History Spotlight, 1/23

The bathyscaphe Trieste is an early deep-diving submarine designed by Auguste Piccard from Switzerland and built in Italy in the 1950's (the character of Captain Picard from Star Trek: The Next Generation is named after him). It spent some time puttering around the Mediterranean before being bought by the US Navy for $250,000.

It has a two-chambered design. The first chamber is the pressure chamber, where the two crew members sit. It is designed to withstand a pressure of 1.25 tons per square inch, which is actually a higher pressure that would be found in the deepest part of the oceans, but it never hurts to over-engineer this kind of thing. Oxygen was recycled through a rebreather system that used canisters of lime to scrub the carbon dioxide out of the used air. Because there was no way to build a sphere big enough for two people and strong enough to withstand the pressure and yet still be neutrally buoyant, the second chamber was a float chamber filled with gasoline. Gasoline is lighter than water and, unlike air, incompressible even at high pressure. The pressure sphere had one window: a several-inch thick cone of Plexiglas.

For ballast, the Trieste carried nine tons of iron shot, held in place in hoppers by electromagnets. If the power failed, the magnets would automatically release the shot and the vessel would float to the surface on its own. A pretty neat design element, and one I wouldn't have thought of until I was seven miles down without power.

On October 5, 1959, the Trieste left for Guam aboard a freighter to take part in Project Nekton: deep dives in the Mariana Trench, the deepest part of the ocean on Earth. 49 years ago today, January 23, 1960, the Trieste touched down at a depth of 35,761 feet (almost seven miles!) on the floor of the Challenger Deep in the southern part of the Mariana Trench. Its crew was Jacques Piccard (Auguste's son) and Lieutenant Dan Walsh, US Navy. It was the first time any craft, manned or robotic, had made it that deep. They spent only 20 minutes on the bottom in near-freezing temperatures, but that was enough time to record soles and flukes, proving that vertebrate animals could survive at that depth, albeit in a much flatter configuration.

The Trieste never went back to the Challenger Deep and was gradually phased out by smaller, more nimble craft like the Alvin, which uses some kind of super foam to provide both buoyancy and structural support. But the Alvin can only go down to 15,000 feet. The only other craft to go to the bottom of the Challenger Deep was the Japanese unmanned submersible Kaiko in 1995. With the loss of that vessel at sea in 2003 and the Trieste in pieces on display in the Naval Historical Center in Washington, DC, no vessel on Earth today is capable of braving such depths.