"Mike Rhino" wrote in message ...
"Ian Stirling" wrote in message
...
Joe Strout wrote:
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth.

I don't think this is true unless you are in an extremely high orbit.
In LEO orbits, like the space station's, satellites go through a
sunrise and sunset about every 90 min. That seriously cuts the amount
of actual light you're getting. Of course as you go higher up, you're
getting less and less earth shaded night--but from about 250-1500 nm
you're in the thick of the Van Allen belts. Any plant growing station
is going to need significant rad protection in htis area.
Anyway the best place to do this would be GEO or lunar L-1, as you're
well above most Van Allen radiation and rarely blocked by the earth.

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.

Chloraphyll is not the only bit of cell machinery that requires
sunlight to work. Many other proteins are formed with help from the
sun, and not all at even visible wavelengths. This is true of nearly
all species on earth, even humans, as UV helps regulate folic acid and
Vitamin D, and is a cause of the existence of different skin colors.
Of course, the result of a frequency deprivation won't always be
death--but less overall crop health is likely.

Unless you need to beam the energy over long distances, the best way
seems to simply be to use mirrors.
The solar collector points at the sun, and bounces the light through
a small window in your rotating greenhouse.
Distribute the light internally.
This beats current solar cells/lights by a factor of several per unit
area.

If you have a multi-layered facility, it might be difficult to bounce light
to all floors.

Not really. Fibre optics, light pipes, and solar diffusers can be used
quite effectively (and still many times more efficiently than solar
cells/lights). The Artemis Project and the Lunar Reclamation society
have done quite a bit of study and research in these areas, although
their focus is on lunar day/night cycles that require a mix of both
natural and artificial light.

Tom Merkle