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53 UUVs | Insight for deployment in natural underwater environments.” He also describes ongoing and future efforts to enhance the AUV’s endurance and power. Currently, the MantaDroid Mark I gets its energy from a lithium-polymer battery rated at 1500 mAh, which gives it the required 10-hour endurance, he says. However, the team is looking to exploit alternative power options, including solar energy with panels integrated onto the MantaDroid’s dorsoventrally flattened body. Each fin is powered by its own electric motor and has an integrated ‘passive flexibility’ capability that allows them to interact in a more natural motion than the propeller thrusters used in many conventional AUVs. The team has considered a range of fin designs, with more than 40 options on the table as of January 2018. Fin development, which has been underway for two years, saw the final selection of a design featuring two flexible pectoral fins made from PVC sheeting. This, according to Associate Professor Chew, provides the UUV with improved mobility and propulsion in pool conditions. “Our aim is to build an AUV platform that can be deployed for long-term underwater operations such as surveillance and environmental monitoring in oceans, lakes or rivers,” he says. The MantaDroid II is scheduled to conduct blue-water trials over the course of this year to identify any issues relating to mobility in underwater currents and high sea states, as well as consider the use of additional fin mechanisms. LDUUVs Another major development driver in the UUV market is LDUUV technology, which in the military domain at least is creating potential new avenues for additional capabilities. Leading examples include the Extra Large UUV (XLUUV) concept from the US Defense Advanced Research Projects Agency and the US Navy. The programme includes multiple variants being designed across industry, with systems integrators Lockheed Martin and Boeing both leading development programmes on behalf of the Navy. The programme aims to develop XLUUV technology to support multiple critical missions in the future operating environment. This, according to programme officials at the US Navy includes the requirement for a “long- range autonomous system with a payload capability to perform a variety of missions, including intelligence, surveillance and reconnaissance; mine countermeasures; indication and warning notification; as well as serve as an anti- submarine warfare training platform”. A statement from Lockheed Martin adds, “These systems can be used for long-endurance surveillance and to deliver other payloads.” Designed in response to what the US Navy calls a Joint Emerging Operational Need, the XLUUV (named Orca) is seeking to comprise a modular, open- architecture, reconfigurable UUV capable of being deployed from a harbour Unmanned Systems Technology | February/March 2018 The US Navy is pursuing the XLUUV programme in order to extend mission endurance and persistence of UUV technology (Courtesy of Boeing Company)