Basic Information:
This design of space colony was first proposed by Princeton
University professor Gerard K. O'Neill in his 1977 book, The
High Frontier: Human Colonies in Space (1977, Morrow
Press/Bantam, ISBN 0-553-11016-0; reprinted 1989, SSI Press, ISBN
0-9622379-0-6; updated 2000, Apogee Books, ISBN 1-896522-67-X). It
was the third and most ambitious of three colonies proposed in the
book. Called "Island Three," the colony is a gigantic rotating
cylinder 20 miles long and four miles in diameter, with
hemispherical endcaps at both ends. Its interior is a landscaped
semi-terrestrial environment divided into six alternating "land"
and "sky" panels that run the length of the cylinder and
terminate at large "mountains" at the endcaps. The land panels
have one small city at either end, and a shared "wilderness" area
in the middle; the sky panels are left empty, and are crossed by
bridges to facilitate travel between the land panels. Sunlight is
reflected in through the sky panels by large mirrors outside the
main colony cylinder which can be rotated to create day and night
- the appearance of these mirrors gives the colonies their nickname,
"sunflower" style colonies.
The entire colony (with the exception of docking bays at the center
of the endcaps) rotates at 1/2 RPM, using centrifugal force to
produce 1G of simulated gravity on the inhabited "land" panels.
Since centrifugal force is dependent on the radius of the
cylinder, as one moves up the mountains at the ends of the colony, the
simulated gravity drops proportionally to one's altitude, reaching
zero at the colony's axis. The zero- and low-gravity areas of the
endcaps are devoted to industry, leaving the rest of the colony
available for habitation. The colony's agricultural needs are served
by external agriculture units arranged in a non-rotating ring
around the colony's sun-facing endcap. The colony supports an
autonomous population of somewhere between three and ten million
people. In the Mobile Suit Gundam anime, in which these
colonies figure prominently, they are placed in groups of 100-150
called Sides. This entire group orbits the Earth at the same rate as
the moon, in one of five gravitationally stable points near the
Earth and the moon known as Lagrange points, after the
mathematician who predicted them.
Construction Details:
The outer colony hull is a meter-thick plate of
titanium-reinforced "mooncrete," a lunar-produced concrete
containing anorthosite, ilmenite, and KREEP (potassium, rare
earth elements, and phosphorus). The inner surface of the hull is
covered in about five meters of topsoil, though some maintenance
buildings may reach down to the outer hull. The sky panels are far
more complex. Each panel is two miles wide and 16 miles long,
composed of eight windows (2x4) of sixty-four sashes (8x8) of
twenty-five panes (5x5) of one hundred frames (four-ply 5x5) of
twenty-five prisms (5x5) of quartz glass. That's a grand total of
32 million prisms, each measuring 3.2 meters on a side (10.4 feet, or a
thousandth of a mile) and weighing about 90 tons. Quartz glass is
essential to the construction both for its strength and for its
transparency to sunlight - if it weren't so transparent, the
greenhouse effect would bake the colonists. This seems like an
absurd amount of quartz - in fact, this amount is easily found in a
single large asteroid. Electricity for the colony is provided by
solar and geothermal power - conductive material running through the
hull takes advantage of the temperature differential between the
sun-facing endcap and the space-facing endcap to generate current.
Though it's not depicted in the Gundam animation, Island Three
colonies have to be lashed together in ballistically coupled pairs
(turning in opposite directions) to ensure zero angular momentum,
which is necessary to keep them pointing towards the sun.
Environmental Oddities:
(or, The Coriolis Force Hates You)
Because of the constant spinning of the external colony cylinder,
and the constant heating of the sunside endcap compared to the
starside endcap, the weather patterns within a Gundam-style Island
Three space colony are bizarre. The weightless air at the center
of the cylinder expands towards the southern endcap as it is heated.
Once it approaches the ground it picks up the rotation of the
cylinder and moves down the mountain and sunward in a helical downspin
spiral, finally reaching the northern endcap and rising back up to
repeat the process. The end result is a spiraling wind from
upspin and starside (southwest), with variations caused by buildings,
people, landscaping, et cetera. Coriolis forces make dust
devils common, and as the clouds follow this spiral pattern as
well, short but heavy showers occur roughly every six hours.
It's nearly impossible to play basketball. Due to the rotation of
the cylinder, all freefalling objects veer upspin. Equally, heading
downspin is fundamentally discouraged - it's considerably harder to
walk downspin than up, as when moving downspin your acceleration is
added to the acceleration of the rotating cylinder and increases your
apparent weight. Furthermore, coriolis forces in the inner ear make
complicated motion disorienting; space basketball is only for the
strong of stomach.
Again due to coriolis forces, elevators can't go straight up (towards
the axis of the cylinder) if they're going to rise any appreciable
distance. The sum of the acceleration of the elevator and the
acceleration of the rotating colony would cause the passengers inside
to feel as if the floor had tilted on a 45-degree angle. To
eliminate this effect, the elevator car would either have to rotate
to compensate (putting the passengers on a 45-degree angle relative
to the ground, but standing normally relative to the apparent
direction of gravity) or it would have to run in a downspin spiral
when going up, and an upspin spiral when going down.
01/16/04
WolfKeeper helpfully corrected my math regarding space basketball. On the inside of the colony hull, where most of the living gets done, the Coriolis force pales in comparison to the centrifugal force causing the artificial "gravity." Even the fastest athlete is going to incur only minor disruptions to the workings of his inner ear. Approaching the center, however, the centrifugal force drops off while the Coriolis force remains the same (so long as you're not in free-fall). So we can reinstate the SpaceNBA, but any plans for low-G Ultimate Frisbee will have to be called off.