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I Growing food in space - a 3rd concept

  1. Jan 18, 2017 #1


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    To grow food in space, I have read about two designs of greenhouse. One is a pressurised greenhouse with wide expanses of thickened glass. The other is indoor stacks of shelves with LEDs driven from solar PVs outside.
    But would this third design work?

    Have a rotating mirror to focus light into a plant habitat. The mirror moves to track the sun and focus light down through a single porthole window. The walls can have shielding a thick as required. The porthole window can be thick, meteorite proof, or even the light could travel down a tunnel with a right angle so there is no line of sight to allow any chance of an impact on the porthole glass. The light is reflected and diffused around once it gets inside. There are no clouds in (local) space, so the mirrors will always work. Mirrors can be just a very thin foil held in low-g by a thin framework. The habitat can be inflatable for lightness.
    Inside, divide the habitat into different sections and mirrors rotate to illuminate different sections on a 24hr cycle.
    Radiators pick up the excess heat and circulate it back outside where shaded radiators dump it as IR - just like in the ISS.
    Advantages are: No bulbs to blow. No need for heavy solar PV. Easy to fix mechanical things. No large expanse of glass vulnerable to meteorite impacts. Shielding.

    This could work in a space station, even at a great distance from the Sun, if you use large mirrors. Or at the Lunar poles (in some places) you can have 24/7 light. Or on asteroids or moons. (Given the regular dust storms this is not possible on Mars.)
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  3. Jan 19, 2017 #2


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    An important thing to keep in mind is the phase space. You cannot focus sunlight arbitrarily well. If your hole has an area of 1 m2, you can easily focus the sunlight of 100 m2 into it - but then the angle has to increase, so you get more losses in mirrors, and bends get much more challenging (some light might be reflected back). If you want to get an even higher concentration factor, the angle has to go up even more.

    Glass windows can be thick enough to provide shielding against radiation and meteorite damage, in combination with maintaining the pressure difference. I'm not sure if other shielding mechanisms plus a mirror light distribution system are much lighter.
    Well, it would limit growth seasons. The big windows would work nicely on Mars - even though the direct sunlight gets scattered, the total light intensity at the ground rarely drops below 50%. Mirror systems would rely on the direct part of the sunlight, they wouldn't work.
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