Author Topic: The case for lower pressure Mars habitats  (Read 19878 times)

Offline Comga

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Re: The case for lower pressure Mars habitats
« Reply #20 on: 01/30/2017 01:09 am »
I'm from the Denver area (5,340, in my case) but I was at 9,600 for the last two days with no noticeable differences.  Most airliners are pressurized to about 8,000 feet and almost everyone from sea-level is fine with that for hours.  I've spent days camping and even waterskiing in Leadville, Colorado (10,000+ feet) with no ill effects.  The town of Leadville is above 10,500 feet and lots of people visit and stay there from many other places.  Altitude sickness is a very, very serious thing but it's easy to avoid entirely if you follow a few very simple rules (don't exercise until you acclimate, stay hydrated, don't drink alcohol while you acclimate, acclimate in steps like sea-level to Denver to high altitude if possible).

My point is, for healthy people, even those who grew up at sea level, living at an equivalent pressure above 10,000 feet should be easy within a couple of days.  Higher oxygen concentrations and lower pressures come with lousy flammability limits.

Living near 2 km altitude and spending a lot of time near and above 3 km altitude I used to make the same argument about oxygen content.  "If they had put the Air Force base in Houston and Manned Spaceflight Control in Colorado Springs, the astronauts would have acclimatized and spacecraft and space stations could be so much lighter."

However, in addition to the problems mentioned above is flammability, Lee Jay's last point.  If you keep the oxygen content constant and reduce the nitrogen things burn easier, and fire in spacecraft is something NASA works hard to avoid.    The Apollo 1 fire, now just over a half century ago, is the extreme example, but it doesn't have to be 100% oxygen or 1 Atm to dramatically increase the risk. 

Now where are they going to get all that nitrogen for Martian cities?

edit:  The martian atmosphere is 1.9% nitrogen, and about 1% of Earth sea level pressure so all one has to do is extract all the nitrogen from 3500 times the volume of your air supply and you have your nitrogen.  3000 if you keep the pressure equivalent to Lee Jay's Denver.  ;)
« Last Edit: 01/30/2017 04:55 am by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online guckyfan

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Re: The case for lower pressure Mars habitats
« Reply #21 on: 01/30/2017 07:29 am »
The martian atmosphere is 1.9% nitrogen, and about 1% of Earth sea level pressure so all one has to do is extract all the nitrogen from 3500 times the volume of your air supply and you have your nitrogen.  3000 if you keep the pressure equivalent to Lee Jay's Denver.  ;)

Extracting the CO2 needed for fuel ISRU will yield all the nitrogen needed. They may or may not have to separate it from the argon which is present at the same procent value.

Offline AegeanBlue

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Re: The case for lower pressure Mars habitats
« Reply #22 on: 02/02/2017 11:49 pm »
In an ecosystem on Earth animals are less than 1% of biomass by weight. Simple mass fraction calculations show that, assuming that food is grown locally, human biomass will not be the majority of the biomass in the Martian habitat, it will be the plant biomass. I think we ought to optimize for the plants rather than the humans and plants do not like lower pressure, it interferes with plant water flows leading to water stress. Plants also do not like if the atmosphere contains too little or much CO2. On Mars we have an atmosphere which we can use as a base to set up the habitat atmosphere. If we grow food in the habitat we will be pumping CO2 and water in the greenhouse which gets converted to O2 and biomass. We will need to remove the O2, MarsOne dies from Oxygen toxicity as the MIT study found. Bars Landorp mentioned an Oxygen concentrator, that can work. Over time if we pump Mars atmosphere we remove both CO2 and O2 (through the concentrator) leading to enrichment of the minor components of the Martian atmosphere. There are issues with this approach, most importantly CO which is toxic to animals but not plants, plants will oxidize it to CO2 but we need to make sure that concentration does not get toxic to the living animals of the habitat, most importantly humans. I am more inclined for variable pressure and composition, we start with barely livable for humans and plants in terms of pressure and composition and then as we establish plants and people we move to closer to earth surface or whatever is optimum for both.

