How cutting-edge UK engineering is revolutionising underwater exploration

The National Oceanography Centre’s fleet of autonomous yellow submarines is a step forward on the road to net zero research. Here’s why that matters.

Published 11 Jan 2022, 13:40 GMT
One of the Boaty McBoatface submersibles on trial in Loch Ness.

One of the Boaty McBoatface submersibles on trial in Loch Ness.  

Photograph by National Oceanography Centre

With a surface area equivalent to the size of Great Britain, any melting of the 74,000 square miles of the Thwaites Glacier in Antarctica could have a potentially serious impact on global sea levels. If the ice melts rapidly and the glacier collapses, scientists warn that sea levels would rise by about 65cm (25 inches) over coming centuries. The glacier is already responsible for about four percent of global sea-level rise.

To assess the atmospheric and oceanic conditions where the ice shelf meets the Amundsen Sea, the icebreaker Nathaniel B Palmer, set out from Punta Arenas, Chile on January 6, carrying a fleet of Autonomous Underwater Vehicles (AUV). By poignant coincidence, the start of the 65-day mission was the centenary of the death of legendary polar explorer, Sir Ernest Shackleton.

The AUVs will monitor the thickness of the ice, measure the melting process, and record the seafloor below, operating in conditions inaccessible to humans.

A huge iceberg dubbed B-46 – with a surface area estimated at 66 square nautical miles – breaks into Pine Island Bay in 2018. The Great Britain-sized Thwaites Glacier – which this new mission is set to assess – also terminates in this bay, and has been labelled the 'Doomsday Glacier' for the catastrophic effect its melting would have on global sea levels.  

Photograph by NASA Goddard Space Flight Centre

“We will deploy two big underwater robots underneath the ice to collect detailed data from this crucial area of the glacier that will enable us to understand what will happen in the future,” said Professor Karen Heywood, from the University of East Anglia and UK lead on the International Thwaites Glacier Collaboration TARSAN project in an official statement.

“By measuring the ocean properties in sub-ice shelf cavities, we can understand how the ocean transports heat and what impact this may have on the glacier. I and my team back at UEA are going to be remotely piloting the six ocean gliders, smaller robots, once the scientists on board launch them into the water.”

Hands-free research

The capabilities of the AUVs represent considerable technological progress. Just a quarter of a century ago, a team of scientists and engineers from the National Oceanography Centre (NOC) carefully launched its first Autonomous Underwater Vehicle (AUV) in Portland Harbour, Dorset. The yellow leviathan spent five minutes submerged, diving to a depth of 3 metres, a pioneering example of the transition from remote control to self-driving operation, using GPS and dead-reckoning to navigate.

Fast forward 25 years, and the NOC’s three new ALR6000 (Autosub Long Range) unmanned submersibles are capable of operating at depths of up to 6,000m, travelling 2,000km and spending months under the sea in a single deployment, while three more ALR1500s have a shallower depth rating of 1,500m but an increased range of up to 6,000km.

The autonomous nature of the submersible research vessels mean that, when developed fully, they will enable researchers to conduct long term projects without the associated carbon footprint of large, staffed expeditions. 

Photograph by UK National Oceanographic Centre

The ALR6000s are charmingly dubbed Boaty McBoatface – picking up the nickname after the Natural Environment Research Council sidestepped a mischievous social media campaign to call its new research ship (now sporting the more dignified RRS Sir David Attenborough) by the same name. This cutting-edge fleet is transforming the exploration of deep oceans and helping scientists to monitor climate change, using net-zero technology to travel under ice, take readings in remote locations and collect data however rough the waves above.

Built for depth

The propellor-driven ALR6000 is a triumph of marine engineering. It measures just 3.62m long, about half the length of the original ‘yellow submarine’, has a cruising speed of about 0.5m per second (it’s capable of moving more quickly for shore-based launches where it might need to contend with faster tidal currents), and weighs 700kg – 800kg depending on the mission set-up.

Two forged aluminium alloy pressure spheres sit at the heart of the AUV, housing its batteries, sensors and monitoring equipment. These spheres are then mounted in a polypropylene frame, wrapped in a yellow, glass-reinforced plastic shell, in a vessel designed to withstand the crushing pressures of deep ocean.

“One of the most exciting deployments we are looking at is a full Arctic crossing from Svalbard to Point Barrow in Alaska, completely under the ice for two months.”

