
Could We Build a Dyson Sphere? - itazula
http://www.popularmechanics.com/science/space/deep/could-we-build-a-dyson-sphere-17110415
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russell
No. In even a modest(hah!)structure like Larry Niven's Ringworld the tensile
strength required to hold it together exceeds that of any known material.
Sorry I'm too lazy to dig up the specific reference, but I'll give you a
pretty picture instead.

[http://www.dennisantinori.com/Resources/Ringworld/](http://www.dennisantinori.com/Resources/Ringworld/)

Edit: a reference

>>> Peter Weston passed the word from a British college professor: the tensile
strength of the Ringworld floor needs to be on the order of the force that
holds an atomic nucleus together. From such stuff you could make a garbage bag
that would hold a thermonuclear explosion.
[http://www.larryniven.net/stories/macrostructures.shtml](http://www.larryniven.net/stories/macrostructures.shtml)

~~~
gliese1337
The Ringworld only requires such enormous tensile strength because it's spun
to produce gravity on the interior surface. If you don't plan to inhabit the
interior surface, there's no need to spin it, and the problem goes away.

A sufficiently thin continuous sphere can be held up entirely by radiation
pressure, but still presents engineering challenges with damping oscillations;
a continuous structure is likely to tear itself apart just because it's
practically impossible to keep everything absolutely perfectly balanced on
such a large scale. Which is why, per the article, the Dyson Swarm, a sphere
made of lots of independently flying satellites, is much more plausible.

Incidentally, there are ways to eliminate the tensile load on a ringworld; you
"just" have to stack enough suborbital mass outside of it (coupled by maglev
rails or some such set up) so that the compression balances it out.

~~~
electromagnetic
I wonder how feasible it would be to rotate a ringworld at a speed not to
replicate gravity, but to negate the sun's gravity. So at 1AU it would orbit
in roughly the same length of time as Earth itself.

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TheLoneWolfling
You'd actually want to rotate it at _slightly_ faster than orbital velocity, I
think.

Tension is much stronger than compression, especially at larger scales.

But then you don't have the "nice" way of keeping the atmosphere in.

~~~
electromagnetic
My thought was something like a Stanford Torus, because then you could simply
add additional rings on different orbital inclinations to build an almost
sphere out of rings (reminiscent of M.C. Eschers drawing) and given good
design you could create rings with day night cycles.

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ufmace
The engineering issues are cool to think about. Setting out to build the whole
sphere at once is too much of an all-or-nothing thing IMHO. Instead, build a
relatively small solar satellite in orbit around the sun at the chosen
distance, maybe between Mars and the asteroid belt. Then build another one,
and connect them together. Keep doing that, working towards a ring around the
sun. That part should be relatively simple, since each of the pieces would be
in a stable orbit by itself.

If you still need more power after that, then you consider the ring to be the
equator of a sphere, and start building out the rest of the sphere, one ring
of latitude at a time. Maybe build it as a basic grid or something initially,
and add the solar collectors as needed. The stress would probably start to get
higher and higher as you built up and down, since the pieces wouldn't be in
orbit anymore, and so would rely on the structure to keep them in position and
connected.

The problems in getting started are probably more along the lines of needing
the kind of robot technology to gather the materials and build something like
the initial satellite without much supervision, being able to gather the
energy, and being able to do something useful with it.

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kimdouglasmason
From the article:

"400 septillion watts per second"

... And the context is talking about solar output, not a rate of change.

Sigh.

~~~
moreati
Considering the source, I almost wish it was intentional - the
science/engineering equivalent of a click bait headline.

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CodeCube
One thing the article didn't talk about in relation to the dyson swarm is that
if each unit is self-contained and collecting energy, how does it then
transmit that energy to ... somewhere else (presumably one of the habitation
units)? Are there obvious answers I'm not thinking about for energy
transmission when you don't have a physical grid of wires to move it through?

~~~
lutusp
A Dyson sphere is a very large embodiment of a simple idea -- inside the
sphere you have a low-entropy high-temperature energy source. Outside the
sphere you have the ultimate heat sink -- space. All you need to do is harvest
the energy from the heat source, and allow the waste heat to radiate into
space.

Imagine a Dyson sphere surface, every square meter of which would have more
than enough potential energy available for virtually any purpose. Imagine
something crude like a steam-driven power plant. A facility at the sphere
surface would heat water to steam below the surface, then drive a piston or
turbine, then recondense the steam to water above the surface by radiating the
waste energy into space.

Or one could use a thermocouple, not very efficient, but very reliable.
There's a thermocouple power supply on the moon right now, it's been there for
about 45 years and it's still going strong. The Curiosity Mars rover has a
thermocouple power supply also. These devices exploit a temperature difference
to generate electricity. Again, not very efficient, but reliable -- no moving
parts.

> Are there obvious answers I'm not thinking about for energy transmission
> when you don't have a physical grid of wires to move it through?

Well, there's no reason not to have wires if that's desired. Just generate
electricity in one of many ways as above, then transmit it to where it's more
useful. An alternative would be to live on a moon orbiting the sphere, and
radiate the power up to the moon in the form of microwaves or laser beams.

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fallingbadgers
QTWTAIN

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allegory
Ignoring the physics entirely, politics and finance would get in the way so,
no.

