Open Air Space Habitats
By Forrest Bishop
Copyright (c) Forrest Bishop, 1997, All Rights Reserved
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.
One example of this is Larry Niven’s "Ringworld", a ring the
diameter of earth’s orbit, circling a sun, and wide enough to contain
oceans and continents [7]. It, and similar proposals, unfortunately
have 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 contemplate 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 occurring
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 hundred thousand ton per second
rates. The "really long" part is being avidly pursued, and we
might see meter-long samples this year (1997) [8]. This in turn
may well spawn an industry that replaces "Carbon Fiber" with
the real thing. The first products will probably be military, aerospace
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" 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 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 2000 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 2000
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 cylinder,
say 500 km long and 2000 km diameter, having over three million square
kilometers of new land- about 2% of Earth’s land area. This now can be
used as e 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 a
rocket propelled craft looming over the new world, 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 perhaps 15 meters
thick for structural reasons, and another three meters of slag might be
sprayed on the outside, for radiation protection. The atmosphere-to-be
will provide the same radiation protection topsides that Earth’s air does.
As we wind 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 200 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. These will have to
be shallow seas, though, unless the shell is made very thick under them.
Mountains ranges might be added to the ends, where the walls rise to hold
the atmosphere.
The interior volume of this world can be left open to space, meaning
each point on the interior living surface has about 200 Km of atmosphere
above it, and then 1600 Km of nothing. Looking upward, at an angle, one
can still see the stars.
Daylight can be either provided naturally, using a suitable arrangement
of mirrors, or artificial. The design presented here uses one or more
artificial suns rotating above the atmosphere at a slower rate than the
habitat is spinning, so as to give a 24 hour day. These lights need about
a thousand million megawatts or more of electricity to power them, some
of which might be provided by photovoltaic cells covering the exterior.
For positions farther from the Sun than Earth is, this power source can
also be augmented or supplanted by off-World Solar Power Satellites beaming
energy back to microwave antennae, as well as separate mirrors to increase
the energy reaching the solar cells. To keep the lit portion of the ring
from lighting up the nightside, a shade is included as part of the artificial
sun system.
If two of these are built simultaneously, they could be made to orbit
one another as a binary system, separated by some thousands of kilometers,
which would prevent them from ever colliding.
So where should we put our new World? If you’re like me, you will want
it very far from Earth. The first candidate places are at the Sun-Earth
L4 and L5 points, where it will stay put without any control needed. These
places are 60 degrees ahead and 60 degrees behind Earth, in Earth orbit.
This gives us a fairly comfortable 150 million kilometers between ourselves
and the nearest politician, but we can do better: there is no reason to
remain in Earth’s orbit, either literally or figuratively [9].
Moving closer to the Sun has the advantage of increased solar energy
density, and not much else. Out past Mars are the serious resources of
the solar system, and of the rest of the Universe. Jupiter’s L4 and L5
(also called Trojan and Greek Points) points are great candidates; they
are easy to get to from Jupiter’s moons and from the main Asteroid Belt,
and also have the distinct advantage of holding substantial materials
in their sway already, perhaps even rivaling the Main Asteroid Belt itself
[1]. They are part of the "high ground" of the Solar
System, more easily defended against attacks from Earth’s gravity well.
An interesting property of these Trojan Points is their extent- they have
a very large volume of space around them in which objects can "orbit"
without leaving the vicinity of the Point. Asteroids can be brought over,
flattened out and made to orbit the New World, if needed for passive defense
against matter and energy beams.
Maintaining a large fleet of space warships is much easier on this type
of world, as the gravity well is much smaller. A ship can leave the Spaceworld
with only a few meters per second needed for escape velocity. Military
bases placed on the spin axis can service quite large warships using raw
materials from the Solar System at large, and finished products from the
New World. Access to the base is a matter of a quick elevator ride from
the surface. The aforementioned millions of megawatts of electric power
for lighting can also be diverted to some nasty-big lasers and such, big
enough to vaporize a ship many millions of kilometers away.
A nanotech cordon sanitaire can be established around a space-based
habitat much more readily than on a planet by tracking and identifying
all objects in its vicinity. Microscopic nanoprobes might be dealt with
by maintaining an ionizing field around the habitat, such as a scanning
ultraviolet laser, perhaps backed up with a layer of free floating "nanobot-phages"
orbiting just outside the World.
A magnetic field can be added to this world without much further effort
by wrapping superconducting wire or film around the circumference to form
a current loop [10]. The resulting magnetic dipole field would
deflect the solar wind much like Earth’s magnetic field protects us from
these charged particles. On Earth, some of these particles are entrained
in the magnetic field, bouncing back and forth between the North and South
Poles, creating the Auroral Lights. The cylinder has no atmosphere at
its "poles", so the particles can either be allowed to circulate
through the center of the cylinder (forming a sort of ionosphere), or
collected and stopped by charged plates at either end of the spin axis.
Well, that was a lot of effort, but how much is a World worth?
References
[1] Lewis, J. S., "Mining the Sky", (1996), Addison-Wesley,
ISBN 0-201-47959-1
[7] Niven, L., "Ringworld",
[8] Smalley, Richard, http://cnst.rice.edu/reshome.html
[9] Heinlein,R., "The Moon is a Harsh Mistress",
[10] Lorrey, M., (1997), transhuman/extropian mailing lists
(March)
[Home] [Articles]
[Contact] [Images]
Copyright ©1967-2004, Forrest Bishop, All Rights Reserved
|
