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Re: Death Star

#21
Cha0zz wrote:Yes, but you can't think of a dyson sphere as one single object (the stress on something that big around an object with the gravity of a sun would be far to great, it would just shatter to pieces) but as a combination of smaller "panels" that each have an independent orbit around the star, their orbits are however calculated/ calibrated so that hey always stay at the same distance relative to each other
Partly true. A Dyson sphere can be described as a bunch of independant objects all in coordinated motion around a star. But it's not an orbit. There is no way to have objects in a synchronized spherical orbit; that's not how orbital motion works.

Instead, it should be visualized as a giant solar sail, held up by the pressure of the solar radiation. That means that the density of the shell is actually quite low per square meter, otherwise it would fall closer to the star. You have billions of solar sails, lashed together.

Note that because gravity falls off at the same rate as radiation pressure (inverse square of the distance), you can have the sphere at just about any distance from the star... you just need more sphere the farther out you are. Assuming a loose arrangement of sphere segments (attached by wires rather than fused into a solid sphere) this allows segments to be added and subtracted anywhere, increasing or decreasing the area and total potential volume accordingly with tiny rearrangements of sail segments.

Allowable weight, per square meter, is only 1.3 grams / m2. We don't have any practical way to do this with current (or even theoretical) material science. Until we can manipulate gravity, I don't think a Dyson sphere is likely to occur.

Also note: That's assuming reflection. Because absorbing the sunlight is how power would be generated, and absorbtion provides less thrust than reflection, the likely practical limit is less than 1 gram per square meter of sphere. For a sphere at 1AU from the sun, a solar supported dyson sphere would weigh less than 1/1000th the mass of the Earth (2.8 x 1020 kg, vs the Earth at 6x1024 kg).
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Re: Death Star

#22
MyrddinE wrote:Allowable weight, per square meter, is only 1.3 grams / m2.
I realized an error: total internal reflection (assuming no loss) would result in infinite light pressure buildup. It's not a sail... it's a balloon (as long as the holes between sails are very small). It's the difference between keeping a tissue aloft with a fan and keeping a balloon inflated.

Internally reflected light would increase in brightness until the energy loss from holes, absorption, and power generation equals the energy added by the sun. Depending on the efficiency, this could be a small number or a high number... but any way you look at it the interior would be an oven far hotter than it was before. This means that either you could have a far larger sphere with the same solar intensity out at the orbit of Jupiter as we currently enjoy at earth, or the intensity of a far hotter star while close in... either way, the supportable weight could be arbitrarily large depending on the reflective efficiency as the enterior would be far brighter than before the sphere encapsulated the star.

Think 'oven' vs 'space heater', or 'kiln' vs 'campfire'.
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Re: Death Star

#23
Assuming an entity could complete a Dyson Sphere, this would not provide an issue.
The entity would have to be assumed to convert heat to energy at a much higher rate than we currently can, as by god a Dyson sphere is a massive undertaking.

We are talking Category 2/3 civilizations here mostly.
Probably would use all the energy to power a massive computer simulation, for a digital race.
(Other uses are probably less useful by the time an entity could build such a device.)
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