Sea Technology

FEB 2013

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Flying Drone for AUV Under-Ice Missions Remotely Controlled Drone Aids Arctic Measurements, Ice Tracking By Sascha Lehmenhecker ��� Thorben Wulff S tarting in 2010, the Alfred Wegener Institute (AWI) has deployed a Bluefn Robotics Corp. (Quincy, Massachusetts) Bluefn-21 AUV in several dives under Arctic sea ice. All dives were conducted close to AWI���s deep-sea observatory, Hausgarten, which is located west of the Svalbard Archipelago in the icemargin zone of the Fram Strait. Since the ice-margin zone is a highly dynamic environment, it is crucial to track the position of the ice edge to defne the AUV���s mission parameters. In 2011, a GPS-based tracking system was developed to mark the ice edge and to observe the ice drift before and during an underice dive. However, deploying the transmitters on the ice turned out to be risky and time-consuming. To facilitate the deployment of the tracking system on the ice, a remotely controlled fying drone was developed for polar operations. Basic Conditions The major goal was to design a vehicle able to carry a GPS transmitter along with other instruments onto the ice and back without using, for example, a rigid infatable boat (RIB) for deployment. Conceptual plans considered the fying drone as a transporter that deploys instruments on the ice and then fies back to the ship. After completing all the measurements, the drone would return and recover the instruments from the ice. However, fog and the ice drift could cause diffculties in fnding the location again. Thus, it was decided the drone would land on the ice and stay there to act as a GPS transmitter. Along with the GPS transmitter, a sensor for photosynthetically active radiation (PAR) would be integrated to measure light on the ice and represent a surface reference for the AUV���s PAR sensor. As AUV dives may take up to 10 hours, an operational time of 14 hours on the ice was considered to be mandatory for the drone. Functional Principle Preliminary tests conducted with a four-engine drone, or quadrocopter in harsh conditions such as crosswinds The hexacopter on the ice edge in the Arctic. proved reduced in-fight stability compared to a six-engine drone concept, or hexacopter. A hexacopter can also lift larger weights than a quadrocopter of the same size and offers bigger safety reserves. For example, a hexacopter is able to compensate for the stability problems caused by an engine failure, whereas a quadrocopter would suffer an uncorrectable thrust imbalance and most likely a crash. The hexacopter���s mainframe consists of an aluminum frame with six arms arrayed radially outward from a center point. The arms are made of square tubes (15 millimeters by 15 millimeters) and have a length of 350 millimeters each. At the center point, the entire electronics of the hexacopter is mounted in a lightweight carbon structure. For insulation, the hexacopter is protected by a 3-centimeter-thick Styrofoam hull. Only the ends of the aluminum arms and the PAR sensor stick out of the hull. Additionally, the insulation offers suffcient buoyancy to make the hexacopter foat in case of a crash or an emergency landing. For visibility reasons, the outer hull of the hexacopter is painted in bright orange. Only a vertical line at the rear side of the hexacopter and the upper side of the hull are painted in black. With the black line, the pilot can determine the hexacopter���s orientation. The black topside of the hull is to minimize the refection of incoming sunlight so that the PAR www.sea-technology.com FEBRUARY 2013 / st 61

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