Magazine article National Defense

Underwater Robots

Magazine article National Defense

Underwater Robots

Article excerpt

The Navy is updating its blueprint for future undersea robotic vehicles to reflect recent changes in military strategy. A revised "master plan," expected in about a year, will emphasize joint-service operations and interoperability between unmanned undersea vehicles and conventional ships.

UUVs would be deployed as underwater scouts and navigation aids. Launched from submarine torpedo tubes, they would search for mines and other underwater threats. Ambitious plans to spread UUVs across the fleet, however, have been toned down by the complexity of the technology and soaring costs.

The existing UUV blueprint, written in 1999, has become outdated as a result of new war-fighting tactics, the state of technology and the planned introduction of the Littoral Combat Ship in 12007. The 1.CS is envisioned as one of the primary carriers of unmanned undersea vehicles.

Unlike commercial submersibles and small UUVs used for explosive ordnance detection, the Navy's future undersea robots must operate autonomously, collect, analyze and transmit intelligence to the host ship.

Emblematic of the technology challenges of underwater robots is the LMRS, or long-range mine reconnaissance system. In development since 1999, the torpedo-size LMRS is intended to deploy from submarines, search for mines clandestinely and identify them. Despite significant cost overruns, the Navy has stuck with LMRS and plans to continue to upgrade it with new sensors and communications systems. One fundamental shortcoming in LMRS, however, is that it can only perform one type of mission. With an expected price tag of $20 million to $30 million per two-vehicle system, LMRS is viewed as too expensive for a single-mission UUV.

Seeking to get more productivity out of these pricey robots, the Navy is planning to introduce by 2009 a "reconfigurable" 21-inch UUV, with a modular design allowing for different sensor payloads that would be tailored for specific missions, such as surveillance, navigation or communications relay.

Before the Navy can set any realistic schedules for fielding UUVs, however, it must improve the performance of the batteries that energize multiple onboard systems.

Powering autonomous underwater robots for long-endurance missions is among the toughest problems that researchers face, because batteries generally fall short on range and stamina. The only high-performance batteries that allow LMRS to complete a 120 nautical-mile sortie are disposable lithium-thionyl-chloride packs, which cost up to $250,000. Because lithium is hazardous to the environment, the Navy must pay several thousand more dollars to dispose of each battery after it's been used. "That makes for an expensive mission," noted an industry expert.

Other options, such as rechargeable lead-acid and silver-zinc battery packs, do not meet the LMRS performance requirements.

"You can't achieve range and endurance with rechargeables," said Capt. Paul Ims, Navy program manager for unmanned undersea vehicles. The rechargeable silver-zinc battery provides about 15 hours of run time. The expendable lithium pack lasts more than 40 hours.

The LMRS prime contractor, the Boeing Company, is searching for better power alternatives. "For future planned upgrades of the LMRS, Boeing is looking at new battery technologies that are more efficient and provide longer operational life," said a company spokesman.

A rechargeable lithium battery would be desirable, but the Navy is reluctant to bring those aboard submarines, as long as they continue to pose safety risks. …

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