They're independent sources of pressure, acting on the same surface area. What makes you think they wouldn't?

Depends on your weight, and the area of your butt/chair interface. One atmosphere is ~10⁵ N.m^-2, making a fifth of an atmosphere the equivalent of ~2000 kg sitting on a square metre. If your torso, head and arms weight 50kg, then you'd need a bottom maybe 15cm square to get the same effect. Perching on one buttock on a soft chair, or sitting normally on a hard chair, might give you the desired effect (assuming you consider it desirable).
The answer is generally a small number of minutes before you get tissue changes, a couple of hours before you get tissue death. People who can't move will start a pressure sore in that time frame. I know a paraplegic doctor who has an electronic alarm that reminds him to shift position regularly while he's in his chair.

The body is actually quite ingeniously designed to keep arteries on the flexor surfaces of your joints, where they're largely protected from areas of pressure when the body is at rest: that way the distal limb retains perfusion even if there's local tissue compression. The main artery in your leg spirals from the front of your leg at the groin to the back of your leg at the knee, for instance, so you can sit or kneel without your feet going white. Clever, eh?

Grant Hutchison

We'd need to crowd in a couple more Richards, too, since parts of your chest are escaping compression, and your abdomen is at present uncompressed. A lot of the volume change associated with breathing is generated by diaphragmatic movement, so abdominal compression is a significant player in this, too.

Grant Hutchison

I'm still reading through it (it's long!), but if you are interested in this subject, here is a PDF I highly recommend reading:

http://chapters.marssociety.org/winn...tivitySuit.pdf

This was actual work done at NASA. They had people in a suit in a vacuum chamber for as long as three hours at a time. The suits had multiple layers, each adding compression, with a number of zippers. To help breathing, they used a "breathing bladder" system. It's obvious improvement was needed, but that certainly doesn't look impossible.

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Imagine a Navy SEAL team with such exoskeletons. Imagine it looks rather insectoid, with helmets with big insect looking eyes. They can run at 60MPH or better, jump 30' or more in the air, with the strength of 10 gorillas.

They come like lightning and start mowing you down before you know what's happenning, breaking and crashing through things with impossible strength. You're off to the side and out of their direct initial assault. You manage to get off a shot at one. But his suit just makes the bullet bounce right off, and maybe knocks him back a little. He's back on his feet in a second.

I tried, but the knowledge that SEAL teams are nothing like this in RL and it's just a Hollywood fantasy having them ruishing in and wiping out an entire base, keeps getting in the way. Sorry.

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PW,

Hee-hee. But that Hollywood image doesn't hurt them in the minds of any potential enemies does it?

And if any shots did have to be fired, I would not want to be on the receiving end of it. One team certainly couldn't take out something the size of a base, but smaller targets are something else. I saw a documentary on Discovery or TLC or somewhere, showing SEAL training exercises. The part about carrying the telephone pole is true.

Then the good part was an exercise where a SEAL team was to take over an enemy boat. It was a mock war game type drill with some other bunch playing the crew of the boat, and they had cameras mounted everywhere so they could review the action.

Well, that team did indeed descend on that boat like lightning, "killing" all the crew and taking over the boat before that crew knew what happened.

-Richard

the strap idea works. what about a simple zipper?

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Depends how cool you are about dying because of a jammed (or popped) zipper, I guess.
It's going to be under considerable tension when zipped. Think of the tightest jeans you ever got into, or helped someone else get into. Multiply by ten.

Grant Hutchison

only when you're inside.

I'd carry a knife too, JIC

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All the time, since the tension is what's keeping you alive outdoors.
The zipper pops when you're outside, your chest inflates and won't deflate. How far can you run on one (big) lungful of air?

Grant Hutchison

First, zippers are important on conventional space suits, so I don't see your point. Second, as stated before, there is no reason for the clothing to force extreme compression, only to limit expansion. Third, the actual experimental suits used multiple layers, not a single layer. That turned out to be far more practical, and safer.

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I'd suggest you read up on the use of the breathing bladder in the SAS suit design.

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you're just a naysayer

As you read from Van Rjin the suit need not compress just guard against expansion. it could be loose until you walked outside. of course then your personal volume would go up slightly.

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Are the zippers on conventional suits responsible for holding them together against their internal pressure?
The expansion will exert 150mmHg on the suit, if that's the pressure of the gas being breathed. The suit has to shove back.
I don't doubt that the experimental suits are well designed and up to the safety standards of experimental designs. My argument here is simply against the idea that we're going to come up with some simple spandex item with a big zip on the front that'll do all the tricks. This seemed to be crosscounty's original take on the problem, and I've just been trying to point out the design constrains that make producing one of these things a hard task.
Again, you're confirming my only two points, which I've already posted clearly:It's tricky and it's not spandex.

