Agriculture Study Mars Pure CO2 Greenhouse

SpaceNut · 2020-02-11 18:02:36

louis wrote:

Can you grow plants at 0.05 bar even with a 100% CO2 atmosphere? I thought - from memory - it had to be closer to 0.2 bar
Terraformer wrote:
I don't like the idea of putting all the purposes of a building on a single layer.
If I were laying out a Martian town, I'd use the tent idea, but at a lower pressure, maybe 50mb. This would be a CO2 dominated atmosphere that would be used to grow adapted plants, producing food, fibre, and oxygen for the town. Within that would be the pressurised complex of buildings that is the town proper, with covered arcades for streets and shielded buildings to cut down on radiation, and including of course some parks, maybe in domes.
One thing that could be good for building pressurised environments is a hexagonal platting system. I have thought of this for Luna. They tessellate, which domes don't, and a circular pressure vessel can fit inside them. With the addition of another hexagon built inside that, you will get thick walls for radiation shielding. Streets would run between the hexagonal blocks. With standardised blocks, they could be used for many purposes - hospitals, hotels, townhouse developments around a square, parks... of course some blocks would need to reserve right of way for more direct routes for any railway added later. When you need more space, build another hexagon and top off the new street. As the city grows, the older parts could be redeveloped, maybe growing a forest of taller buildings from them that would reach above the pressurised streets.

edit
For earth 0.1 bar we are given 1.47 psi pressure
Mars is not a total co2 but has a mix at 0.15 psi

math follows in post 29

SpaceNut · 2020-02-11 19:54:20

http://pods.dasnr.okstate.edu/docushare … 723web.pdf

https://torontoplantman.wordpress.com/t … nt-growth/

https://link.springer.com/article/10.1007/BF00346400

tahanson43206 · 2020-02-12 08:30:02

In another topic, Louis asked for a short summary of progress made by this topic.

As of today, I find that I cannot offer a solution to the question posed in the opening post. The topic has acquired a substantial amount of related links and quoted information, primarily due to the (to me remarkable) contributions of SpaceNut. However, at this point, I am left with the impression that there are no plants known at the present time to thrive in what this topic proposes... a full Earth normal pressure environment of Mars atmosphere.

What I ** have ** learned is that plants on Earth have evolved to handle varying amounts of CO2 in the atmosphere of Earth. As the amount of CO2 increases, the number of CO2 intake ports on leaves decreases, and vice versa when CO2 levels decrease.

Another takeaway from this topic that I retain, is the understanding that there is a sweet spot of CO2 concentration for most plants tested. The figure that sticks with me is 1000 ppm, but it should be noted that this figure is for a standard Earth atmosphere in which the 999,000 ppm are inert gas molecules or Oxygen, which is used by plants for respiration when illumination is not present.

For the purposes of this topic, the imagined greenhouse atmosphere would consist of almost entirely CO2 compressed from the Mars atmosphere without filtering of any kind.

I admit to not having read all the links that SpaceNut found, so the answer may be out in those links. What is needed is someone willing to tackle the hard labor of going through all the links to see if someone somewhere has actually attempted to answer the question.

In the mean time, I call again for a research program to be carried out under the auspices and direction of a qualified research institution, to test a great number of plants in a 100% CO2 atmosphere held in sealed terrariums on Earth.

Most plants will die immediately or shortly after introduction to the proposed test environment. A tiny number will survive. I suppose it is better to say that a tiny number MAY survive. If any do, then their offspring will contain the genes that can be given a chance to grow in later iterations of the test.

(th)

Last edited by tahanson43206 (2020-02-12 08:32:13)

SpaceNut · 2020-02-12 13:19:40

The answer is that any atmospher needs a mixed level of gasses in a proportion as to make the plants grow as well as for men to be able to enter it without space suits.

The overall mixed pressure is with earth ratios of dry air contains (I have added in the % psi values)
78.09% nitrogen ( 11.47923 psi), < 791.46504 mb>
20.95% oxygen ( 3.07956 psi), < 212.32818 mb>
0.93% argon ( 0.13671 psi), < 9.42582 mb>
0.039% (0.005733 psi) carbon dioxide, < 0.39527 mb>

and small amounts of other gases.levels with all others contributing to the ramaining that make up total 14.7 psi on earth or 1 Bars. Altitude sickness is known to set in at heights as little as 2500 meters or 8,000 feet high danger altitude on the Mount Everest ascent,

Mars is not a total co2 but has a mix at 0.15 psi < 10.34213 mb> that is below the the Armstrong limit of 0.87 psi. of course getting quite sick with continued exposure to that level even in pure oxygen.

