Giant Robots Are the Future of Underwater Mining

How an army of weirdly assorted monster machines work together to bring up riches from the seabed.

Nautilus Minerals

A 700-foot-long ship sits off the coast of Papua New Guinea. But this beast isn't even the star of the show—it is the control platform for a trio of even more colossal robots that are about to undertake a daredevil mission to the bottom of the sea.

Their target is the called the Solwara 1 seabed, a place that contains silver and copper deposits with more than ten times the concentration you'd find on land. Way down there, seawater is superheated to around 750 degrees Fahrenheit by volcanic activity and jets from the sea bed. The hot water mixes with cold seawater and leaves behind tall rock chimneys rich in resources, deposits called seafloor massive sulfides (SMS).

Canadian company Nautilus Minerals has been preparing for years to begin excavating in this difficult-to-reach place, because mining a mile under the sea requires some extreme engineering. "Everything you do on land is ten times more difficult underwater," Mark Collins, Managing Director of ROV Systems at Soil Machine Dynamics, tells Popular Mechanics.

Solwara 1 is such a big task that is requires an equally big machine—three of them, to be exact, with the smallest weighing in at more than two hundred tons. Now Nautilus just needs to find out if these extreme machines are actually up to the task.

Mothership Connection

The control room on board the Production Support Vessel.
Nautilus Minerals

The Production Support Vessel is a 700-foot mothership that controls not only the three giant drilling machines, but also the smaller scout bots that will go to the seabed first. The ship has an opening where cables and pipes snake down to the tank-like robots on the seafloor. Like other tracked vehicles, these megabots are steered by levers controlling the speed of each track. Each robot has a variety of sensors, including seven cameras, nine sonar heads pointing in different directions, gyros, accelerometers, and positioning sensors.

Some of the time, operators are driving blind. The robots have powerful lights, but mining operations turns water cloudy pretty quickly. When things get too murky, maneuvering depends on 3D sonar and positioning sensors.

Once the machines safely arrive at their destination, other sensors help pull off all the cutting and collecting. Instruments show vibration and pumping pressure, and an underwater microphone, called a hydrophone, lets the operator hear the sounds of the cutting head slicing through different types of rock.

The Abyss AUV
Nautilus Minerals

Send in the Scouts

Before Nautilus can start digging, it needs to know where it’s going first. Before the monster machines start working, it's time to send in the scouts.

The first scout machine, called the Abyss Autonomous Underwater Vehicle, is a torpedo-shaped craft 13 feet long and weighing just under a ton. AUVs like Abyss are autonomous, free-roaming, and can carry out missions following a pre-programmed plan. Abyss hits its maximum depth at 30,000 feet and can be in action for a full 24 hours.

Aboard the Abyss are two types of surveying tools. The first is sonar, so the Abyss can map the contours and landscape features of the sea bed. The other is a sensitive magnetometer, which works like a metal detector. This way surveyors can make a complete magnetic map of the potential dig site. Metal ores distort the Earth’s magnetic field, so the map reveals the location of the most concentrated deposits.

The "work class" ROV.
Nautilus Minerals

"Work-class" ROVs (Remotely Operated Vehicles)—bigger than the AUVs and weighing in between two and four tons—are tiny compared to the monster mining machines that follow. These machines are tethered with a communications cable connecting them to an operator on board the Production Support Vessel. Though not as mobile as AUVs, the ROVs have water jets pointing in all directions for both horizontal and vertical motion, so they can be positioned precisely and hover in place wherever they’re needed.

“Work class” means the machines are there to do some serious work. With powerful, hydraulic arms equipped with pincers for collecting mineral samples, the ROV can also mount a drill for collecting rock core samples. After nudging a piece of rock free, the arm is dexterous enough to place samples in a collecting slot. It can even to pick up a snail without hurting it.

The ROVs will break into the volcanic chimney rocks to take ore samples and create a cross section of what’s inside. Then, finally, Nautilus calls in the big guns.

Auxiliary Cutter: The Trailblazer

Auxillary Cutter.
Nautilus Minerals

First up is the 250-ton auxiliary cutter. Built by British company Soil Machine Dynamics, the cutter’s design draws from tech used in underwater ploughs for cable laying and other seabed machinery. While this vehicles is certainly formidable, so are the obstacles it will face.

"You have a lot of underwater terrain features—cliffs, pockets, outcrops—that you can’t get around,” says Collins, Managing Director of ROV Systems at Soil Machine Dynamics. “It's like sending a tank down a rocky beach. It can fall down a hole, so you have to plan your moves carefully."

