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30 testing in our workshop using smaller acrylic versions of the pressure tanks in order to prove out the variable ballast system,” Meikle adds. By ensuring the exhaust water is distributed equally among these 10 compartments, the internal ‘sloshing’ of water is greatly limited, minimising the degree to which the centres of buoyancy and mass move about. While much of the Solus-LR’s operation takes place autonomously, both pre- programming and human-in-the-loop control take place while the vehicle is surfaced. For the latter, a comprehensive control software suite has been designed from a blank sheet by the company. The control software interface consists of a number of different selectable panels, most important of which (for UUV operations) is the ‘pilot’ panel. This includes directional controls such as horizontally from the rudder and vertically from the thruster. Additional panels are available for monitoring power, diagnostics, acoustics, and a range of other onboard systems. When the Solus-LR is surfaced, it can be given preset missions to carry out autonomously. The pilots are then limited to monitoring feedback from the vehicle (which is also displayed on the pilot panel), although the data link is greatly attenuated as the vehicle submerges. For example, during the final month- long mission this coming summer, the vehicle will be assigned to run laps up and down the Indian Arm, a body of water outside Vancouver. During each lap, the BlueComm optical modem will enable data uploads to the boat and to an LBL beacon stationed by Cellula at the end of the Indian Arm. At these junctures, the drift of the UUV’s INS will be corrected if necessary. While waypoints for the vehicle have been programmed manually for tests thus far, a separate and dedicated mission- planner software suite is in development. It will simplify mission planning for end- users, enabling functional setting of key GNSS points at which to survey the seafloor, to surface and upload data via the Iridium satcom system, to deploy the suction anchor, and so on. The vehicle has used ROS as its middleware for software development. Many such systems were considered, but ROS was selected because it is being taught to students in a significant and growing range of maritime and academic institutions. “It has other advantages too,” Crees notes. “It’s open source, it has good modelling and visualisation tools, and the general set-up gels well with how Eric [Jackson] and I envisioned our hierarchical control systems, as opposed to some of the other options.” Suction anchor As mentioned, the Solus-LR’s suction anchor is critical for holding position and depth at key locations. Since the thruster is the biggest consumer of power on the craft, the anchor saves the UUV energy and prolongs its endurance. Its largest component is a cylindrical February/March 2020 | Unmanned Systems Technology Dossier | Cellula Robotics Solus-LR The payload canister houses several serial and Ethernet servers for connecting and installing mission sensors (Author’s image) The fuel storage section contains two tanks of hydrogen gas, a tank of oxygen, and two variable ballast tanks for collecting and distributing exhaust water vapour from the fuel cell (Author’s image)