So Mars has 25 times as much carbon dioxide as compared to a volume of air pressure.

So earth PPM to percentage were the post of co2 is closer to 400 ppm currently so lets to make math easy says its 390 ppm.

So converting percent to 0.000390 is equal to 390 ppm as indicated above.

So for that sweet spot where just the correct levels of co2 and heat, light and moisture make for good food growth.

So 1,000 ppm to 1,500 ppm coverts to 0.001000 to 0.001500 or 0.1% to 0.15%. or 0.0147 psi to 0.02205 psi of the earth values < 1.01352 mb> to <1.52029 mb> .

Mars is not a total co2 but has a mix at 0.15 psi < 10.34213 mb>
So fill the tent with all co2 reduced by 1/10th to add in the correct percentages for earth's atmosphere and they will growth just as they do here with the same level of light at the rich co2 levels.

tahanson43206 · 2020-02-12 21:53:17

For SpaceNut re #29

Thank you for investing the time and care to create this post. I need to study it so will take the time needed.

You may be on to something, but I'm not sure. If I have the correct impression after this first reading, I ** think ** you are proposing to configure the greenhouse to deliver the quantity of CO2 molecules that Earth plants need and expect (ie, 1000 ppm of Earth normal atmosphere) by reducing the pressure in the greenhouse so that just that quantity of molecules are presented to the leaves for photosynthesis.

I need to study your post a while to see if I understand it and then I need to try to understand if your proposal would yield an environment that humans could visit safely.

Please keep in mind that your proposal (if I understand it) is NOT to do what was originally proposed for this topic, but to do something else. Since I created the topic, I have the opportunity to adjust my thinking if your proposal stands up to evaluation.

For all readers who might "tune in" at just this moment in the development of the topic, the topic was originally created to explore the idea of creating a greenhouse with an atmospheric pressure equivalent to Earth normal, but composed solely of the gases present in the Martian atmosphere.

The question in that case would have been: What plants can thrive under those conditions. A preliminary investigation yielded a result indicating that there exist NO plants that can survive in the conditions proposed.

SpaceNut has proposed (if I follow the argument correctly) that we forget about trying to make the greenhouse shirtsleeve comfortable for humans, and instead, make it comfortable for the plants.

I will attempt to arrive at an understanding of the atmospheric pressure that would be needed inside the greenhouse filled with Martian atmosphere gases that would deliver the 1000 ppm equivalent number of CO2 molecules to the plants.

I tip my hat to SpaceNut and others who more readily arrive at this understanding without a struggle.

(th)

SpaceNut · 2020-02-12 22:52:47

Its not just the air for plants that is needed as its got to be warm enough with moisture as well for the roots to draw up the food that they need. On Mars we need to change the tables to allow them to flourish.

https://sciencing.com/how-does-altitude … 32172.html

The Timber line is where on earth its to cold, not enouigh water, to little co2 and that is why trees and plants stop once we get there.
The sub-alpine extends downward from about 11,500 feet to 9,000.
We can grow crops at high altitude but its got to be warmer.
Coffee crops grow at altitudes of up to 7,000 feet in the Bolivian Andes.

Indirectly, altitude plays a part in pollination. If the altitude is inhospitable to the bees or other insects that pollinate the blossoms of fruit trees and plants, crops can suffer. The long-tongued bee fly common to elevations between 4,500 and 5,500 feet has a profound effect on the pollination of nectar-producing flowers, but the bee fly cannot survive outside its habitat, so again, altitude is in control.

https://www.planetnatural.com/high-altitude-gardening/

tahanson43206 · 2020-02-13 07:40:24

For SpaceNut re #31

Thanks for the reminder of the need for a comfortable temperature in the greenhouse.

As a baseline, this topic proposes a comfortable temperature for humans to work in shirtsleeves while wearing unobtrusive breathing apparatus.

Temperature proposed for this topic: 70 degrees Fahrenheit 21 degrees Celcius

The issue we are working in this topic is the pressure of the atmosphere to be maintained inside the greenhouse.

It has been determined to the extent possible at this point, that an atmosphere compressed to Earth standard sea level pressure would be inhospitable to Earth plants.

It has been proposed by SpaceNut that the atmosphere inside the greenhouse be compressed (from Mars standard) to JUST the point that the plants experience CO2 contact that is equivalent to the 1000 ppm rate found to be optimum on Earth.

