From: Stirling Westrup (sti@cam.org)
Date: Wed Dec 06 2000 - 18:53:08 MST
Jeff Davis wrote:
> Extropes,
>
> The predicted instability of the solid version of the dyson sphere has been
> a source of disappointment for moi ever since I heard about it. The idea
> of the fully enclosed star was so delightful to me, and so elegant, that I
> pondered long over the matter seeking some remedy, some bit of phenomenon
> to rescue me from my despair.
Interesting. That too, was my reaction, many years ago.
> Radiation pressure, baby. It ain't big, but it's real.
I thought about this long ago, and rejected it. As best I could figure at
the time, any minor perturbation of the sphere (such as caused by a major
asteroidal collision) would impart more energy than the restorative force
of the solar radiation, although I admit that I didn't take the time to
work in out on paper. I ended up being more concerned by the total lack of
gravity on the inner edge of the sphere, and decided that that too, needed
to be solved.
> Someone may say that radiation forces are puny in the inertial arena. I
> agree, but if they're the only forces in play, then they must dominate.
> Response times are just very long.
They are only the only forces in play if you have 1) swept the entire
solar system clear of debris (I admit that this is likely) and 2) can
guarantee that the sun will burn evenly, so that it produces a uniform
flux. This last point worries me.
> Candidate number two is something of a mystery to me. I know it's there,
> but I frankly don't know how it acts on the system or how it compares in
> magnitude of effect to radiation pressure.
>
> Magnetic field effects.
>
Hmm. I must admit that I never even *considered* magnetic fields.
What I came up with was to spin the sphere so as to cause pseudo-gravity
by centrifical force at the inside equator (and really make it hard to
image what substrate would be strong enough to build with). In order to
ensure that the inner pseudo-gravity was strictly normal to the surface at
all points, carefully sculpted masses would be added to the rotational
poles, so that the gravity felt on the inside would be the sum of
gravitational and centrifical vectors.
The upshot of this would be that the dyson sphere would be stable on two
axes, but still unstable along its rotational axis. Its not a total
solution, but it does make the problem more managable.
I've never managed to solve the equations that govern the distribution of
masses at the poles that is needed to create the correct inner gradients,
but I've had a few folks tell me that it looks like the best that can be
achieved with finite masses is to have all vectors within some epsilon of
being normal to the inner surfaces. Provided epsilon is less than 5
degrees or so, I don't think there would be a big problem.
--
Stirling Westrup | Use of the Internet by this poster
sti@cam.org | is not to be construed as a tacit
| endorsement of Western Technological
| Civilization or its appurtenances.
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