Offline Robotbeat

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Re: The case for lower pressure Mars habitats
« Reply #23 on: 02/03/2017 12:42 am »
I HIGHLY doubt we will copy Earth's biosphere for the interior of the habitat. It'd have to be so enormous (and so expensive) that even a large colony could only support a tiny human population.

And we'll probably develop plants that can survive straight on Mars's surface, if not right away then immediately after terraforming starts to slightly thicken the atmosphere.
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Online guckyfan

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Re: The case for lower pressure Mars habitats
« Reply #24 on: 02/03/2017 07:49 am »
I think we ought to optimize for the plants rather than the humans and plants do not like lower pressure, it interferes with plant water flows leading to water stress. Plants also do not like if the atmosphere contains too little or much CO2.

Large greenhouses will be optimized to different parameters than human habitats. I remember that issue with water stress. It became apparent at pressures of 3, maybe 2 psi. I would like to see a pressure in greenhouses that would allow to work with no more than oxygen masks or rebreathers.

Offline john smith 19

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Re: The case for lower pressure Mars habitats
« Reply #25 on: 02/03/2017 10:04 am »
I HIGHLY doubt we will copy Earth's biosphere for the interior of the habitat. It'd have to be so enormous (and so expensive) that even a large colony could only support a tiny human population.

And we'll probably develop plants that can survive straight on Mars's surface, if not right away then immediately after terraforming starts to slightly thicken the atmosphere.
It looks like they already can

http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html/

So a minimal green house which supplied some liquid water and a fairly low air pressure would help a lot.
it also suggests there is a fairly solid basis from which to genetically engineer further plants.

Carbon capture is viewed as a key process for turning a CO2 atmosphere (created by releasing the contents of the South Pole ice cap) into one that's breathable.

BTW in all this there seems to be no analysis wheather raising the atmospheric pressure would supress  those large scale dust storms that are seen, or wheather it would turn them into phenomenally destructive months long super tornadoes, making them immensely more destructive. 
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Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #26 on: 02/03/2017 04:37 pm »
I think we ought to optimize for the plants rather than the humans and plants do not like lower pressure, it interferes with plant water flows leading to water stress.

Quite to the contrary, plants generally like low nitrogen partial pressures, so long as the O2 and CO2 partial pressures remain the same.  Not always, but most often.  And they can survive much lower pressures than humans.

Here's some random studies from the last time I checked (need to translate my notes from Icelandic...).  Since you guys normally seem to work in PSI, I'll note that 1 atmosphere is 101,325 pascals.

Mansell et al, 1968: No negative effects in Brassica rapa (bok choy / turbip) at 50kPa, just more water loss.
Rule and Staby, 1981: Tomatoes @17 kPa constricted;  @33kPa were stronger that tomatoes grown at @100kPa, but not bigger.
Daunicht and Brinkjans, 1992: tomatoes @40kPa and @70kPa constricted
Andre & Richaux, 1986: barley grows better @3kPa in a nitrogenless atmosphere than a conventional O2/N2 one.
Gale, 1972: CO2 is easier to take up when the pressure is lower.
Smith & Donahue, 1991: At 50kPa+,  CO2 uptake is inversely proportional to pressure.
Andre & Massimino, 1992: Wheat can sprout @10 kPa and grows better at @20kPa than @100kPa if N2 is low  (O2@14 kPa, N2@ 3,4kPa, CO2@ 3,4 kPa). Appears that lowering N2 in general helps.
Musgrave et al, 1988: Mung beans grow independent of  O2 partial pressure, and general pressure reduction is negative (tested @21kPa)
Goto et al, 2002: Rice can grow @25kPa and @50kPa; having O2 partial pressure at least.10 kPa prevents damage.
Spanarkel & Drew, 2002: Lettuce @ 70kPa grows similar or better than @101kPa
He et al, 2003:  Plants in general grow similar or better at @ 30kPa vs. @1atm because of better removal of ethylene.
Wheeler et al, 2001: Corey et al, 2002: Plants grow similar or better at 30kPa
Ferl et al, 2002: In addition to plants already doing well at low pressures, there's significant potential for genetic improvement to increase it (aka avoiding the drought response).

Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #27 on: 02/03/2017 04:40 pm »
However, in addition to the problems mentioned above is flammability, Lee Jay's last point.  If you keep the oxygen content constant and reduce the nitrogen things burn easier, and fire in spacecraft is something NASA works hard to avoid.    The Apollo 1 fire, now just over a half century ago, is the extreme example, but it doesn't have to be 100% oxygen or 1 Atm to dramatically increase the risk. 

Reference(s)?  The Apollo capsule was 100% O2 at *above* atmospheric pressure - 6x the normal O2 partial pressure.

Offline AegeanBlue

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Re: The case for lower pressure Mars habitats
« Reply #28 on: 02/03/2017 04:52 pm »
Well, whether lichens qualify as plants is subject to debate. When I was an undergrad we considered them plants, according to Wikipedia today we do not. They are a symbiosis of cyanobacteria and fungus and none of them are edible by people, at least most of the time. Some are edible by some animals but if you read the article it is debatable just how much lichen agriculture is viable: We would need to have a lichen that somehow thrives in Martian conditions (survive and thrive are different things), harvest them and according to the article they were growing sheltered in cracks rather than in the open and then feed them to say reindeer living inside the habitat with humans. Also pure lichen is not a balanced reindeer diet. From

http://animals.howstuffworks.com/mammals/reindeer-find-food1.htm

Quote
However, lichen isn't a particularly hearty food, and for that reason, reindeer will eat 4 to 11 pounds (1.8 to 4.9 kilograms) of reindeer moss each day [source: Dieterich and Morton]. That's why reindeer pack on the pounds in the warmer months when there's more to choose from. In fact, these animals gradually lose weight starting in the fall and continuing to March [source: University of Alaska Fairbanks].

I am not claiming to redo a natural terran biosphere, I am trying to show how we need to put our emphasis on viability elsewhere than just people. The average American eats a little under 1 metric ton of food every year. We have mentioned the ISS astronaut in the forum, I do not remember if it is 500 kgs or 800 kgs per year but even if we use the 500 kgs food/yr value producing it requires another 1000 kgs of plant biomass, above and below ground. But let us assume that for simplicity's sake this food is harvested for times a year and that we fully recycle the biomass of one crop to the next (impossible). So for every 75 kg astronaut there are 1500/4 = 375 kgs of plant biomass providing food. As Napoleon said, armies march on their stomach. So do astronauts.

I think we ought to optimize for the plants rather than the humans and plants do not like lower pressure, it interferes with plant water flows leading to water stress.

Quite to the contrary, plants generally like low nitrogen partial pressures, so long as the O2 and CO2 partial pressures remain the same.  Not always, but most often.  And they can survive much lower pressures than humans.

Here's some random studies from the last time I checked (need to translate my notes from Icelandic...).  Since you guys normally seem to work in PSI, I'll note that 1 atmosphere is 101,325 pascals.

