Author Topic: Mars ISRU for food crops and consumables.  (Read 96522 times)

Offline aero

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Re: Mars ISRU for food crops and consumables.
« Reply #20 on: 09/03/2012 11:07 pm »
Here is my spreadsheet for the layer pressures.

------------------------------------------------water   Mars
Layer   Radius   Force   Layer psi   Total psi   head psi   Head psi
1   96   301.59   1.99   14.57   3.68   1.40
2   102   320.44   1.87   12.58   3.90   1.48
3   108   339.29   1.77   10.71   4.13   1.57
4   114   358.14   1.68   8.94   4.36   1.66
5   120   376.99   1.59   7.26   4.59   1.75
6   126   395.84   1.52   5.67   4.82   1.83
7   132   414.69   1.45   4.16   5.05   1.92
8   138   433.54   1.38   2.71   5.28   2.01
9   144   452.39   1.33   1.33   5.51   2.09

I think it is quite risky to lower the pressure much below sealevel pressure. Remember, it must work, our lives depend on it.

As for filling a layer or layers with water, the layers range from 8 to 12 feet tall. Atmospheric pressure on earth is about 32 feet of water head so 8 feet of head on earth would be one fourth of 14.7 psi = 3.675 psi and 12 feet of head on earth would be 5.51 psi. Gravitational attraction on Mars is about 38% of earth's, so those heads become 1.40 psi and 2.09 psi. The concern is blowout at the bottom, where the water pressure is greatest.

The point of this exercize has been to show that a greenhouse could be designed for use on Mars. In fact, using the same layered approach moderate sized domes could be constructed. What is moderate size? It depends on how many layers you are willing to use and how much light attenuation you will accept. A company like Bigalow Aerospace could tell you how much a particular size would cost and what it's mass would be. Mass to Mars is afterall still a constraint on the colony build out.
« Last Edit: 09/03/2012 11:11 pm by aero »
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Online guckyfan

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Re: Mars ISRU for food crops and consumables.
« Reply #21 on: 09/04/2012 05:40 am »
I think it is quite risky to lower the pressure much below sealevel pressure. Remember, it must work, our lives depend on it.

Even in commercial airplanes the pressure is only 3/4 that of sea level. Plants need a partial pressure of CO2 that is even much lower than the pressure of mars. They need a partial pressure of oxygen that is very much lower than humans need. I don't think they need a partial pressure of nitrogen but it should be present for fire protection. The Mt. Everest pressure of app. 1/3 of sea level I proposed is for the humans working there. I am positive, that plants need a lot less. But a safe level would have to be determined in tests on earth before the greenhouses are designed.

As for filling a layer or layers with water, the layers range from 8 to 12 feet tall. Atmospheric pressure on earth is about 32 feet of water head so 8 feet of head on earth would be one fourth of 14.7 psi = 3.675 psi and 12 feet of head on earth would be 5.51 psi. Gravitational attraction on Mars is about 38% of earth's, so those heads become 1.40 psi and 2.09 psi. The concern is blowout at the bottom, where the water pressure is greatest.

That much water would attenuate too much. I would go for no more than 1/2 inch each layer. Blowout would be of no concern. It is much less than the force of water from a hose, which would come out at maybe 30 psi, while the water at the planthouse would come out only at the differential pressure of 5 psi for 3 layers. It is more like a trickle.

A company like Bigalow Aerospace could tell you how much a particular size would cost and what it's mass would be. Mass to Mars is afterall still a constraint on the colony build out.

Yes Bigelow could provide valuable experience. But they use Kevlar fibres or similar for maximum micrometeorite protection. They are not concerned with transparency.

Probably there would be greenhouses with different pressures. If people need to work without protection, for example on vegetables,the pressure would be chosen high. For staple food (if you don't like algae :) ) you need much space for the calories so you would go very low. Bearing in mind the cost of shipping from earth.

Offline aero

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Re: Mars ISRU for food crops and consumables.
« Reply #22 on: 09/04/2012 03:03 pm »
Quote
That much water would attenuate too much. I would go for no more than 1/2 inch each layer. Blowout would be of no concern. It is much less than the force of water from a hose, which would come out at maybe 30 psi, while the water at the planthouse would come out only at the differential pressure of 5 psi for 3 layers. It is more like a trickle.

