Re: >H Open Air Space Habitats

Forrest Bishop (forrestb@ix.netcom.com)
Sat, 1 Mar 1997 23:03:06 -0600 (CST)


At 02:51 AM 3/1/97 -0600, Forrest Bishop wrote:

>This is part of a chapter of a new book on nanotech.

>Oh boy! This will be a must-buy book!

[[Thank you, Carl. I have one chapter of this particular project.]]

>The only example this author
>knows of is Larry Niven's "Ringworld", a ring the diameter of Earth's
orbit, circling a sun,
>and wide enough to contain oceans and continents. It, unfortunately, had to
be built of
>"Unobtainium" to perform this mighty feat.

Also, the "Orbitals" appearing in some novels by Iain Banks, "The Player of
Games", "Consider Phlebas", "Use of Weapons" and "Excession". These are
rings like you describe, but they have a radius chosen so they rotate in one
day and produce one gee on the inside. This permits a comfy day-night cycle
without the use of mirrors. My calculations indicate they have a radius of
1.9 million kilometers, and a tangential velocity of 21.8 km/sec. In the
books, they're built of Unobtanium, but they might not have to be! Pure
diamond is restricted to a tangential velocity of 17.5 km/sec; buckyfiber
may be capable of 21.8 km/sec (I haven't done that calculation).

[[Iíll check it out! Iím using 150 Gpa (!) as the Ultimate Tensile Strength
of Buckyfiber. I donít know its speed of sound.]]

> "Carbon Fiber" (also mis-named
>"Graphite Fiber")

It's a fiber consisting of pure graphite, i.e. carbon. How is this a misnomer?

[[As I understand it, Carbon Fiber come in different grades, and is made by pyrolyzing
various polymeric hydrocarbons, like rayon or nylon. The resulting fiber is (*I think*)
a mixed up conglomeration of sp2 and sp3 hybrid bonds. Maybe it is mostly graphitic-
Iíll put that aside aside.]]

>The shell needs to be about three meters thick for structural reasons,

Is that counting the dirt, trees, etc that one will want spread across
the
interior? If not, how thick are you assuming these amenities are?

[[I gave a safety factor of three to the shell for the slag and the
atmosphere- so it will have
to be thicker if you want serious dirt. I was assuming a few inches
average.]]

>and another three
>meters of slag should be sprayed on the outside, for radiation
protection.

Why spin the slag? Put it in a nonrotating shell well away from the
cylinder, and you save big on structural mass.

[[Yes, this will work too. I was looking at precessing the spinning
mass in
Solar free orbit, e.g at Earth-Sun L5, which a non-spinning component
would
complicate.]]

>As this is an "open-air" design, the ends only have to come up from
the
cylinder wall
>about 150 kilometers, and can be very thin near the top, as will be
the
enclosed
>atmosphere.

That gives an atmospheric half-life of only 60,000 years. Why not make
the
wall a little higher? You get a factor of ten in half-life for every
10 km
of height.

[[Only 60,000 years eh?. BTW, I just guessed at the height. Did you use
a
planetary or planar gas kinetic equation for this? Assuming a mean free
path
on the order of100 Km, a good portion of the escaping molecule flux
ends up
back in the atmosphere-on the other side of the world!]]

> The interior volume of this world can be left open to space,
meaning
each point on the
>interior living surface has about 150 Km of atmosphere above it, and
then
700 Km of
>nothing. Looking upward, at an angle, one can still see the stars.

It will be very bright at night, with a 28 degree wide arch of sunlit
land
spread across the sky. The stars will be too dim to be seen. This is
an
argument for a narrower ring, or perhaps some sort of parasol (sleep
mask?).

[[Yeah, I was thinking ďsleep maskĒ. Itís in the accompanying drawing,
along with
the (morphing) mirrors and some radial cabling.]]

> That was a lot of work, but what is a World worth?

About ten trillion dollars, if you're trying to sell it to present-day
Americans. If you're trying to sell it in the future, who knows? Land
might be dirt cheap.

--CarlF

[[Oh yeah??? If I give the human race 10 terabucks, can I kick
everybody off?

Forrest
(your new landlord)
Bishop
]]