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Pressure for suits, ISS and future.
by
KelvinZero
on 07 Feb, 2011 07:19
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Hi, I understand that spacesuits use lower pressures with more oxygen in order to increase flexibility. I thought the ISS also had lower pressure than earth but apparently this is not true.
How long does it take to prepare yourself for a suit atmosphere. I assume there is the risk of the bends.
What is the pressure and mix used in a spacesuit,
What are the disadvantages of suit pressure/atmosphere. (ie why does the ISS not just stay at suit pressure)
What pressures and mixes of air would we probably use in future? Would we use full earth pressure in a base on the moon or mars, on a trip to an asteroid? Would future suit pressures be higher? How long will they take to adapt to?
Would we use suit pressure in pressurized lunar or mars rovers so we could step straight in to them?
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#1
by
arkaska
on 07 Feb, 2011 09:59
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Hi, I understand that spacesuits use lower pressures with more oxygen in order to increase flexibility. I thought the ISS also had lower pressure than earth but apparently this is not true.
1. How long does it take to prepare yourself for a suit atmosphere. I assume there is the risk of the bends.
2. What is the pressure and mix used in a spacesuit,
3. What are the disadvantages of suit pressure/atmosphere. (ie why does the ISS not just stay at suit pressure)
What pressures and mixes of air would we probably use in future? Would we use full earth pressure in a base on the moon or mars, on a trip to an asteroid? Would future suit pressures be higher? How long will they take to adapt to?
Would we use suit pressure in pressurized lunar or mars rovers so we could step straight in to them?
1. They sleep overnight in the A/L with lowered pressure to prepare. There is a back-up plan involving work-out on the CVIS while breathing pure oxygen instead of the camp-out.
2. 4.3 psi and pure Oxygen
3. The main advantage is increased flexibility.
All the above is for the US EMU since I assume that's what you're asking about. The Russian Orland suit operates at the same pressure as the rest of ISS and need to camp-out. It is on the other hand not as flexible as the EMU but you can get into it by yourself.
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#2
by
hop
on 08 Feb, 2011 14:34
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All the above is for the US EMU since I assume that's what you're asking about. The Russian Orland suit operates at the same pressure as the rest of ISS and need to camp-out.
Orlan definitely does not run at the same pressure as ISS. It's slightly higher (~1.5PSI IIRC) than the US EMU, which does shorten the pre-breath a lot. Still pure oxygen.
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#3
by
KelvinZero
on 11 Feb, 2011 09:28
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What are the disadvantages of suit pressure (or a compromise somewhere in between) for the entire station?
I guess on the ISS there are only a few times to go outside so there isnt much reason to optimize for EVAs. What about if VSE had put a permanent base on the moon with frequent excursions. What pressures were planned for the base and for the rovers there and what factors drove these choices?
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#4
by
arkaska
on 11 Feb, 2011 10:37
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What are the disadvantages of suit pressure (or a compromise somewhere in between) for the entire station?
I guess on the ISS there are only a few times to go outside so there isnt much reason to optimize for EVAs. What about if VSE had put a permanent base on the moon with frequent excursions. What pressures were planned for the base and for the rovers there and what factors drove these choices?
Apollo was on a lower pressure (5 psi) but that was made possible by the pure oxygen environment. I don't think it's possible to work in a 5 psi environment when it's regular air as in ISS.
Debate over the upsides and downsides of pure oxygen has been discussed several times on this board.
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#5
by
spacejulien
on 11 Feb, 2011 10:39
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I have had the same question in mind for a Mars mission. Definitively away from any 1 bar / 14.5 psi environment for 2.5 years. So no need to keep up 1 bar for all those mission elements and it could facilitate Mars surface excursions and rescue/fail safe scenarios, if no pre-breathing would be required before doing a Mars-walk. So two questions:
1) Up to which pressure could the habitat(s) be pressurized without the requirement for pre-breathing, assuming a suit pressure at todays level.
2) Down to which pressure and Oxygen / inert gases ratio is deemed safe and healthy in long term application (2.5 years).
~spacejulien
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#6
by
JayP
on 11 Feb, 2011 14:00
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I have had the same question in mind for a Mars mission. Definitively away from any 1 bar / 14.5 psi environment for 2.5 years. So no need to keep up 1 bar for all those mission elements and it could facilitate Mars surface excursions and rescue/fail safe scenarios, if no pre-breathing would be required before doing a Mars-walk. So two questions:
1) Up to which pressure could the habitat(s) be pressurized without the requirement for pre-breathing, assuming a suit pressure at todays level.
2) Down to which pressure and Oxygen / inert gases ratio is deemed safe and healthy in long term application (2.5 years).
~spacejulien
it is all about the partial preasure of oxygen in the mix. Anytime you decompress while breathing a gas that involves oxygen mixed with something else, there is the issue of the other gas bubbling in your blood stream (A.K.A the bends). A higher PPO2 carries with it an increased fire risk.
