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#1 2014-12-03 15:36:37

RobertDyck
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From: Winnipeg, Canada
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Habitat air

We have had long discussions that often became arguments regarding this. Let's keep it in a separate thread.

Back in 2005, I calculated habitat air for the Mars Homestead Project, phase 1. Lower pressure in spacesuit results in less counterforce to joint movement, so easier to move. An old Air Force study found pilots could breathe 2.5 psi pure oxygen if they were healthy, pilot age, and went through high altitude training. They could breathe 2.0 psi pure oxygen for up to 30 minutes before blacking out. And pilots could breathe 2.0 psi partial pressure oxygen indefinitely if total pressure was higher, but I forget the number. The link to the Air Force document was on the original Mars Society forum, before NewMars. But 3.0 psi pure oxygen has the same partial pressure O2 as Earth at sea level, so anyone can do that without any preconditioning. So I recommend 3.0 psi pure oxygen for suits.

Apollo used 5.0 psi total pressure for the spacecraft, with 60% O2 and 40% N2 by volume. That is 3.0 psi partial pressure O2, and 2.0 psi partial pressure N2. Skylab used the same as Apollo. And Apollo spacesuits used 3.3 psi pure oxygen, which allowed for 10% pressure loss while still having the same partial pressure O2 as the spacecraft. So a 10% pressure leak would result in O2 astronauts were used to. Following that same rationale, give the Mars habitat 2.7 psi partial pressure oxygen. Boulder, Colorado, has 2.53 psi partial pressure O2, so that's definitely fine.

Mars should allow astronauts to get in a spacesuit and go outside. Easily. So zero prebreathe time. The Space Shuttle used the same air pressure as the launch site at KSC. The EMU suit used slightly elevated pressure to reduce prebreathe time, but that required hard shoulder and hip joints to deal with the pressure. And astronauts report their hands are sore after doing significant work. Joint counterforce, especially in gloves, is significant. But even with 4.3 psi pressure for the EMU suit, Space Shuttle astronauts required 17 hours of oxygen prebreathe time before decompression. On Mars, we want zero prebreathe time.

One NASA document gives a guideline:
Advanced Life Support Program - Requirements Definition and Design Considerations

EVA prebreathe time

* prebreathe time decreases as the partial pressure of diluent gas (N2) in the habitat decreases

* prebreathing can be eliminated when partial pressure of diluent gas exceeds the suit pressure by a "bends" ratio, R, of 1.2 or less (Shuttle EVA suits operate at 29.6 kPa (R = 2.7 at P = 101.4 kPa; R = 1.6 at P = 70.3 kPa)

Using these numbers: 3.0 psi spacesuit pressure * 1.2 = 3.6 psi partial pressure nitrogen. That's the maximum, lower nitrogen is Ok. But Impaler has raised concern over flammability, and fire safety. Apollo used 2.0 psi partial pressure N2, but my recommendation for Mars Homestead was the full 3.6 psi. Ok, let's stick with that.

Mars has both nitrogen and argon in its atmosphere. So I recommended we use argon as well in the habitat. And keep the nitrogen:argon ratio the same as Mars atmosphere, because that makes harvesting easy. Viking 2 measured 2.7% N2, and 1.6% Ar. The concentration of CO2 can change with weather, but the proportions of everything else remain stable. So assuming 3.6 psi N2, then that results in 2.133 psi Ar.

Adding this up: 2.7 psi O2 + 3.6 psi N2 + 2.133 psi Ar = 8.433 psi total.

That sounds good, but is it safe? There is a maximum amount of argon in the higher pressure environment to allow zero prebreathe time. What is that? And do N2 and Ar interact, preventing us from just adding partial pressures? I have no data for this. But the Mars Homestead Project needed something to work with, and the guys wanted elevated pressure vs Apollo, so I recommended we just go with that. Besides, this results in less argon than nitrogen.

GW Johnson estimated partial pressure of argon. Using NASA's figure for nitrogen, and based on molecular weight, he calculated a ratio of 0.86:1. That's less than nitrogen. For spacesuit pressure of 3.0 psi, that works out to 2.58 psi partial pressure Ar. Ok, that's more than the 2.133 psi Ar that I calculated.