Naysayers sometimes turn out to be right.
But I actually agree with Van Rijn, that the technical challenges could be overcome if we had the will and the money, but I'm not sure there would be advantages in safety, mobility or ease of use over conventional suits.

Grant Hutchison

It's certainly interesting reading: thanks Van Rijn. Good to see how the various problems have been dealt with, and which were easy (breathing compensation) and which were hard (suit donning).
It also confirms everything I've been talking about in this thread:

Raised lung pressure, if not properly matched by external compression, causes circulatory collapse (p4)
150mmHg is seen as a minimum working pressure for health (p10)
Matching pressure to oppose this working pressure must be applied over the whole body (p11)
Breathing can't be supported by a simple elastic garment alone, but needs an additional mechanism to maintain constant pressure during the large volume excursions of the chest (p10)
Trunk zippers are almost impossible to close at working pressures over 45mmHg (p22)
These garments (as designed in this study) are not loose-fitting indoors: they're elastic garments that maintain their high compression even at one atmosphere ambient (p57)
This constant high level of compression creates problems during donning and doffing, requiring the wearer to breathe from a stepwise increasing overpressure source while the garment is progressively assembled around him (p67)
This complicates donning and doffing: assistance is needed and it took 45 minutes to suit up; impressively, only seven minutes for doffing, however (p67)

Now, I've no doubt that further research and improved technology could massively improve the efficiency of these things, making them both easier to get in and out of and less complex in their multilayer construction. I am certainly not naysaying that possibility.
But I am right (and this report bears me out in detail) when I claim that matters are considerably more complicated than putting on a simple stretchy fabric suit and an oxygen mask, and then stepping out on to Mars.

Grant Hutchison

Hi there. If I may add something here. I am involved in the development of spacesuits, and have (over the past 15 years) seen many claims of this and that as the solution to the bulky spacesuit. There are too many problems in spacesuit design, which seem simple at first glance, or to the armchair engineer, that are actually very difficult to solve. If, and this is a big if, you can solve the numerous problems faced by mechanical counter pressure suits, practical MCP spacesuits are at best a very long way off.
Here are just some of the issues with this type of suit:
One, custom fit required, modern CNC cutting and measuring can do this in the cutting and patterning of the garment, but sewing is still by hand fed machine and the same experianced person can sew two pieces of fabric, the same way and they will react differently. Currently there is not a material or technique that I am aware of that can be “sprayed on” as a solution for this problem. Advancements in materials seldom lead to revolutionary breakthroughs in product invention. They do, generally after many years, offer an improved product. Then to new products.
Two, the hollows of the body. Forget elbows and knees, how about areas like your crotch, you still have to walk remember. Keep in mind, any small area that doesn’t receive the correct counter pressure will be affected like sticking a vacuum cleaner on you skin, after a while you have a big “hickey” and then the skin is very tender and sore. I think you get the picture
Three, donning and doffing in an emergency, or donning or doffing in any case? Very difficult with a suit tight enough to do you any good. Getting a suit on in a hurry is a big consideration.
Four, Sores on the body, or "hot spots" from small excesses of pressure in one area of the body. Rest your body on a fold of fabric or a bump for anytime and your skin and under tissue get sore and stays sore for a long time. I have been a diver for many years and a wet suit worn on the surface for a long time can get uncomfortable, and it doesn’t have anywhere near the amount of squeeze needed.
So perhaps in the next 50 years we may see something in this are that is a better trade off than a full atmospheric pressure suit, but there are a bunch of things, beyond a cool new material that would need to be solved. I have seen many of the "new skin suits" and they don't address many of the above problems, in fact I have some of my own ideas that I am experimenting with for a mechanical counter pressure suit, but some same problems will be there even if my system works. So you have to weigh the trade offs of those problems verses the problems of a full pressure suit.
Currently the “Mark III, Zero prebreath suit” is the most likely candidate for the return to the Moon or a trip to Mars. It offers higher working pressure (8 to 9 psi) with very little impact on mobility. It is far superior to the Apollo A7Lb in mobility and durability. One has to remember that the Apollo suits where a compromise in suit design, they had three different jobs to do and had to be engineered to do all three, instead of optimized for one. Also, in addition to the already mentioned benefits of higher cabin pressure to a lower one, at lower pressures, cooling of equipment is a problem. For example fans need to be bigger to move the thinner atmosphere and are also noisier. So a higher cabin pressure is desirable for many reasons. Thus a suit that can operate at a higher pressure is also desirable.
Cheers.

good info.

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Yes, thanks, RHAMX.

Grant Hutchison