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[agesilaus]

Nothing exotic would be needed. Steel, Aluminum or composites like carbon fiber or glass for that matter. Your scuba tank is pressurized to 200 Bars or more. At 1000 feet you are talking about 30 bars or so, a lot less than a scuba tank. So a 4 foot sphere made of 1/4 inch (6 mm) steel would probably work. The hatch would be the weak point.

That sphere could be going rather fast by the time it got to the surface. Maybe too fast.

BK

 

[Grenouille]

Maybe they can come up with a system to slow it down by activating some kind of control from the inside. Now, you say aluminum, but richkeller told me the material that make aircrafts would never work because it's made to keep the pressure inside, not resist to the outside pressure. But most planes I believe are made of aluminum or composite materials, so doesn't that mean they could use that to make the sphere? Either that or richkeller is right and you're wrong about the aluminum? My characters have been trying to find material to build that thing for years, in vain, if they find a pod that was initially made to resist tsunamis etc, it makes sense that they could use it, but if they could really build a sphere with aluminum, then maybe it's a wonder why they didn't just use plane wreckage.
That said, once you got the sphere, how would you go about O2, would you just place someone inside and you need nothing else, considering they'll be on the surface in probably less than 10-15mn if they slow it down, so if they don't breathe too much, they don't need any kind of air supply or anything?

 

[Rich Keller]

The material is not the problem, turning it into something that can withstand the pressure and maintain one atmosphere is the problem. At 300 meters the pressure on every square inch of that pod would be 438lbs. To put that into perspective using an average size door in your house that measures 30"x80" the pressure on a door that size would total 1,051,200lbs or 525.6 tons. That is why the life boat idea will not work, the pod would need to be a sphere so the external pressure on the pod is self canceling. You could use the life boat as a lift bag attached to a small section of the habitat that could then be disconnected and sent to the surface.

 

[Grenouille]

I can't do that, there's no way to cut the habitat into anything. But okay, if the problem is that it's got to be a sphere and you can't build such a sphere, then I can use my pod idea, can't I? If it's a sphere already, all they have to do is seal it, find a system to send it up and slow it down, no? Sounds to me like it works, given what you're telling me.

Also, I had another question. Does it seem plausible to you guys that divers with a limited amount of air at their disposal would train to breathe "less" so that they progressively learn to use less air, therefore going further in their explorations than they could before? I've seen in movies that astronauts and divers that are running out of air are advised to save their breath and air, it just seems logical to me that if you're trying to optimize your time outside, you could learn and develop skills over the years to breathe very little, so you can be outside longer and further. Does that sound dumb to you?

 

[Rich Keller]

A habitat that size could not be made in one piece with todays technology so there should be sections that could be disconnected. The ride to the surface would be short so the air in that part of the habitat might be enough. If not they could breath off a scuba tank instead of the internal air. If you take a sphere from airplane wreckage and reinforce it like they do with carbon fiber wrapped scuba tanks it might work but reinforcing the hatch would be a problem. You could use a pressure hatch from the habitat that is made to handle the pressure and attach it to a reinforced sphere. Breathing less is really not an option, the body needs as much air as it needs, the only way to reduce that is to reduce the bodies needs by limiting your movement and remaining as calm as possible.

 

[agesilaus]

Scuba Tanks can be and are made of Aluminum. The Aluminum wall thickness is much greater than steel however. Where a steel tank has a wall thickness of 3/8" (9 mm or so) an aluminum tank is an inch or so thick (25mm) and that is because Aluminum is weaker than steel in this application. And there is no difference between internal pressure and external pressure.

As for slowing the ascent, maybe a sea anchor would work. That is essentially a drogue parachute. The sea anchor size would have to be matched to the weight and drag of the escape capsule tho.

BTW a 80 CF Steel LP tank filled to 200 bars has a force on the inside if the tank over 1,000,000 pounds.