Thats not the way pressure head works. Pressure head is caused by gravity and as we know, a feather (thin layer of water) and a bolling ball (thick layer of water) are accelerated by gravity at the same rate. It is this gravitational pull from the top of the greenhouse to the bottom of the greenhouse (8 to 12 feet in my example) that drives the pressure. Here is a reference.

http://www.ehow.com/how_7231875_calculate-water-head-pressure.html

Now you have enough information to design the greenhouse with water layers yourself. Shetch up an illustration and do a force balance for both vertical and lateral forces on the Mylar. Remember to account for the weight of the water as well as its pressure head and the pressure from adjacent layers, then post it where we can look at and critque it. As I wrote in a previous post, it is to much math for me and I don't want to do it.

As for the design atmospheric pressure of the greenhouse, I've stated my opinion and you've stated yours. I think we can agree that more study should be done. Lacking more study or any information from existing studies, my opinion remains unchanged.
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Offline A_M_Swallow

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Re: Mars ISRU for food crops and consumables.
« Reply #23 on: 09/04/2012 03:33 pm »
{snip}
Probably there would be greenhouses with different pressures. If people need to work without protection, for example on vegetables,the pressure would be chosen high. For staple food (if you don't like algae :) ) you need much space for the calories so you would go very low. Bearing in mind the cost of shipping from earth.

The air for the greenhouses does not need shipping from Earth.  It can be made from Mars' CO2 atmosphere.  A pump will pressurize gas.

Interesting to calculate how long the plants will take to convert CO2 to O2.  (The starter green house will have to be brought from Earth.)

Offline Patchouli

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Re: Mars ISRU for food crops and consumables.
« Reply #24 on: 09/04/2012 04:52 pm »
{snip}
Probably there would be greenhouses with different pressures. If people need to work without protection, for example on vegetables,the pressure would be chosen high. For staple food (if you don't like algae :) ) you need much space for the calories so you would go very low. Bearing in mind the cost of shipping from earth.

The air for the greenhouses does not need shipping from Earth.  It can be made from Mars' CO2 atmosphere.  A pump will pressurize gas.

Interesting to calculate how long the plants will take to convert CO2 to O2.  (The starter green house will have to be brought from Earth.)

You probably can even get the nitrogen for the other part of the atmosphere from Martian materials.

I think the internal atmosphere also may not need to be an Earth atmosphere either.
The Skylab atmosphere 74% oxygen and 26% nitrogen at 5 psi also should work and would save a lot on construction.

On how I'd go about pulling off food ISRU I would not try to get full self sufficiency right away as that would be asking for failure.
Instead I'd do it incrementally.
First I'd go with crops that can supplement freeze dried and shelf stable foods making them more palatable.
Next look into providing the bulk of the calories then most of the macro nutrients.
Then once these mile stones have been met look into full self sufficiency.

« Last Edit: 09/04/2012 05:06 pm by Patchouli »

Online guckyfan

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Re: Mars ISRU for food crops and consumables.
« Reply #25 on: 09/04/2012 05:03 pm »
The air for the greenhouses does not need shipping from Earth.  It can be made from Mars' CO2 atmosphere.  A pump will pressurize gas.

Interesting to calculate how long the plants will take to convert CO2 to O2.  (The starter green house will have to be brought from Earth.)

With shipping from earth I was referring to the greenhouse. Higher pressure means stronger material and more weight for the same size greenhouse.

But the air inside is not as easy as pressurizing the local atmosphere. That is almost all CO2 plus little N2. Higher plants need some oxygen to thrive. Without oxygen you would have to start with lower plants to provide the oxygen. I am also not sure how acidic the water would get in a pure CO2 atmosphere, very likely too acidic for many earth plants and even if partly reduced by oxygen still poisonous to people. So it would better to lower the CO2 content by adding nitrogen and if available oxygen. If there is ISRU for producing rocket fuel, both nitrogen, as a byproduct, and oxygen would be available for the purpose.


I think the internal atmosphere also may not need to be an Earth atmosphere either.
The Skylab atmosphere 74% oxygen and 26% nitrogen at 5 psi also should work and would save a lot on construction.

Yes, there are lots of advantages using a high oxygen, low nitrogen atmosphere. But because of fire hazard they got away from using it. Remember the Apollo fire desaster.

Offline Patchouli

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Re: Mars ISRU for food crops and consumables.
« Reply #26 on: 09/04/2012 06:14 pm »

Yes, there are lots of advantages using a high oxygen, low nitrogen atmosphere. But because of fire hazard they got away from using it. Remember the Apollo fire desaster.

The was pure O2 at 16 psi or greater then 1ATM during a pressure test of the capsule.

