[ExI] rebuilding a saturn v today

spike spike66 at att.net
Tue Mar 29 20:12:24 UTC 2011

... On Behalf Of Mike Dougherty
Subject: Re: [ExI] rebuilding a saturn v today

On Tue, Mar 29, 2011 at 1:26 PM, spike <spike66 at att.net> wrote:
> For instance, we send a number of manufacturing robots to an asteroid 
> which begin to manufacture reflective light sails, which use photon 
> pressure from the sun to return to a medium high near-equatorial earth 
> orbit, perhaps 20Mm.  These then steer themselves such that they 
> reflect sunlight down on a desert solar farms, in the Mojave and the 
> Sahara for instance, so that these places can operate near peak watts
always instead of a few hours a day.
> I envision individual reflectors about the size of a dinner plate, 20 
> to 25 cm diameter, mass of about a gram, numbering in the quadrillions.

Does this array focus light so efficiently that we don't see it at night
(aside from atmospheric diffraction) or are we going to have the dull-white
moon share the sky with a bright ribbon of reflected sunlight?

I guess by the time we've engineered that into reality, proles won't be
going outside anyway  :)

You bring up an interesting question which can be solved with our
mathematical tools.  The system I envision would suffer from a huge
drawback: scattered light off of the reflectors would put out an enormous
amount of light pollution.  I have envisioned a band of reflectors, altitude
anywhere from 10 to 20 thousand km near-equatorial orbit, which reflect
light to a number of ground stations near the equator.  The view at night
from one of those stations would be a streak of very bright light, (perhaps
a milliradian width, or a tenth the apparent diameter of the moon if you
prefer those units, or a 20th of a degree if you prefer those) with a length
of about a radian or so.

The cumulative brightness of that streak would make it about as bright as
noon on the summer solstice near the equator.

However... to make these light enough that they can be steered though about
a radian in about 5 hours would require that it would be very thin, about
the thickness of two sheets of typical kitchen aluminum foil.  Result, there
would be scattered light.  No way around it that is very obvious to me.
Along the equator there would be a hell of a lot of stray light.  In those
places that are on a path between two collection stations, it would never
get very dark.  Don't know what to do about that problem.

Of course, nearly everyone on that path could get very cheap solar power:
they could get perhaps twice the output from their panels at no extra


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