Re: >H Open Air Space Habitats

Carl Feynman (
Sat, 01 Mar 1997 18:48:10 -0500

At 02:51 AM 3/1/97 -0600, Forrest Bishop wrote:
>Transhuman Mailing List
>This is part of a chapter of a new book on nanotech.

Oh boy! This will be a must-buy book!
> A home in space need not be the enclosed volume usually described in
most movies,
>books and articles. If a strong enough material is used, a rotating
cylinder can be so large
>that it holds an entire atmosphere against its inner surface. 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).

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

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

>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?

>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.

>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

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.

> 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?).

> 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.