The fire hazard with the Skylab atmosphere is roughly the same as standard Earth sea level atmosphere since the partial pressures of oxygen are similar.
« Last Edit: 09/04/2012 06:26 pm by Patchouli »

Offline Space Frog

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Re: Mars ISRU for food crops and consumables.
« Reply #27 on: 09/04/2012 06:18 pm »
CO2 fertilization is well-understood for growing plants.  I use a tank of CO2 to fertilize my aquarium plants.  You just have to monitor the pH.  You can buy a pH controller and solonoid custom-built for delivering CO2 to plants for $150.  The same CO2-absorbing medium proposed by Zubrin for the Sabatier reactor could also provide supplemental CO2 for the greenhouses. 

But you're going to need a LOT of greenhouses.

The limiting factor for plant growth is almost always light - the more the better, and earth-normal would be the ideal. 

But you want to let in all of the light possible, so I'm skeptical about multiple layers between the sun and your plants.  Normal Mars sunlight won't be enough for optimal growth (meaning you'd get slower growth and lower yields than a similar greenhouse on earth).  You need the highest yields possible for the limited pressurized area. I'd build a long, narrow greenhouse oriented east-west with a transparent roof and then a half-cylinder reflector structure north of it to bounce additional light in a narrow band to a diffusing strip-reflector inside the greenhouse.  This way you get the most possible light into the smallest pressurized volume, maybe even above earth-normal in the summer.  If you added supplemental CO2, Martian N and P, and reflected light - then you can grow a lot of food in a small area.

In my mind one of the biggest ISRU challenges we'll face at Mars is finding a way to manufacture glues and sealants for pressure vessels.  You could build greenhouses out of Martian rock, smelted Martian metals, and Martian glass, but you can't seal them without glue - and I can't think of a good way to produce that stuff on Mars.


Offline Patchouli

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Re: Mars ISRU for food crops and consumables.
« Reply #28 on: 09/04/2012 07:11 pm »
CO2 fertilization is well-understood for growing plants.  I use a tank of CO2 to fertilize my aquarium plants.  You just have to monitor the pH.  You can buy a pH controller and solonoid custom-built for delivering CO2 to plants for $150.  The same CO2-absorbing medium proposed by Zubrin for the Sabatier reactor could also provide supplemental CO2 for the greenhouses. 

But you're going to need a LOT of greenhouses.

The limiting factor for plant growth is almost always light - the more the better, and earth-normal would be the ideal. 

But you want to let in all of the light possible, so I'm skeptical about multiple layers between the sun and your plants.  Normal Mars sunlight won't be enough for optimal growth (meaning you'd get slower growth and lower yields than a similar greenhouse on earth).  You need the highest yields possible for the limited pressurized area. I'd build a long, narrow greenhouse oriented east-west with a transparent roof and then a half-cylinder reflector structure north of it to bounce additional light in a narrow band to a diffusing strip-reflector inside the greenhouse.  This way you get the most possible light into the smallest pressurized volume, maybe even above earth-normal in the summer.  If you added supplemental CO2, Martian N and P, and reflected light - then you can grow a lot of food in a small area.

In my mind one of the biggest ISRU challenges we'll face at Mars is finding a way to manufacture glues and sealants for pressure vessels.  You could build greenhouses out of Martian rock, smelted Martian metals, and Martian glass, but you can't seal them without glue - and I can't think of a good way to produce that stuff on Mars.



Some seals can be made from a malleable metal such as copper and you can make plastic from plants.
« Last Edit: 09/04/2012 07:12 pm by Patchouli »

Online guckyfan

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Re: Mars ISRU for food crops and consumables.
« Reply #29 on: 09/04/2012 07:22 pm »
Plastics can be made directly from Methane produced from CO2 and water. Simple plastics with reflective coating will be good enough for reflectors to increase light in greenhouses.

Producing high quality plastics for greenhouses are certainly more difficult but I believe they are still the better method than massive pressure resistant greenhouses.


Offline aero

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Re: Mars ISRU for food crops and consumables.
« Reply #30 on: 09/04/2012 08:00 pm »
Greenhouse size -  Using the same dimensions as previously, that is, an 8 foot high half cylinder construction for the greenhouse, that's 16 ft = 4.877 meters wide. One acre = 43560 square foot = 4046.86 square meters. Dividing area by width gives the length per acre of 2722.5 feet or 829.8 meters. That's pretty long. I would consider using several shorter greenhouses per acre  instead of a single one that long. Leveling the ground for a half mile long greenhouse would be a challange and it would need to be level, else water would find the lowest end, complicating our greenhouse operations.

