Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

78 In operation | Hefring Engineering OceanScout The vehicle can also be recovered using a boat hook, crane, davit or A-frame. Carbon fibre handles integrated into the tail fin are designed to make recovery by hand or boat hook both easier and safer. Preparing the OceanScout for a new mission means cleaning off any bio- fouling that may have accumulated, installing a fresh set of batteries and loading a new set of mission commands detailing where the vehicle must go, along with a few data collection settings. Ordonez singles out the battery change procedure as an example of the effort the Hefring team put into the design for ease of operation. The first step is to relieve the internal vacuum (maintained as an indicator of watertight integrity), then comes removal of the nose cone, disengagement of a single connector and the removal of the battery securing plate. This allows the batteries to be removed from the front of the vehicle. “These steps are then performed in reverse to complete the task, with the whole process taking only a few minutes,” he says. The nose section houses the sensors, both navigational and scientific, so swapping the nose cone for another changes the sensor package, and the process is similar to that for replacing the batteries. “Safe handling and easy preparation lower the stress these operations put on users,” Ordonez says. “As a result, smaller teams can handle larger glider fleets. The smaller, lighter vehicles also use less material, further reducing production costs.” Optimised for shallow water Optimised for continental shelf and upper ocean measurements, the OceanScout has an operational depth limit of 200 m, which also limits the stresses to which the structure is subjected. This is essentially what allows it to be made lighter, leading to a lower displacement and enabling buoyancy to be changed over a larger range than would be possible with otherwise comparable vehicles of larger displacement, Ordonez says. The OceanScout displaces 22 litres of water when submerged and is fitted with a 0.8 litre, single-piston variable buoyancy engine (VBE) that moves water in and out of the vehicle’s ballast chamber. Combined with low weight, this relatively large VBE compared with the vehicle’s displacement allows it to exercise a greater influence than it would have over a heavier vehicle that displaces more water. In turn, that enables the glider to operate in a wider range of oceanic water densities and endows it with true self-ballasting capability, Ordonez explains. The VBE’s piston is driven into the ballast chamber against hydrostatic pressure by an electrically powered ball screw actuator in the tail section. This forces water out to increase the glider’s buoyancy, while withdrawing the piston from the ballast chamber lets water back in, reducing buoyancy. The actuator is housed in the tail spike and changes the December/January 2022 | Unmanned Systems Technology Designed for launch & recovery by one person, the OceanScout comes with a trolley/cradle that can be wheeled around or secured to the side of a boat Overall length changes as the OceanScout’s variable buoyancy engine extends and retracts its piston, which is actuated by an electrically powered ball screw