UST030

controller and sensor for maintaining the concentration of oxygen in the canister at 21%, another water condenser, and an enclosure containing the control electronics for the fuel cell (which is referred to as the RWS – Reactant, Waste removal and Safety – board). At the bottom sits a sump pump for extracting water that has condensed near the floor of the canister, as well as the water ballast pump manifold for collecting all the water vapour and sending it to the ballast tanks. Beneath the fuel cell canister are two canisters of pressure regulators for the hydrogen and the O 2 to reduce them both to 1 bar for use by the fuel cells’ anodes and cathodes. Each set starts with two high-pressure regulators, one of which is a redundant back-up. The highest pressures pose an over- pressurisation risk to the dome, the fuel cell canister and its components, so the regulators step the reactant down from the 431 or 335 bar. A low-pressure regulator then further reduces the gases to 1 bar. “Tescom supplied and did some extra modelling and customisation for our pressure regulators,” Meikle says. “For example, because we’re storing oxygen at what is a very high pressure for it, the metals from which they’re made were specially selected to minimise the risk of a particle ignition amid the very high flow velocities. Tescom also did a lot of work on minimising the units’ sizes, to give us the smallest form factor possible.” Each canister also has a safety relief valve to release gases from them in the event of a leak from the gas line, to prevent the canisters from bursting open. A liquid-cooling system removes excess heat from the fuel cells and the electronics enclosure. Three heat exchangers – one for each system – are installed in the flooded space between the reactant storage cylinders and the rear end-plate, with the seawater acting as a practically limitless heat sink. Six pipes carry coolant back and forth between the heat exchangers and the heat-generating systems, with the coolant pumps circulating about 2 litres per minute. The heat exchanger model selected for the Solus-LR has been tested to 28 February/March 2020 | Unmanned Systems Technology Range: 2000 km Length: 8.5 m Diameter: 1 m Weight: 3700 kg (in air) Operating speed: 1 m/s Nominal endurance at operating speed without stopping: 24 days Top speed: 2 m/s Variable buoyancy system: 50 kg displacement Fuel cell: high-pressure hydrogen-oxygen Usable energy: 250 KWh Secondary battery: lithium-ion Control architecture: ROS-based Some key suppliers Fuel cells: Ballard Pressure regulators: Tescom Pressure transducers/ transmitters: TE Connectivity Solenoid valves: Parker Hannafin Sump pumps: Parker Hannafin Battery: SubCtech Flow control sensors: Alicat Scientific Hydrogen and oxygen pressure vessels: Worthington Industries Embedded computers: BeagleBoard Embedded computers: Arduino Embedded computers: SBRio Serial device servers: Perle Ethernet switches: Netgear Ethernet switches: Red Lion Repeater power supply: Wika Gas concentration sensors: Neodym Technologies Poppet check valves: Swagelok Multi-beam sonar: Imagenex Hydrophone: Ocean Sonics INS-DVL: Sonardyne Optical modem: Sonardyne Sound velocity sensor: Valeport Iridium modem: MetOcean Telematics Indicating beacon: MetOcean Telematics Magnetometer: Ocean Floor Geophysics Linear actuators: Ultra Motion Rotary actuators: Volz Specifications The thruster draws the most power, so maintaining position using the suction anchor enables the UUV to operate for months between maintenance stops (Author’s image)