Some will say that we should use lower pressure allowing wider and shorter greenhouses per acre. Until we can calculate the crop production with justification, assuming lower pressure is inherently to risky for me. If lower pressure greenhouses produced a lower crop yield, then more greenhouse space would be needed to produce the same amount of food. Study is needed, unless we design for near earth normal atmosphere and augmented sunlight to near earth normal. If we design to reproduce earth normal conditions we don't need to study, we can just build them and put in enough earth soil to know they will work.

One acre of crop can actually produce quite a lot of nutritional Calories. In continuous production using numbers I calculated before, (150 bu/acre corn) one acre of cropland could sustain the Caloric needs of about 20 people. That's a good start but someone should check those figures because greenhouse acreage is critical to self sufficiency on Mars.

Added edit - How big an oven do you need to bake enough bread for 20 people? How much wheat do you need to grind into flour for the bread? How much space do you need to raise the wheat? How do you winnow the wheat on Mars? What do you do with the chaff? How much wheat flour do you set aside to make paste and sealant. Are there any societies like the Amish whos members would get on a spaceship to help setup the agrarian economy and get it started?

Second Add - Just to add another fly to the ointment, consider this:

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

What is the ideal range (size of greenhouse) for bees to thrive?
« Last Edit: 09/05/2012 01:14 am by aero »
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Offline KelvinZero

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Re: Mars ISRU for food crops and consumables.
« Reply #31 on: 09/05/2012 01:35 am »
Some will say that we should use lower pressure allowing wider and shorter greenhouses per acre. Until we can calculate the crop production with justification, assuming lower pressure is inherently to risky for me.
Just one of those things we have to investigate. (and is probably comparatively cheap to investigate)

thank goodness at least some study is underway.
http://science.nasa.gov/science-news/science-at-nasa/2004/25feb_greenhouses/

There are some other links around too.. maybe the answer is already out there.

Offline DARPA-86

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Re: Mars ISRU for food crops and consumables.
« Reply #32 on: 09/05/2012 02:20 am »
. Leveling the ground for a half mile long greenhouse would be a challange and it would need to be level, else water would find the lowest end, complicating our greenhouse operations.

 we can just build them and put in enough earth soil to know they will work.

One acre of crop can actually produce quite a lot of nutritional Calories. In continuous production using numbers I calculated before, (150 bu/acre corn) one acre of cropland could sustain the Caloric needs of about 20 people.

Added edit - How big an oven do you need to bake enough bread for 20 people?  Are there any societies like the Amish whos members would get on a spaceship to help setup the agrarian economy and get it started?




# 1 Most hydroponic greenhouses have tables with adjustable legs in which the plants are grown.

# 2 Earth soil is heavy, or in rocket science terms has "mass" which would tend to take up a lot of volume for otherwise important cargo, you can grow just about anything in any soil - if the Ph content is right and you have adequete nitrogen.

# 3 certain hybrids of corn under optium conditions yield in excess of 220 bushels per acre, again see nitrogen - perhaps we now know what to do with the latrine surplus from 20 new "martians".

# 4 Your oven size only needs to be big enough to cook two, or four loaves at a time - or one medium pizza.  Your not going to be eating the bread as fast as you cook it, unless you are having guests over for dinner.

And as for the Amish - there are plenty of folks out there (like Seed Savers in Decorah, Iowa) that have agricultural knowledge in biodiversity and grains that are not in mainstay commerical production that could be applicable to this situation.  Besides it could prove problematic to fit the helmet on the pressure suit over those long beards.

Offline aero

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Re: Mars ISRU for food crops and consumables.
« Reply #33 on: 09/05/2012 03:24 am »
. Leveling the ground for a half mile long greenhouse would be a challange and it would need to be level, else water would find the lowest end, complicating our greenhouse operations.

 we can just build them and put in enough earth soil to know they will work.

One acre of crop can actually produce quite a lot of nutritional Calories. In continuous production using numbers I calculated before, (150 bu/acre corn) one acre of cropland could sustain the Caloric needs of about 20 people.

Added edit - How big an oven do you need to bake enough bread for 20 people?  Are there any societies like the Amish whos members would get on a spaceship to help setup the agrarian economy and get it started?




