”