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Growing Plants In Lunar Gravity
smooth wombat writes "If everything goes according to plan, an experiment designed to test whether plants can grow in the limited lunar gravity will hitch a ride with a competitor for the Google Lunar X Prize. 'The current prototype for the greenhouse is a 15-inch-high (37.5-centimeter-high) reinforced glass cylinder that's about 7 inches (18 centimeters) wide on the bottom. Seeds for a rapid-cycle type of Brassica plant — basically, mustard seeds — would be planted in Earth soil within the container.' The press release from Paragon Space Development Corporation outlines its partnership with Odyssey Moon to be the first to grow a plant on another world. In addition to the experiment, Paragon will be helping Odyssey with the thermal control system and lander design. To win the prize, Odyssey must land its craft on the lunar surface by the end of 2014."
I would think that plants would grow faster with little to no gravity.
Maybe. But the question might be more related to how healthy or productive the plants are. Even on Earth we can accelerate plant growth by (as an example) growing light adapted plants in low-light conditions with ample nutrients, or by introducing growth hormones such as gibberellins or adjusting the photoperiod. Often the plants are not 'healthy' though. Stem elongation, weak cell walls, abnormal tugor, reduced or inhibited fecundity all may exhibit themselves. So, to me, the question isn't whether it's possible (it probably is), but whether or not the result is a healthy plant that is able to reproduce and/or meet some other goal like production yields (in the case of vegetative growth then I guess that could easily be met, in the case of grain [seed] production I think it might be harder...)
Couldn't this same experiment be done on a centrifuge in Earth's gravity? Centrifuges usually are used to increase apparent gravity, but if it were shaped so that the plant and soil faced outward, at the right speed, wouldn't one be able to mimic that 1/6 g?
No. A centrifuge can only add to gravity.
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That of course assumes the extrapolation is meaningful, but it might give a rough indication of what to expect with very little expenditure.
That's been done I bet, but you still need to run the experiment to check whether that extrapolation really is meaningful. There isn't really any substitute, because the fundamental problem with all models (and theories and extrapolations) is that they leave out details, and if you push the model far out of where it was designed for you can get other effects dominating.
For example, you can extrapolate gravitation down to the nanometer scale, but that doesn't mean that it lets you fully understand the behavior of matter in that domain. Electrostatic effects tend to rule at that level instead, yet they're not part of any (sane) model of gravitation that I've heard of. Overall, this just tells you to beware of taking models too far.
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The biggest problem with the soil is that it's sharp. There's no weathering on the moon; the "soil" is dust and grit with very sharp points and edges. The plants would be enduring constant irritation and injury.
Of course, you could sift the dust through a concentrated beam of sunlight and melt it into little spheroids. That would still be cheaper than grinding or importing something softer. The point is, you'd have to process your lunar resource of choice somehow; you can't use it "straight up."
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