Dr Maaten Furlong

Reflecting on the technological advancements since 1996, Dr Maaten Furlong, Head of the Marine Autonomous & Robotic Systems Group at the NOC, says every element of the AUV has improved. “The design tools, batteries, electronics and sensors are all a lot better, as is the software you can utilise,” he says.

Far from being watertight, the ALR6000 is ‘free flooding’; its batteries, sensors and electronics housed in two large, forged pressure spheres to withstand the 600-bar pressure at the bottom of the ocean. These spheres also provide most of the buoyancy for the ALR6000, aided by syntactic foam, formed from small glass microsphere set in a resin matrix. The sub has to be positively buoyant at the surface, but needs to be as close to neutrally buoyant as possible under water, relying on the angle of its wings to dive or resurface.

This presents a tough engineering challenge, because if the spheres and foam compress faster than the sea water, they would become negatively buoyant, which means they would sink if they stopped moving. A mechanical fault could leave several hundred thousand pounds worth of components and an untold fortune in intellectual property and mission data on the ocean floor. Yet calculating the perfect buoyancy poses a mathematical conundrum because sea water compresses as it gets deeper. This change in density, from 1,026kg per m−3 on the surface to 1,051kg per m−3 at 6,000m deep, “means it produces more lift, so the sub becomes more buoyant as it dives,” explains Furlong. Higher density sea water also explains why it’s easier for humans to float in the salty Dead Sea than a freshwater lake.

The National Oceanographic Centre's underwater fleet are displayed next to the research vessel Discovery at the centre's mooring in Southampton. On January 6th – the centenary of Ernest Shackleton's death – the fleet set sail aboard the  US National Science Foundation's icebreaker Nathaniel B. Palmer, bound for the Thwaites Glacier, Antarctica where they will be used to determine the effect of the glacier's melt on sea level rise.    

Photograph by UK National Oceanographic Centre

Add into the equation the fact that the ALR will also compress slightly at depths, and the calculations to stay about 0.3% positively buoyant (it is ballasted to be 2.5kg positively buoyant in about 800kg weight) are fiendishly complex.

“As the AUV doesn’t compress quickly enough to accurately track the seawater compression, we use a combination of bags of silicon oil and air bladders to tune the buoyancy when operating in deep water,” said Furlong.

The NOC does have two lab-based pressure vessels in which to investigate the impact of extreme pressures, but even the bigger vessel is only about 95cm in diameter and 1.2m long – far too small to assess a complete Boaty McBoatface. “We can put all the sub components in the pressure vessels, but not a complete vehicle,” confirms Furlong.

The long view

The impressive sea-crossing range of the ALR6000s is due in no small part to the high energy-density of their lithium-thioynl chloride cells, built into the ALR’s battery pack. These represent a quantum leap forward on the lead acid batteries of the original subs, and have almost three times higher energy density than the batteries in a mobile phone. The sub’s batteries cannot, however, be recharged. 

The good news is that the ambient temperature at the bottom of the ocean is still 4 to 5 degrees Celsius, which is warm enough to avoid compromising the battery performance in the way that a sharp frost or snow can shorten the range of an electric car.

This matters because the NOC is preparing for expeditions in areas with the coldest surface temperatures on the planet.

“One of the most exciting deployments we are looking at is a full Arctic crossing from Svalbard to Point Barrow in Alaska, completely under the ice for two months,” said Furlong.

A further project aims to spend a full calendar year in Antarctica, with the ALR patrolling and monitoring a transect, then anchoring itself to the seabed, before repeating the process at fixed intervals over a 12-month period, as the sea freezes then thaws, so scientists can gain greater insights into the seasonal cycle of the polar environment.

Net zero research

One of the major advantages of this autonomy is that ocean science can be conducted in a more climate-friendly fashion.

“One of the great challenges of oceanographic research is that you have to send out really big ships to carry the instruments you need, and our ships would typically burn 11 tonnes per day of marine gas oil when they are steaming,” said Furlong. “The move towards using marine robotics significantly reduces the carbon footprint of this research and enables the transition towards net-zero observations. Autonomous vehicles can do some but not all of what ships can do, which is why we are working so hard to increase the capability of AUVs to compensate for not using ships.”

Jonathan Manning is a freelance journalist based in the East Midlands. Read more of his articles for National Geographic here

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