[ExI] Solving the real problem, energy was cure for global warming

[Keith Henson]

On Thu, Dec 30, 2010 at 5:00 AM,  Samantha Atkins <sjatkins at mac.com> wrote:

(context of lots of PV on the earth)

> Sure. Someday.  But not first to attempt to gain cheap and plentiful enough energy to keep our technological momentum up.  We need that long before we are capable of deploying SPS systems in GEO and/or on the moon.

I spent three years hunting for a solution and I think it could be
done with only relatively small advances over current technology.

snip

> Lets see.  4000 - 20000 metric tons of panels, concentrators, antennae and so on for an SPS.

Very close.  The current estimates have an 85 to one range from 5
kg/kW (Dr. Phil Chapman, me) to 1/17th of a kg/kW (Solaren).

Taking the heavy end, that's 5 t per MW or 5000 t per GW.  For optical
reasons, 5 GW is about the lower limit, so 25,000 tons per.

> Assuming you can get it out of the gravity well (or mine and manufacture in near earth space) then there is a huge need for workers / devices of some kind to assemble and maintain all that lot in GEO or on the moon.  We don't have anywhere near that many astronauts and do not field them for space walks in GEO on an extended basis in any case (much harsher radiation danger than LEO).   So having humans do it is not going to cut it, not in the next decade or two at least.

You train them up.  It's not that hard and you need around a thousand
of them.  There is no need for the construction of the vast majority
of the things to be particularly complicated.  The really complicated
pieces come up from earth.

One way I have looked at is making the structural beams out of coils
of thin metal and spot welding the connections.  At the speed you
expect from a roll former (material comes out at a fast walk) it only
takes a few of them to meet a 200 GW per year construction rate.

snip

> You can't beyond a certain range for anything requiring relatively continuous adjustments.  But you can run more nearly autonomous bots at greater distance.  But we don't have hardly any construction bots fully proven out in space.  Some of the attempts have had serious problems such as joints that freeze up if the power ever drops.

I am not against construction bots.  But as you point out, they are
not proven.  And supporting people in such an environment is *cheap*.
1000 people, 10 kg/day supplies, 10 tons.  That's in the context of
2500 tons per day of parts coming up.

snip

> Personally I think the moon is the wrong target for doing near earth space infrastructure.  There is more variety of useful and lucrative material in near earth asteroids more easy to get to.    No problem with doing both but I think the bounty of near earth asteroids is very seriously overlooked.

I agree.  A processing plant to convert asteroid metal to useful stuff
like coils of thin Invar sheet might mass 50,000 tons for a production
rate of 1000 t per day.  That gives a mass payback of 50 days.

snip

> At $2000 - $10000 / kg?

For power satellites to really contribute to solving the energy
problem, the cost to GEO has to get down to $100/kg.  Since relatively
high efficiency laser diodes have come along, I make a case it is
possible.

But there may be less expensive ways (such as StratoSolar) to solve
the problem that don't involve the expense of building a low cost
method to get into space.

Keith