Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

90 Digest | Accession Class USV bilge pump is running, for example, and each compartment also contains a camera and LED strip lighting to provide the operator with visuals of what is happening. As with all the other loads, these can also be turned on and off remotely to minimise energy consumption. Built-in redundancy Much of the design effort that went into the boat’s power system was directed towards flexibility, redundancy and graceful degradation by minimising single points of failure. “Everything has redundancy,” Wittamore says. “There are two power supplies, so if one goes offline the other can take up the load. If any single point fails you still have a fighting chance of keeping the boat fully operational. You can turn a lot of things off and it will still work.” Inevitably that brings a degree of complexity to the overall power management system, which incorporates a control panel located behind a transparent hatch cover in the aft bulkhead on the forward superstructure. “You open that up and start it with a key, then the PLC powers up the boat’s systems in the correct order, interrogating the individual batteries to find their states of charge,” Williams explains. In the original proof-of-concept boat, the power management system was built from discrete parts including off-the-shelf cables and switches, but the production- ready system is a ground-up industrial design. “As well as the PLC it has re- settable, controllable electronic circuit breakers, so if anything trips we know what tripped and why, and we have a chance to restart it,” Wittamore says. This can also be done remotely, via satcom from the main operational control system or from an app on a smartphone if the USV is within wi-fi or cellular comms range. “I can log into the boat and, say, close the breakers associated with the generator, or shut down the entire stern section for safety reasons, if there’s somebody in the water nearby for example,” Wittamore says. Comms and navigation Visually prominent on the vessel are two ‘trees’, one forward and one aft, which are masts that support antennas for the comms and navigation suites. The rear tree folds down to reduce the overall height for transport and storage in a 20 ft container, while the top antennas pivot back to provide full access to all the connectors. The largest antenna is the dome of the Intellian system that connects with the Iridium satellite network, whose services are provided through USS’ partner AST Global. Other bearers include dual wi-fi systems and 3/4/5G cellular comms. The comms management system is programmed to choose the bearer offering the best combination of signal strength, bandwidth and cost at any given moment, Wittamore says. Wi-fi is normally the preferred bearer for operations near the shore, but at the exhibition centre dockside there were many systems competing for bandwidth and causing interference, Wittamore notes, so the Accession’s comms management software had automatically switched to Iridium satcom. “It has lower bandwidth than wi-fi or 4G, but it is still enough for remote desktop control and over-the-horizon operations,” Williams adds. The forward and aft trees each June/July 2022 | Uncrewed Systems Technology Red lines across the deck show the ends of the 0.75 m payload module installed in the Accession 425. The black cylinder hanging from the stern frame is the SVP from Valeport (Author’s photo) Forward antenna tree on the bow supports GNSS, AIS and comms antennas, the vertical hatch protects power management panel, and a solar panel charges auxiliary batteries (Author’s photo)