[ExI] High power orbital greenhouses

[Anders Sandberg]

Adrian Tymes wrote:
> To rip a thought experiment from the game SMAC: suppose you had a
> kilometer-long orbital greenhouse, with a vast array of solar panels to
> provide all the power you'd need.  (If you need a number, then
> extrapolating near-future photovoltaic panels to square kilometer sizes,
> assume a few gigawatt-hours per day, distributed among the entire
> greenhouse.  More is possible.)  How would it work?  What types of
> mass inputs and outputs could you have?  Would capturing a comet
> for local water ice help?
>   

While the orbital greenhouses are amazing in SMAC, in practice there are 
some problems. First, you need the mass inputs that allow you to grow 
plants. This could largely be handled with asteroid or comet matter, 
because you mainly need water, carbon dioxide, a certain list of trace 
nutrients... and nitrogen.
http://www.cartage.org.lb/en/themes/Sciences/BotanicalSciences/PlantHormones/EssentialPlant/EssentialPlant.htm
Nitrogen is IMHO going to be the headache: it is not that common in the 
inner solar system, yet you need to get it and fix it to grow plants. So 
you likely need to grab something with ammonia ice from the outer solar 
system.

Second, assuming you have a working orbiting greenhouse where plants 
grow happily and hydroponically, you need to get them down to Earth. 
That requires enough delta-v to get to an aerobraking orbit, and some 
form of capsule that can survive re-entry. So you need to build 
disposable spacecraft too - lots of them.

All in all, you could likely build a lot of greenhouses and factories 
out there. But it would be cheaper and simpler to build them in the 
Sahara desert!

Space products will likely be competitive only if they cannot be made on 
Earth, have some radical economy of scale (maybe asteroid mining for 
elements relatively rare on Earth) or the market is in space.

I think, however, that high efficiency hydroponic farming has a good 
chance of solving some food production problems. However, as noted in 
this week's The Economist (they have a whole supplement about the future 
of food production, see http://www.economist.com/node/18229412 ), the 
real problem is not exactly production. It lies in a great deal of 
waste, the use of inefficient or damaging methods, bad distribution 
methods and really wrong pricing models.

But it would have been great if space would have been the solution to 
the food crisis! Now we need to find another business model for going 
there.

-- 
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University