Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

64 sea, for missions over four days at a time. It includes a patented navigation system with obstacle avoidance, which considers the international regulations for preventing collisions at sea. It follows on from the 9 m Silver Marlin, which was the company’s first USV programme in 2006, and the 3 m Stingray USV platforms. Kraken Sonar is supplying its Katfish towed sonar system to Elbit for mine detection. The system provides resolution down to 3 cm in three dimensions, and when towed behind the USV a gigabit Ethernet link feeds data to the craft for onboard analysis. It is an active system that compensates for any movement or turbulence in the water and can control its depth using intelligent bottom-following and bottom- avoidance routines. This provides higher resolution images in a shorter time than underwater craft or payloads in the body of the USV, says Karl Kenny, president of Kraken Sonar. “When our synthetic aperture sonar is integrated into Elbit’s Seagull USV, the system can provide remotely operated, unmanned, end-to-end mine hunting operations. These can detect very small objects hidden on the seabed and enter confined spaces where underwater explosives are likely to be hidden,” he says. Knowing exactly where the data comes from on the seabed is essential, and Kraken acquired technology from Marine Robotics in the US that includes a navigation system with self-calibration routines, to allow in-situ calibration of the navigation system sensors while out at sea. This avoids the need for high- precision alignment between vehicle navigation sensors, particularly after vehicle maintenance, battery replacement or payload swap. A different approach being taken is the Sea Hunter, a much larger autonomous craft than the CUSV or Seagull that can track the submarines that lay the mines. The 42 m craft, built by Leidos for the US Defense and Research Projects Agency, uses a trimaran design with a narrow hull that contains just three rooms: a machine room at either end of the hull and a central command and control centre using electronics from Leidos. The vessel is built from fibreglass, using a mould and sandwiching foam core between layers of fibreglass, then vacuuming the air and pouring in resin that cures and hardens within a few hours, with one mould for the hull and a second for the deck. Sea Hunter has an endurance of months from a fuel capacity of 40 t, and can track a submarine at speeds of up to 27 knots in all weather conditions using a modular sonar system from Raytheon that is mounted on the hull and integrated with the Leidos control system. It costs around $20,000 a day to operate, compared with $700,000 a day for a destroyer, and the ships will cost around $20m each if they are built; testing of the prototype system began in July 2016. Refuelling and data transfer The US Navy is looking for technology to refuel its USVs at sea and download terabytes of data from the sensors. The first technology demonstrator will refuel a ‘fleet- class USV’ such as the UISS CUSV, which carries up to 650 US gallons of marine diesel fuel. The Navy has tried to refuel USVs at sea before but had problems with the interaction of the waves between the USV and the refuelling craft, which could be a large vessel or a barge. It found that as the two vessels get closer, the waves and the motion of the water change, and how this happens has had to be accurately modelled using computational fluid dynamics (see Focus on page 32) as part of the new programme. This means the technology has so far been seen as TRL level 4, or a laboratory demonstration. The aim of this new programme is to get this up to TRL level 6 and fit for a full system development. A major additional technical challenge the Navy wants to overcome is downloading data from the USV while it is being refuelled. It has specified this to be 2 Tbytes of data, and the challenge at the moment is that the current craft being re-fuelled has no external data port, so how the two vessels would make the connection has yet to be determined. This lends itself to a direct, high-bandwidth wireless connection between the two, rather than adding a physical external port. August/September 2016 | Unmanned Systems Technology Insight | USVs In an alternative approach to minesweeping, the Sea Hunter can track the submarines that lay the mines