I sent an email to a Mars Society member who is a medical doctor, and used to specialize in decompression sickness. He recommended I read published work by Andrew Pilmanis and JT Webb. I found this on PubMed:
Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures.

INTRODUCTION: The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia.

METHOD: During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography.

RESULTS: Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B).

CONCLUSION: Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.

Well, that's not exactly what I hoped. That doesn't answer my questions. What is the ratio of partial pressure argon to total spacesuit pressure, for zero prebreathe time? And do nitrogen and argon interact, requiring lower partial pressures?

This study apparently hoped that oxygen/argon would reduce oxygen prebreathe time for decompression. Or to phrase that the other way, astronauts could breathe more partial pressure argon for zero prebreathe time. That assumes Argox, which is argon/oxygen, not all three gasses. And the estimate by GW Johnson had predicted lower Argox anyway.

Last edited by RobertDyck (2014-12-03 20:44:48)

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#2 2014-12-03 16:37:44

Terraformer
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From: Lancashire
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Re: Habitat air

Again, don't forget the possibility of using CO2 in the habitat. Humans can adapt to at least 50mb CO2, though I'm not sure whether they can go straight back to an atmosphere without CO2 - the blood might get too alkali. 150mb O2, 50mb CO2, 180mb N2, 120mb Argon... that's a total of 500mb, 30% O2 (the CO2 should suppress flammability somewhat?), and possibly requiring zero pre-breathe time.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#3 2014-12-03 16:45:32

RobertDyck
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Re: Habitat air

Health effects of respiratory exposure to carbon dioxide -  The International Volcanic Health Hazard Network

(% in air) Health Effects
2-3     Unnoticed at rest, but on exertion there may be marked shortness of breath
3     Breathing becomes noticeably deeper and more frequent at rest
3-5     Breathing rhythm accelerates. Repeated exposure provokes headaches
5     Breathing becomes extremely laboured, headaches, sweating and bounding pulse
7.5     Rapid breathing, increased heart rate, headaches, sweating, dizziness, shortness of breath, muscular weakness, loss of mental abilities, drowsiness, and ringing in the ears
8-15     Headache, vertigo, vomiting, loss of consciousness and possibly death if the patient is not immediately given oxygen
10     Respiratory distress develops rapidly with loss of consciousness in 10-15 minutes
15     Lethal concentration, exposure to levels above this are intolerable
25+     Convulsions occur and rapid loss of consciousness ensues after a few breaths. Death will occur if level is maintained.

This is for Earth atmosphere, so you may have to convert that to partial pressure.

Last edited by RobertDyck (2014-12-03 16:46:40)

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#4 2014-12-03 19:14:13

SpaceNut
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Re: Habitat air

The reason for O2 at 2 psi with a higher atmospheric pressure works has to do with lung capacity (volume)with each breath taken that allows the oxygen to enter the blood stream in sufficient amount to keep one from passing out.

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#5 2014-12-04 06:29:06

Terraformer
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Re: Habitat air

Robert, notice the key words - "adapt, acclimatise". Obviously you're going to get problems if you take someone from an Earthlike atmosphere straight to one containing 50mb CO2, because of blood acidity. But if you gradually increase the CO2 partial pressure, the body will adapt by shifting the buffer in the blood (CO2 is dissolved in the blood, forming Carbonic acid; the body has to compensate for this to prevent the blood becoming too acidic). Of course, you might not be able to go straight back into a CO2 depleted atmosphere...


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#6 2014-12-04 08:22:16

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habitat air

Terraformer wrote:

Robert, notice the key words - "adapt, acclimatise". Obviously you're going to get problems if you take someone from an Earthlike atmosphere straight to one containing 50mb CO2, because of blood acidity. But if you gradually increase the CO2 partial pressure, the body will adapt by shifting the buffer in the blood (CO2 is dissolved in the blood, forming Carbonic acid; the body has to compensate for this to prevent the blood becoming too acidic). Of course, you might not be able to go straight back into a CO2 depleted atmosphere...

This should provide you with the information you need on CO2 long-term toxicity.

http://ston.jsc.nasa.gov/collections/tr … 217358.pdf

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#7 2014-12-04 10:36:21

Terraformer
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From: Lancashire
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Re: Habitat air

It doesn't load up...

