You have made a very valuable step in doing a practical analysis of this system, and I thank you ^.^ I hadn't yet gotten around to it ^.^
It is true that I assumed a large source of energy for this process. When I posed it, I did so as part of a major supposition that the first thing to build upon landing would be more solar panels. They would unfortunately be relatively inefficient and imperfect, nowhere near 25% (which, I know, hurts my cause more). This increase in energy capacity would, however, be the most important thing on their list, while much of the carbon takedown is done while they work using any extra energy they may have after life support and such... however I also made the hopeful supposition that there could initially also be at least one main other sources of energy. 1. if they used non-chemical propellant, they might be able to continue to run their engine as a source of power (I have heard, for example, of a boron-hydrogen fusion technology being developed, at least I think that's what it was), or 2. if they used chemical propellant, the remaining chemical propellant could act as an initial carbon source, which would provide the plastic for building the initial solar cells. In fact if they use conventional rocket fuel, they could use it for carbon and capture nitrogen as nitrates for later use as fertilizers.
As a side note about the O2 produced, instead of recombining it to regain lost energy, one could instead use it to supplement O2 that would otherwise have to be produced by the life support systems in OTHER energy intensive reactions, freeing up some energy to use for the processes in question... which means it will be recombining with carbon becoming CO2 again, through our biological processes... Anyway, Life support is quite frankly a B*tch that I look forward to dealing with conceptually, but I need to learn more about how they usually do it on submarines and such.
What you say is why I envision it taking a rather long time. While I had not done the calculations myself, I had figured that it would be taking at least several weeks to get enough Plexiglas to make a small makeshift greenhouse or algal tank. The algal tank would, however, become an alternate and rather automatic carbon source... But they wouldn't even do that until long after they had landed because they would first have to build more solar panels, which involves the extremely energy-intensive processes of silicon extraction and processing. Meanwhile they would be continuing to subsist on their capsules life support functions. I have said this before, the entire endeavour must be planned so that the initial colony most likely will NOT turn into a race against the clock... because the clock will likely win. By the second earth year, they might finally have enough plastic to be starting to build additions to the original capsule, and might by then be using some of their energy to extract iron in an arc furnace... another relatively energy intensive process, and another blatant drain on produced power. But likely necessary.
One thing I will claim in my favor is that polymerization reactions are usually energetically favorable, often requiring little to no energy input, depending on the type. Thus, though you posited that above the cost of one-mer production for polymerization, there may be no actual extra energy needed other then the production of the (admittedly expensive) monomers. A free radical polymerization, for example, may need merely exposure to ionizing radiation, or need a small amount of a radical initiator, because the radical always transfers to the end of the molecule, growing the chain... Other spontaneous polymerizations include those of common 'epoxy's but I doubt that they will want to lug the technology to produce those the compounds necessary for them (though the epoxide could be produced from acetylene or your proposed ethylene...). One used in my lab for fixing specimens is PVLG: Poly Vinyl Lactic Acid Glycerol, which must merely be kept at above ~60* for several days to harden. Finally, my proposed Plexiglas production is similar to the acrylic embedding done in preserving biological specimens. These are indeed my abovementioned free radical polymerizations, requiring only a free radical producer to begin polymerization (the common one seems to be Benzoyl peroxide). I think it could make use of exposure to Mars's natural ionizing radiation therefore requiring no addition of a specific radical initiator, though I really should get around to doing the calculations for if that is viable at some point ^.^
Finally, you are right, I left out some things that I figured were obvious enough: The H2 would likely be from electrolysis of water (the only abundant hydrogen source on mars, as far as I know), and a common practice because it is also a quick initial source of oxygen. Water on Mars may not be as difficult to find as previously supposed: while the partial pressure is low, the martian atmosphere does remain relatively saturated in water, which could be extracted by (the energy intensive process of, because of the volumes of gas that would need to be cooled) condensation... But other sources include the ground inside some craters, which, as it turns out, are so high in salts that they are hygroscopic and may maintain water. The reason they are high in salts is for the same reason why a desert pool is so: what little influx of water there is goes to the lowest point, and evaporates, leaving behind all the salts it disolved from soils and rock along the way... I can't remember which of the recent rovers it was that accidentally found this, but I think it was the one with the bad wheel...
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Topic: Mars Fortress (Read 5822 times)