Space Farms

Gerard O'Neill designed vacuum chambers that encased large particle
accelerators. Particle accelerators like those of CERN can be miles in
extent. He noted that these large chambers could equally operate as
pressure vessels. If built in space these large pressure vessels might
be very very large space stations that he called space colonies. These
stations are large enough to sustain their own micro-ecologies that
require very little to maintain them once they're set up.

One near term use of these large space stations could be to provide a
controlled environment to grow food and fiber for people on Earth
without adversely affecting the Earth's environment.

A cylindrical pressure vessel about 1 mile in diameter and 4.5 miles
long, with spherical endcaps, spinning along its length, could provide
10 square miles of growing area maintained under ideal growing
conditions year round. The peak of the spherical endcaps (the poles)
could be equipped with windows into which light could be concentrated
with parabolic dishes. The concentrated sunlight could be filtered and
projected onto the growing surfaces inside the spinning cylinder by
conical mirrors. The interior would be evenly illuminated in this way,
and the mirrors would change position to induce a day/night cycle
across the surface over a 24 hour period.

Long wave light energy would be modulated to control the temperature of
the interior. Light not used for growing food would fall on high
intensity photocells to power whatever machinery was needed to maintain
high levels of production.

In a highly controlled environment it would be possible to provide
10,000 people per square mile with all the food and fiber needed to
sustain each person with the same amounts of food and fiber (wood,
cotton, paper) consumed per capita by the top quartile of the US
population ($150,000 per person per year or more).

That means that each cylinder described above would produce food and
fiber for 100,000 people. Each person consuming 10 pounds of material
per day would mean that 1,000,000 pounds would be processed per day by
the station. If extracted from the 'soil' coating the interior of the
station, this would subtract 1/1600th inch of thickness from that soil
layer per day. Seven feet of growth material would be reduced by half
its thickness over a 150 year period. Three feet of soil matrix would
be required for radiation protection.

100,000 stations placed in a sun-synchronous polar lpiporbit would be
sufficient to provide a high level of food and fiber to a world
population of 10 billion people. Delivery would take place by rail
gun. Silica aerogel aerobraking bodies would encase delivery capsules
containing all manner of food and fiber for direct consumption on
Earth.
Where would we obtain the massive amounts of material to build

http://www.space.com/businesstechnol...ng_000211.html