Also, the SkyLab experiments seemed to confirm for me that plants in lower gees would be taller and more spindly than here on Earth. My corn is maybe 6'-7' hi; lower than the 8'+ I've had in previous gardens. I'm thinking that the corn plants on Mars will be 12'-16' high. The appearance of the garden will be quite different from earthly ones.
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.
You could possibly operate the greenhouse at very low pressures, as long as you had a pressure above the Armstrong Limit (possibly even less than that, though it wouldn't be as safe). This would mean an order of magnitude less mass. Of course, that may affect plant yield, but I am not an expert in that.
Another possibility that would reduce the mass is to use a net of much higher strength/mass ratio material, like Kevlar or Spectra. The mylar could be much thinner in that case (or the volume much larger for the same thickness), since it'd only be holding back the pressure over a tiny area instead of the whole circumference.
And, since we are primarily concerned with ground area covered and not volume, at the greatest limit, you want your greenhouse as low of a height as feasible... At the extreme limit, you could imagine just thin-walled tubes of algae. These could be manufactured (and "seeded"?) in a continuous process... as the biomass got to a certain level, you could just process the whole entire tube in bulk, plastic and all.
Second Add - Just to add another fly to the ointment, consider this:http://en.wikipedia.org/wiki/List_of_crop_plants_pollinated_by_beesWhat is the ideal range (size of greenhouse) for bees to thrive?
A very important remark. Many plants need to be pollinated by bees for good yield. Those are the ones which would need a higher air pressure level for bees to fly and have enough oxygen. As their weight is less than on earth the pressure should not need to be too high. This is something that cannot be tested on earth. How do bees fly on mars? Do they need as much oxygen as humans?{snip}
We will need meat and dairy products to establish the colony in a self sustainable way.
Regarding pressure needed for a walk about area, would it need to be nearly the same pressure as the habitat to avoid the bends or pre-breathing waste of time. Or could such problems be overcame with the air mix in the respirator? I also imagine people working on large projects "outside" where a full Mars suit might slow the work progress.
Quote from: aero on 09/05/2012 03:24 amWe will need meat and dairy products to establish the colony in a self sustainable way. I am sure beef and milk is a nice to have. But we don't really need it. Milk is a relatively recent addition to our diet, many people are lactose intolerant as it is not in our genes to drink milk after infancy.
Do you have any idea what life was like before the safe availability of dairy products?
Quote from: guckyfan on 09/06/2012 05:47 amQuote from: aero on 09/05/2012 03:24 amWe will need meat and dairy products to establish the colony in a self sustainable way. I am sure beef and milk is a nice to have. But we don't really need it. Milk is a relatively recent addition to our diet, many people are lactose intolerant as it is not in our genes to drink milk after infancy.Do you have any idea what life was like before the safe availability of dairy products?
Quote from: aero on 09/05/2012 03:24 amWe will need meat and dairy products to establish the colony in a self sustainable way. I am sure beef and milk is a nice to have. But we don't really need it. Milk is a relatively recent addition to our diet, many people are lactose intolerant as it is not in our genes to drink milk after infancy.If we want beef and milk we would feed the cattle algae. To get them to Mars we would probably send dwarf varieties and implant fertilized eggs of larger breeds to get the breeds we want.Initially I believe we would go for fish, shrimp and chicken if we want animal protein. Again the feedstock would be algae.Especially fish and shrimps would not require large structures. Pipes or inflatable plastics of maybe 1m diameter would require much less resistant materials.Edit: If we chose to ignore cultural preferences, insects would be a perfect addition to our diets. Meal worms are easy to raise and a good addition to the diet.Quote from: aero on 09/06/2012 05:08 amRegarding pressure needed for a walk about area, would it need to be nearly the same pressure as the habitat to avoid the bends or pre-breathing waste of time. Or could such problems be overcame with the air mix in the respirator? I also imagine people working on large projects "outside" where a full Mars suit might slow the work progress.The problem comes with the Nitrogen partial pressure in the breathing air. If we breathe an atmosphere with nitrogen we need an adaption time to get rid of the nitrogen. That makes space walks on the ISS difficult. The night before going out is used to get rid of the nitrogen in an all oxygen atmosphere or else there are health risks similar to that of divers coming up from deep dives.Unfortunately the problem cannot be addressed with the air mixture breathed. We need the partial pressure of oxygen to work and additional nitrogen will increase the total pressure.According to a german blog I read NASA was actually considering a low pressure all oxygen atmosphere on Mars stations for that reason. But I don't like the idea because of fire hazard.For working larger aeras probably some kind of acricultural machines would be used. Either remotely controlled or with a pressurized cabin. Large agricultural machines on earth are allready using climatized cabins.For outside work a new type of pressure suits is in development. Bio-Suits will not use internal air pressure but provide mechanical pressure directly to the skin. They are lighter, less bulky and will make it much easier to work with. They are also much less critical for small ruptures as internal pressure will not be affected or only locally. But they do not eliminate the nitrogen problem unfortunately unless they are so efficient you can increase the total pressure.http://www.astronautix.com/craft/biosuit.htmI have read about a recent developement for fish farming. As the water becomes an evironmental problem a new system was developed. The water from the fishtanks goes through biological filters and is then fed to aqua culture tomatoes for fertilizer. A closed circuit of water can be established that way. The method is economically viable and the beauty of it is, that you cannot use antibiotics on the fish because it would destroy the filters.
I won't grant the handwave of launching the DNA sequence of a cow or goat, and then growing it on site.
Quote from: JohnFornaro on 09/06/2012 02:25 pmI won't grant the handwave of launching the DNA sequence of a cow or goat, and then growing it on site. Actually I believe they would do exactly this. Just launch the DNA - in form of a fertilized egg. Plus a female of some dwarf cattle variety.Implant the egg and you have the desired breed without the launch cost. Continue to use imported fertilized eggs for genetic variety.
I'm more with John on this. Artificial insemination is well established in animal husbandry, but implanting a fertilized egg is more difficult as is giving birth to a larger variety of offspring. Risky techniques should be reserved for later. Risking one or two of a small herd of Mars bred dwarf cattle is one thing, risking the first cow that came from Earth is quite another.
Anyway, it will take time to establish the crop lands to feed the cattle.
Quote from: guckyfan on 09/05/2012 08:50 pmA very important remark. Many plants need to be pollinated by bees for good yield. Those are the ones which would need a higher air pressure level for bees to fly and have enough oxygen. As their weight is less than on earth the pressure should not need to be too high. This is something that cannot be tested on earth. How do bees fly on mars? Do they need as much oxygen as humans?{snip}The breathing of insects will need a through investigation. They do not have lungs but some sort of air tubes.Low air pressure can be tested on Earth.Insects are small so a centrifuge can be used to test their flying. This could be on the ISS or say a Dragonlab.
Realistically, given that you have to feed an animal 10 calories for every calorie in meat produced, meat is a luxury we will not be able to afford for a long, long time on a colony! You can have a human live on the caloric intake of a pig!
Face it guys, a mostly vegetarian diet with aquaculture will be the most manageable approach,
you just have to accept that a different planet wll have a different menu...