Mansell et al, 1968: No negative effects in Brassica rapa (bok choy / turbip) at 50kPa, just more water loss.
Rule and Staby, 1981: Tomatoes @17 kPa constricted;  @33kPa were stronger that tomatoes grown at @100kPa, but not bigger.
Daunicht and Brinkjans, 1992: tomatoes @40kPa and @70kPa constricted
Andre & Richaux, 1986: barley grows better @3kPa in a nitrogenless atmosphere than a conventional O2/N2 one.
Gale, 1972: CO2 is easier to take up when the pressure is lower.
Smith & Donahue, 1991: At 50kPa+,  CO2 uptake is inversely proportional to pressure.
Andre & Massimino, 1992: Wheat can sprout @10 kPa and grows better at @20kPa than @100kPa if N2 is low  (O2@14 kPa, N2@ 3,4kPa, CO2@ 3,4 kPa). Appears that lowering N2 in general helps.
Musgrave et al, 1988: Mung beans grow independent of  O2 partial pressure, and general pressure reduction is negative (tested @21kPa)
Goto et al, 2002: Rice can grow @25kPa and @50kPa; having O2 partial pressure at least.10 kPa prevents damage.
Spanarkel & Drew, 2002: Lettuce @ 70kPa grows similar or better than @101kPa
He et al, 2003:  Plants in general grow similar or better at @ 30kPa vs. @1atm because of better removal of ethylene.
Wheeler et al, 2001: Corey et al, 2002: Plants grow similar or better at 30kPa
Ferl et al, 2002: In addition to plants already doing well at low pressures, there's significant potential for genetic improvement to increase it (aka avoiding the drought response).


Thanks for the literature but I want to mention again, survive and thrive are different.

Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #29 on: 02/04/2017 12:32 am »
As you'll note, most were "same or better" - without any selective breeding / genetic engineering.  Plants uptake CO2 and remove waste products better when the nitrogen partial pressure is reduced.  Given that reducing pressure also reduces system mass, there's no reason not to do it.

Offline Dalhousie

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Re: The case for lower pressure Mars habitats
« Reply #30 on: 02/05/2017 08:34 am »
As you'll note, most were "same or better" - without any selective breeding / genetic engineering. Plants uptake CO2 and remove waste products better when the nitrogen partial pressure is reduced.  Given that reducing pressure also reduces system mass, there's no reason not to do it.

This has been stated several times in this thread but I can find little evidence for it. Do you have a reference?
Apologies in advance for any lack of civility - it's unintended

Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #31 on: 02/06/2017 01:53 am »
As you'll note, most were "same or better" - without any selective breeding / genetic engineering. Plants uptake CO2 and remove waste products better when the nitrogen partial pressure is reduced.  Given that reducing pressure also reduces system mass, there's no reason not to do it.

This has been stated several times in this thread but I can find little evidence for it. Do you have a reference?

Did I not just post a giant list of references?  Do you need full APA-format cites to look them up?
« Last Edit: 02/06/2017 01:53 am by Rei »

Offline Robotbeat

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Re: The case for lower pressure Mars habitats
« Reply #32 on: 02/06/2017 02:39 am »
Actually, yeah. You shouldn't expect people to spend an entire day picking through a long list of references for a single fact you mentioned.
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Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #33 on: 02/06/2017 09:03 am »
Actually, yeah. You shouldn't expect people to spend an entire day picking through a long list of references for a single fact you mentioned.

Except that I wrote what's in each of them, so you don't have to.  :Þ

Offline john smith 19

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Re: The case for lower pressure Mars habitats
« Reply #34 on: 02/07/2017 10:43 pm »
I am not claiming to redo a natural terran biosphere, I am trying to show how we need to put our emphasis on viability elsewhere than just people. The average American eats a little under 1 metric ton of food every year. We have mentioned the ISS astronaut in the forum, I do not remember if it is 500 kgs or 800 kgs per year but even if we use the 500 kgs food/yr value producing it requires another 1000 kgs of plant biomass, above and below ground. But let us assume that for simplicity's sake this food is harvested for times a year and that we fully recycle the biomass of one crop to the next (impossible). So for every 75 kg astronaut there are 1500/4 = 375 kgs of plant biomass providing food. As Napoleon said, armies march on their stomach. So do astronauts.

Well the NASA standard for consumables is 5Kg/day. That's food, water and oxygen. That's 1825Kg/Year/person.  A good reason to start working on something more like a farm than a chemical plant.

TBH I was thinking more in  terms of terraforming than food, where a fairly light cover would provide a few pounds over pressure and keep wind and sand off. The real benefits of lichen is that peat bogs are more effective carbon capture systems than trees or any mechanical systems. They would let you turn the CO2 from the South Polar (dry) ice cap into Oxygen.