There is this collection of posts from Midoshi - http://newmars.wikispaces.com/Minimally … Atmosphere Though unfortunately, it doesn't have the links to the studies.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#8 2014-12-04 12:00:52

RobertDyck
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Re: Habitat air

One technique in published papers on hybernation uses reduced O2 and increased CO2. This forces the body into anoxic metabolism. It reduces metabolic rate. I don't think we want to put astronauts to sleep.

Air on Earth has 0.034% to 0.039% CO2, depending which source you read, where and when measurements were taken. Humans can tolerate up to 2% without noticable effect, but as the table above shows, starting at 2% it causes shortness of breath on exertion. Again, all these figures are for one Earth atmosphere of pressure, they would have to be converted to partial pressure. Increasing from a little less than 0.04% to a little less than 2% is a significant increase. But any more than that interferes with physical activity. I don't think we want to do that.

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#9 2014-12-04 14:17:42

Terraformer
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From: Lancashire
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Re: Habitat air

Again, you're ignoring the fact that humans can acclimatise.

Again, acclimatisation

A third time, acclim- oh I give up, you don't seem to be interested in facts anyway.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#10 2014-12-04 15:27:54

RobertDyck
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Re: Habitat air

I don't think humans can acclimatise to that much CO2. Trying to do so just results in the subject getting used to the metabolic effects. CO2 is a basic gas, animal metabolism has evolved to deal with it for millions of years. You can acclimatise, but that just means you get used to marked shortness of breath on exertion.

When humans go through high altitude training, they acclimatise to lower oxygen. Their body does this by growing more red blood cells. There is a specific metabolic response that is the acclimatisation. Groups who have lived at high altitude for multiple thousands of years have adapted to lower oxygen without the need for more red blood cells. For example, the Sherpas of Tibet. But they did this by evolving larger blood vessels. That allows for more oxygen transport without increased red blood cell density. Too great red blood cell density can be dangerous, risking blood clots. But changing blood vessel size is adaptation through evolution, which a species or race can do, not individuals.

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#11 2014-12-04 19:20:36

Impaler
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From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Habitat air

Much of the prior threads atmosphere discussion could be moved here to provide context, it was becoming marginally off-topic in the greenhouse thread anyways, what admin would be needed to do this and how should we go about doing it?

I'd said it a dozen times and provided links to the papers that show your mix of Argon/Nitrogen can not be combined in the way you want it to.  You have the DATA, just stop ignoring it.  The paper I referenced which tested a N2/Ar/O2 mix and compared it too Ar/O2 and N2/O2 stated that Bends ratios are basically proportional to the weighted average of the ratios from each gas in the mix.  High molecular weight gasses had lower ratios, so the addition of any gasses higher in molecular mass to Nitrogen mix makes it worse.  The fundamental flaw is trying to add Bending ratios, that is not how it works.  This Argon mix idea is dead until you find some evidence that it is even as good as Nitrogen rather then worse in every way.  Helium on the other hand might get the ratio needed to make your idea work but you won't be getting that on Mars so it would be a precious import (heck Helium is getting rather precious even here on Earth).

NASA is simply going to make suits that support higher pressures with Zero-Pre-Breath and they will have an O2/N2 mix rather then pure O2 with pressure adjustable between 0 and 8.4 psi, the suit is already in development and IS vastly lighter then the EMU, Z-1 is 160 pounds with life-support pack and the second version is aiming for 140 which will be sufficient to bring an astronauts total carried weight to equivalent to their weight on Earth.  The suit-port concept promises to allow fast access to and from EVA as well.  It fulfills all the needs of a Mars suit without imposing pressure requirements on the Hab.  Habitats will almost certainly continue to have full Sea-level pressure and may even evolve to higher pressures to reduce fire-hazards.

Why is this development pathways not good enough for you???

Last edited by Impaler (2014-12-04 19:36:10)

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#12 2014-12-04 19:39:28

RobertDyck
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Re: Habitat air

Full sea level pressure is not an option. That imposes extreme structural stress, as well as extreme prebreathe restrictions on EVA. High pressure suits have are still significantly lower pressure than full sea level pressure, so require multiple hours of oxygen prebreathe before decompression. If you're locked in a habitat with multiple hours of preparation before opening the door to go outside, that's prison, not a new frontier. And high pressure suits have the problem of joint counter force. Most important is gloves, because no one has been able to devise an accordion joint for glove fingers.