While it appears that SpaceNut may have computed the elevation (on Earth) where the proposed density of CO2 might exist, I have not yet had time to try to follow his logic, so I do not know what that elevation equivalent would be.

The computed elevation equivalent may be above the timber line, or below it.

Edit#1: Humans use a variety of ways of describing Nature. Nature itself does not know about or care about what units humans might use to try to understand it. To a leaf, on Earth, Carbon Dioxide presents itself as individual molecules in a mixture of molecules of various gases. The leaf selectively pulls Carbon Dioxide molecules out of the mix and makes Carbon compounds of of the Carbon they contain. In the process the leaf releases the Oxygen, which it does not need at that time.

The natural phenomenon I am trying to understand is the number of Carbon Dioxide molecules that are knocking on the door at the surface of the leaf, on Earth, at sea level, at a temperature of 70 Degrees Fahrenheit or 21 Degrees Celsius.

I asked Mr. Google for help, and landed on a long Wiki discussion of partial pressures. The discussion seemed authoritative, but I did not come away from it better off. I am working on the assumption that if plants like a Carbon Dioxide density of 1000 ppm on Earth at sea level at 70 degrees Fahrenheit, then they will like the exact same number of Carbon Dioxide molecules presenting themselves in an artificial atmosphere made from the natural atmosphere of Mars through compression and heating.

In other words, on Mars, I am imagining an atmosphere in a greenhouse that presents the equivalent number of Carbon Dioxide molecules to the surface of the leaf, but in the case of the Mars atmosphere, the gas mixture would be almost entirely Carbon Dioxide.

SpaceNut may have already computed the answer, and I have printed his post in hopes of understanding it.

However, while I do that, if there is anyone among the NewMars membership who can provide a hint to two, you are welcome to do so.

If there is a reader of this forum who is not yet a member, registration is ridiculously easy, as the constant appearance of spam "guests" illustrates.

The specific question to be answered (as distinct from the purpose of this topic) is: What pressure of Mars atmosphere is needed inside a greenhouse to deliver the same number of Carbon Dioxide molecules to the surface of a leaf at 70 degrees Fahrenheit/21 degrees Celsius?

As a reminder the purpose of THIS topic is to find (or select for) plants that can thrive in an atmosphere of almost pure CO2 at one Earth atmospheric pressure.

To my knowledge the work to find such plants has not been done, and one of the objectives of this topic is to encourage such research.

Edit#2: Here is a simplified discussion of the operation of a leaf: https://www.bbc.co.uk/bitesize/guides/z … revision/1

Edit#3: Here is an article describing a proposal to use modern automation to search rapidly through DNA combinations to find plants able to grow on Mars.

http://theconversation.com/how-to-grow- … anet-99943

Briardo Llorente
CSIRO Synthetic Biology Future Science Fellow, Macquarie University

Plants on Earth have evolved for hundreds of millions of years and are adapted to terrestrial conditions, but they will not grow well on Mars.
This means that substantial resources that would be scarce and priceless for humans on Mars, like liquid water and energy, would need to be allocated to achieve efficient farming by artificially creating optimal plant growth conditions.

Mr. Liorente appears to be advocating a process similar to the one this topic was set up to explore, with the difference that Mr. Liorente appears to be going for FULL compatibility with the surface of Mars. This topic was created to find plants that would be able to thrive in a full Earth sea level pressure atmosphere compressed from Mars native atmosphere.

A more rational alternative is to use synthetic biology to develop crops specifically for Mars. This formidable challenge can be tackled and fast-tracked by building a plant-focused Mars biofoundry.

While I applaud the ambition of this proposal, the theme of this topic calls for a less ambitious goal, to find plants able to thrive in an atmosphere held at a pressure of Earth sea level, but comprised of gases compressed from the native atmosphere of Mars.

(th)

Last edited by tahanson43206 (2020-02-13 10:04:23)

tahanson43206 · 2020-02-13 12:09:35

For SpaceNut re #29

I'm back from marking up a printout of your post.

Thank you for your contribution to the topic!

As a reminder, your contribution takes the discussion in a different direction than was intended for this topic. However, it seems potentially fruitful, so I'm going to pursue it here.

I liked the flow of Post #29, and I'm with you all the way to the final paragraph/conclusion.

First of all, I am proposing for the purposes of this topic that we NOT add ANYTHING to the gas mixture being supplied to the greenhouse.

