Sander Vesik wrote in message ...
william mook wrote:

The absorption maxima of chlorophyll a are 430 and 662 nm, that of
chlorophyll b are at 453 and 642 nm.


http://www.biologie.uni-hamburg.de/b-online/e24/3.htm

So, solid state LEDs that emit around these frequencies would be very
efficient at growing plants.

Looking at the spectrum of the sun ...

http://zebu.uoregon.edu/~js/glossary/planck_curve.html

(there are 10 angrstoms per nm)

and multiplying the chlorophyl response curve by the solar spectrum,
we can see that its possible to grow plants with the right colors of
light at about 5% of the energy of full spectrum sunlight.

This suggests that dyes, or high-efficiency solar cells powering high
efficiency LEDs of the right colors might be capable of growing more
food per unit area than natural sunlight.

It would appear that using PV cells getting ~ 15 - 20% of energy from
sunlight would allow one to build 3-5 high greenhouses that were much
more space efficent (which is not a trivial concern) than ones directly
using sunlight.

That's one possibility. Others might be slightly more efficient
certainly.


So to solve teh worlds food supply problems for a long time one would then
just need a cheap way to de-orbit food.

Well, if you're talking about doing stuff in space, the deorbit
portion isn't a problem. Using a commercial version of JDAM
technology and a computer controlled rail-gun powered by sunlight,
aboard a polar orbiting satellite gets you any product on orbit to any
point on Earth within 12 hours.

http://home.insightbb.com/~jmengel4/...ntro.html#rail
http://www.powerlabs.org/railgun.htm

http://www.fas.org/man/dod-101/sys/smart/jdam.htm
http://www.boeing.com/defense-space/.../jdam_back.htm

http://www-istp.gsfc.nasa.gov/Education/wlopolar.html


Getting the masses needed in orbit in the first place is the problem.
But that's only a problem to current launcher technology. If you read
GEORGE DYSON's new book ORION - you'll see that since the 1950s we've
had the ability to move massive payloads throughout the solar system
using atomic bomb technology.

http://www.chron.com/cs/CDA/story.ht...eviews/1393393

Using this sort of rocket we could survey the asteroid belt for
asteroids of the right size, shape and composition to bring into orbit
around the Earth. Then, using sunlight and remotely controlled robots
via telepresence to process these asteroids into products


http://world.honda.com/ASIMO/
http://telepresence.dmem.strath.ac.uk/
http://www.teleroboticsurgeons.com/

- including large space colony type biospheres. Here we could grow
all the food and fiber humanity needs (with or without spectrum tricks
as those described above) in orbiting forests and farms.

http://www.l5news.org/ bernalspheredetail.htm

Then from a ring of factorysats, forestsats and farmsats inn polar
orbit we make anything that's possible to make on Earth with remotely
controlled robots. Products are deorbited using solar powered rail
guns and low cost commercial versions of JDAMs to bring products
directly to anyone anywhere on Earth in minutes after ordering them.

Everything, including energy, is made in orbit;

http://www.wws.princeton.edu/~ota/di...81/8124_n.html

and used on Earth -

This allows all industry, farms, and commercial forestry operations on
Earth to be suspended and moved to orbit. The only industry remaining
on Earth is recycling and disposal. The entire Earth is converted
into one vast residential park connected by distributed communications
and power networks from space, supported by supply lines originating
in space.

Even roads are dispensed with as space based lasers are capable of
delivering propulsive energy to small high performance VTOL aircraft
which can silently speed people and things anywhere in the world in
minutes using nothing more than sunlight converted to laser light;

http://pakhomov.uah.edu/Facilities.htm
http://www-phys.llnl.gov/clementine/ATP/Lsrprp1s.gif
http://www-phys.llnl.gov/clementine/ATP/Lsrprp2.gif
http://www.howstuffworks.com/light-propulsion.htm

People will live anywhere since energy information and material can be
delivered anywhere. People will work anywhere no matter where they
live, since they can report to work via telerobotics. People will
travel anywhere in minutes without roads or wings - using laser
propelled light craft.

As mentioned above, all mines, industry, commercial forests and farms
will be moved to orbit where they operate independently of the Earth's
biosphere - leaving only recycling and disposal industries to operate
on Earth powered by sunlight and supported by orbiting industrial
operations.

A concentrating mirror can focus sunlight onto an appropriate
apparatus that simultaneously produces electricity and increases
growing efficiency and area underneath the mirrors. The electricity
can be used in part to take nitrogen and water vapor in the air and
combine it to produce ammonia based fertilizers from sunlight and air.

But there are not just plants that have nitrogen fixing symbiotic bacteria
(which includes soybeans, and other beans / peas which are likely to be
in the crops list) and also many free-living bacteria do this. So is a
separate process other than reprocessing results of biological processes.

Also, many photosynthesising cyanobacteria are also nitrifying.

Do they use chlorophyll? If so, they'll use the same colors as the
plants. What intensities of light do they need? Plainly my analysis
was incomplete and was only illustrative of what might be possible.
You fail to mention the colors the cyanobacteria need. Further, what
other light needs does a biosphere need? This opens the potential of
using the relative intensities of light to control how much energy
goes into each process in a biosphere, and in this way change the
balance of things without having to insert sow agents or materials
directly.

One interesting thing to note about space based agriculture is that
sunlight is about twice as intense as the most intense light on Earth.
In fact, if one takes a look at the most productive regions of Earth,
sunlight in space is on average 6x greater. This implies that just by
cutting back the intensity and controlling the times things are
illuminated, one may take a square meter of collector and grow six
square meters of crop very productively. Of course if spectrum tricks
like the one mentioned earlier is effective in getting say a 4x
increase over that - then that 1 square meter could support 24 square
meters of crops! A 24 story hot house! Of course, if a portion of
the sunlight is used to power equipment on orbit - then this is
reduced.