[snikt]
> 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.
[snikt]

I'm sorry, it seems that I messed up radius with diameter somewhere in my
calculations. A cylinder with its length equal to its diameter and with a
surface area equal to that of Earth itself would have the *same* diameter as
Earth, that is, 12.76 Mm ...

Talking a little more about a-planets, I mused about how much matter it
would take to make and "Earth-sized" a-planet. First, I assumed a
cylindrical "crust" just a hundred metters thick. Why a hundred metters?
First, its is a nice round number ;-); second, it would allow shallow oceans
that would, on the other hand, be deep enough for the use of very large
ships; and, finally, even a one-megaton nuke wouldn't be able to puncture a
hole on a crust that thick... (And, since a-planets depend upon the
existence of supermaterials, I guess that any puncture would need a *really*
big nuke.) Using that thickness, and assuming that your raw materials are
100% used either in the form of structural support of just for making soil
and mountains and oceans, then an Earth-sized a-planet would consume an
asteroid with a diameter of 460 Km .

That is certainly a *big* asteroid, and there is just a handful of them in
the Asteroid Belt. However, the estimates for the Kuipier Belt are around
30,000 objects with diameters over 100 Km, and so it seems reasonable to
supose that there are a few hundreds of asteroids big enough out there to
produce the same number of a-planets. Of course, since the Kuipier Belt is
just *so* far away from the Sun, that mirror system that I proposed would be
difficult to use. Perhaps some sort of hydrogen-fusion "articial sun"
shinning at the geometric center of the a-planet would be the best
solution...

Lucio Coelho

In a message dated 6/4/01 1:42:52 AM Eastern Daylight Time,
dromni@... writes:

<< I'm sorry, it seems that I messed up radius with diameter somewhere in my
calculations. A cylinder with its length equal to its diameter and with a
surface area equal to that of Earth itself would have the *same* diameter as
Earth, that is, 12.76 Mm ...

Talking a little more about a-planets, I mused about how much matter it
would take to make and "Earth-sized" a-planet. First, I assumed a
cylindrical "crust" just a hundred metters thick. Why a hundred metters?
First, its is a nice round number ;-); second, it would allow shallow oceans
that would, on the other hand, be deep enough for the use of very large
ships; and, finally, even a one-megaton nuke wouldn't be able to puncture a
hole on a crust that thick... (And, since a-planets depend upon the
existence of supermaterials, I guess that any puncture would need a *really*
big nuke.) Using that thickness, and assuming that your raw materials are
100% used either in the form of structural support of just for making soil
and mountains and oceans, then an Earth-sized a-planet would consume an
asteroid with a diameter of 460 Km .

That is certainly a *big* asteroid, and there is just a handful of them in
the Asteroid Belt. However, the estimates for the Kuipier Belt are around
30,000 objects with diameters over 100 Km, and so it seems reasonable to
supose that there are a few hundreds of asteroids big enough out there to
produce the same number of a-planets. Of course, since the Kuipier Belt is
just *so* far away from the Sun, that mirror system that I proposed would be
difficult to use. Perhaps some sort of hydrogen-fusion "articial sun"
shinning at the geometric center of the a-planet would be the best
solution...

Lucio Coelho
>>

Ceres is big enough. Also remember and artificial planet doesn't have to be
Earth-sized, it could be Pluto-sized. An artificial planet could even be
bigger than Earth diameter-wise. I think Ceres is a good candidate asteroid
to build the first one out of. I don't think we'll need too many at first.
Also if you use a fusion powered artifical sun, you could turn the whole
think into an Earth-sized starship. One might not want to live too close to
the leading endcap because of the cosmic rays the starship would encounter
and relativistic velocities. An Interstellar Ramjet would provide a continous
source of power as long as the worldship was moving faster than 6% of the
speed of light. I think that as well as scooping up interstellar hydrogen for
fuel, the ship might scoop up other material that might be used for further
construction, but I think the ship might have too slow down every now and
then to offload surplus population and perhaps build additional worldships.
The ship could travel in a huge circle revisiting the same star system once
every few thousand years while experiencing a few decades ship time. While
traveling at relativistic velocities the inhabitants of the ship could
remotely direct terraforming operations of a primordial Earthlike planet,
introducing cellular life forms that can quickly convert CO2 to O2 and seeing
the results in the ship inhabitants lifetime. When completely terraformed,
the ship will slowdown into the system and offload surplus population onto
the planet and then head to another star system.

Tom Kalbfus

[snikt]
> Ceres is big enough. Also remember and artificial planet doesn't have to
be
> Earth-sized, it could be Pluto-sized. An artificial planet could even be
> bigger than Earth diameter-wise. I think Ceres is a good candidate
asteroid
> to build the first one out of. I don't think we'll need too many at first.

I don't think so. Historical experience shows that, when a new frontier is
open (e.g., settlement of the Americas, colonization of the American West,
etc), it is rapidly populated. (It seems that population growth in the Old
West was around 8%/year, which is an AWESOME growth rate. There are even
higher rates at some "population focus": my city, for example, suffered a
gargantuan growth rate of about 50% per year during the first years after
its foundation - mostly due to immigration, of course.) Even if growth rates
would kept at a normal level, Earth itself would need a new a-planet to put
surplus population every thirty years or so. (Of course that is an
unrealistic hypothesis, for I see no conceivable way to send 6 billion
people to space in only three decades... However, migration between
a-planets would be vastly easier, and it is reasonable to think that an
overpopulated a-planet could rapidly colonize a new, empty one.)

Therefore, I think that any new a-planet would be rapidly populated to its
full capacity. I also have the gut feeling that the construction of an
a-planet would be really slow, as slow as terraforming a natural planet, and
that it would also take centuries, becoming the main bottleneck of the
process. Anyway, considering exponential growth, the whole Kuipier Belt
would be converted in a-planets in a few millennia...

[snikt]
> Tom Kalbfus
[snikt]

Lucio Coelho

What is the advantage of producing a single, huge, planet-sized habitat,
over a million or so island-3 habitats? If might take several centuries to
produce an a-planet. On the other hand, a large automated factory at L5,
could produce island -1 colonies in much the same way as car factories
produce cars, by the million. A giant automated factory like this, could
produce tens of thousands of island-1 colonies per year, from imported
lunar material. This is much easier than attempting to produce a single,
enormous habitat, as a one-off project.

Tony