A caveat is that ** some ** moisture may need to be added to give the plant leaves a reprieve from what would otherwise be excessive desiccation.

Where you lost me is your estimate of 1/10th?

My expectation is that we will take Martian atmosphere in using pumps, until the gas mixture delivers the amount of CO2 to the surface of the leaf that is equivalent to the amount found at the surface of the leaf on Earth, in Earth-normal atmosphere and Earth standard (sea level) pressure.

I have no idea why you are talking here about "reducing" CO2, but perhaps I am just not seeing the connection.

It is possible one more post, with a focus on the final paragraph of #29, will help me over the hurdle.

There is a very ** small ** chance a focus on that final paragraph will lead to additions or adjustments, but I'll have to wait to see.

Edit#1: What I am looking for is the pressure inside the greenhouse that would deliver equivalent CO2 to the surface of the leaf as that leaf would experience if it were on Earth at sea level on a balmy sunny day. The proposal is to pump Martian atmosphere into the greenhouse until the magic number is achieved. What will then emerge from the computation is an answer as to whether a human garden tender could enter the greenhouse without wearing a pressure suit.

In terms of altitude on Earth, the top of Mount Everest gives us a reasonable guide. Humans need oxygen at that altitude, but their blood does not boil.

Reducing CO2 would NOT be a procedure that would make sense to me, because the native Martian atmosphere is already reduced in CO2 pressure below the amount that a plant needs to survive, let alone thrive.

Edit#1: The article at the link below dates to 2004 ... it describes and reports on NASA sponsored research using low pressure with plants.
A takeaway for me was the discovery that low pressure may help to preserve some plant products for shipment on Earth.

https://www.nasa.gov/vision/earth/livin … ouses.html

Edit#2: The article at the link below is from late 2019. It reports success in the Netherlands growing crops in simulated Martian soil:
https://modernfarmer.com/2019/10/study- … s-on-mars/

The article did NOT report pressure or other characteristics of the growing environment.

Edit#3: A pdf file of the original research is available at a link to the university where the work was done.

The experiment was carried out under Earth atmosphere,
gravity, and light conditions in a normal greenhouse in
Wageningen (51.9692° N, 5.6654° E). During the experimental
period, average temperature was 21.1 ± 3.0 °C and
air humidity was 65.0 ± 15.5%, based on 24 hour recording
at 5 minute intervals (day and night). Daylight lasted 16
hours. Lamps yielding 80 μmol m-2s-1 (HS2000 from Hortilux
Schréder) were used when the sunlight intensity was
below 150 watt/m². Ambient air was used and no extra CO2
was added (400 ppm in 2015 in De Bilt, The Netherlands).

As a reminder, the purpose of THIS topic (as adjusted from the original purpose) is to find the optimum atmospheric pressure in a greenhouse on Mars to provide plants with the optimum availability of CO2 using ONLY Martian atmosphere as the input.

It is assumed that some moisture will be needed to supplement the Martian atmosphere which will otherwise be too dry.

(th)

Last edited by tahanson43206 (2020-02-13 15:03:02)

Terraformer · 2020-02-13 14:39:49

I think it was RobertDyck who posted something quite a while back about plants surviving pressures as low as 100mb, provided they receive enough water.

tahanson43206 · 2020-02-13 14:49:16

For Terraformer re #34

Thanks for your contribution to the topic, and for the tip about RobertDyck's insight!

The purpose of THIS topic is (now) twofold ...

Originally the topic was created to find plants that could thrive at a full Earth-normal atmospheric pressure where the atmosphere consisted of compressed Martian atmosphere. The preliminary result reported earlier in this topic is there exist (at present) no such plants.

SpaceNut has taken the topic in a somewhat different direction, and I'm going along with it because it shows promise of arriving at a useful result. The new direction is to find the pressure of Martian atmosphere in a greenhouse that will match the abundance of CO2 presented to the surface of a leaf on Earth (that abundance is between 390 and 1000 ppm at Earth normal pressure and Earth gas mixture).

I am hoping SpaceNut (or someone else) will take the new branch of the topic over the finish line.

The result would be a number for the atmospheric pressure in a greenhouse where plants are provided the optimum amount of CO2 to thrive, using ONLY Martian atmosphere as the feedstock.

Hopefully the result will reveal an atmospheric pressure to sustain a human being without a pressure suit, although that human being will (of course) be wearing an oxygen mask. The "magic" number is a number equal to or less than of the altitude of Mount Everest, where humans can function without a pressure suit, but while wearing an oxygen mask. The looked-for greenhouse environment would NOT be as cold or windy as Mount Everest, of course. It would instead be operated at a balmy 70 degrees Fahrenheit or so, and with sufficient humidity to match the ideal growing conditions for the plants.

