[Agemegos]

Originally Posted by Johnny1A.2

Plausibility caution: keep in mind that photosynthesis is limited by both its effiiciency of energy conversion and the supply amd quality of ambient light. On Mars, the supply of light will be less, to the tune of about .44 that of Earth, IIRC. So any given plant only has 44% of the light that is available on Earth. Clearer skies and thinner air might make up for some of that, but won't compensate entirely.

That's right. All agriculture on Mars that is limited by the availability of light (rather than by the availability of water or minerals or warmth) will be significantly less productive than similar agriculture limited by lack of light on Earth. I get a figure of 39%.

Absent superscience, this puts fairly hard limits on what your bioplants can do in a given time. That's not to say they can't work, but they won't be fast for anything that requries a lot of energy to process or make.

Sure, but they will be at least as fast as growing a feedstock in fields and then processing it to a final product in a chemical plant.

So if a plant makes fuel, then it's going to make modest amounts over a period of time, unless you've got huge areas of ground covered in plants to make the fuel for a few vehicles and machines (which might actually form a useful basis for the power politics of a region).

Quite. The process will have fundamental limit on its fuel production per hectare that is lower than the fundamental limit on making biofuels in Brazilian sugar-cane fields. But it might equal present Brazilian bioethanol production by not wasting energy on a continual production of cellulose. And it can save the fermentation step.

One could imagine fights over control over a square mile of dark-green-leaved fuel plants, but with attacker and defender carefully avoiding damaging the plantation itself...

Good point. It's like the reputed difference between to politics of coffee colonies and sugar colonies. The established plantations will be an important form of valuable capital, more so and more universally than on Earth, where a standing crop might very likely consist of annuals.

Food is no big problem, cosmetics, clothing fibers probably not, they shouldn't take huge amounts of energy, and if the plants make them to last, that's a viable approach. OTOH, fuel is a bitch, if it's being converted from solar power, there's just no way around the fact that such a plant will need long periods of sunlight to make fairly modest amounts of fuel or propellant. There is only 'x' amount of energy to be harvested from a square meter of sunlight, and the plant can't convert it all.

The same issue bites with food. A typical 2,000 kcalorie diet is 8.37 MJ/person/day, and requires as much energy as 0.064 gallons of gasoline.

Alien farming: one might see vast fields of plants, with leaves of a green so dark that it could be mistaken for light black, surrounded by fields of polished metal mirrors that gather additional sunlight and focus it onto the fields of plants, to raise the incident energy level. The mirrors need not be sophisticated, they could be simple polished copper or brass or the like, though they'd have to be regularly adjusted for maximum effect.

I think it would be cheaper just to sow seed over an area than to cover it with mirrors. You can't increase the average productivity, so its a matter of whether concentrating it with mirrors is cheaper than collecting it with extra plants. I guess concentrating it would reduced harvesting costs, too, but I think that's only viable is mirrors are both durable and very cheap.

[i]They might not have been that specialized. If one used genegineering to make a miniature 'elephant', maybe with multiple trunks capped with manipulative hands, on all sides of its body, and gave it a mind that was able to learn from experience but programmed for doglike devotion, you might have a very versatile and effective field worker, and one that might be able to make it in the wild if need be, too. It could be a traction machine, a field hand, or a guard dog, all in the same animal.[/QUOTE]

Possibly, but I'm always suspicious of Swiss Army knives. As the Space Shuttle and the F-35 show, multi-function equipment usually turns out to be less economical than a set of specialised tools. Unless you capital is underemployed and usually idle, that is.