An MCP suit has the advantage that the entire suit fits within the helmet. Small, compact. And machine washable. An MCP suit is just fabric, it can be washed. Mars is dirty, so is the Moon. Suits get dirty. You can put an MCP suit into a washing machine. You can't put a balloon suit into a washing machine. The neoprene pressure bladder keeps water and detergent out, so doesn't wash.

You keep obsessing about sea level pressure. The Mars Society was founded in Robert Zubrin's home town: Boulder, Colorado. Atmospheric pressure is lower there. And I live in Winnipeg, Canada. Not in the Rocky Mountains, it's in the Prairies, but still higher altitude than the ocean coast. You don't need sea level pressure.

I'm going to re-phrase your own question. Both Apollo and Skylab used 5.0 psi. Why is that not good enough for you?

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#13 2014-12-04 21:17:16

Impaler
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From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Habitat air

Everything bit of space-hardware in service now or in development can hold 1 atmosphere, further more they hardly benefit from shaved that light on structural mass as to be unable to hold 1 atmosphere, Apollo did all kinds of ridiculously aggressive mass savings because our rocket technology was so shitty back then and they had no mass growth margins.  One atmosphere is not simply an option it is the DEFAULT.

Finger joints for gloves were developed in 2007 and won the NASA glove challenge a second time in 2009, the winner created a company to further develop the tech and market the glove, these will likely be the basis of NASA's future gloves that will go on the Z series suits, http://www.flagsuit.com/110202_FLAGSUIT … ntract.pdf  They have contracted the inventor to develop gloves that work at 8.3 psi, and he even claims to be able to make them work at a full 1 atmosphere differential pressure for using in vacuum chambers here on Earth.  Your repeated harping on EMU level glove and suit performance as an argument that we need to go to a completely new tech (MCP) is unwarranted because we have not remotely maxed out what a balloon-suit can do yet.

I said explicitly Pre-Breath is already going away under current development plans because new suits will be within comfortably within bends ratios and will use Suit-ports.  That combination simply CRUSHES the MCP's time to don.  MCP (IF they achieve all desired development goals) only looks good compared to EMU suits (which are already inferior to Russian Orlan) and no one is suggesting we take EMU to Mars.  Dust contamination is not something you 'wash-off' of a suit in a washing machine inside the habitat (though I could see some kind of exterior cleaning procedure in which a suited astronaut cleans the outside of another suit that is unoccupied), the crew needs to not bring dust into the habitat at all or be exposed to it in any way, the MCP would guarantee dust contamination of the occupant and subsequently the habitat due to it's long dofing time in an air-lock, again suit-port is the superior choice and it is whats being developed.

Denver pressure is 12 psi, that's hardly worth sneezing at as a difference over Sea-level when it comes to structural stress, pre-breathing or any other the other things your siting as drivers to make radical changes.  Would 12 psi work?  Sure so long as you keep 21% O2 for fire-safety.  But your clearly wanting radically lower pressures then that and were proposing 8.4 earlier, so which is it?  The 5 psi is clearly out because of fire, we have been over that a million times already, you know as well as I do what the problem is with it and don't need to ask me.

For what ever reason you seem to have got an obsession with MCP suits and or low pressure habitats, I don't know which one of these things is the one your married too and which one is being dragged along for the ride, but the combination is still inferior to the conventional Earth like (sea-level, Denver take your pick) habitat pressure and the next generation balloon-suits.

Last edited by Impaler (2014-12-04 21:40:57)

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#14 2014-12-04 21:38:54

RobertDyck
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From: Winnipeg, Canada
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Re: Habitat air

Apollo is the default. Shuttle used 1 atmosphere for various experiments, not for fire safety and not for crew health. ISS uses 1 atmosphere because Shuttle did, and to screw the Russians. Period. And Shuttle was never able to fly beyond Earth orbit. As many science commentators said, if you view the Earth as a peach, then Shuttle skimmed the peach fuzz. Look at it: Shuttle flew 185km altitude for science missions, ISS orbit varies from 407km to 390km. I read a website that claims ISS varies more, both up and down. But Earth is 12,750km diameter. And the Moon is 384,400km from Earth.

