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Non-replenished CH4 gets eliminated in about 300 years in the Martian atmosphere, due to photochemistry with the Sun's UV. There needs to be a replenishment. What that source is, that's the 800 million dollar question.
It still is, in my opinion, one of the easiest way to build radiation shielding and protection against the elements, with self-repairing properties. Have you ever seen the building of cement, yeah, that's CEMENT, bubbles on Earth?
[http://www.monolithic.com/thedome/index.html]http://www.monolithic.com/thedome/index.html
Of any materials, I'd rather pick frozen water as a main constituant of an habitat rather than cement, steel or aluminum habitats.
At the moment, there is no cement factories, cement needs water too, steel runs into the same problem, casting elements from steel, but how does one produce steel at arrival on Mars? And make sure it's air-tight...
And where do you get your aluminum from on Mars? Electrolysys of Al-rich rocks? Fine, you need a lot of power...
So for all those constraints, I maintain the claim that ice domes of reasonable sizes (no more than two or three stories high), stabilized by internal carbon fiber struts, as was proposed in the initial proposal, along with annular flow stopers and spacers, would be best.
As for the problems of possible liquefaction of ice at the base, which I myself raised, I proposed passive cooling. Passive cooling -does not- require a lot of power, it's done on every thing sent into space, heck it's even done as we speak in the computer you're using for reading this thread!
A base annular metallic segment, in direct contact with the ice being a good heat conductor, could passively maintain a low enough contact temperature at the base to prevent pressure-induced liquefaction. Pressure in the context of "weight applied to a surface (the base)", and not "gaseous" enveloppe pressure.
Also, such a design would be very well suited for polar or mid-latitude applications. It might or might not work well for equatorial temperatures, but even so, the temperatures are so low even in summer during the night that I doubt that it would have a real impact.
Wires would cut into the ice like, well, cheese cutters. Remember those school experiments with a steel wire attached to weights that, left to gravity, cut itself into the ice cube? Same thing here, instead, it's the ice which moves relative to the wire...
That's why one would need a panel to stop ice flow. Maybe a combination of aluminum/carbon fiber annular spacers/ice holders held into place by longitudinal carbon ribs. Since the ice would contribute to support itself, the structure would merely prevent deformation.
What about annular segments, parallel to the surface, serving has both spacers and compartimenting the ice, inside the enveloppes?
Transparency really is not an obligation. If thermal control requires insulation in the form of polyethylene/urethane material, so be it!
Also, the idea of inflated bubbles serving as scafolding/mold was to shorten and simplify actual deployment of the structures...
How about this: Use this technology for greenhouses, while using a more resilient honeycombed approach for habitats.
Mind you, liquid water has it's problems too... It conducts heat more efficiently than ice (which can be made to contain a high percentage of air bubbles, increasing insulation at the expanse of material strenght), and might form ice anyway in those honeycombs...
Ever forgot a soda can in the freezer because you did not have ice but you wanted it cold and you wanted it now? :;):
It's still winter you know, how about doing an experiment right now while it's still winter? How would you do it with household/warehouse stuff?
I forgot one thing: The insulation layer...
Here's a crossview in ASCII of the structure:
. . . . . Martian atmosphere
External enveloppe
///////////// Water ice saturated with CO2
========= Insulating enveloppe
|||||||||||| Polyurethane foam emulsified with CO2
------------ Internal enveloppe
. . . . . . . . . O2 pressurized atmosphere
Ice has a rather good insulation factor, igloos can manage to keep a 30?C+ temperature gradient between inside and outside temperatures, without melting. By keeping the outermost enveloppe's pressure low enough, -after- the formation of the ice dome, it might be possible to prevent the formation of liquid water.
The reference to liquid water forming at the base and pressure monitoring is because under it's own weight, the base of the dome could have a thing layer melt, therefore a passive or even active cooling system might be employed to prevent so.
I forgot to talk about the optionnal insulation enveloppe, which could be foam inserted between the inner O2-containing enveloppe and the ice enveloppes.
Also, it might be possible to reduce strain on the material by using varying levels of pressure, going from Martian atmosphere to breathable environnement
What I have in mind would be an inflatable habitat, which really would be 3 inflatable structures imbricked like Russian dolls.
The Outer structure would be inflated first by pure water vapor and CO2. A second envelope, inside the first one, would then be inflated simultaneously with O2. A gap of about 30-90 centimeters would separate the two inflated envelopes. This gap, filled with water vapor, would slowly form an ice shell, like an igloo.
Gas would be inserted by the center of the bags, the cold Martian air would cause condensation of the water vapor, which would drip to the external sides by gravity. Pressure would be monitored so that liquid water doesn't accumulate at the base of the dome. The ice shell protects the inhabitants from incoming radiation.
Ice is able to withstand great mechanical loads. You can walk safely on a few inches thick, and drive an SUV on a meter thick sheet of ice. At the current low temperatures of Mars, it should have at least the mechanical properties approaching some low quality cements. Reinforced with carbon struts and ribs, the domes could quite possibly be very resilient even to impact from micrometeroids.
Using pure water, it would be transparent to light, but additives could be added to the water to make it more UV absorbing. Also, having a third of the gravity and seismologicaly inactive, Mars ice domes could be substantially voluminous without risks of colapse.
The arctic and antarctic regions often are compared to Mars... How about imitating the inhabitants of the Great North to protect ourselves from the harsh martian conditions?
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