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If I'm remembering correctly, regular air is equivalent 78% nitrogen and
21%
oxygen, with the remainder carbon dioxide, water vapor and various noble gases (exceptions as always... NOx in LA, ozone here, methane over the midwest from cows and over DC from all the politicians), but the consistency has to change due to physiological effects of raised of lowered pressure, but that's besides the point of the email. Plants do require nitrogen, but no plant can use gaseous nitrogen. However, the best way to handle this issue is to simply grow some legumes or other plants that have captive (symbiotic, actually) nitrogen capturing bacteria, and use the gaseous nitrogen that's in the cabin air rather than hauling along liquid nitrogen or any other generally caustic/poisonous nitrogen bearing chemicals like ammonia, urea, varied nitrates (yeah, you try to get a load of ammonium nitrate cargo approved for space flight nowadays). If it's the all-important mass factor that's at stake here, you save precious ounces by a) including the nitrogen in the cabin air rather than bringing it extra, b) simply including the bacterial charge in the soil, instead of extra, and c) utilizing the legumes in the biosphere. Just my 3 cents. Mike Free > On Thu, 20 Feb 2003, Bill Clawson wrote: > > I am of the belief that you don't require tons of > > atmospheric Nitrogen to run a successful colony. Most > > plants don't require gaseous nitrogen to subsist... > > However, humans do -- both to keep fire hazards down (even low-pressure > pure oxygen is much worse than normal air) and to avoid long-term lung > problems (alveoli can and do collapse if the gas in them is all highly > soluble in blood, and they don't uncollapse easily). > > This is why Skylab had about 25% nitrogen in its 5psi atmosphere. > > I'm not sure that anyone has characterized the limits of the lung > problems. For the fire hazard, there is extensive data from industrial > fire prevention on "atmospheres of increased burning rate". To keep > roughly a sea-level oxygen content while avoiding that classification -- > which is probably advisable if only to avoid lawsuits -- your atmosphere > has to be about 12psi, i.e. mostly nitrogen. So you're looking at circa > half a kilogram of nitrogen per cubic meter of interior volume. |