Apollo went to the Moon. Apollo succeeded. Why do you want to disrespect Apollo? We've developed further technology to build upon Apollo, but claiming a fundamental of Apollo is unsafe?

You remind me of some engineers I spoke to about space stations. One engineer pointed out the idea of a self-launching space station. A two stage rocket, where the upper stage launches itself into orbit. Once in orbit, fuel tanks for the upper stage are purged, and filled with air. To ensure this can be used as a space station, the upper stage has thermal protection and micrometeor shields installed before launch. Consoles and internal equipment are installed inside the fuel tank before launch. Secured to ensure they don't come lose, and the tank is designed with a structure that acts as anti-vortex and anti-slosh baffle during launch, but that same structure acts as floor or ceiling of the habitat once on-orbit. Obviously all equipment must be designed to withstand cryogenic cooling of liquid hydrogen. Electronics will not operate at that temperature, the station will have to be purged and warmed before electronics can turn on. But equipment has to withstand storage at liquid hydrogen temperature, because it will be immersed in liquid hydrogen during launch. I described this to several NASA engineers while the Shuttle was flying. They all looked at me like I was crazy, like I just said something absurdly stupid. They claimed it would never work, and gave elaborate reasons why. Then I gave the name of this space station: Skylab.

So most Shuttle era engineers could not design Skylab. They don't even understand Skylab. And they're unwilling to learn about Skylab. But Skylab did work. Now you are trying to claim that Apollo is fundamentally unsafe. Uh huh. And why would I treat you as anything more than a troll?

Last edited by RobertDyck (2014-12-05 08:04:11)

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#15 2014-12-05 07:36:05

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habitat air

I am in no way an authority on suits and don't have much real knowledge of the physiology of blood gases and the need for pre-breathing.

But it seems to me that beyond the initial exploratory missions, a lot of EVA man-hours will be needed for Mars base construction.  Ultimately, everyone living on a Mars base and eventually in Martian cities, will need a suit.  Suits will need to be both flexible for working in and affordable items for everyone, so no more than $1000 each.  That suggests that the amount of technology and complexity embedded within a suit needs to be limited.  Basically, we are aiming at a minimum cost design space suit.  And ideally, weight should not greatly exceed that of normal clothing.  That seems to be what this thread is aiming at and ultimately, the cheapest solution is the one that will win.

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#16 2014-12-05 08:08:25

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habitat air

Seems to me that this discussion needs good quality information on how fire risk increases as N2 partial pressure goes down.  What level can we live with?  Can we mitigate the fire risk in other ways?

Alternatively, perhaps a habitat can be divided between low N2 and high N2 areas.  Prior to EVA, you move to a low-N2 area and you breakfast, brief and suit up in that area.  The time taken to do that is part of the pre-breathing time.  Maybe time could be further reduced by exercise, which would increase respiration rate.  Different materials control and fire safety standards will need to apply to the two areas.

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#17 2014-12-05 08:34:03

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habitat air

I ran a quick calc that may help with the glove issue.

Human skin is 2-3mm thick over most of the human body.  I have assumed 2mm thick on the hands.

http://en.wikipedia.org/wiki/Human_skin

The tensile strength of human skin is 27.2 +/- 9.3MPa.  The youngs modulus of skin is ~100MPa.

http://www.ircobi.org/downloads/irc12/pdf_files/59.pdf

If an astronaut is breathing air at 3PSI (20KPa) and is counterpressured to 3PSI also, what would the stress and elongation be in his skin if his hands were exposed to vacuum?  I modelled the hand as a sphere 10cm in diameter, about the diameter of a clenched fist and used the thin walled pressure vessel equation.  Basically, I assume that the skin is a pressure vessel for all of the soft internals of the hand.  I assumed the skin was 2mm thick.

The stress works out at 250KPa, which is 0.7-1.4% of the tensile strength of the skin.  Swelling would increase the surface area of the skin by 0.5%.  So unless I've missed something, it would seem that a counter-pressured astronaut could work with his hands in vacuum, so long as his internal pressure remains fairly low.  There is unlikely to be any bruising.  Obviously, there are other reasons for wanting gloves, such as not getting frostbite at typical Martian temperatures.  Evaporation of skin moisture may aggrevate that problem.