I just found a link to a study of plant success in simulated Martian regolith. The original source of the material reported in the article is here: https://www.degruyter.com/view/j/opag.2 … 9-0051.xml

The university site offers a pdf download which (I presume) will include details of the study.

(th)

Last edited by tahanson43206 (2020-02-13 14:56:23)

SpaceNut · 2020-02-13 17:16:06

Have added in the mbar values in red.
The 100mb is reduced earth pressure so its mixed gasses.
Mars is only at 1/10th for psi or just 10mb for a near all co2 value.

That said what would you like the other 90mb in the greenhouse to be as the value for the PPM is above.

Botanical literature reveals that plants demand Oxygen for root respiration. This could limit the introduction of most plants on Mars until after terraforming has raised the atmospheric pO2 to 20-100 mbar even in a greenhouse.

https://www.ncbi.nlm.nih.gov/pubmed/17155885
Exposure of Arabidopsis thaliana to hypobaric environments: implications for low-pressure bioregenerative life support systems for human exploration missions and terraforming on Mars.

https://plantmethods.biomedcentral.com/ … 015-0088-0
How well do you know your growth chambers? Testing for chamber effect using plant traits

tahanson43206 · 2020-02-13 18:42:56

For SpaceNut re #36

By any chance, did you mean 1000mb in this post?

Quote from Google:

Search Results
Featured snippet from the web
The standard, or near-average, atmospheric pressure at sea level on the Earth is 1013.25 millibars, or about 14.7 pounds per square inch. The gauge pressure in my automobile tires is a little more than twice that value.
What is the average air pressure at the surface of the Earth?
iridl.ldeo.columbia.edu › dochelp › Basic › atmos_press

For Mars, the figure you cited in #36 looks similar to this;

Quote from Google:

Relative to Earth, the air on Mars is extremely thin. Standard sea-level air pressure on Earth is 1,013 millibars. On Mars the surface pressure varies through the year, but it averages 6 to 7 millibars.
Atmosphere - Mars Education | Developing the Next ...

(th)

Last edited by tahanson43206 (2020-02-13 18:46:13)

SpaceNut · 2020-02-13 19:05:06

That was the reduced chamber pressure at the 100mb levels which are the low pressure steps needed to not pressurize a greenhouse to earth pressures as that requires a higher level of building to make it possible. It is still a partial mix of earth gasses in that chamber.

tahanson43206 · 2020-02-13 19:34:17

For SpaceNut re #38

Thanks for explaining where the 100 mb figure came from.

The purpose of this discussion (as I am trying to carry it forward) is to find a pressure to match the needs of the plants.

The 100 mb limit appears to come from an engineering limit of some kind.

For the purposes of ** this ** discussion, let's assume the pressure vessel is strong enough to hold Earth normal (1000 mb) if necessary.

What I'm trying to get to is ... What pressure of Mars atmosphere will deliver the same number of CO2 molecules to the surface of a leaf as that leaf experiences when waving gently in the breeze on Earth on a warm, balmy day?

Here is a figure to shoot for:
From Google: https://scied.ucar.edu/virtual-ballooning-activity

~316 millibars
~0.31
~31.6
8,840
29,002
Top of Mt. Everest

Can we somehow find a way to establish that the pressure of Mars atmosphere, when compressed to meet the expectations of a leaf that sees 400-1000 ppm of CO2 on Earth at sea level, is at least 316 millibars?

If we ** can ** establish that equivalence, then we can be assured that a human worker can safely enter a greenhouse without needing a pressure suit.

It seems possible that the information needed is close at hand, but I have not yet seen it.

(th)

Last edited by tahanson43206 (2020-02-13 19:35:04)

SpaceNut · 2020-02-13 20:20:11

The issue is that pressure is the buildup of the PPM with in a volume of the mole mass percentages.
https://www.lenntech.com/calculators/pp … illion.htm
Top of everest has very little co2 and is icy cold were the volume is huge but a greeenhouse is not.
Measurements are incomplete to missing information for the relative co2 at 1000 ppm so we need to build from mars pressure and atmosphere to a pressure level that plants are able to do. That seems to be near that 100mb but its not all the information that we need.

