The biggest technological difficulty was the design of the launch and recovery system, Stephane Meltzheim, head of the Espadon project at ECA, told Aviation Week. It is harder to get two autonomous machines to connect in high seas than in outer space. There are currents, winds and waves to contend with and the DGA specified that the vessels must be operational in Sea State 5. A traditional minehunter cannot operate beyond Sea State 3.
The solution resembles the drogue and hose used in inflight refueling: using one of its world-first features, the Sterenn Du unwinds a cable that the AUV clamps onto and the cable then draws the AUV inside a cage between the two hulls of the catamaran, another first. Meltzheim adds with some pride that there has been close to a 100% success rate in tests with the system, which ECA has patented.
The third innovation is active and passive shock-absorbing systems in the cage, which means the AUV stays as stable as possible despite any movements of the ship. Once the AUV is in its cage, it is brought up inside the Sterenn Du.
Each of the three AUVs has a specific role. The first to be launched would be the DCL (detection, classification and localization) AUV. It is 5 meters long, weighs between 800-1,000 kg (1,764-2,200 lb.), has a range of 40 km (25 mi.) and an endurance of between 10 to 20 hr., depending on the type of battery installed. The DCL vehicle carries a sonar to detect and classify underwater objects. “This vessel has the intelligence to work by itself and overcome any unexpected problems it may come across,” says Meltzheim. The vessel was developed in 2006-09 but the automatic recovery system was added for the Espadon program.
Data collected by the DCL AUV is transmitted back to the mothership, where operators decide what objects need to be observed more closely, then program the second AUV and send it out. “This catamaran AUV, specifically developed for this project, is extremely maneuverable, with two propellers at the front and two at the rear, four cameras, lighting and a small sonar,” Meltzheim explains. “It is programmed with all the [mine-like contacts], which were identified by the DCL, and it observes them one by one,” acquiring still and moving imagery. It goes over each contact at least once and when it has completed its mission, it returns to the Sterenn Du.
At this point, the third AUV comes into play. Until now, the project has used a reusable vehicle which is wire-guided to the mine, drops an explosive charge next to it and retreats before detonating the charge to destroy the mine. “However, the tendency today is toward using expendable and much cheaper kamikaze-style robots, guided to the mine by an operator,” says Meltzheim.
Once sea trials are completed in the next few months, the next step will be to launch a second prototype, which will be co-financed by France and the U.K. in the framework of the November 2010 Lancaster House treaties.
Another major USV development appearing at Euronaval also reflects the use of new and mature technology to match a developing conops: a new and larger version of the Protector USV from Israel's Rafael. Work on the 11- meter craft started about three years ago. After evaluating smaller craft, the developers saw a need for a vessel that could operate in higher sea states, as well as provide better speed and endurance—up to 48 hr. in some conditions—and a bigger payload.
With a larger and more costly USV performing longer and more distant missions, a dual, fully redundant diesel-and-waterjet drive system became a priority to ensure that no single failure would prevent the operator from returning the vessel to base. Redundancy extends to the electrical and control systems, and new features have been added to enhance damage control capabilities and system health monitoring.