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

77 Buoyancy propulsion As the term suggests, buoyancy-driven gliders propel themselves by changing their buoyancy, usually by pumping oil between two chambers, one of which might be a flexible bladder that contracts as it empties, allowing denser water into the space in the hull it previously occupied. The OceanScout uses a slightly different method though. Changing buoyancy would merely alter their depth without some means of forward propulsion, which gliders achieve with lift-generating surfaces including wings that can be flat or formed with hydrodynamic profiles, or simply with tail fins. Changing buoyancy and pitch angle enables the vehicles to dive and climb, combining vertical motion with horizontal, Ordonez explains. That gives their movement through the water its characteristic sawtooth profile. Pitch and roll moments are generated by shifting the vehicle’s centre of gravity by moving the battery back and forth, and swinging it from side to side. Gliders’ leisurely, frugal progress through the ocean is guided by following programmed waypoints, and they typically collect water profile data such as temperature and salinity, although they can support various other sensors so long as their energy consumption is modest. Data from the sensors, navigation system and vehicle status are transmitted to the operator via satellite using an antenna in the tail that is periodically exposed above the surface. “From this basic operational framework, glider users develop a variety of missions to observe aspects of the ocean, such as boundary currents like the Gulf Stream surrounding continents, or measuring oceanic heat ahead of an approaching hurricane,” Ordonez explains. Like other gliders, the OceanScout is a UUV designed for long-duration ocean observation missions using very small amounts of power for propulsion, control, sensing and comms. One mission for which the OceanScout is intended is gathering acoustic data, for which the vehicle uses an integrated passive acoustic monitoring (PAM) system. OceanScout-PAM deployments, Ordonez says, are designed to characterise features in the acoustic environment by establishing an archive of ambient acoustic baselines to show what measured volumes of water normally sound like, and charting marine mammal distribution and behaviour along with noise of human origin and the causal links between them. “Future development of our PAM system is designed to enable real-time acoustic measurements and actionable data for time-critical actions and mitigations, such as preventing harmful noise exposure to marine mammals.” Operational simplicity With its design driven by the goal of making glider operations simpler and less costly, the OceanScout has a number of features that Ordonez says are unique. He points out that at an approximate weight of 22 kg, the glider is light enough for one person to move, deploy and recover. Deployment from a manned vessel involves pivoting the glider’s cradle over the side and releasing the latch, while recovery is a matter of lifting it from the water and sliding it into the cradle, which is secured to the side of the support vessel, and locking it in place with a latch that operates much like a seat belt buckle. Hefring Engineering OceanScout | In operation We are lowering the entire cost of ownership, not just that of the vehicle but the costs of deployment and recovery, personnel and expertise Unmanned Systems Technology | December/January 2022 The OceanScout manoeuvres in pitch and roll by moving its battery longitudinally and swinging it laterally to change the centre of gravity, eliminating movable control surfaces