How do you build a submarine that can withstand the enormous pressure found at the ocean’s deepest depths? Explorer Sylvia Earle thinks the answer might be simple – build it from glass.

When Sylvia Earle travels many miles below sea level, to the depths of the Marianas Trench, she wants a good view of the alien life dwelling in the abyss. “As a scientist, I want to be able to see what’s out there – that’s the whole point of going myself,” she says. While down there, she also wants to be able to gently gather organisms using a kind of ocean hoover. And her vehicle will also need to move without making noise, to save scaring the creatures.

Her vision is audacious. If she has her way, the sub that will take her miles below the surface will have a pressure hull made of glass. It’s almost as if she will be travelling in a giant snow globe. “You turn the sub and it’s like turning your body,” she imagines. “You can see things out of the corner of your eye if you have a clear sphere around you. If you’re just looking through a small porthole or through the lens of a camera, you don’t get that same sense of being there.”

Sylvia Earle wants to discover what lives in the icy ocean depths (Science Photo Library))

Sylvia Earle wants to discover what lives in the icy ocean depths (Science Photo Library))

We normally think of glass as a brittle, fragile substance. But in deep sea conditions, it undergoes molecular changes that make it the perfect material for ocean exploration – better than steel or titanium. “For science it’s a phenomenal solution,” says Tony Lawson, Earle’s engineering director at Deep Ocean and Exploration Research Marine. Even so, manufacturing such a large glass orb will present some unique challenges and dangers.

The project will be the culmination of Earle’s distinguished career as one of the world’s leading marine biologists. She won’t be the first to reach those depths: the Trieste sub carried a team of two in 1960; more recently, James Cameron filmed the bottom of the ocean for his Deepsea Challenge 3D film. But if she succeeds, she will be the first to do so while protected by a glass shell.

‘Pilot and scientist’

The US Navy had, in fact, first looked into the idea of a glass submersible in the 60s – but it turned out not to be suited to some of their demands. “Glass doesn’t like explosions – end of story,” says Lawson. Although glass subs do sometimes carry scientific equipment to such depths, they haven’t been used for manned missions. Yet the other alternatives – such as cameras placed on the outside of a sub, just wouldn’t have given Earle the freedom she wants. “You might as well be operating them on the surface,” she says.

In some ways, her attitude harks back to the scientist-explorers of old, who had a hand in every part of their mission. “I want to be there with every fibre of my sensory system on full alert. That’s what it’s like to be in a submarine, especially a submarine that you’re driving yourself – I love the idea of being a pilot and a scientist enjoying all the wonderful benefits of the engineering skills that have gone into providing access to the sea.”

This video is no longer available

This video is no longer available

Lawson admits the prospect was daunting. “She was pushing very hard for a glass sphere, and at first I was pretty hesitant,” he says. “Glass is the oldest material known to man and one of the least understood.” He was soon convinced however when they began to explore what we do know about glass’s properties under high-pressure. For one thing, it has a higgledy-piggledy molecular structure a bit like a liquid, rather than the ordered lattices often found in other solids. As a result, when glass is evenly squeezed from all sides – as it would be under the ocean – the molecules cram closer together and form a tighter structure. The result is that a glass sphere about four-to-six inches (10-15cm) thick should be able to withstand most of the blows of ocean exploration. “You’d have a hard time breaking it,” says Earle. That should protect you from a collision below the surface, which might take a chip out of the glass. “The force has to be bigger to take a chip out of glass because it’s held so tightly,” says Lawson. “And even if it takes out a surface chip, the material in the main body is sufficiently strong that it won’t collapse on you.”

Perfect structure

Certain kinds of stress could still be a danger, however – particularly if they come from within the sphere itself. One of the biggest challenges is designing a hatch for the crew to enter the glass orb, since any fixtures could create tensile forces along the surface that could cause it to crack; because the metal contracts at a different rate to the glass, it causes friction. So Lawson is working on designs that would ease the load.

Manufacturing such an enormous glass sphere will be a feat in itself. Lawson says they have a head start thanks to technology developed to make huge telescopes that are now peering into the depths of the cosmos. Such telescopes use gigantic mirrors – sometimes 10m in diameter – that take up to six months to cool after they have been moulded, to ensure they form the perfect structure without cracking. The huge glass sphere used to build Earle’s Deep Search vehicle would almost certainly require a similar process.

The submarine's glass hull might need to be made in a similar way to giant telescope lenses (Science Photo Library)

The submarine's glass hull might need to be made in a similar way to giant telescope lenses (Science Photo Library)

So far, they have talked to a couple of glass manufacturers about the way it could be put together. One option would be to cast it whole. Another would be to melt the glass and drape it into hemispherical moulds, before fusing them together so that there is no longer a marked join – which could be a weak point in the shell.

Earle will also need to develop a kind of vacuum than can delicately pick up sea creatures for further study. “I don’t know how to make it, but I know how to talk the engineers into making it.”

Her ultimate vision is to open up similar opportunities for anyone who is interested. “I want to be able to go and go again and again, and I want to go and have access for anyone – little kids, other scientists, of course, decision-makers – even poets and song-writers,” she says. “Whoever wants to have the joy of being within the systems that maintain life on Earth, the ocean. And to be able to go to the deepest place means that you can go any place: you’re not limited any more by the technology.”

And do the dangers of descending to the ocean floor in a glass submersible ever daunt her? “Well, it’s today a lot safer getting into submersibles, than getting into a car,” says Earle. “Getting into a car and driving down the highway – I think that is the most dangerous thing I do.”

If you would like to comment on this, or anything else you have seen on Future, head over to our Facebook or Google+ page, or message us on Twitter.

Around the BBC