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50 The Superior is intended to operate at 6000 m using all of Kongsberg’s newest and most powerful payloads. To enable that, the width will stay the same but the length will increase. HISAS arrays range in length from 1.2 to 2.4 m, which means the length of the vehicle must be increased, although some of the foam that would typically have been built into the Superior is being removed to provide space and weight for the HISAS. The result is that the Superior is roughly 6.5 m long. “It’s not a big difference, but there are limits to how long you can usefully design an AUV relative to its width, for controllability and stability, as well as ease of recovery,” Mills says. “We’re also now on the third generation of synthetic aperture sonar [SAS] processing, with a complete software and mechanical redesign of how we process SAS imagery. That streamlines many of the constituent SAS processes, speeds up the processing time, and reduces the overall processing load and power requirement. “Such are the reductions in size, weight, and power of SAS processors that we can run SAS image processing on board during missions, so that 60 Gbytes of data are refined down to 1 or 2 Gbytes of actionable data by the time end-users recover the AUV.” Research Connecticut-based Exocetus Autonomous Systems has delivered its first MOD2 glider AUV to John Hopkins University’s Applied Physics Laboratory (APL). “They bought the first system, and they’re planning to buy a couple more,” says Joe Turner, co-founder and COO of Exocetus. “They’re using it for an internal r&d project, and they have several applications they think it will be useful for, so they’re now proving those out. These could include physics or other scientific research, or investigations they’ve been hired by the government to do.” Exocetus has built three MOD2s so far, one for the APL and two for in-house use such as for demonstrations. The AUV’s hardware is tested and proven, with software development continuing with Exocetus’ partner Greensea Systems, which is responsible for providing the control software. Greensea’s extensive programming library creates the potential for integrating thousands of sensors, as well as a wide range of unique missions and behaviours for the vehicle. These, Turner says, are a consequence of the open approach to the software’s architecture and development kits given to users to enable them to modify AUV behaviours. “Most AUVs have closed software, owing to worries about the integrity of the vehicle or that modifications could result in the loss of the system,” he says. “Greensea’s software however has allowed us to put in enough back-ups so that if some critical error occurs, the vehicle can rescue itself.” While all the vehicle’s functions are programmed and operational, the ongoing software development aims to optimise the power management and improve autonomy. That includes manoeuvres such as loitering for a time until being autonomously triggered into action by a specific event, or spiralling in the water to gather concentrated information in one slender column of the sea. The typical advantage of glider AUVs compared with propeller-driven types is duration. Weeks or months of endurance can be added with a buoyancy drive such as that on the MOD2, enabling a wider swathe of area to be surveyed. The MOD2 carries a relatively large buoyancy engine for a glider – 5 litres – varying about 7% of its weight in water February/March 2019 | Unmanned Systems Technology The MOD2 glider AUV from Exocetus will conduct demonstrations for universities and researchers in the next few months (Courtesy of Exocetus)