For human crops I think plants can tolerate surprisingly low pressures, less than half SL pressure. the question is what can the humans tolerate routinely? The MIT "biosuit" can exert 30%of full SL pressure so if people can handle that (with appropriate adjustments for CO2 and N2 and O2 levels) people can just put one on to do an EVA.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Rei

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Re: The case for lower pressure Mars habitats
« Reply #35 on: 02/08/2017 01:36 pm »
TBH I was thinking more in  terms of terraforming than food, where a fairly light cover would provide a few pounds over pressure...

This statement got me off and thinking (I was going to doubling the radius of a dome doubles tensile requirements in the envelope, so such Mars domes would either have to be kept proportionally small, or have an elaborate reinforcement system).  But the side thought:Ignoring all the issues of difficulty in producing such a thing:has anyone ever proposed a system of terraforming a planet involving weighing down the whole atmosphere?  I mean a literal planetwide floating row cover, transparent polymer withstanding 1ATM, loads transferred to fibre reinforcement to catenary curtains to cables, with a net loading on them of ~20 tonnes per square meter (something in that ballpark).

I'm not saying I find it a realistic option.  But when we're talking crazy megaengineering plans....  ;)  I mean, you could do that sort of thing on any body, even barren moons, and simultaneously reduce gas escape.  The only difference is you need a lot more mass to weigh it down when gravity is lower (although the stresses on the materials remain the same)
« Last Edit: 02/08/2017 01:39 pm by Rei »

Online Jim Davis

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Re: The case for lower pressure Mars habitats
« Reply #36 on: 02/08/2017 04:04 pm »
I mean a literal planetwide floating row cover, transparent polymer withstanding 1ATM, loads transferred to fibre reinforcement to catenary curtains to cables, with a net loading on them of ~20 tonnes per square meter (something in that ballpark).

If you can do that why bother with the planet at all?

Offline lamontagne

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Re: The case for lower pressure Mars habitats
« Reply #37 on: 02/08/2017 04:19 pm »
TBH I was thinking more in  terms of terraforming than food, where a fairly light cover would provide a few pounds over pressure...

This statement got me off and thinking (I was going to doubling the radius of a dome doubles tensile requirements in the envelope, so such Mars domes would either have to be kept proportionally small, or have an elaborate reinforcement system).  But the side thought:Ignoring all the issues of difficulty in producing such a thing:has anyone ever proposed a system of terraforming a planet involving weighing down the whole atmosphere?  I mean a literal planetwide floating row cover, transparent polymer withstanding 1ATM, loads transferred to fibre reinforcement to catenary curtains to cables, with a net loading on them of ~20 tonnes per square meter (something in that ballpark).

I'm not saying I find it a realistic option.  But when we're talking crazy megaengineering plans....  ;)  I mean, you could do that sort of thing on any body, even barren moons, and simultaneously reduce gas escape.  The only difference is you need a lot more mass to weigh it down when gravity is lower (although the stresses on the materials remain the same)
Yet, it's called a shell world, and was proposed a few years ago by Kennedy & all in the JBIS.  See joined paper.
« Last Edit: 02/08/2017 04:21 pm by lamontagne »

Offline Nomadd

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Re: The case for lower pressure Mars habitats
« Reply #38 on: 02/08/2017 04:22 pm »
As I mentioned in another thread, I spent a week in Cusco, and few people seemed to have any trouble at 9.4 psi after the first day. And the city is all walking up and down steep hills to get around.
« Last Edit: 02/08/2017 04:22 pm by Nomadd »
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Offline john smith 19

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Re: The case for lower pressure Mars habitats
« Reply #39 on: 02/08/2017 06:49 pm »
As I mentioned in another thread, I spent a week in Cusco, and few people seemed to have any trouble at 9.4 psi after the first day. And the city is all walking up and down steep hills to get around.
However to be able to slip into an MIT Biosuit you need to go down to more like 4.4psi.

I don't say it can't be done but I think at that level there will be other consequences.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

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