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A solid Dyson sphere made of normal matter is known to be
unworkable within our present knowledge of physics. Even
if it were kept in place around the star with rocketry it
would have to have a density around that of degenerate
matter to be strong enough to prevent collapse. Regularly
constantly firing rockets haven't been theorized as a
mechanism of support as far as I know because there
wouldn't be enough reaction mass to run them.
Imagine, if you will, a pressurized shipping container in
space. Inside two people are throwing a baseball back and
forth. The shipping container will go nowhere, but the ball
players will be pushing the ends of the container apart.
Now imagine the shipping container is made of springs. If
the ball is thrown hard enough the ball players can expand
the shipping container beyond the limits imposed by
This Dyson sphere would have regularly spaced rockets as
closely packed and powerful as you like. They would use as
reaction mass material funneled up from the star by
electromagnets. For power, electricity gathered by solar
Article mentions required strength, but with no proof.
[scad mientist, May 07 2015]
Pine 2x4s and jute twine...
[normzone, May 07 2015]
||I got stuck imagining those two people throwing a
baseball in a pressurized shipping container in space.
They hate each other, but there's nothing else to
||Niven ? His latest includes a half sphere functioning as a travel vehicle.
||I don't get it. Is it like an Hoberman-Dyson sphere that can stretch in any direction?
||I think it's a way to keep a Dyson sphere from collapsing - as any Dyson sphere made out of known materials would be wont to do, apparently.
||I say apparently, as I haven't read up on it personally. I'm a little curious about [Voice]'s equating density with strength. Not sure what that's based on.
||I do wonder how the light and radiation (solar wind, etc) pressure balances against gravitation for a Dyson sphere.
||Anyhoo, my solution would be instead of a sphere, make a ring, which you can spin at an appropriate speed to counteract gravity and minimise hoop stresses.
||Attaching rockets sort of feels like building the whole thing out of pine 2x4s and jute twine. Wouldn't a tech adequate to build a Dyson sphere be able to do better? Maybe bend space to reduce gravity? Maybe set up little chunks of neutron star at intervals outside the sphere to precisely balance the pull from the star?
||//A solid Dyson sphere made of normal matter is
known to be unworkable within our present
knowledge of physics. //
||Why? Is it because it will tend to drift off-centre
relative to the star?
||[EDIT] Ah, OK - it seems that yes, it would drift, but
the main problem is the sheer compressive strength
||//A solid Dyson sphere made of normal matter
||Errr. I don't think it's meant to be solid, otherwise
how do you get the star in there? Having once fitted
a door lock and forgotten to drill the key hole, before
I slammed it shut.... trust me, it's a bugger.
||The reason to make is solid (or more precisely
continuous) is the concept that
humans would keep using more an more energy.
At the point where we are using all of the energy
produced by the sun, we'll need a solid sphere (or
other shape) to capture it. If it's not spinning, a
sphere is the logical choice.
||It seems like construction really has to start with a
ring spinning at orbital velocity. If we then speed
it up so we can feel a "downward" force with the
sun overhead, it would make sense to continue
building the ring wider so it starts looking like a
cylinder. But as the ring gets wider than the sun,
it will be further from the sun, so the radius must
be reduced to keep the same net "downward"
force for the occupants. The shape might
eventually be similar to the shape of an American
||I'm not sure whether it would be possible to
eventually close the points of the football or not.
I think that with this shape, the compression
force would be significantly reduced compared to
a sphere, but would still be quite huge.