[AR] Re: Freeman Dyson, RIP
- From: Keith Henson <hkeithhenson@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 6 Mar 2020 08:27:24 -0800
Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
snip
If you want <100nm (skip the Mylar and keep the aluminum), now *that*
probably needs an in-space factory.
Before he got into nanotechnology, Eric Drexler made 200 nm thick
solar sail material. You could see a strong light right through the
sail material. I should look it up, but my memory is that he made it
with aluminum vapor deposition on top of a glass slide with a soap
layer then floated the aluminum off by carefully submerging the slide
in water.
snip
But then, again, we're talking about sending most of the light, and the
radiated heat, *inward*. Which is fine for individual craft, and totally
unacceptable for a Dyson sphere because of what it would eventually do to
the Sun (hard to say just what that would be, but the possibilities all
look unappealing).
This is something the stellar modeling people could answer, but I
really doubt heating up the outer layers of a star would do much to
the burn rate deep in the center.
About the time Drexler was working on this, we proposed hanging a
hemisphere of sails light enough to float in sunlight. They have to
be actively controlled since both light pressure and gravity fall off
by one over r squared. A more or less impractical use would be to
turn a star into a fusion-photon drive. The performance was
remarkably bad, but still, a fresh G-type star could cross the
distance between galaxies before it burned out. As I recall, this was
not a new idea. I commissioned artwork, but can't find a copy.
A more likely use would be heating up the surface of an M-type to look
more like a G. The light would come out along a slit to illuminate
the planets (or O'Neill cylinders).
For a viable Dyson sphere, the heat flow *outward*
(measured in watts) must equal the Sun's output, so there is no net
buildup of energy inside.
Yep.
Keith
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