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#31
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"Henry Spencer" wrote in message
... With a normal elastic material, if you want to stretch it twice as far, you have to apply about twice as much force. But there are some materials, Spandex being one of them if I recall correctly, which are different. They start out the normal way, but when you reach a particular amount of stretch, the curve flattens out: the material stretches, and stretches more, and stretches still more, with only the most minute increase of force. Eventually the required force starts rising again, but there's a wide flat section in the middle of the curve. This is exactly what's wanted for a skinsuit: essentially constant force over a wide range of stretch. Not only does this accommodate flexing of the body, but if that range is wide enough, it can also accommodate some discrepancy between the design size and the actual size of the body. But at donning time, you're still trying to put on something that's squeezing hard all the time. What's needed is a way to turn that off and on, either on command or automatically in response to ambient pressure (a fabric that shrinks in vacuum). Not simple. A possible approach that might get over some of these problems, but not all, would be a double skin suit with both skins sealed together into little squares perhaps a few millimeters to a side. Like a lilo but on a much smaller scale. By pressurizing between the two skins you can cause the suit to shrink down to 2/pi in any direction, and regulate body pressure. This could be sufficient for getting the suit on, and because the inflated thickness is very small, (and can be partially balanced), movement should be little impeded. Obviously this still tries to make every part of the body circular, not dealing well with body corners, flats, or hollows. Perhaps hybrid solutions might be possible. Pete. |
#32
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In article ,
Pete Lynn wrote: ...Obviously this still tries to make every part of the body circular, not dealing well with body corners, flats, or hollows... Although this is a real issue with skinsuit concepts, the extent of it is exaggerated. Hollows, and to some extent flats, are dealt with by putting shaped air-filled balloons inside the suit. (In particular, you want a substantial flat balloon, connected to the air system, on the chest so that you can inhale without fighting several psi of pressure or needing very tricky air-system controls.) A fabric with the non-linear stretch characteristics I mentioned helps with corners and such, and careful tailoring plus the non-linearity can at least reduce the circularization problem. -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
#33
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Joann Evans wrote:
Earl Colby Pottinger wrote: Why does prebreath take so long? Bubbles? But at the lower pressure tere is not that much gas in the blood, is there? People often dive to 30 to 50 feet and come back up in time measured in minutes not hours. So why so long? And if caution is the main reason for such a long time how much can it be cut back for an emergency? The length of time one stays at a given depth, determines how long decompression time* will be....up to a point. Then one's tissues are saturated, and decompression time doesn't get any longer, no matter how much longer one stays at that pressure. One thing that I don't recall seeing mentioned in the discussion this time around is the bends ratio. This is the ratio of ppN2 to Pfinal. A ratio of 1.0 or less is safe. A ratio of 1.3 or less is safe for well conditioned people who are selected for bends resistance (people's susceptability varies widely among populations). The risks increase as the ratio climbs from 1.4 to 1.6. Above 1.6 is probably not safe without very extensive prebreathing. One thing which would seem to have huge potential benefits for spacefaring humankind would be looking at alternate atmosphere mixes or running at moderately lowered habitat pressures. There has been on and off research, but not with the sort of vigor and support required. There is some diving related research on various options; they use nitrogen, helium, and oxygen mixes, and a few mixtures using neon. Argon, which is a good choice for spacecraft, isn't considered for diving because it becomes a narcotic under higher pressure than sea level. There have been extended research runs with helium-oxygen before, deep dives and deep research stations. But those were at high pressure. Looking at sea level and moderately lower pressure effects (say down to 10 PSI, but most likely 12 PSI) would be valuable. There are a few studies on normoxic argon mixtures at sea level, which seem to indicate that it's safe for moderate periods of time. I suspect that mixtures with nitrogen and other gases will be better choices than simple argon-oxygen mixes, but simplicity in the life support system may push towards argon-oxygen two gas systems. Dr Andrew Pilmanis among others has been doing research on argon-oxygen mixtures for space habitat usage. So far, the argon isn't proving a magic bullet but it appears a lot better than nitrogen is. -george william herbert |
