Photograph by Mark Thiessen. During the descent, James Cameron will occupy the pilot sphere. The sphere is held in position with straps. Green cloth covers the sphere
Engineers made the pilot’s chamber spherical because the shape can be both strong and light. They also made the steel 2.5 inches (6.4 centimeters) thick to withstand the crushing pressure of the deep. If they had made the chamber a cylinder, by comparison, the hull would have needed to have been three times as thick to stand up to the pressure. The hull, complete with its hatch and viewport, was tested twice in a pressure chamber at Pennsylvania State University to an equivalent full-ocean-depth pressure of 16,500 pounds per square inch (1,138 bars). It passed both tests. Twenty-two strain gauges attached to the sphere gave data that indicated the sphere could withstand up to 140 percent of the test pressure without buckling.
When designing the sub, James Cameron and Ron Allum kept the sphere’s internal diameter to 43 inches (109 centimeters) because, as the heaviest part of the sub, its weight dramatically impacts the overall size of the vehicle. The heavier the sphere, the more foam would be needed to float the entire structure back to the surface. And the foam itself, capable of withstanding the crushing pressures at full ocean depth, is quite dense. More weight, more foam. More foam … more weight. It adds up quickly and dramatically. To keep the sub small enough to launch and recover from a ship, as opposed to being towed to the site like the Trieste, it was critical to have as small a sphere as possible.
The sub is equipped with two compressed oxygen cylinders, which contain enough O2 to keep the pilot breathing for up to 56 hours—seven times the amount of time he expects to spend diving the Challenger Deep. Cameron trained for the dive by doing exercises to increase his lung capacity and his body’s oxygen efficiency. He’s been running and free diving regularly.
Deep Sea Sub
Facts about the sub
The pilot is descending almost 36,000 feet, but his ears won’t pop during the journey; the pressure inside the pilot’s sphere stays constant.
The sub’s giant beam of syntactic foam shrinks about 2.5 inches (6.4 centimeters) under the immense water pressure at the ocean’s bottom.
The pilot chamber is a sphere because it is the strongest shape for resisting pressure—if the pilot sat in a cylinder the walls would need to be three times thicker.
If the sub’s 1,100 pounds (500 kilograms) of ballast weights don’t drop when commanded, a back-up galvanic release will corrode in the seawater within a fixed period of time, freeing the sub to rise to the surface.
Small “bladders” inside the oil-filled external battery boxes will take in seawater. The bladders are made from medical drip bags. These “compensation bladders” are a critical part of the deep ocean electronics system, because the oil compresses at depth.
The sub’s batteries are made up of over 1,000 pouch-type lithium ion cells, bigger versions of the batteries hobbyists use for model airplanes.
The sub’s four external cameras are a tenth the size of previous deep ocean HD cameras. The housings were designed by the DEEPSEA CHALLENGE team, and the cameras themselves were created from scratch, from the sensor up.
Illustration courtesy Acheron Project Pty Ltd DEEPSEA CHALLENGER
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