Auxillary cutter’s blades.
Nautilus Minerals

That’s where the auxiliary cutter comes in, carving out flat working surfaces called "benches" from the uneven seabed. It can sit on a slope as steep as twenty degrees and still cut level. The operator positions the Auxiliary Cutter at the rock faces, deploys its stabilizers, and carries out of series of sweeps with the cutting head, eating away at the rock until it reaches the desired shape. It also demolishes projecting chimneys that can disrupt excavation.

Achieving this without getting stuck or damaged needs careful planning, and a thorough survey so there are no unpleasant surprises. "You need a very detailed map of sea floor,” says Collins “That's the technology that unlocks the potential of the seabed."

Once it has dug these benches, the auxiliary cutter can join in the fun of grinding up ore, or it simply moves on to start another site while this next machine gets to work.

Bulk Cutter: The Big Beast

Bulk Cutter
Nautilus Minerals

At 310 tons, the bulk cutter is the largest of the three seafloor robots. Like the others, it is electrically powered and connected to the surface with a long umbilical cable. It is not as stable as the auxiliary cutter, so it moves around carefully on the flat benches. Getting a track caught on a protruding rock, or worse, toppling over, would be a disaster. While the top speed is only half-a-mile an hour, normal operations are carried at a much slower pace.

"It's like driving a bulldozer by remote control, with separate controls for the left and right tracks," says Stef Kapusniak, project director at SMD. Now, imagine doing all of that while driving blind.

At 300 tons, the bulk cutter is the largest of the three seafloor robots.

"Visibility can be bad, if there are black smokers adjacent to the area or near-field turbidity from the mining,” says Kapusniak, referring to the cloud of debris thrown up while cutting. “The pilots rely on sonar and inertial navigation.”

The 46-foot-long bulk cutter’s main feature is its immense cutting drum, built by Swedish company Sandvik. The drum is based on cutters used by continuous mining machines in coal mines and is powered by two 800-horsepower motors, and it eats away at an exposed rock face.

Once the ore is mashed into gravel, this pulverized rock remains on the sea bed, ready for the third—and final—member of the underwater robot team.

Collecting Machine: The Super Sucker

Collecting machine.
Nautilus Minerals

Borrowing heavily from tech often used in dredging operations, the collecting machine is basically a gigantic vacuum cleaner with the device on the end of its boom is a dredging crown cutter. The operator uses this to agitate the piles of material left by the previous two robots, stirring it up with seawater so it can be sucked up in a slurry. This slurry passes through three 440-horsepower dredge pumps to the Subsea Slurry Lift Pump, and from there it is piped up to the surface.

One of the big challenges is maintaining the correct concentration of ore in the slurry mix. If you have too little, you’re wasting energy by just pumping water. If you have too much, the pipes clog up and the whole thing stops.

Rem Etive, the Production Support Vessel.
Nautilus Minerals

Once the collecting machine creates the perfect mix, the massive robots’ work done, but the job is far from over. The riser system brings the slurry through flexible pipes to the Production Support Vessel on the surface.

The slurry is dried out and an advanced, automated cargo handling system takes over. There are two scraper conveyor belts mounted on frames which can move both horizontally and vertically through the hold. These pick up the ore and load it into bucket elevators, which transfer it to mobile telescoping pipes.

Then these pipes carry the ore to the hold of a vessel moored alongside, a fifty-thousand-ton bulk ore carrier known as a "Handymax," which the sets sail for China for smelting.

By Land or By Sea?

"Work class" ROV delicately handling a snail.
Nautilus Minerals

On land, an operation like this would involve a vast pit with a fleet of trucks in constant movement, a cloud of dust, and plenty of safety hazards. At sea, there is nothing to see on the surface as the ore is pumped on board.

Having done several environmental impact analyses with universities and environmental institutions, Nautilus says their mining operation will cause little disturbance compared to terrestrial mines. Using a commonly used measure of impact, the Nautilus project will cause around one-tenth as much disruption as an equivalent terrestrial mine.

Environmental concerns have been a key factor in pushing oil exploration offshore, and opening a new mine underwater may prove much easier than getting the necessary permits on land. Studies suggest that the seabed recovers rapidly, new chimneys start forming almost immediately and are recolonised by marine wildlife after all the machinery moves on.

Of course no one has tried this type of mining before, and whether it will become the future of mining remains an open question. But if it’s successful, it would mean the creation of a whole new mining industry, largely invisible, offshore, and underwater— with a workforce of giant robots hard at work on the seabed.

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