Mars atmospheric information: 0.15 psi < 10.34213 mb>
95% carbon dioxide, 0.1425 psi, < 9.82503 mb>
3% nitrogen, 0.0045 psi, < 0.31026 mb>
1.6% argon, 0.0024 psi, < 0.16547 mb>
0.01% oxygen 0.0001 psi, < 0.00689 mb>
The averages 6 to 7 millibars seasonally varying is close enough to the 10 above....

https://science.nasa.gov/science-news/s … reenhouses

http://www.marshome.org/files2/Bucklin2.pdf

http://bigidea.nianet.org/wp-content/up … -et-al.pdf

Terraformer · 2020-02-14 09:09:07

th,

A 'greenhouse' with the same partial pressure of CO2 as sea level on Terra and same composition of the Martian atmosphere would be even more of a vacuum than Mars has already.

In any case, I don't think plants suffer CO2 toxicity. Their problem is the lack of oxygen, not the abundance of CO2.

Calliban · 2020-02-14 09:22:53

CO2 is not an inert gas. It is highly soluble in water and forms carbonic acid when it combines with a water molecule. High CO2 partial pressure is toxic to both humans and plants, because it screws with the pH of blood and sap. In humans, this has both short and long term toxicity effects. Long term, high blood acidity levels demineralises bones. Toilets on submarines, which typically have much higher CO2 partial pressures than ordinary air, are clogged with calcium carbonate deposits. The submariners are literally pissing out their bones and rates of arthritis and osteoporosis are higher amongst submariners than the general population.

tahanson43206 · 2020-02-14 15:04:40

For SpaceNut re #40 ...
For Terraformer re #41 ...
For Calliban re #42

Thank you all for your contributions to the topic.

SpaceNut, the links you provided seemed to all be about the same set of studies done in 2002 or so, with differing coverage or audiences. You've shown those before, and this is a helpful reminder of their content, which I appreciate. For those who have not had time to read the studies, they are about construction and operation of a model (tiny) automated greenhouse which might be deployed on Mars. The tiny greenhouse was itself enclosed in a dome which simulated Mars' atmosphere.

For Terraformer, your points are supported by the NASA documents SpaceNut cited, although I'm afraid you lost me in your logic regarding partial pressures. As you will see if you have time to look at the NASA studies, the atmosphere inside the greenhouse is much more than Martian ambient, but much less than Earth normal. The researchers did indeed find it necessary to inject oxygen into the enclosure to give the seedlings a start in life, but then the plants produced more oxygen as they consumed CO2, so the protocol changed to adding CO2 and removing oxygen, as well as managing water vapor, which needs to exist in a relatively narrow range for optimum plant growth.

For Calliban, thank you for the timely reminder of risks associated with an atmosphere elevated in CO2. Your observation about risks faced by submarine crews was a surprise (to me at least) because I would have thought/hoped that by now engineers would have found ways to better manage gas mixtures in submarines. I can certainly understand poor atmospheric planning in World War II, but it is definitely surprising that in the nuclear submarine age, such problems would be allowed to persist.

However, the MAIN insight I take away from your word of warning is that any designer of habitat for humans away from Earth needs to take this issue very much to heart. I would assume (hoping anyway) that NASA and the Russian Space Agency are managing the atmosphere in the ISS so that the problems you've described are not present.

For all who might be interested in the topic ...

This topic was created to explore the hypothesis that it might be possible to design a greenhouse for Mars able to operate at Earth normal pressure, using just the atmosphere of Mars as the input. Along the way in exploring this idea, a variety of studies and other resources have made clear that (at present) there exist no plants which could tolerate such an environment.

The alternative, which is to operate the greenhouse at a pressure lower than Earth normal, appears quite promising, but it leads to the need for air locks between the greenhouse facility and the human habitat to which they would be attached (in some cases).

Stand alone greenhouses would (of course) require air locks, since (at present) there is NO prospect of success growing plants (from Earth) in a native Mars atmosphere.

My interest was to try to find a solution (mixture of gases) that would allow the greenhouse to operate at the same pressure as the human habitat, so that a pressure differential would not exist, and so that human workers could enter the greenhouse in shirtsleeves, while wearing unobtrusive oxygen supply equipment.

That vision may still be possible, but it would (apparently) require use of an inert gas to allow the right partial pressures for CO2, oxygen and water vapor to meet the plants' requirements. In other words, the gas proportions would very nearly match those found to be successful on Earth, although the specific inert gas chosen might differ from Nitrogen.