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#18 2014-12-05 09:28:20

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Habitat air

I found some information on 'suction cup therapy' which appears to indicate the differential pressures required to induce bruising in human skin:

'...blisters could be raised within two hours by a pressure of 200 mm Hg below the atmospheric pressure. By employing a slightly different suction cup Bielicky (11) had attempted to quantitate the Nikolsky phenomenon, but never was able to produce suction blisters on healthy human skin. He did, however, work with too short suction times (up to 30 min.) and applied too forceful a suction (500 mm Hg), the latter resulting in bruising.'

http://www.nature.com/jid/journal/v50/n … 6815a.html

A pressure of 200mm Hg is 26.66KPa.  This apparently produces skin bruising after 2 hours.  It suggests that there may be scope to relax the need for gloves if the counterpressure is kept low enough (say <20KPa).  Maybe you could where normal boots as well.  I suspect that underwear would need to be rubberised, in order to prevent spontaneous defeacating.  At <20KPa, dehydration would start to become a real problem.

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#19 2014-12-05 10:19:32

GW Johnson
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Re: Habitat air

This usable-atmosphere thing is mostly an arguing-in-a-vacuum thing here on the forums,  because the proper experiments don’t seem to have been run.  Navy deep-sea diving experience is relevant,  yes,  but focuses on high total pressures,  not low.  So it’s not a perfect fit.

My latest blog posting posits a habitat atmosphere near 1 atm total pressure and 21% oxygen (which answers the fire hazard thing,  so that issue just went away).  But,  I do it with a mix of diluent gases instead of just nitrogen,  to cut down on individual diluent dissolved partial pressures in the blood.  It is those partial pressures that drive smooth vs bubbly outgassing as atmosphere composition and total pressure change,  that’s just the physical chemistry of diffusion.  And thus that’s a falsifiable scientific hypothesis to test.

I’m recommending lower suit oxygen pressures to make more,  and more varied,  suit designs feasible,  which flies in the face of current practices,  yes.  But,  all such suit design approaches have a place and an application.  The notion of one-design-fits-all is a self-limiting dead end.  It always has been,  in all other walks of life!  To expect differently here is the insanity that it really is. 

Bureaucracies have historically proven to be very fond of self-imposed insanity,  though.  No surprises there.  Only an opportunity to do something different,  it might well be better.  Much of human history proves that. 

One could start in an ordinary chemistry lab with simple bell jar experiments.  Use brine of blood salinity as a surrogate for blood.  Simple open-top beakers.  Expose the brine to 1 atm and a proposed gas mix under a bell jar long enough to equilibriate.  Then quickly place it in a bell jar of oxygen only,  and reduce that bell jar pressure quickly to proposed suit pressure levels.  The brine sample either fizzes or it doesn’t,  and it’s visible through the glass bell jar for all to see (simple go/no-go outcome).  You can even be compulsive about it and quantify the decompression rates to prevent fizzing. 

If an atmosphere mix,  or set of atmosphere mixes,  doesn’t fizz at quick decompression times,  then that’s what you are looking for.  Try it (them) with mice instead of brine samples.  Either the mice become ill with the bends,  or they do not (another simple go/no-go outcome).  Check the stats on this over a very large sample,  for confidence. 

If it bears up,  try it experimentally with human volunteers in ground test vacuum tank chambers. 

If it works on the ground,  try it in space on the ISS.  One could temporarily modify the atmosphere in the one module where the EVA airlock is,  to see if pre-breathe time can be dropped by using a multi-gas mix in an all-up demonstration.  Existing suits can be operated at the lower experimental pressures just as easily as the normal higher pressures.  This need not wait for a new suit design. 

There I went and wrote you the outline of a program plan to find out what we can and cannot do,  and whether we really need high-pressure suits with complicated and difficult glove designs as the “only feasible thing to do”.  No new suit designs,  no new facilities.  No expensive gravy-train R&D programs.  Just get the job done,  quickly and efficiently,  with what we already have. 

Does anybody have bell jars and bottled gases?  You could run the initial feasibility tests yourself!