#34
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#35
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In article ,
George William Herbert wrote: A ratio of 1.3 or less is safe for well conditioned people who are selected for bends resistance (people's susceptability varies widely among populations). The risks increase as the ratio climbs from 1.4 to 1.6. Above 1.6 is probably not safe without very extensive prebreathing. As of about ten years ago (and probably still today), NASA's operating rule was 1.4, which included a conscious decision to accept some chance of mild symptoms. (Spacewalk crews take aspirin beforehand.) There are other variables which seem to affect the results but haven't been well studied: + Oddly enough, the probability of overt symptoms is rather lower when you're in a spacesuit than when you're in shirtsleeves. Perhaps the reduced mobility makes bubble formation in the joints less likely? + There are some hints that people who start from a low initial air pressure are more susceptible than people from sea level, which is a concern for proposals to use a lower cabin pressure. + Physical fitness is desirable -- body fat is a nitrogen reservoir -- but intense levels of physical activity seem to make you more susceptible, perhaps because minor tissue damage encourages bubble formation. + Women seem to be more vulnerable than men, and it seems to vary with their menstrual cycle for some reason. One big poorly-known variable is how honest the reporting of symptoms is, especially when symptoms would affect the subject's career. It's clear that a *lot* of low-level symptoms go unreported. -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
#36
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"Henry Spencer" wrote in message
... Although this is a real issue with skinsuit concepts, the extent of it is exaggerated. Hollows, and to some extent flats, are dealt with by putting shaped air-filled balloons inside the suit. (In particular, you want a substantial flat balloon, connected to the air system, on the chest so that you can inhale without fighting several psi of pressure or needing very tricky air-system controls.) Is it possible to mix skin & traditional suit components? For example, use "skinsuits" just for the forearms and hands and traditional suit components for everything else. That would seem simpler than the above though the seam between the traditional and skin suit parts might be tricky. A more extreme version would be some type of "paint-on" glove that protects the skin from exposure to vacuum but does not provide any significant presure. Would the (slightly reinforced) skin have enough strength to prevent your hands from swelling to the point that they could not be used? |
#37
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In article ,
David Pugh wrote: Although this is a real issue with skinsuit concepts, the extent of it is exaggerated. Hollows, and to some extent flats, are dealt with by putting shaped air-filled balloons inside the suit... Is it possible to mix skin & traditional suit components? For example, use "skinsuits" just for the forearms and hands and traditional suit components for everything else. Yes, there has been some work on giving the traditional suits skinsuit gloves, since the gloves are the big disaster area in existing suits. The idea does appear to be viable... provided you stick to low-pressure suits. A more extreme version would be some type of "paint-on" glove that protects the skin from exposure to vacuum but does not provide any significant presure. Would the (slightly reinforced) skin have enough strength to prevent your hands from swelling to the point that they could not be used? Unfortunately, almost certainly not. There actually isn't any real requirement to protect the skin from vacuum exposure *apart* from the need for pressure. Indeed, that's one of the basic ideas behind the skinsuit: that your skin is quite adequate as an interface to vacuum, given mechanical support to supply pressurization. In particular, a skinsuit's cooling system is that you sweat into vacuum. (Typically there would be overgarments providing some overall temperature control, and protection against hot/cold surfaces, but they wouldn't be pressure-tight, indeed they'd be vented.) -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
#38
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#39
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"Rand Simberg" wrote in message .. . I remain skeptical that we have enough data/experience to confidently extrapolate hyperbaric situations to hypobaric ones. Especially when complaints about "minor" problems with the bends could have an adverse effect on one's astronaut career. At the very least, such complaints could severely limit the opportunities for future EVAs, especially if other astronauts don't complain about the very same aches and pains. Jeff -- Remove icky phrase from email address to get a valid address. |
#40
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