a-planets

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> The air pressure is slightly less around the glass tube than it would be
for
> floor windows also this design is expandable. Using materials such as
> graphite nanotubes (ala space elevator) it should be possible to make
really
> huge Island three habitats, the cylinder could be so big that no glass
tube
> would be needed to keep the atmosphere in as centrepetal forces will cause
> the atmosphere to attenuate to vacuum as its height approaches the opening
in
> the endcap. You could even allow some clearance to allow spaceships to
enter
> through the opening in the endcaps and land on the inside of the cylinder.
> Ultimately the final evolution of the cylinder space colony would be
towards
> making "artifical planets" such as this. There are only so many planets to
> terraform in the Solar System. If a cylinder is big enough, the
atmosphere's
> own weight will hold it to the outside of the interior of the cylinder in
> much the same way as the Earth's atmosphere is held to its surface by
gravity.
>

If we are talking about "artificial planets" built with yet-to-be-invented
super-materials, then I think that the best option would be a cylinder
*without* endcaps properly said. Suppose an artificial planet 9 Mm in
diameter and in length - the surface area of this thing would be the *same*
of Earth (oceans included), and the a-planet would be able to sustain
billions of inhabitants. Well, the borders of the cylindrical surface would
not be straight, but instead they would curve gently upward and then inward
the cylinder, in a semicircular curve 100 Km in diameter. The whole
atmosphere would be contained inside the limits of the curved borders as
water is contained inside a bowl.

Lighting? Well, in this case I think that mirrors are indeed the best
option. Just put a behemoth (8.8 Mm in diameter) hollow sphere with a
mirrored surface at the center - it could be a silvery balloon inflated with
a pressure barely discernible from the vacuum. The sphere would *stay* at
the center naturally, for it would be the gravity center of the structure.
Now, I'm assuming that the a-planet has a spin axis perpendicular to its
orbit around the Sun, so we would need two additional mirrors, this time
flat ones, positioned "above" and "below" the a-planet, tilted 45 degrees in
order to reflect sunlight over the central sphere. (For structures of this
size, I think its is better to keep things without physical contact. The
flat mirrors could use magnetic repulsion for maintaining their correct
position and attitude relatively to the a-planet - though maybe this is
tricky due to solar wind...)

It is interesting to note that this arrangement would produce an "equatorial
zone" with a lot of sunlight at the center strip of the cylinder and
"temperate zones" to the north and to the south - much like on Earth. Due to
the altitude and weak sunlight, one would expect a lot of ice accumulated at
the curved borders - the a-planet would have "ice rims" instead of the ice
caps of a natural planet...

As for spaceships, I think that they still should enter the a-planet as if
it was an ordinary space settlement. Perhaps docking to a maglev in the
outside of the cylinder, and then being accelerated along the equator until
reaching the same speed of the cylinder, when then the spaceship would be
passed through airlocks and emerge from the internal surface. Making
spaceships enter the atmosphere as if in a natural planet would kill the
enormous advantage that an a-planet, like a space settlement, has over a
natural planet: negligible natural gravity, and extremely low escape
velocity...

> Tom Kalbfus
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