Re: Solar concentration mirrors in the outer solar system

From: Alex Terrell (alexterrell_at_yahoo.com)
Date: 07/09/04 

Date: 9 Jul 2004 03:59:35 -0700

"Perplexed in Peoria" <jimmenegay@sbcglobal.net> wrote in message news:<A31Bc.25910$eH1.12158781@newssvr28.news.prodigy.com>...

> >
> > The edge of sunlight, commonly put at 3 A.U., could possibly be
> > extended to hundreds of times that by using extremely thin mirrors to
> > concentrate the attenuated solar light. The mirrors could be aluminum
> > a few tens of atoms thick, and an array of flat mirrors could be aimed
> > with a support structure to focus this for useful solar energy and/or
> > light.
> [snip]
> > distance area required mass required
> > (A.U.) (m2) (kg)
> >
> > orbit of Pluto 35 5.83 x 10^9 2.33 x 10^6
> >
> > current outer
> > edge of the Kuiper belt 70 2.33 x 10^10 9.32 x 10^6
> >
> > furthest orbit of Sedna,
> > inner edge of the Oort cloud 900 3.86 x 10^12 1.54 x 10^9
> >
> > These could be made from chunks of aluminum only 10, 16, and 83 meters
> > across respectively.
>
> It takes a lot of energy to find and refine that aluminum and to form it
> into mirrors. Such an installation will have to pay for its own cost
> of construction in less than 10 years to be worth doing. So, if you
> can estimate the energy cost of construction, you can construct a
> graph showing how time to pay back construction energy increases with
> distance from the sun. The point where that line rises past 10 years
> or so represents the real economic "edge of sunlight". It may be farther
> out than 3AU, but I'll bet it is well inside the Oort cloud.
>
The economics of far out settlements are a completely different
subject. Suffice to say for the moment, that:

- The masses are small compared to the settlement mass, upto the inner
edge of the Oort cloud.

- Current nuclear reactors weigh about 25 tons per MW, or 25 E6 Kg per
GW. Sure - this will improve, but they could still cost more than
mirrors at 70 AU, especially as the radiators need to use fluids
operating across ~5K to 800K temperature range.

I suspect (using forseeable technology - which is not realistic) a
large space settlement at 100 AU would use big mirrors for light, and
nuclear power for electricity, with each able to back up the other.

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