Lunar Settlement Artificial Atmosphere
The lunar colony will have a pressurized selection of acceptable gaseous environments. We have experimental knowledge with some artificial atmospheres,say, space stations like ISS or the MIR. Yet, we need to experiment more on the effects of long term exposure. On the Moon, the atmosphere will be made in accordance with the architecture followed. Some variables like the use of Air Locks, the thickness and materials of the walls may change the gas composition, pressure and other variables.
Gas Combination
See also: Atmosphere
Oxygen is expected to be a major by-product of manufacturing activities on the moon. As such, a pure oxygen atmosphere is attractive as it is likely to be the easiest (and hence, cheapest) gas to procure on the moon. A pure oxygen atmosphere also carries the advantages of allowing a much lower habitat pressure, and greatly simplifying the machinery needed to maintain the atmospheric mix. For these reasons, a pure oxygen atmosphere was utilized in the Gemini project, as well as the early designs of the Apollo spacecraft. However, some studies suggest that a pure oxygen atmosphere becomes poisonous to the inhabitants on long term exposure, making it unsuitable for a lunar habitat.[1]
A combination of one or more inert gases with Oxygen would allow proper oxygenation over longer time-frames. A nitrogen-oxygen mix could be utilized, as it is in earths atmosphere, though the low availability of nitrogen in lunar soil (compared to other volatiles) could raise difficulties in this regard. Helium could also be added to the oxygen mix, as it is significantly more abundant in lunar soil. However, the addition of any appreciable quantities of Helium to the atmosphere would result in a higher vocal pitch for those persons breathing it, similar to (though less intense than) the effects of inhaling pure helium. This effect is currently seen on earth in very deep diving operations, where helium-oxygen mixes are utilized, sometimes facilitating the need for a digital voice alteration device.
Lower Pressure
Plants [2] and Humans can live in lower pressure atmospheres properly oxygenated. The limit is clear: when the vapor of a liquid inside equals the pressure outside, the liquid boils. Blood and other body fluids will boil if an abrupt drop of the pressure occurs.
We would need to lower the pressure inside the buildings to lower the force applied to the walls (somewhere around 40kPa would be ideal for many structures). Also, precise atmospheric pressure controls would be needed to prevent gas leaking.
