How It Works-Amazing Vehicles

O

n 26 March 2012, director James Cameron

ascended from the deepest part of the

deepest oceanic rift in the world: the

Mariana Trench, in the western Pacifi c. He

wasn’t the fi rst person to reach the abyssal

11-kilometre (6.8-mile)-deep valley in its fl oor, the

Challenger Deep, and the publicit y around the event

probably had as much to do with his celebrity status

as anything else.

Cameron was actually the third person to go there

(after Don Walsh and Jacques Piccard’s 1960 descent

in the Bathyscaphe Trieste), but he was part of the

second manned mission to the Challenger Deep and

the fi rst person to reach the bottom of the Mariana

Trench solo. A nd to put all that into better

perspective, NASA alone has sent 24 men to the

Moon, 12 of them actually leav ing their command

modules and walking around on its surface, which

would have been an impossible feat for this trio of

intrepid aquanauts.

So what are the challenges posed by this

geological giant, which could swallow Mount

Everest and still leave over t wo kilometres (1.25

miles) of water above its highest peak? The biggest

obstacle for any submersible div ing to these depths

is the extreme pressure. Because seawater has more

mass than air per volume – typically 1,025 kilograms

per cubic metre (64 pounds per cubic foot) versus 1.23

kilograms per cubic metre (0.08 pounds per cubic

foot), for roughly ever y ten metres (32 feet) you dive

into the ocean, the pressure increases by one

standard atmosphere (one bar). So the pressure near

the bottom of the Challenger Deep exceeds 1,000

bars, or 1,000 kilograms per square centimetre

(14,500 pounds per square inch), although

temperature and other factors mean this varies.

Naturally such extreme pressures would crush us

to a pulp, so a manned submersible that v isits the

Challenger Deep needs to have enormous

compressive strength to maintain the habitat inside

it, while keeping its human occupants warm and

supplying them with breathable air.

Cameron’s Deepsea Challenger had a similar

structure to the Bathyscaphe Trieste, though its

torpedo shape was designed to descend lengthways.

At one end is the pilot sphere, the only line of defence

against a wall of deadly water. To minimise weight

and increase strength, the interior is just 109

centimetres (43 inches) in diameter, while the hull is

made of 6.4-centimetre (2.5-inch)-thick steel. The

spherical shape of the chamber makes it much

stronger; if it was c ylindrical like the rest of the sub,

it would need to be three times as thick. To facilitate

its descent, 450 kilograms (1,000 pounds) of steel

How do manned submersibles

safely descend to the deadly

depths of the oceanic trenches?

Extreme

submarines

SEA