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

92 support a GNSS antenna. These are far enough apart to allow the navigation system to work out the boat’s vector heading from the difference in their measured positions, Wittamore says. Providing survey-grade accuracy, these systems are part of the survey payload. Back-up position and heading are provided by a permanently installed Hemisphere GNSS system, with the Atlas system that receives error-correction signals from ground stations relayed via satellites. The rear tree is home to several more antennas serving, for example, 2.4 and 5 GHz wi-fi signals, Bluetooth comms with a winch-deployed sound velocity profiler (SVP), and comms with the remote control unit that provides local direct control capability. The antenna trees also support an Automatic Identification System (AIS) from Weather Dock and a set of day/ night-capable cameras on the rear tree to support all-round situational awareness. Floating cradle Although USS has mostly been launching and recovering the Accession 425 from a trailer, the vessel is fitted with four lifting eyes for a crane, and the company is also developing a floating cradle system designed to enable launch & recovery at sea. “It is almost like an RHIB with inflatable fenders around it. You drive the boat into it and then just lift the whole assembly in one go,” Wittamore explains. “The cradle can be towed at 4 knots through the water while the USV drives into it, so it is a boat in its own right.” Remote operations Operations can be managed from a mother ship or from a shoreside remote operations centre, with the boat under human supervision at all times. “We have a USV operator with a minimum of an RYA Powerboat Level 2 qualification, and then we have a master mariner who overseas them,” Williams says. This crew can be enlarged to suit the operational circumstances. “For 24-hour operations, depending on where and how we are working, there will be two or three operators plus a master mariner overseeing operations, and we will have surveyors looking after the payload,” Williams adds. While the AIS works all the time, Williams says the system does not stream camera images constantly during over-the-horizon operations, because of the cost of satcom bandwidth. Instead, the camera imagery is processed locally by Guardian Vision software from Marine AI that recognises nearby objects and alerts the operator, who then streams the camera imagery and determines whether any avoiding action needs to be taken. Autopilot development Developed by Reygar, the autopilot can execute all the usual waypoint- defined survey route plans that would be expected, and accommodates direct manual control via satcom and from the short-range RC handset. However, it also incorporates a number of advanced behaviours specified by USS to cope with contingencies such as comms outages and/or the loss of a thruster. While simple solutions such as carrying on with the planned mission, turning back to port and drifting in ‘dead ship’ mode are also options. The autopilot can be programmed to go into passive or active loiter mode as well. A passive loiter will see the USV motor back to a selected position if it drifts more than a set distance from that position – 5 or 10 m for example – before switching its thrusters off again. In an active loiter mode it will continually June/July 2022 | Uncrewed Systems Technology A rear antenna tree supports mostly comms equipment. The dome houses Iridium satcom, and pole antennas serve cellular and wi-fi bearers (Courtesy of USS) The boat can be driven manually by remote control over wi-fi or cellular comms, using a professional handset customised for the purpose by USS (Author’s photo)