From: Adrian Tymes (wingcat@pacbell.net)
Date: Fri Dec 01 2000 - 12:06:00 MST
Jeff Davis wrote:
> Solar radiation on the interior of the sphere will tend to drive the sphere
> so that the center of the sphere describes an 'orbit' around the star. To
> see why this is so, consider what happens if the star is off-center. The
> portion of the sphere nearest the star has the greater density of incident
> photons to both absorb and reflect. It will reach a higher temperature and
> thus a higher albedo, so it will reflect (rather than absorb) a higher
> percentage of the incident photons than the more distant (and thus cooler)
> interior surface.
Especially if one can vary the reflectiveness of the sun-facing
surfaces, to reflect more in the side one wishes to accelerate away from
the center, and absorb more in the other side.
> The star may have a magnetic field. The field lines may extend out into
> space. How far out do they extend? They may interact with the dyson
> sphere. They may be conducted through the dyson sphere. What is the
> sphere made of? If it were made metallic and isotropic, would the star and
> sphere be magnetically drawn together, or held stably concentric? Could a
> non-isotropic or non-metallic sphere design take advantage of or circumvent
> magnetic effects to passively achieve spherical concentricity?
Modern technology, believe it or not. The keywords you want are
"intertially contained fusion": basically, keeping a plasma contained at
the center of a (spherical, usually) shell. They're still working on
the "fusion" part, granted, but people have contained plasmas this way
before. This would appear to be that, just on a much larger scale.
> One last note. Though the 800 lb gorilla appears neutral in this matter,
> that's only first order effects. Second order gravitational effects may
> come into play. If the non-uniform heating of one side of the sphere
> causes it to distort, or tidal forces cause it to distort, then
> gravitational forces may again come into play. The devil's in the details.
Even with an undistorted sphere, would the pull of gravity not be larger
on the point of the sphere closest to the star's center than on the
opposite point? This would seem to be the biggest argument for keeping
the star centered (so there is no poin substantially closer to the
center). Also, in practice, it may be desirable to support spheres with
non-uniform mass distribution - say, for docking large spaceships, or
for manufacturing, or for sentients residing in a similar fashion as
sentients on the surface of the Earth today (that is, clustering in
cities, migrating, et cetera) - though this may be best handled by
figuring the current center of mass and moving the star there with
respect to the sphere.
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