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#20 2014-12-05 14:02:22

Void
Member
Registered: 2011-12-29
Posts: 3,175

Re: Habitat air

I may not understand how these things work, but my assumptions now are;

1) That breathing pure Oxygen allows the body to be rid of Nitrogen over time.
2) Then a relatively fast depressurization is permitted, because the body consumes excess Oxygen before it can cause bends?


Could something like this lead to an agreement between opposing parties?

Compromise Trial Balloon:

If this is the correct understanding I suggest the habitat be split into three primary sections with different pressures, with two special airlocks partially filled with water between them.

Section: 1 Bar of pressure in a habitat where "Dry" and ignition prone processes can be enclosed. (Using a mixture of gasses)

Between these two, a small "Swimming Pool" air lock.  (With emergency air supplies at the bottom of the pools)

Section: 0.625 bar for a wet processes section, where ignition prone devices and materials are prohibited.  This could be large enough for processes such as aquaculture, (Using a mixture of gasses)

Between these two, a small "Swimming Pool" air lock.  (With emergency air supplies at the bottom of the pools)

Section: 0.25 bar, a sleeping/bathroom/kitchen  section for persons working outside the habitat in minimum pressure suits.  This will be a small section, and again have a significant basin filled with water and will be largely made of combustion safe materials.

A regular air lock.

One of the things I am looking at is a statement I think I saw that said that it took 17 hours for the shuttle crew to get ready for a EVA.  So, I am thinking that people who are good at sleeping could sleep in one of the airlocks for say 9 hours (Sleep and breakfast I suppose), and be adjusted to the next section by morning.



.

Last edited by Void (2014-12-05 14:10:39)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#21 2014-12-05 17:29:27

Impaler
Member
From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Habitat air

GW Johnson wrote:

Either the mice become ill with the bends,  or they do not (another simple go/no-go outcome).

That experiment was done in 1985, the rats got the Bends, it's a simple no-go outcome.  Yes it is high-pressure (4 to 6 atmosphere) to a rapid surface pressure, but everything we know about decompression tells us that it is pressure ratios that matter, that was the first observation of caisson worker that lead to the very concept, from any given pressure the loss of more then half that pressure resulting in symptoms.

http://www.pubfacts.com/detail/2999061/ … es-in-rats

Last edited by Impaler (2014-12-05 17:37:30)

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#22 2014-12-05 18:33:09

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
Website

Re: Habitat air

Of course it is known that decompression from 5.0 psi total pressure to 3.3 psi total pressure is fine, with no decompression issues at all. Apollo astronauts did it. And detailed studies show the ratio is partial pressure N2 to total pressure in the lower pressure environment. So simply using 2.7 psi O2 + 3.6 psi N2 would premit decompression to spacesuit pressure at 3.0 psi pure oxygen. The problem arrises when we try to add argon to increase habitat pressure. We just don't have sufficient data.

As I said, when I wrote work for the Mars Homestead Project, the guys wanted higher habitat pressure. I tried to do that with argon. My rationale was the Navy uses it for deep diving. But I had no data to confirm the numbers. But I had to give the Mars Homestead Project something, so we just went with it. Does it require further study before doing it on Mars? Definately! The paper I linked by Andrew Pilmanis and JT Webb appears to be the most relevant, but that just confirms lower partial pressure argon than nitrogen. It doesn't say anything about interactions with a tri-gas mix. I wonder if we could convince one of those two researchers to do the experiment?

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#23 2014-12-05 19:29:27

Impaler
Member
From: South Hill, Virginia
Registered: 2012-05-14
Posts: 286

Re: Habitat air

We have sufficient data, read the link.  You keep saying the experiments need to be done but these experiments have been done and were done decades ago, you need to research the body of experiments rather then just throwing out any idea that your own knowledge doesn't invalidate.

If you say we should RE-RUN and experiment on the slim chance that something has been missed or is in error then fine, but your going to be operating under the hypothesis that the original result will be confirmed and your not going to put the unlikely to be overturned hypothesis on the mission baseline.

