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Re: (TFT) Mars - Plants get too hot on Luna.

At 9:00 -0400 8/10/11, Denis wrote:
I wonder if the roast/freeze equation on the moon could be altered if a
colony could be built in the permanent "twilight zone" along the day/night
hemisphere boundary ...

There isn't one (stationary day/night hemisphere boundary). The Moon is tide-locked to the Earth, so one face always faces us, but *not* to the Sun. From a Sun point of view, the Moon just spins once/28 days. So the day/night terminator moves slowly compared to the one on Earth, but it does get around the Moon once every 28 days...

Except at the poles! The lunar north and lunar south poles are pretty much always on the terminator, although the terminator crosses them at a continually varying angle. Even better, the Moon's orbit is much nearer the ecliptic than the equatorial plane, which means there's not much of a winter/summer on the Moon, so neither pole suffers 6 months of deep dark or 6 months of deep light like Earth's poles do.

It has been suggested that solar array towers on those points would be incredibly valuable, since they'd be on the Moon but would never lose sun for 14 days at a time. I would submit that greenhouses around those points could have light directed to them by mirrors on the towers, switching on a 24-hour cycle just by moving the mirrors (to a different greenhouse, presumably).

 I would think that PV cells would be much more efficient on the moon,...


In free space near Earth (or on the Moon's surface), you get about 1.366 kiloWatts/square meter. That goes like 1/r^2 for different distances from the Sun; Mars is about 1.52 times farther away than Earth, so it gets about 43% as much (in free space). Atmospheres cut down on that to varying degrees; there was a pretty good mathematical treatment of that in an article in Physics Today, Jan 2011. (Infrared Radiation and planetary temperature, Raymond T. Pierrehumbert). Reprints at:


(ick, long url)
if it's not in your library.

The best multiple-junction solar cells for space use now run about 29% efficient (beginning of life).


....but better cells are rumored.


None of these are very cheap.

Solar thermal would also be pretty efficient, so maybe the energy to run
artificial light during the darker periods would be easier to come by.



Says thermal gets up to 48%, depending on thermodynamics which in this context means how well you can dump waste heat, basically. So that's not much of a win over direct PV.

						- Mark     210-379-4635
Large Asteroids headed toward planets
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