Open Air Space Habitats (excerpted)
Forrest Bishop (forrestb@ix.netcom.com)
Tue, 25 Mar 1997 16:15:06 -0600 (CST)
Open Air Space Habitats (excerpted)
A home in space need not be the enclosed volume usually described
in most movies, books and articles
[McKendree]. 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 [Niven]. It, and similar
proposals [REF], 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) [Smalley]. 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
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
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 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 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 million megawatts (a terawatt) or
more of electricity to power them, 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 rotating artificial sun system.
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 [Heinlein].
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 [Lewis]. 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 into the Point,
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 terawatt 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.
This Spaceworld is curiously resistant to nuclear weapons. With a
safety factor greater than three, a hole
blown in the side would not enlarge, and the outgassing of the
atmosphere would carry away the fallout (at
some point the hole should be repaired to keep the rest of the
atmosphere in).
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 [Lorrey].
The resulting magnetic dipole field
would deflect the solar wind much like Earth's magnetic field protects us from these charged particles. On
Earth, 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?
Space Warfare
So. How do we defend all this stuff? You might have noticed above
that practically everything mentioned
in the Interworld Rapid Transit System [Bishop] works just as well when
"fired in anger". The traffic
control, pointing, tracking and ranging systems, as well as Smart
Pellets, are virtually identical to those
required for space warfare. Indeed, I got the idea for Smart Pellets
from the "Smart Rock" kinetic kill
projectiles of the US Star Wars program.
A really large Spaceworld, like the "Open Air Habitat" would have
production, material and energy
resources far in excess of Earth's, along with perhaps an "Interworld
Rapid Transit" Station or some other
type of spacecraft support systems at its disposal...
[ ] McKendree, T, "Implications of Molecular Nanotechnology
Technical Performance Parameters on
Previously Defined Space Systems Architectures", (1995), Fourth
Foresight Conference on
Molecular Nanotechnology
[ ] Niven, L., "Ringworld",
[ ] Bishop, F., "InterPlanetary Mass Driver", (1982), unpublished
[ ] Bishop, F., "The InterWorld Rapid Transit System", (1997),
submitted to JBIS
[ ] Heinlein,R., "The Moon is a Harsh Mistress",
[1] Lewis, J. S., "Mining the Sky", (1996), Addison-Wesley, ISBN
0-201-47959-1
[ ] Lorrey, M., "Re: Open Air space Habitats", transhuman mailing
list