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#24 2014-12-05 19:53:08

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
Website

Re: Habitat air

When I first joined the Mars Society, I hadn't heard of mechanical counterpressure. I thought anything like that was science fiction. The medical doctor Tam Czarnik told me about Paul Webb's work. I asked for a copy of the paper; he mailed a photocopy to me. The paper was written in 1966, published in 1967, so no electronic copy was available. Then I discovered NASA's technical reports server, available on the internet. I found Dr. Webb's contractor report to NASA, in 1971. It's amazing! And another Mars Society member who is an aerospace engineer pointed out contamination that Apollo suits suffered on the Moon. And she pointed out that an MCP suit is the only one that's machine washable. You can't wash a gas bag spacesuit, because wash water won't flow through. But an MCP suit is not air tight, it's elastic fabric. One fabric researched in 1971 was Spandex. Lunar astronauts had a problem with missions that lasted hours or days, but a Mars mission will be more than a year on the surface. A machine washable spacesuit is definitely an asset.

I think most members on this forum are familiar with MCP. It has greater ranger of motion for each joint than any other suit. Less joint counterforce. Greater dexterity and much less fatigue. And if a suit gets a tear or a cut just 1 cm long, a gas bag suit will decompress in seconds. But an MCP suit will expose skin beneath the breach to vacuum, resulting in a nasty bruise. Death vs bruise; I know which I would prefer. Decompression close to an airlock may not result in death, but would still result in severe decompression sickness, incapacitating the astronaut. So MCP has much greater safety.

Furthermore, an MCP suit does not require a cooling system. The cooling system is sweat. So the entire cooling system consists of a bottle of drinking water, with a tube to the helmet and a drinking nipple. This could be incredibly light. It could be nothing more than a 1 litre PET bottle, the same as a pop bottle on Earth, locked in the PLSS backpack for safety. With a plastic bag liner filled with water. And a tube for air leading from the bottle cap back to the counter-lung vest of the MCP suit. This is very light weight, very simple, maintains constant volume, and keeps drinking water separated from air. So this would work in zero-G as well as planetary gravity. Of course, hours of sweating into a spandex MCP suit while doing vigorous work outside would further increase the need to be laundered.

For Mars you may want to use a fancy plastic instead of PET, something like PCTFE. But if protected from UV in a PLSS backpack, and kept warm enough to keep the water liquid, then even PET would be good enough.

Furthermore, an MCP suit is compatible with a head-worn helmet. Mercury and Gemini suits had such a helmet, but the neck was stiff. Apollo suits overcame this with a "fish bowl" helmet, also known as a shoulder-worn helmet. But work done by the Mars Society at MDRS has identified a major problem: it isn't a crash helmet. Wearing such a helmet while riding a 4-wheel ATV is just not safe. So crews typically go "out of sim" and replace their plastic suit helmet with a motorcycle helmet while riding. But an MCP suit with its fabric neck could use a crash helmet. This would allow driving a rover on Mars.

The single draw-back of an MCP suit is donning. It's difficult to put on. Once on, it's very comfortable. But it's tight, because that's the point. And MCP on one body part, and not the whole body, results in differential pressure that restricts blood flow. It's comfortable when the whole thing is on, but wearing a portion of the suit is uncomfortable. Those working on current gas bag suits have used this to argue against their competition.

So I'm arguing that MCP is the ideal Mars suit. As GW Johnson said, there is no "one size fits all". MCP is a specialty suit for planetary surfaces, useful on the Moon or Mars. The EMU is a specialty suit optimized for LEO.

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#25 2014-12-05 20:34:58

RobertDyck
Moderator
From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 5,929
Website

Re: Habitat air

I can't download the full paper. The abstract appears to relate to what we're talking about here, but is not definative. I would have to read the whole paper.

Impaler, I've given long-winded explanations, many anecdotes of individuals working together. But you keep trying to win. You can't win as long as you try to win. You are belligerent, argumentative, confrontational, insulting, and hostile. In short, a troll. And the fact you keep arguing nothing short of one full atmosphere is safe, completely eliminates any credibility. You demonstrate inability to work with others.

For many of us, this is not only an attempt to achieve something we dreamed about since youth. This is also a refuge from everyday life. We really don't need a bully here. The fact you are able to cite credible sources, while at the same time insulting others work and being intransigent over a fundamental of the Apollo program, just makes it worse. Makes you worse.

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