The U.S. Navy’s Office of Naval Research plans to take robot submarines to a new level. Current Navy unmanned underwater systems (UUS) are small vehicles controlled by an operator nearby, for missions lasting a few hours. The Large Displacement Unmanned Underwater Vehicle (LDUUV) will be large and highly autonomous, carrying out missions at long distances for months. It will act as a mothership, deploying and operating static and mobile sensors for persistent surveillance in coastal waters. Ultimately, it is likely to be armed. The program sounds ambitious, but much of the technology has already been proven.
Boeing’s Echo Ranger is setting the pace for LDUUV technology. Originally built in 2001, the Echo Ranger is a 5.5- meter (18-ft.), 5-ton craft that can dive to 10,000 ft. “In terms of autonomous operation, we’re pretty much there,” says Mark Kosko, program manager for Boeing’s Unmanned Undersea Systems group.
The Navy’s autonomy requirements call for it to operate without human assistance in shallow water littered with obstacles. In the first 18-month phase the craft will work at shallow depths of as little as 100 ft., calling on an operator via satellite link in challenging situations. The second phase, which will take up to three years, will extend operations to open ocean and working without any human intervention.
The LDUUV will have to detect and avoid surface and submerged vessels, and other hazards such as marine mammals and fishing nets. It will sense and maneuver around fixed obstacles, including piers, moorings and underwater terrain, and plot an efficient course to take.
Echo Ranger has already worked in this type of environment. Sonar gives it short-range obstacle sensing, and acoustic sensors warn of approaching vessels from several miles away. The vehicle then moves out of the way to avoid collision. Echo Ranger’s developers have also learned how to avoid static obstacles, sometimes the hard way—on one occasion it got stuck in a kelp bed.
“You only have to learn that lesson once,” says Kosko.
Another element of the LDUUV program concentrates on endurance, aiming to boost the amount of energy stored per-pound by 10 times. Again, there will be two phases: the first, taking two years, will see the LDUUV operating for up to 30 days at a stretch, increasing to 70 days in the second phase.
Echo Ranger is powered by batteries with an endurance of 28 hr., although Kosko says diesel engines or fuel cells could prolong that time. These technologies might be difficult to apply on small unmanned vessels, but the LDUUV power unit will weigh 3.5 tons, and Kosko says it is largely a matter of packaging existing technology.
A third development effort addresses reliability needed for longer missions. Again, Kosko says this has been explored with Echo Ranger. Drawing on Boeing’s expertise with satellites to airliners, developers have looked at redundant systems, improved component reliability and also self-monitoring capability. The craft needs to be able to compensate for the loss of a sensor, and gauge the seriousness of other problems.
“It has to be able to sense a leak and say ‘Hey, it’s time to go,’” says Kosko.
The LDUUV will have a large payload bay, making it capable of releasing sensors, communication buoys, smaller UUS and weapons. The Navy’s current emphasis is on persistent surveillance “over the horizon.” However, its most significant impact could be in mine warfare, both offensive and defensive.
In the counter-mine role, the LDUUV will be able to detect and locate mines, then engage and neutralize them safely. And the LDUUV could make offensive mine laying more controllable and clandestine. In the transformational mine concept, the LDUUV lays networked sensors across a wide area. These track and identify every vessel within range. Depending on the situation, any vessel can be engaged, by either an anchored weapon or a torpedo from the UUV itself. The advantage of using an LDUUV is that the minefield can be switched on or off, or changed in size. It can be emplaced in advance, and never activated. De-mining and clear-up do not pose the major problem that they do with traditional mines.
The Navy plans to release a request for proposals for the LDUUV in 2014. Last October Rear Adm. Barry Bruner, the Navy’s undersea warfare director, indicated that up to 10 LDUUVs would be procured. The LDUUV is being pitched as a helper to complement manned submarines. However, if it achieves the technology goals for endurance and autonomy, it will pose serious questions of what exactly large unmanned craft could not ultimately do.
By David Hambling
April 12, 2012