92 vehicles without reference points, and therefore especially vulnerable, with one company planning to use the sun as an autopilot reference point. Many precedents for this exist. For centuries, sailors navigated by the sun using sextants and other tools, and some satellites and crewed aircraft today reference the sun for navigation. So, a system for autonomous solar navigation could be built around cameras to recognise the sun (thermal cameras are likely to be used by USVs and low-altitude UAVs to prevent overcast conditions from causing failures) and use its position relative to the ground or horizon to feed internal solar-tracking models. Test results indicate that an autopilot designed with such a function can estimate heading accurately and smoothly, and be able to do so for long periods of GNSS outages. On the ocean While the subject of autopilots tends to focus particularly on the needs of uncrewed aircraft, there is a growing supply of marine autopilots in the industry, as well as multi-domain autopilots that can be used for both air and sea (and sometimes also land) vehicles. Such solutions must be designed around an integrated ecosystem, incorporating steering control and propulsion control, as well as the appropriate electronic navigational charts and integration of radar, automatic identification systems (AIS) and other vital marine navigation safety systems. Depending on the context, forwardlooking sonars and doppler velocity logs may be useful for marine navigation and collision avoidance. The front end of such software must accordingly be built for USV-applicable mission planning, localisation, steering and power control, with additional features in the back-end programmed with alignment to appropriate maritime standards. For instance, USV autopilot engineers in the UK are moving towards adherence with the UK Maritime & Coastguard Agency’s (MCA) Workboat Code, Edition 3, Annex 2 for ROUVs (remotely operated unmanned vessels, as the UK MCA calls them). Published in December 2023, this covers safety standards for USVs in failure mode, how to handle hot handovers of control, assurance requirements, and other critical factors for marine autopilot software and hardware. On top of this, one must distinguish between the autopilot requirements of smaller versus larger USVs, given that professional, uncrewed vessels now range from less than a metre to dozens of metres in length, and in some cases (particularly in large-scale freight and defence) even hundreds of metres. Professional 3-12 m USVs can get by on a computer system good enough to enable autonomous navigation with software processing and sensor interfacing for obstacle detection, collision avoidance, anti-grounding and potentially a few simple vessel system controls, such as bilge-pump operation algorithms. For USVs closing on or exceeding 20-25 m in length, a very tight integration of all these capabilities with all vessel systems is likely to be needed, along with added intelligent functions, such as virtual anchors or a return-to-base mode upon loss of control. All types of USVs operating at sea must combine their use of radar, vision, AIS, sonar and so on with the requirements of the Convention on the International Regulations for Preventing Collisions at Sea (COLREG) to satisfy maritime regulation agencies of safe behaviour – even if certain COLREGs can suffer vague wording regarding such things as value judgements on safe distances and clearances between one’s vessel and a nearby vessel, which merit real-time analysis of a USV’s speed, attitude and surroundings by an autopilot. Designing an autopilot Despite autopilot products being ordered in larger quantities, integrators still frequently want them to be tailored to parameters specific to their vehicle, environment and mission set. Wherever possible, autopilot suppliers will try to cater for very specific requirements through tuning software, as customising hardware is an expensive and arduous process, typically affordable only to large customer orders. To that end, autopilots are increasingly designed with hardware architectures that can run different versions of navigation and control software, depending on which of five discernible categories of uncrewed system are to be April/May 2024 | Uncrewed Systems Technology Heavy-duty USVs, like this large, hydrogen-fuelled vessel, increasingly use marine autopilots such as Robosys’ VOYAGER AI solution (Image courtesy of ACUA Ocean)
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