[ExI] High power orbital greenhouses

[Adrian Tymes]

On Thu, Mar 3, 2011 at 6:03 AM, Anders Sandberg <anders at aleph.se> wrote:
> 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.

Or, you know, reusable spacecraft, where the problem is mainly refueling
and servicing them.  Ship plants down, ship nutrients up.

If you had infinite energy, you could do on-orbit antimatter production, which
would handily provide all the fuel you'd need, though you'd need to develop
rockets which could hold and use antimatter fuel.  (There have also been
studies on scooping antimatter from the Van Allen belt.)  Short of that, you
could manufacture other high-energy fuels, which might tap into the nitrogen
you're bringing up.  (Granted, it might seem wasteful to ship the fuel
components up if you could manufacture them on the ground.  Part of the
point here is, you can't assume useful ground infrastructure where the food
needs to get to, and thus where the spaceships will be on the ground.)

> 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!

Only if you look at the greenhouse in isolation.  Shipping product around is
part of the problem - and product from orbit can be dropped anywhere in the
world.  *If* you can do on-orbit refueling and service of the spacecraft, then
the economics might start to be favorable.

Granted, you'd be spending profligate amounts of energy in the process.
The assumption is that energy is much easier to obtain in orbit (just build
more solar panels, without worrying about environmental impact, night/day
cycle, weather, maintenance - at least to the same degree - since there
aren't any moving parts, and so on), and thus of much lower price in orbit.
This breaks with our usual experience, where higher energy always means
higher cost, so it might seem counterintuitive.

(Again, we're assuming the ground we're dealing with - the areas most in
need of food - won't be able to support infrastructure, such as rectennas to
receive beamed energy or factories to turn it into fuel.  It is possible to
locate that infrastructure elsewhere on the ground, though - but then, after
delivering the food, the spaceship would have to make a suborbital hop to
ground factories elsewhere and then return home, as opposed to simply
returning home.  Granted, this assumes that nitrogen and other nutrients are
simple enough to gather - nitrogen, for instance, can be scooped out of the
air mid-flight; almost anywhere on land you'd deliver to, there's dirt of some
sort, albeit of varying grades.)

> 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.

Asteroid mining is a simpler business case to make, yes.  I think I've
detailed one plan for bootstrapping space industry using asteroid mining
on this list before.  (Survey to find a probably-platinum-rich
asteroid, bring it
into very high Earth orbit, send up simple processing equipment, send down
mostly-platinum-group meteorites for ground pickup by the organization's
agents, and sell for much profit.)  This would be something to do after there's
an infrastructure - say, start by making fuel for reusable rockets to ferry
people and cargo around, then start making food for people who are already
in orbit, and then expand the greenhouses to start doing this.  Much further
down the road from where we are today.

> 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.

That's the thing here.  The inefficiency is in something that we can afford to
waste (energy - again, only if it turns out that energy is that much cheaper
to obtain in orbit), there is no environment to damage, and the distribution
model is direct to the customer (wherever the hungry are, that's where you
land; even if someone else is buying for them, this saves on the buyer's
transportation costs, and so will probably be the buyer's preferred delivery
location).  Pricing models...well, there isn't a technical fix to
everything, but
at least this wouldn't be inherently worse.