This is from the wikipedia article on breathing gas mixtures so you don't have to look it up;
The minimum safe partial pressure of oxygen in a breathing gas is commonly held to be 16 kPa (0.16 bar). Below this partial pressure the diver may be at risk of unconsciousness and death due to hypoxia, depending on factors including individual physiology and level of exertion. When a hypoxic mix is breathed in shallow water it may not have a high enough ppO2 to keep the diver conscious. For this reason normoxic or hyperoxic "travel gases" are used at medium depth between the "bottom" and "decompression" phases of the dive.
The maximum safe ppO2 in a breathing gas depends on exposure time, the level of exercise and the security of the breathing equipment being used. It is typically between 100 kPa (1 bar) and 160 kPa (1.6 bar) but for dives of less than three hours is commonly considered to be 140 kPa (1.4 bar), although the U.S. Navy has been known to authorize dives with a ppO2 of as much as 180 kPa (1.8 bar). At high ppO2 or longer exposures, the diver risks oxygen toxicity including a seizure. Each breathing gas has a maximum operating depth that is determined by its oxygen content
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#7
by
gospacex
on 11 Feb, 2011 17:35
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I have had the same question in mind for a Mars mission. Definitively away from any 1 bar / 14.5 psi environment for 2.5 years. So no need to keep up 1 bar for all those mission elements and it could facilitate Mars surface excursions and rescue/fail safe scenarios, if no pre-breathing would be required before doing a Mars-walk. So two questions:
1) Up to which pressure could the habitat(s) be pressurized without the requirement for pre-breathing, assuming a suit pressure at todays level.
2) Down to which pressure and Oxygen / inert gases ratio is deemed safe and healthy in long term application (2.5 years).
~spacejulien
it is all about the partial preasure of oxygen in the mix. Anytime you decompress while breathing a gas that involves oxygen mixed with something else, there is the issue of the other gas bubbling in your blood stream (A.K.A the bends). A higher PPO2 carries with it an increased fire risk.
This is from the wikipedia article on breathing gas mixtures so you don't have to look it up;
The minimum safe partial pressure of oxygen in a breathing gas is commonly held to be 16 kPa (0.16 bar). Below this partial pressure the diver may be at risk of unconsciousness and death due to hypoxia, depending on factors including individual physiology and level of exertion.
This is kinda strange, considering that sea level partial pressure of O2 is 20 kPa, and large groups of people are known to live their entire lives at 2 and even 3 km altitudes.
IIRC serious problems (long term effects, not immediate danger) start around 4 km.
At 5 km, partial pressure of O2 is ~10 kPa. At 3 km, it should be no more than 14 kPa.
So how come 16 kPa is "risk of unconsciousness and death"? To me it looks like a level at which people can live indefinitely, be healthy, have children etc...
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#8
by
KelvinZero
on 12 Feb, 2011 09:20
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Apollo was on a lower pressure (5 psi) but that was made possible by the pure oxygen environment. I don't think it's possible to work in a 5 psi environment when it's regular air as in ISS.
Debate over the upsides and downsides of pure oxygen has been discussed several times on this board.
Hi, thanks and sorry if this has been done to death elsewhere.
I did some searching but I couldnt think of a good search term. Oxygen, and pressure are no good
This thread brought up the term "partial pressure" which allowed me to find this thread.
http://forum.nasaspaceflight.com/index.php?topic=11026.0Someone mentioned in this thread that the main disadvantage of pure oxygen, low pressure is fire risks?
Any other links would be appreciated.
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#9
by
arkaska
on 12 Feb, 2011 09:27
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#10
by
KelvinZero
on 16 Feb, 2011 08:16
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Thanks.. took a while for someone to get around to translating Jim, but it seems like fire risk is the only mentioned disadvantage of low pressure, pure oxygen? Has there been any experience with long term breathing of that sort of atmosphere?
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#11
by
JayP
on 16 Feb, 2011 17:37
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Thanks.. took a while for someone to get around to translating Jim, but it seems like fire risk is the only mentioned disadvantage of low pressure, pure oxygen? Has there been any experience with long term breathing of that sort of atmosphere?
Sure, the most relevant for this discussion was Skylab. The third crew spent 3 months in a low pressure atmosphere. Their major complaint was that they could not hear each other talking unless they were right next to each other (lower density materials don't transmit mechanical vibrations as well.)
One issue of any modificatios to the atmosphere is if you are doing studies into biomedical effects of spaceflight. A different atmosphere would be another thing that you have to take into account when evaluating your results. using a seallevel atmosphere simplifies things.
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#12
by
Robotbeat
on 16 Feb, 2011 18:51
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...One issue of any modificatios to the atmosphere is if you are doing studies into biomedical effects of spaceflight. A different atmosphere would be another thing that you have to take into account when evaluating your results. using a seallevel atmosphere simplifies things.
Which is almost totally irrelevant for exploration missions.