---------- Post added February 10th, 2014 at 04:45 PM ----------

A habitat that size could not be made in one piece with todays technology so there should be sections that could be disconnected. The ride to the surface would be short so the air in that part of the habitat might be enough. If not they could breath off a scuba tank instead of the internal air. If you take a sphere from airplane wreckage and reinforce it like they do with carbon fiber wrapped scuba tanks it might work but reinforcing the hatch would be a problem. You could use a pressure hatch from the habitat that is made to handle the pressure and attach it to a reinforced sphere. Breathing less is really not an option, the body needs as much air as it needs, the only way to reduce that is to reduce the bodies needs by limiting your movement and remaining as calm as possible.

I don't think the actual hatch would be a problem, but the seals and maybe the hinges would be.

 

[Grenouille]

Cool well it sounds like the pod idea works then, I just have to tackle the hinges and maybe the hatch, make sure they take that into account. How would you go about getting it to go up, though? The pod will be too heavy, even filled with O2, it'll just sink to the bottom if you don't attach to something, right?
As for the breathing, some monks have developed amazing techniques, I really think it's possible, but it's like you said, it's about being as calm and effortless as possible, but I think you can really save O2 by training your body to use less air, it's completely logical, I don't think it's true to say that we all need the same amount of air and that you can't do anything about it. It's like saying your body needs as much food as it needs and that's it, it's not true, you're supposed to eat 1200-2000 calories a day, but people can train to only need 500-600 and survive on that and be healthy. Sounds like the exact same thing to me, even if it's hard to imagine spiritually how someone can get to control their air intake in that way.
Oh, and the habitat isn't really what you're picturing, it used to be different in our minds, more traditional, but it was boring as hell, now it's more like a sphere, a dome covering a sort of town, the dome is made of a scifiish material developed by the inventor to resist pressure more efficiently than the materials that currently exist, so there's no way you can cut a part of the habitat and use it to go up.

 

[agesilaus]

Sheck Exley talks about techniques to slow breathing and conserve gas in his book. I get the impression that it is risky for those divers who aren't at Sheck Exley's skill level. There is one treatment to reduce oxygen use, you can sedate people and put them to sleep. They aren't moving around and that burns less O2. This is supposedly what might be done on a sunken submarine while waiting for rescue.

BK

 

[Grenouille]

Haha the sedating thing is pretty cool, but not very useful when you're trying to reach a plane wreck to go grab some equipment
We're talking about a population of humans that have been developing a technique for about 7-8 years, with a specific goal in mind, they really need to do this. Humans are capable of doing extraordinary things when their back is against the wall and they have no other choice. If a man is capable of staying more than 11 minutes underwater without breathing at all, others might be capable of pushing their limits while breathing O2 from a tank, and make it last longer by developing original techniques. It's hard to fight our instinct, but it's doable. People who practice yoga and other sorts of healthy activities know of slow breathing as a rewarding experience which, like meditation, offers multiple rewards, one of which is the decrease of your oxygen consumption. I don't see why it couldn't be applied to a diver in a one-atmosphere suit, even if they're in movement. You obviously can't push it too far, but you can definitely optimize your time by a lot if you develop the proper techniques.

 

[Diver0001]

Sheck Exley talks about techniques to slow breathing and conserve gas in his book. I get the impression that it is risky for those divers who aren't at Sheck Exley's skill level. There is one treatment to reduce oxygen use, you can sedate people and put them to sleep. They aren't moving around and that burns less O2. This is supposedly what might be done on a sunken submarine while waiting for rescue.

BK

In a sunken submarine, slowing breathing to conserve air would make absolutely no sense whatsoever. The reason being that you breathe the air back into the same container where it came from. The O2 levels aren't going to drop any slower if you slow your breathing.

What *might* make sense is to remain as still as possible so you don't burn any O2 that you didn't really need to burn. Rising CO2 levels, dropping O2 levels and the intense cold that is sure to develop in an "sunken sub" scenario will all have their problems.

If for some reason the author needs to "believably" extend the crew's O2 supply then they can make use of oxygen in large buffer tanks that would be attached to a small on-board decompression chamber. If such a thing isn't standard on subs then make it experimental (always a way out). The crew can release the pure O2 into the air and extend their available air-supply.

R..