Open Air Space Habitats

Forrest Bishop (
Sat, 1 Mar 1997 02:51:42 -0600 (CST)

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

Copyright (c) 1997, Forrest Bishop, All Rights Reserved

Open Air Space Habitats

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.
We now have a material close at hand that can do something like this, albeit on a much
smaller scale. The smaller the diameter of the rotating ring or cylinder, the less demands
are put on its main structural material. Instead of encircling a star, we can now contem-
plate building artificial worlds with land areas comparable to Earth that are open to
space- a feature we've grown accustomed to on this world.
This fabulous new material is the long sought Carbon-Carbon chain molecule. Its
existence was posited several decades ago, but no one knew how to make it. The answer
turned out to be one of those delicious tales of scientific discovery, like Goodyear stumbling
on vulcanization. We've come to know of a "third form" of pure Carbon, not
diamond nor graphite. This "new"-to us- stuff is called Buckminsterfullerene, or
Buckyballs and Buckytubes. Now that we know what to look for, this stuff has turned up
in four billion year old meteorites, interstellar gas clouds, and right here on Earth: in
ordinary candle soot, where it was discovered occuring naturally.
With the clarity of hindsight, it is obvious that a "sheet" of ordinary graphite could be
rolled up and joined to form tube- I'll wager someone thought of it many years ago. What
is amazing about this is that it happens all the time, naturally. Now comes the hard part-
make the tube really, really long, and do it at thousand ton per second rates. The "really
long" part is being avidly pursued, and we might see meter-long samples this year (1997).
This in turn may well spawn an industry that replaces "Carbon Fiber" (also mis-named
"Graphite Fiber") with the real thing. The first products will probably be military, aero and
spacecraft parts, as was the case with Carbon Fiber. Then come the bicycle frames, tennis
rackets, golf clubs and such. These products will weigh perhaps half of an equivalent
Carbon Fiber part. More importantly, they establish "Buckyfiber" (which should have been
called "Graphite Fiber") as a viable, nanotech industry.
To make this material in the quantities we really want, some parts of the production
have to be done by self-replicated tools, or 'Special Assemblers". The nice thing about
"Graphenes" (Buckytubes) is they self-assemble to a large extent (cf. "candle flame").
Therefore, the Special Assembler does not need to do direct, positional-control chemistry
on the forming tube, it only needs to mediate, or catalyze, the process, and move the
finished end of the tube along and out of the way, where more conventional machinery can
take over. Since this is essentially a one-dimensional product (like wire or yarn), the
Special Assemblers can be arranged in a plane, with the Buckyfibers emanating
perpendicular to that plane.
Given the above capabilities, we can now speak of creating new worlds. In this
example, we'll make a 1000 kilometer diameter world, just for fun. A space-based
industrial capacity, having the tremendous resources of just the inner Solar System at its
disposal, along with some nanotech self-replication capabilities, can do this kind of thing.
Beginning with the alluded to giant spools of Buckyfiber, a cylindrical structure can be
"filament-wound" in deep space. To do this, one need a rotating mandrel, or round mold,
to wind the fiber onto. This can be made in several different ways. One is to start with a
long, thin, superconducting wire, formed into a loop, and charge it with an electric
current. It then naturally springs out to form a near-perfect circle. Using several of these
connected together in a row, and reinforced with Buckyfiber-cloth, makes a short cylinder,
say 100 meters long by 1000 km diameter. This now can be brought up to some rotational
speed in several ways. One efficient way is to build two worlds at the same time, spinning
in opposite directions, and use a motor between them.
The gathered ends of Buckyfibers are led off of the spools (which are also spinning) and
brought to rendezvous with the outer surface of the spinning hoop. The shell is wound to
a thickness of perhaps a few centimeters. Depending on the masses (moments of inertia),
allowable fiber tensions, rotational speeds of the hoop and spools and so on, the hoop can
be made to slow down as the fiber runs out. Now the supercurrent is quenched, allowing
the mandrel to go somewhat slack (it still has some centrifugal force pushing it against the
new Buckyfiber cylinder). The mandrel is released from the inner surface of the new
cylinder wall, and moved along another 100 meters or so, like a concrete slip-form.
Another gang of Buckyfiber spools is brought in and the process repeated. After doing
this a few hundred times, we are left with a big, thin, slowly spinning clyinder, say 500 km
long and 1000 km diameter, having almost two million square kilometers of new land.
This now can be used as the mandrel for the rest of the construction.
Leaving this cylinder spinning slowly, we bring in fleets of these Buckytube spools. The
fiber should be wound at a slight angle, maybe 10 degrees, which means we need a shuttle,
like on a loom. This might have to be rocket propelled, like a Shuttle. Another way is to
build a 500 kilometer beam with the shuttles on it that sits in space next to the cylinder.
The shell needs to be about three meters thick for structural reasons, and another three
meters of slag should be sprayed on the outside, for radiation protection. The atmosphere-
to-be will provide the same radiation protection topsides that Earth's air does.
After winding the main bulk of this world, we have to consider what to do about the
ends. 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. These end walls can be made by wrapping the fiber over the edge of the
cylinder, letting it run in a straight line for a ways across the open end, then wrapping back

up onto the cylinder. Using a thin plastic membrane across the end, with a small amount of
air inside for pressurization, can help make the end rounded, as they ideally should be.
After the main shell is built, the rest of the atmosphere can be brought in, the nitrogen and
oxygen distilled from asteroids and cometary nuclei. Oceans are easy; there is lots of
accessible water ice strewn about in asteroids and small moons, out past Earth's orbit.
Mountains ranges might be added to the ends, where the walls rise to hold the
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.
That was a lot of work, but what is a World worth?