56 In operation | Robotican’s Goshawk counter-UAV Capture and disposal Notably, the capture mechanism in the Goshawk has not been designed for any firing of net- or water-based projectiles, or jamming signals, as sometimes seen in automated, remotely piloted or handheld C-UAS devices. Instead, a ‘net’, typically consisting of four cords, hangs from beneath the UAV like a curtain. The net’s cords are linked together by a single rod at their lower end and from a long, rod-shaped magazine payload suspended just below the multirotor hub. These two structural rods ensure the Robotican’s unusual form of net doesn’t twist or tangle in the wind. In almost all instances, it hangs in the same direction, with the cords running along the breadth of the Goshawk. Capture works by the Goshawk intercepting a target drone, releasing a net to unroll and hang below, and then flying such that the arms and propellers of the target become entangled (nondestructively, it is important to note) and its motors are jammed. The craft is hence arrested and carried securely by the Goshawk. “The Interceptor will specifically aim to fly above the target to catch it in the net hanging below. That’s harder to do than just flying into the target, like I know some self-destructive C-UAS drones have been made to do, because the Interceptor doesn’t always have a clear view of the target from above,” Geva explains. “It’s also much easier computationally than aiming and firing a net, for which you’d have to do a bunch of targeting calculations, as if you were firing ordnance. Those kinds of solutions also sometimes require that the UAV firing the net comes in a really specific direction relative to the target. They need really precise timing to pull off the shot exactly right, and they also often have to take greater account of the wind speed and direction than we do.” The Goshawk’s algorithms pertaining to capture include some predictive measures in addition to the flight-path calculations being made post take-off, as it must consistently be able to capture potentially threatening moving targets, whether a head-to-head approach is taking place or a chase scenario in which the Interceptor must catch up to a drone and not allow it to escape. “Luckily, the Goshawk is faster than most commercially available UAVs, to the point that it can perform captures from many different angles of attack, including coming up behind a target multirotor, and then quickly surpassing it, and doing a U-turn to capture it and drag it away from wherever it was headed, such as its intended target,” Geva says. “The bracket holding the net before it is deployed isn’t a single-fire solution. Each Interceptor can carry a magazine stocked with multiple nets, and each net can be electromechanically detached from the UAV in order to dispose of the net and thereby drop the captured hostile drone in a place that the end-user chooses.” Carrying multiple nets has benefits beyond swarming attack scenarios requiring multiple captures per flight. In some rare cases, the Goshawk may miscalculate its angle of attack and fail to capture its target, damaging its net on the target’s propellers or obstacles such as tree branches in the process. In such situations it is important that the UAV can discard the affected net to switch to one functioning optimally. “Creating this net took a lot of trial and error. We tested a lot of different capturing solutions, including many inspired by other C-UAS drones, and although defence buyers tend to like the idea of shooting a net from a UAVmounted cannon, in the end they need a solution that works consistently in capture and disposal, and doesn’t place too much computation burden on the Interceptor,” Balshai says. The optimal disposal location depends entirely on the use-case and the security risk. Locations where attacking drones are suspected to carry ordnance (including improvised explosive devices) will require a highly isolated drop-off location, deserted of personnel and devoid of anything that could cause harmful shrapnel to fly far away. “Although a mission should be fully autonomous, if the end-user wishes they can take control of the gimbal to pan down and look at the captured drone, to assess its model or view if it’s carrying anything of concern,” Geva notes. Regardless of the location, dropping both the net and the offending drone there ensures the latter remains entangled and hence immobilised until a specialist team can arrive to take care of it, if necessary. “Lowering the net and releasing it works via a combination of an electromechanical actuator that moves to first release the net, and an electromotorised wheel for unrolling it, so it is suspended below the Goshawk. April/May 2024 | Uncrewed Systems Technology Once it has captured a hostile drone, the Goshawk can fly it to a user-specified disposal area, where it electromechanically releases the net and drops off the drone
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