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23 cell-based power system. Second, the development of a suction anchor, and third, to put them together in an AUV we could take into the sea and conduct proof-of-concept trials. “Instead of the 1000 km goal though, we set one of 2000 km over multiple months, partly because we wanted to go beyond what was already available in the market at the time.” The open call closed in January 2017, and three months later Cellula was notified that its proposal had been successful, with the contract being signed later that year. The fuel cell development project began soon after, and entailed investigations of different fuel cell configurations and oxygen storage methods. The result of that was the selection of hydrogen fuel cell power, as it has the fewest variables and potential points of failure. “We lab-tested a range of things, going as far as trialling a direct methanol fuel cell [DMFC], which uses sodium borohydride for fuel and hydrogen peroxide as the oxidant,” Woodroffe says. “They were all successful, but not quite as simple as just using bottled oxygen, nor did they match the energy density of the hydrogen system.” The main contract to build the vehicle started in May 2018, and after a number of iterations the prototype was developed, built and approved to begin sea trials that started in mid-October last year. “Initially, the sea trials were conducted with just the ‘stubby’ version of the Solus- LR – that is, without the long mid-section containing the hydrogen and oxygen tanks and the suction anchor – to test and prove standard UUV tasks such as diving, traversing a waypoint, collecting data and returning to its launch point,” Woodroffe recalls. “We also have a test pool in a tank at our workshop, which has proved vital for trialling and iterating the UUV’s subsystems. Having concluded our first phase of sea trials as of November last year, the schedule going forward is to take it back to the shop for any modifications, and integrate the fuel cell reactants and suction anchor. “We’ll then factory-test those key systems in the pool for endurance and reliability, before starting the second round of sea trials this March, in which the vehicle will be powered by the fuel cell.” Mission considerations Cellula Robotics anticipates the Solus-LR being deployed in port-to-port missions, potentially covering 1000-2000 km of seafloor before refuelling at a docking point at its destination. This represents a distinct shift away from the conventional launch and recovery of UUVs from large, manned vessels, which requires significant labour, equipment and costs, and risks damaging the UUV as it is hauled back on deck. The volume inside the UUV also enables integration of a wide range of payloads, potentially enabling navies around the world to move many of the intelligence, surveillance and reconnaissance duties traditionally assigned to submarine crews onto the Solus-LR. To that end, Cellula’s software engineers are developing a remote interface through which select users will be able to log on and view the UUV’s position, heading and data as they are periodically uploaded by satellite link or by surface and subsurface nodes. The Solus-LR can be launched in different ways. The sea trials so far have used a four-wheeled gantry crane to lower the UUV into and out of the water. It can also be mounted on a trailer, similar to that used for boats but custom-built for Cellula’s use, allowing it to be towed by a road vehicle to a given harbour Cellula Robotics Solus-LR | Dossier We tested various fuel cell types but they were not as simple, nor did they match the energy density, of a hydrogen- oxygen system Unmanned Systems Technology | February/March 2020 The Solus-LR is a hydrogen-powered UUV with a 2000 km operating range, and was developed following a grant from the Canadian government (Courtesy of Cellula Robotics)