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#13
by
gospacex
on 16 Feb, 2011 19:13
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I am thinking about long-term. In the long-term, off-Earth bases (Moon/Mars/asteroids/orbital stations) definitely won't have any reasons to stick with 1 atm 80/20 N2/O2 mix, while they will have plenty of reasons to standardize on lower pressure mix.
Judging by arguments in this thread, currently we know that partial O2 pressure can be lowered by about 20% from Earth sea-level value and still be safe, even in the long term.
It's unclear whether any research was done into limits of long term safe levels of N2 depleted, lower than sea level pressure mixes.
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#14
by
KelvinZero
on 20 Feb, 2011 04:13
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Thanks.. took a while for someone to get around to translating Jim, but it seems like fire risk is the only mentioned disadvantage of low pressure, pure oxygen? Has there been any experience with long term breathing of that sort of atmosphere?
Sure, the most relevant for this discussion was Skylab. The third crew spent 3 months in a low pressure atmosphere. Their major complaint was that they could not hear each other talking unless they were right next to each other (lower density materials don't transmit mechanical vibrations as well.)
One issue of any modificatios to the atmosphere is if you are doing studies into biomedical effects of spaceflight. A different atmosphere would be another thing that you have to take into account when evaluating your results. using a seallevel atmosphere simplifies things.
Thanks, two interesting tidbits in there: the sound damping and the research advantage of standard mix, which I guess implies that when we are past research and there to do a 9-5 job, the reason for a standard mix is reduced further.
I actually hadnt intended this to be an ISS topic specifically. Someone moved it here. However they may know best and this might be the best forum to get good input on data about the health effects of space.
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#15
by
spacejulien
on 23 Feb, 2011 01:52
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#16
by
spacejulien
on 24 Feb, 2011 00:03
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An increment on the cabin pressure chart.
I didn't look for further details for partial pressures of former and current suits, so the assumption of 100% Oxygen atmosphere is still in place.
I implemented the "Alveolar gas equation".
http://en.wikipedia.org/wiki/Alveolar_gas_equationBelow the Oxygen partial pressure line (pO2) there is a line giving the corresponding Alveolar Oxygen partial pressures (pA O2) for 3000m Alt, 1860m Alt and sea level.
These three pAO2 values are now kept constant until a 100% oxygen atmosphere is reached. The corresponding pO2 curves originate at the three pO2 levels for the three elevations and end at the pTotal-line.
Interestingly, the line providing sea level Alveolar Oxygen pressure ends up at exactly the Apollo suit pressure. So this is a good sanity check.
One can see the minimum imaginable cabin pressure at 18.6 kPa, which would be similar to living at 3000m altitude, but in a 100% Oxygen atmosphere.
I didn't cover any security risks, yet. Also, bends ratio remains to be assessed.
Does anyone know a source giving a safety requirement like "no more than 40% of Oxygen in cabin air..."? That would greatly narrow the possibilities.
Sources for today's increment:
http://en.wikipedia.org/wiki/Space_suithttp://en.wikipedia.org/wiki/Alveolar_gas_equation
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#17
by
telomerase99
on 24 Feb, 2011 00:48
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Question: I am in the medical field and we use pubmed.org to quickly query all peer reviewed medical papers published on a subject.
Is there a central database of aerospace data that is publicly query-able?
Forgive me for my ignorance.
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#18
by
Robotbeat
on 24 Feb, 2011 00:54
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Question: I am in the medical field and we use pubmed.org to quickly query all peer reviewed medical papers published on a subject.
Is there a central database of aerospace data that is publicly query-able?
Forgive me for my ignorance.
NASA Technical Reports server:
http://ntrs.nasa.gov (freely available... mostly)
and the other big repository is:
http://www.aiaa.org (not entirely free... often shows the first page for free)
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#19
by
spacejulien
on 24 Feb, 2011 12:16
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#20
by
spacejulien
on 24 Feb, 2011 12:23
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#21
by
Robotbeat
on 24 Feb, 2011 15:28
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Just found this plot in the Man-System Integration Standards (NASA-STD-3000 Volume 1) in section 5.1 http://msis.jsc.nasa.gov/sections/section05.htm#_5.1_ATMOSPHERE
I've seen that graph, as well... I have reason to believe that the lower bound is not really exactly accurate when you get to the right side of the graph (though is decently accurate on the left hand side) based on research that actually cites that graph.
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#22
by
KelvinZero
on 01 Oct, 2011 11:21
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bump.
I want a simple answer and I get.. graphs!
It looks from above like about 50% and 30% oxygen has no health issues and is safe re fire, so we would at least go that low if people were living and working in the moon?
How would this affect pre breathing time? Apparently a suit can be called zero-prebreathe if it works at 50% of earth pressure.. If we started at 50% could we step straight in a 25% earth pressure suit without pre breathing?
btw is there any number already chosen for a permanent moon base supposing we were to proceed? It seems to me the pressure it would work at would be one of the earliest things established before you started designing the thing.
