Issue 55 Uncrewed Systems Technology Apr/May 2024 Sellafield’s UAV equipment l Applied EV Blanc Robot l Battery tech l Robotican’s Goshawk l UGVs l UAVHE RW1 rotary l Roboat UVD l Autopilots l Arkeocean UVD l UMEX 2024 l CycloTech UVD

101 Swarm overview Industry literature specifies a variety of different swarm types, with varying permutations of command, control and communication (C3) orderings and hierarchies, as well as different degrees of autonomy within individual uncrewed systems and across the group. Arkeocean’s swarm has a distinctly top-down structure: the Incas do not communicate with each other, as installing an acoustic modem would have taken up the limited internal space and production costs per unit (with little benefit in terms of actual data bandwidth). “The C2 centre is at the top of the swarm control structure, and there, via the Mayas, we receive the survey data and the time of arrival (TOA) of the positioning signals emitted by each Inca, and then transmit any position adjustment commands to the Mayas, who then communicate those commands to the Incas,” Brizard says. To do this, the Mayas travel vertically up and down from the surface to the Incas, thrusting up to the surface to communicate with the C2 centre using their wi-fi and then returning to the next Inca afterwards. This is key to the effectiveness of the antennas. The Incas do not actually engage in constant position-holding while actively listening for submarines as this would mean constantly spinning up their thrusters and muffling potential ULF noise. Instead, they drift for much of the time, thereby increasing the signalto-noise ratio of their ULF recordings. Total endurance figures have not been determined as yet, being highly dependent on currents during operations. Arkeocean continually collects data during its deployments to gauge the suitability of its battery packs for the CONOPS, although it anticipates needing to increase the capacity of the packs on its micro-AUVs in future versions. Drifting for too long obviously risks dispersing the Incas, and hence harming the antenna’s integrity. So, based on position adjustment commands delivered by the Mayas, the Incas will very occasionally activate their thrusters to maintain the geometry of the antenna, which may be a vertical line in the water column or a grid. In most cases so far, Proteus has been trialled as a ‘2D vertical antenna’, with a flat, vertical panel of Incas running down through the water, thereby operating similarly to an air traffic surveillance radar, although Arkeocean notes that antennas with 3D shapes are possible too. “In terms of the number of AUVs per operation, the nodes in the antenna sampling for ULF readings should be spaced apart at half the wavelength of the higher end of the band,” Brizard says. “As the higher end of ULF is 100 Hz, and the wavelength at that frequency is 15 m, half of that is 7.5 m. Hence, we would theoretically need an Inca AUV every 7.5 m, but if you want an antenna several kilometres long or wide, you will need a lot of AUVs to do it this way. “So, we borrow a trick from the radar world; that is, we form what’s called a sparse antenna. By intelligently reducing the number of receiving nodes in the antenna and using some estimation algorithms to compensate, we can maintain an acceptable performance as a fully populated antenna with a fraction of the AUVs needed.” Long baseline from surface Theoretically, embedding AI software in the Incas could have enabled the swarm to self-adjust, communicating with one another via acoustic modems to localise, based on each other’s positions, correct themselves for current-caused drift, and reactively change their collective geometry in response to submarines or other detected threats. However, the amount of processing power needed for such software would have driven up the cost of each unit prohibitively (as would the integration of acoustic modems on each one). Instead, real-time and accurate localisation of the Incas is performed by using the Mayas as long baseline (LBL) beacons. As our readers in the maritime industry will know, LBL networks typically work through seafloor-installed, acoustic positioning transceivers, which Uncrewed Systems Technology | April/May 2024 The Incas are configured to be able to hold position, but they spend most of their time underwater, drifting freely to conserve battery energy