(th)

Last edited by tahanson43206 (2020-02-15 07:49:37)

SpaceNut · 2020-02-14 16:56:48

For the submarine build up of co2 is by compensating the rising levels with a counter levels of oxygen to keep the proportions the same which is simular to the seeds germination and growing as we fluctuate the levels of these to keep the plants happy.
The partial is just a lower psi but with simular earth gas ratios of which we can tinker with levels of some of them without any harm to plant or people.

Earth atmospheric information: 14.7 psi < 1,000 mb > Mars atmospheric information: 0.15 psi < 10.34213 mb> 1/100th
78.09% nitrogen ( 11.47923 psi), < 791.46504 mb> 3% nitrogen, 0.0045 psi, < 0.31026 mb>
20.95% oxygen ( 3.07956 psi), < 212.32818 mb> 0.01% oxygen 0.0001 psi, < 0.00689 mb>
0.93% argon ( 0.13671 psi), < 9.42582 mb> 1.6% argon, 0.0024 psi, < 0.16547 mb>
0.039% (0.005733 psi) carbon dioxide, < 0.39527 mb> 95% carbon dioxide, 0.1425 psi, < 9.82503 mb>

So for 100mb mars the multiplier is 10 volumes crammed into the same space as we are trying to enclose with this being the results of drawing in that much of it to fill the greenhouse.

95% carbon dioxide, 1.425 psi, < 98.2503 mb>
3% nitrogen, 0.045 psi, < 3.1026 mb>
1.6% argon, 0.024 psi, < 1.6547 mb>
0.01% oxygen 0.001 psi, < 0.0689 mb>

So as you see we are very difficient with regards to level of oxygen for the growth to correctly happen and that was why I was trying to get earth information for growth on mountians to solve for the level of oxygen to which man can tolerate without being a pure oxygen atmosphere which would be about 3 psi.with next to no other gasses in the mix.
So is that lower limit to get good growth half of the earths level (7.35 psi at the same ratios) or can we go lower?

tahanson43206 · 2020-02-14 21:02:32

For SpaceNut re #44 and #29 earlier

Thanks for the additional clarification with data for Earth and Mars.

Before I go on to report success in understanding #29, I'd like to comment that the issue of submarine CO2 may have been solved since the reports that Calliban was referencing were written (I sure hope so!). As I understand Calliban's warning, the amount of CO2 in submarines exceeds (or has exceeded in the past) the 0.039% of the "normal" air mixture which you cited in Post #29. If I understood Calliban's warning correctly, the issue is the percentage of CO2 with respect to the entire set of gases, and NOT with respect to Oxygen specifically. If I understood Calliban's warning correctly, it will be necessary for engineers who manage the atmosphere in ANY vehicle away from Earth so that CO2 levels do not exceed (by some amount not clear to me) the 0.039% level you reported in Post #29.

Now I'd like to report that after allowing background noise to fade out, and concentrating on Post #29, I've come to understand what you had written about the atmosphere of Mars.

Please correct if this is wrong, but I think you had proposed to increase the density of Martian atmosphere by a factor of 100, to bring it to a pressure above the Armstrong limit. The pressure would then be 15 psi.

Because CO2 is the predominant gas in the Martian atmosphere, its pressure would then exceed the range between 0.005733 psi to 0.02205 psi that appears to be agreeable to plants on Earth.

It was at THAT point you proposed "... with all CO2 reduced by 1/10th"

***
I'd like to point out that in your closing paragraph of Post #44, you mentioned oxygen, as did Terraformer in a recent message.

Oxygen is needed to give seeds the ability to set and to grow the body of the plant until it has functioning leaves. At that point, the plant will make Oxygen by consuming CO2. The details of this are laid out in the articles at the links you provided a few posts ago. After the initial infusion of Oxygen to start plant growth, it is no longer necessary for the greenhouse operator to supply Oxygen. Instead, the greenhouse operator must REMOVE oxygen, and add CO2 to maintain the needed balance of gases.

In the case of the research greenhouse described in the articles, management of the gases was performed by a microcontroller which reported its activities and sensor readings to an outside computer, which could be on Earth if the experiment were placed on Mars.

It should be pointed out that the research greenhouse succeeded in growing healthy lettuce leaves in an atmosphere greatly reduced in pressure from Earth normal pressure, but greater than Mars normal pressure. I'd have to go back to reread the article(s) to find the pressures and percentages of gases used, but whatever they were they were satisfactory to the plants.

Thanks again for Post #29 and other posts in this topic, including #44.