# 1 Most hydroponic greenhouses have tables with adjustable legs in which the plants are grown.

# 2 Earth soil is heavy, or in rocket science terms has "mass" which would tend to take up a lot of volume for otherwise important cargo, you can grow just about anything in any soil - if the Ph content is right and you have adequete nitrogen.

# 3 certain hybrids of corn under optium conditions yield in excess of 220 bushels per acre, again see nitrogen - perhaps we now know what to do with the latrine surplus from 20 new "martians".

# 4 Your oven size only needs to be big enough to cook two, or four loaves at a time - or one medium pizza.  Your not going to be eating the bread as fast as you cook it, unless you are having guests over for dinner.

And as for the Amish - there are plenty of folks out there (like Seed Savers in Decorah, Iowa) that have agricultural knowledge in biodiversity and grains that are not in mainstay commerical production that could be applicable to this situation.  Besides it could prove problematic to fit the helmet on the pressure suit over those long beards.

Thank you for that contribution.

On reading I have discovered that about 75% of all US grain products are made from wheat so wheat will be a primary crop. Average US wheat production is 37.1 bu/acre. Hopefully, we can do better than average. Also, one bushel of wheat will yield 60 pounds of whole wheat cerial or make 90 one-pound loaves of whole wheat bread, 16 slices per loaf. But it also takes yeast, salt, sugar, vegetable shortening or butter, and milk, along with the flour.

We will need meat and dairy products to establish the colony in a self sustainable way. That means we need larger enclosed areas than the 16 foot wide greenhouses discussed previously but it can be done. All that is needed is to add strengthening members to the Mylar. Imagine strong nylon tape side to side over each tunnel layer, say, 5 foot center to center. Or imagine strong beams running lengthwise of the greenhouse, with the beams anchored by guy wires. My description of layered construction used 20 mil Mylar, but imagine using a stronger material or just thicker Mylar. I imagine that the structure could be made to be strong enough that the anchors would become the weak point in the structure. I'm not a civil engineer or an architect though, so I won't try to take this further. I do see the need for several acres under one cover. After all, we will need to grow a lot of hops and barley to raise our beer fed beef.
« Last Edit: 09/05/2012 04:37 am by aero »
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Offline A_M_Swallow

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Re: Mars ISRU for food crops and consumables.
« Reply #34 on: 09/05/2012 04:45 am »
Nitrogen gas can be extracted from the atmosphere of Mars by cooling the atmosphere below about -70 F.  (Boiling point of CO2 is -57 C, 216.6 K, -70 F (at 5.185 bar).)  For agricultural purposes any argon produced can be ignored.

edit : spelling
« Last Edit: 09/05/2012 04:46 am by A_M_Swallow »

Offline QuantumG

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Re: Mars ISRU for food crops and consumables.
« Reply #35 on: 09/05/2012 04:51 am »
Nitrogen gas can be extracted from the atmosphere of Mars by cooling the atmosphere below about -70 F.  (Boiling point of CO2 is -57 C, 216.6 K, -70 F (at 5.185 bar).)  For agricultural purposes any argon produced can be ignored.

5.185 bar? Did you mean psi? Even that seems way too high. The pressure at surface level is only 0.636 kPa.

If you feel like going through the math to calculate this, I'd appreciate it.
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Offline A_M_Swallow

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Re: Mars ISRU for food crops and consumables.
« Reply #36 on: 09/05/2012 04:55 am »
{snip}
On reading I have discovered that about 75% of all US grain products are made from wheat so wheat will be a primary crop. Average US wheat production is 37.1 bu/acre. Hopefully, we can do better than average. Also, one bushel of wheat will yield 60 pounds of whole wheat cerial or make 90 one-pound loaves of whole wheat bread, 16 slices per loaf. But it also takes yeast, salt, sugar, vegetable shortening or butter, and milk, along with the flour.

We will need meat and dairy products to establish the colony in a self sustainable way. That means we need larger enclosed areas than the 16 foot wide greenhouses discussed previously but it can be done. All that is needed is to add strengthening members to the Mylar. Imagine strong nylon tape side to side over each tunnel layer, say, 5 foot center to center. Or imagine strong beams running lengthwise of the greenhouse, with the beams anchored by guy wires. My description of layered construction used 20 mil Mylar, but imagine using a stronger material or just thicker Mylar. I imagine that the structure could be made to be strong enough that the anchors would become the weak point in the structure. I'm not a civil engineer or an architect though, so I won't try to take this further. I do see the need for several acres under one cover. After all, we will need to grow a lot of hops and barley to raise our beer fed beef.

