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.
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.
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.
{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.
Quote from: guckyfan on 09/04/2012 05:40 am{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.)
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.)
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.
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 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.
. 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?
Quote from: aero on 09/04/2012 08:00 pm. 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.
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.
{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.
Quote from: A_M_Swallow on 09/05/2012 04:45 amNitrogen 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.
Quote from: DARPA-86 on 09/05/2012 02:20 amQuote from: aero on 09/04/2012 08:00 pm. 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.
Quote from: aero on 09/04/2012 08:00 pm. 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.
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What is the ideal range (size of greenhouse) for bees to thrive?
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...