Robotic underwater glider sets out to circumnavigate the globe

A small robot submarine is setting out to go around the world for the first time. Teledyne Marine and Rutgers University New Brunswick in New Jersey are launching an underwater glider called Redwing on its Sentinel Mission from Martha’s Vineyard in Massachusetts on 11 October.

Researchers have been using underwater gliders since the 1990s. Rather than a propeller, gliders have a buoyancy engine, a gas-filled piston that slightly changes the craft’s overall buoyancy. An electric motor pushes the piston in to make the glider heavier than water so it slowly sinks, coasting downwards at a shallow angle. On reaching the bottom of the dive at around 1000 metres, the piston is pulled out and the submarine, now buoyant, glides upwards. The result is slow and steady progress along a sawtooth trajectory. Auxiliary propellers can be engaged where needed, but the aim is to avoid this.

“Redwing will be gliding with the currents rather than fighting them, travelling at an average speed of 0.75 knots”, or just under 1 mile per hour, says Shea Quinn at Teledyne Marine, who is leading the Sentinel Mission.

At 2.57 metres long, Redwing is no bigger than a surfboard, but weighs 171 kilograms. Previous gliders carried out missions lasting months – Redwing’s fuselage is packed with batteries, giving it even greater endurance.

“The historic Sentinel Mission aims to achieve its circumnavigation in around five years,” Brian Maguire at Teledyne Marine. Redwing will travel alone, tracked by engineers from Teledyne Webb Research and students from Rutgers University, as it surfaces and communicates via satellite. Mission control will adjust the glider’s heading twice a day to keep it on the projected flightpath. During the five-year-long journey, it will probably need a battery change halfway through, says Maguire.

Redwing will follow the path of explorer Ferdinand Magellan’s 1519-1522 circumnavigation, calling at Gran Canaria off north-western Africa, Cape Town in South Africa, Western Australia, New Zealand, the Falkland Islands in the South Atlantic and possibly Brazil, before returning to Cape Cod, a journey of around 73,000 kilometres.

Gliders can carry out long-range, long-endurance research missions without expensive support ships, and they have become vital for tracking data key to understanding climate change. Redwing will gather data on ocean currents and sea temperature in relatively unknown regions with a variety of instruments.

“We believe this is the most sustained open ocean sampling exercise ever undertaken,” says Maguire.

Previous glider missions crossed the Atlantic in 2009 and the Pacific in 2011, and have travelled under the Ross ice shelf and other inaccessible spots. “Gliders are brilliant tools to make measurements in areas that are too risky to send a ship – like the middle of a storm or hurricane, or in front of a calving glacier,” says Karen Heywood at the University of East Anglia in the UK. The main hazards to completing the mission are likely to be fishing nets and shipping lanes rather than weather conditions. “Gliders are actually remarkably resilient, and are able to withstand strong winds and rough seas,” she says.

Alexander Phillips at the National Oceanography Centre in the UK says the glider will have to contend with other hazards too, including sharks and biofouling, in which plants and algae accumulate on the vessel’s outer shell. “Biofouling can make a glider inoperable due to marine growth on the glider’s exterior. In certain areas of the ocean, gliders have been lost due to sharks. Shipping and fishing occasionally damage or result in loss of gliders.”

Data from the mission will be shared with universities, schools and other institutions worldwide, but the main aim is to highlight the capabilities of gliders and inspire future missions.