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

[Mark Tapley <mtapley@swri.edu>]

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,...


http://en.wikipedia.org/wiki/Solar_constant

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:

http://www.physicstoday.org/search?q=pierrehumbert&searchzone=2&searchtype=&faceted=faceted&ignoredates=true&alias=&todate=2011-8-10&fromdate=1901-1-1&showMap=&sortby=newestdate&recordspage=25&possible1=pierrehumbert&possible1zone=author&bool1=and&possible2=&possible2zone=article&bool2=and&possible3=&possible3zone=article&z=&displayid=AIP&key=PHTOAD&fromvolume=&fromissue=&tovolume=&toissue=&submit0=Update+Search

(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).

http://www.spectrolab.com/solarcells.htm

....but better cells are rumored.

http://www.engadget.com/2010/11/27/boeings-spectrolab-subsidiary-set-to-mass-produce-39-2-percent/

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.

Maybe.

http://en.wikipedia.org/wiki/Thermal_power_station

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
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Large Asteroids headed toward planets
inhabited by beings that don't have
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