The Tech Behind James Cameron's Trench-Bound Submarine

MrSeb writes "Yesterday, James Cameron completed a five-mile-deep test dive in the Pacific Ocean, in preparation for a seven-mile (36,000ft, 11,000m) dive to Challenger Deep, in the Mariana Trench; the deepest place in the world. We don't know when the actual dive will occur, but it will probably be soon. At 36,000ft, the pressure exerted on the hull is 16,000 psi; over 1000 atmospheres, and equivalent to eight tons pushing down on every square inch of your body. Understandably, building a submersible (and equipment, such as cameras, motors, and batteries) that can withstand that kind of pressure, and then safely return to the surface, is difficult. This article digs into the technology required to get Cameron safely to the bottom of the ocean, film some 3D, IMAX footage, and then return to the surface."

Comments

Onion

[Anonymous Coward]

Um, maybe it's not this simple, but...

Lets say you have a submarine with a metal shell that can withstand the pressure at 1000 feet below sea level. (For simplicity, call it a pressure of '1000'.). You can lower it only that far into the water before the pressure exceeds the amount it can handle, and the shell collapses. Okay. Now, what if you place that shell inside an slightly larger one? Lower them both to, say 999 feet, then open a valve to let the water in between the shells. Close the valve, and drop the shells another 999 feet. The inner shell has the pressure of 999 pressing in, which it can withstand. But that 999 water also presses out. The outer shell then has 999 pressing out and 1998 pressing in, a net of 999 pressing in, which it can withstand.

Repeat with however many layers you need, and you should be able to go down to the bottom of the Mariana Trench, no?

Re:Onion

[tragedy]

A few problems with that approach. Among other things, I don't think you'd want an incompressible (or at least difficult to compress) fluid between the outer and inner shell. If it's "pushing out" on the outer shell, then it's also pushing in on the inner shell. Not to mention that you actually want to be able to see out of the thing with a window. Given the complexity of a window and how well our cameras work these days, the window represents a whole lot of complex engineering for very little benefit, but if you're going to have a manned craft, you might as well have a window, otherwise you have to shrug your shoulders and mumble when someone asks you why you bothered to actually go down there rather than spend that engineering money on a telepresence system you could operate from a ship on the surface or even from the comfort of home. So, if you need a window, you would have to have a window in every layer of your system and figure out a very complex system with super-high precision optics that work properly even when the high pressure has warped their shape. Then there's your connections between the controls in the inner part of the sub and all the equipment outside. I imagine the sub has two or more power systems with one or more for the cockpit and one or more living at outside pressure for the outside of the sub and with all the equipment outside the cockpit controlled "wirelessly" (or using the whole cockpit hull for a "wire" anyway). Having nested shells is going to require such a system to be very complicated and to be multi-layered as well, with each layer presenting another point of failure. Overall, you're better off in just about every way if your multiple shells are all merged into one shell.

Essentially, the only special technology you need for a human to survive to that depth is a thick enough shell around them. Nothing technologically amazing or any new ideas needed. Having a well sealed hatch and a well-sealed window are the more complicated parts, since those may not deform evenly with the rest of the shell, but even those aren't really hugely complex engineering problems. The trickier problems are getting all the stuff that needs to survive _outside_ the shell to survive at that pressure and to not explode from internal pressure back up at sea-level. Every single little part needs to considered,and not just mechanically since, at that pressure, materials may have altered chemical and electrical properties. The cockpit is simple and well-understood by comparison.

For some reason I'm not quite clear on, your suggestion has made me think of _Star Trek IV_, when Scotty trades the formula for transparent aluminium for plexiglass to make the aquarium for the whales since plexiglass is the best substitute for transparent aluminium. I still to this day have not been able to fathom why they couldn't just use regular, non-transparent aluminium, or whatever metal the Klingon ships inner structure was made from to make their tank. Why did it need to be transparent? I don't know and I don't know why this conversation so strongly reminds me of that.

Re:Avatar

[Anonymous Coward]

I've found that people with an IQ over 120 generally think Avatar was an okay (not particularly bad or amazing) movie with pretty good visuals and a rehashed plot that was still decent as it has been for many previous stories, while those with an IQ between 100 and 120 (or age below 25) think it sucked.