Where a single leak can destroy the greenhouse and its crops the building needs dividing into compartments.

Try having a main access corridor with rooms running off the sides.  The rooms would have sloping walls and windows making them greenhouses.  To contain leaks the doors need to be airtight.

Offline A_M_Swallow

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Re: Mars ISRU for food crops and consumables.
« Reply #37 on: 09/05/2012 05:37 am »
Nitrogen gas can be extracted from the atmosphere of Mars by cooling the atmosphere below about -70 F.  (Boiling point of CO2 is -57 C, 216.6 K, -70 F (at 5.185 bar).)  For agricultural purposes any argon produced can be ignored.

5.185 bar? Did you mean psi? Even that seems way too high. The pressure at surface level is only 0.636 kPa.

If you feel like going through the math to calculate this, I'd appreciate it.

The reference books do mean 5 times the Earth's atmosphere pressure, below that CO2 has no liquid phase.  So Mars's atmosphere would either have to be pressurised or cooled until the CO2 becomes dry ice.  Fortunately the melting point of carbon dioxide is only -78 C, 194.7 K, -109 F.
http://en.wikipedia.org/wiki/Carbon_dioxide
« Last Edit: 09/05/2012 05:39 am by A_M_Swallow »

Offline DARPA-86

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Re: Mars ISRU for food crops and consumables.
« Reply #38 on: 09/05/2012 11:50 am »
.





Thank you for that contribution.

On reading I have discovered that about 75% of all US grain products are made from wheat so wheat will be a primary crop. Average US wheat production is 37.1 bu/acre.

We will need meat and dairy products to establish the colony in a self sustainable way. That means we need larger enclosed areas than the 16 foot wide greenhouses discussed previously but it can be done.  After all, we will need to grow a lot of hops and barley to raise our beer fed beef.

Filet Mignon will be a rarity on Mars; Martians could probably be fish eaters.  I have previously been part of a study on how to cut the logistics chain and produce the greatest amount of food stuff in the least amount of area - we came up with fish farms as the most effective.  We used a series of prisons as examples - you have a close by population inside a fence on marginal soil (prisons for example are rarely sited on prime real estate) that has requirements to produce fresh food stuffs inside the wire to cut down on a) costs and b) problems assoicated with a steady stream of delivery trucks coming thru the gate.

Soybeans rather than wheat offers the best option as a precursor crop; it matures inside a pod, rather than with chaff at the end of a stem (your chaff issue illustration mentioned earlier in 1/3rd gravity).  Soybeans can be converted to pellets for fish food - and the yield per acre is comprable to your cited figures for wheat.  Soybeans can be safely consumed by humans as a protein filler (you have consumed soybeans if you ate the meat at McDonald's, Taco Bell etc.) and actually add nitrogen as a nutrient to the soil - and thus thru leeching - will add nitrogen to the closed loop atmphoshere raising pressure over time.

With small exceptions for the female egg layers, fish hatchery set ups generally utilize linear runs, 16 foot wide is plenty adequete.

Offline JohnFornaro

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Re: Mars ISRU for food crops and consumables.
« Reply #39 on: 09/05/2012 01:09 pm »
What is the ideal range (size of greenhouse) for bees to thrive?

A common rule of thumb for beekeepers is one hive per acre.

Earth soil is heavy, or in rocket science terms has "mass" which would tend to take up a lot of volume for otherwise important cargo...

It's not so much the volume as it is the mass itself.

The benefit for having a rich forestry type soil is that you could import a complete mini-ecosystem, guaranteed to grow Earth crops.  Starting with bare naked martian soil and amending it would require the setting up, Earthside, of a one acre dome, sterile soil, and build up the garden from scratch, learning all the ins and outs of that sort of "artificial" gardening.  Using Earth soil would also import a good number of bugs, some pollinators, some helpful and some harmful bugs, fungi, and so forth.  Starting with just a chemical brew would have no extra life forms, which would be good for the harmful critters, but bad for diversity.  Artificial soil amendments would be low mass, but also low radiation protection, for the trip up.

I made a guess at 250-260 tons of Earth soil, which is a lot, but which would also supply virtually everything to operate a garden, given the greenhouse, which you'd have to grant in either case.  But that's still an awful lot of tonnage.

As to Aero's Amish question: they would be more likely to go with the Earth soil, and less likely to go with the artificial soil.  I have no idea about their feelings on such a type of colonization.
Sometimes I just flat out don't get it.

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