It is post #44, showing 1.425 psi CO2 in the Martian atmosphere, that explains the 1/10th recommendation in Post #29. 1/10th of 1.425 would be .1425 psi, which is at the upper range of what plants appear to like on Earth.

After all these posts and articles, I'm ready to throw in the towel and simply settle for a full Earth normal pressure in the greenhouse on Mars, with gas mixture managed so that CO2 amounts to between 0.039% and 0.15% of the total. If Oxygen is in ample supply in the settlement, then it could be supplied to the greenhouse so that it and the human habitat are essentially running the same mixture, and workers can move freely between the sections of the complex.

If Oxygen is in SHORT supply, then the entirety of the non-CO2 portion could be inert gas, and the human would have to wear an unobtrusive oxygen mask.

As described earlier in this post, Oxygen would ONLY be added when seeds are planted and as needed until the plants are mature and producing Oxygen on their own.

Edit#1: To repeat (or state if this is the first time) the comments of the researchers who wrote the articles at the links you gave earlier, the pressure in the Mars greenhouse does NOT have to be Earth normal to satisfy the plants. I would have to go back to the article to see if the pressure maintained inside the test greenhouse exceeded the Armstrong limit, but I am guessing it would.

The concern of the researchers was to try to keep internal pressure in the test greenhouse to the lowest possible value in order to save on mass for the test article. I would deduce they found the "sweet spot" we've been discussing, at which point the plants are happy but pressure is less than Earth normal.

The study reported was done ca 2002, so it is likely subsequent studies have added knowledge in this area of interest.

(th)

Last edited by tahanson43206 (2020-02-14 21:10:22)

SpaceNut · 2020-02-15 08:30:05

With any volume of gasses in between the 10 to 100 multiplier for a desired internal psi, we could then supply a moxie unit to convert co2 with in the growing chamber and expire the co to the outside. The converted oxygen would exit into the chamber with over time creating a better breather atmosphere.

Moxie and only Moxie

kbd512 · 2020-02-15 17:41:29

SpaceNut,

Are you talking about the proposal to enclose a large area in PTFE film and then using MOXIE to remove the Carbon and leave a partial pressure of O2 in its place?

If so, then we'd still have to suck in additional atmosphere to do that. We could reduce the power required to do that by sucking in colder CO2 at night, but that's likely the extent of the efficiency improvement we could reasonably expect.

SpaceNut · 2020-02-15 18:01:30

That would do for the first time but to get additional pressure one would need to process the co2 and then store it leaving a near vaccumn each day to once more to do it again each night to build up the gas levels for a partial air pressure environment. So hopefully moxie will prove successful and that a scaled up version will require less power, more through put processing amount and have less mass for shipping to mars. But in the mean time if we use multiple units to achieve inflation of the greenhouse and then move all others that are not needed for other activities for mars. Leaving just one to maintain the internal pressure and gas contents to allow for food growth to be more efficient with the elevated co2 ppm. Short term men could go in with short sleeves and work in a short period of time then exit to an airlock for processing back into a habitat space. .

SpaceNut · 2020-02-16 15:41:05

If skylab is an example of atmosphere for mars then these might be the target values

oxygen partial pressure equal to 22.6 kPa < 3.27785 psi> ( 225.99980 mb)
nitrogen partial pressure equal to 10 kPa < 1.45038 psi> ( 100.00018 mb)
water partial pressure equal to 1.3 kPa < 0.18855 psi> ( 13.00006 mb)
carbon dioxide partial pressure equal to 6.7 kPa < 0.971753 psi> ( 67.00001 mb)

if the nitrogen is the target from mars then 30 volumes of atmospher gets us to its value
in take of co2 to convert to oxygen will be excessive but we can always store it for later.

SpaceNut · 2020-02-16 17:52:52

Ancient Mars wrote:

Why don't we just use plants? All the colonists have to do is introduce some of the CO2 into the greenhouse and the plants will do the rest, right? This seems much simpler to me.

SpaceNut wrote:

Actually not true with the mars level atmosphere as we must compress a level to allow for the plants to take root as they need oxygen and nitrogen to at a comparible level and you can find that in the other topic. The moxie system is used to convert co2 for our breathing and other uses.
Agriculture Study Mars Pure CO2 Greenhouse
Optimal air pressures.. - Which is best? More O2 or more pressure?

Why is the greenhouse starts out empty of any useable atmosphere and the means to reduce mass for the mars trip is to have a system that can be used to build it up as well as to be able to use it for man itself for other uses.

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