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Progress City
Posted: Thu May 18, 2006 6:29 pm
Guest
I just spent the past couple days doing some reading on orbitals and
ring worlds.... The concept is nice, but they both have one major
problem. They require an exotic form of matter that doesn't exist, and
probably never will.

What would be the maximum size of an orbital if it were made out of
carbon nanotubes?

Would it be possible to place a few billion of these around the Sun, in
an orbit suitable for human life?
Perry E. Metzger
Posted: Fri May 19, 2006 7:15 pm
Guest
John.S.Novak@panix.com, III <jsn@panix.com> writes:
Quote:
In article <126q0rm34nl1377@news.supernews.com>, progresscity@gmail.com
says...

I just spent the past couple days doing some reading on orbitals and
ring worlds.... The concept is nice, but they both have one major
problem. They require an exotic form of matter that doesn't exist, and
probably never will.

What would be the maximum size of an orbital if it were made out of
carbon nanotubes?

Would it be possible to place a few billion of these around the Sun, in
an orbit suitable for human life?

Almost certainly not.

Even at the strictly magical tensile strength required to create the
Ringworld as described, the thing massed about a thousand times the
Earth itself, or, about as much as Jupiter. It also required
centuries' worth of solar output equivalent in energy to set in motion.

Given that hypothetical variants made out of far far weaker carbon
materials would probably be heavier, then even assuming you could
dynamically stabilize one (somehow) implies that you simply don't have
enough material in the solar system to build even one, let alone a
billion, let alone set them all moving.

Nanotechnology is not magic.

I don't know what is meant by an "orbital" in this context, so I'm not
quite so dismissive. Although Larry Niven style ringworlds are flat
out impossible given our understanding of physics, both because of the
materials and because they would not be stable, "ordinary" space
habitats with enough spin to provide 1g environments are not
impossible.

Perry
Toby Kelsey
Posted: Fri May 19, 2006 7:18 pm
Guest
John.S.Novak@panix.com wrote:
Quote:
In article <126q0rm34nl1377@news.supernews.com>, progresscity@gmail.com
says...

I just spent the past couple days doing some reading on orbitals and
ring worlds.... The concept is nice, but they both have one major
problem. They require an exotic form of matter that doesn't exist, and
probably never will.

What would be the maximum size of an orbital if it were made out of
carbon nanotubes?

Would it be possible to place a few billion of these around the Sun, in
an orbit suitable for human life?


Almost certainly not.

Even at the strictly magical tensile strength required to create the
Ringworld as described, the thing massed about a thousand times the
Earth itself, or, about as much as Jupiter. It also required
centuries' worth of solar output equivalent in energy to set in motion.

Ringworld and solid Dyson spheres are dynamically unstable and are the sort of
megastructures which are sociologically unlikely. Leaving aside the economic
issue, space settlements such as O'Neill cylinders with kilometre dimensions are
feasible with current materials.

The mass of the asteroid belt is ~3x10^21 kg, about 0.1% of Earth's mass. If an
O'Neill cylinder masses about 10^12 kg (guessing for Island Three), you could
construct about 3 billion of them if all the material is useable, so "billions"
of settlements are possible.

With about 100 square kilometres per cylinder you would have 3x10^11 square
kilometres of habitable area. The human population density of Earth is
currently about 43 per square kilometre of land, so they could contain a
population of about 10^13 people, or over 1000 Earth's worth. Allowing for
city-like densities or multiple levels could multiply this by perhaps 30-fold.

Looking at <http://www.islandone.org/LEOBiblio/SPBI1MA.HTM> nanotubes have
theoretical advantages over steel and Spectra, but often theoretical strengths
are never reached due to unavoidable material defects. It is possible that MNT
couild lead to active materials which repair themselves or automate replacement
when they become damaged which would allow stronger materials. Nanotubes could
allow larger space structures to be built than with steel, but whether larger
sizes are advantageous is another matter.

Quote:
Nanotechnology is not magic.

Indeed, it is too easy to fall into the "flying car" syndrome. All innovations
occur in an industrial and social context and must make economic sense.

Toby
Phillip Huggan
Posted: Fri May 19, 2006 8:15 pm
Guest
I don't know what ring-worlds are but I know what
Dyson Spheres are. There is enough mass in the Kuiper
Belt (estimates start at 1/3 Earth's mass) to permit
large engineering projects. Volatiles are the fuel
and solar sails or ion engines are the propulsion. It
may take years or decades to position the habitats. I
would think terraforming Venus will be ultimately
easier on human physiology.

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