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Tropical climate *and* perpendicular gravity for everyone!
Inspired by [TheLightsAreOnBut]'s idea of
a uniform tropical climate on Cylinder
World, and the ensuing discussion on the
problem of non-perpendicular gravity on
cylinder. As was established by fellow
halfbakers, massive celestial bodies tend
to morph into a spheroid over time,
the accumulated effects of
Another way of obtaining gravity-like
conditions is by exploiting the centripetal
force of a rotating hollow object,
effectively pushing contents against the
inside of its outer wall.
Helix World (illustration provided) is built
on this concept,
a quantity of mass which does not
generate significant gravitational pull on
its components. The fact that it is hollow
(as opposed to the earth) very much
contributes to its lightness, making
structural stability feasible. Note that if
stability is insufficient, a double-helix
approach with links between opposing
strands can be used, with the added
coolness of having two separate
Now onto the tropical part! The sun will
shine through the helix's cracks and
the inside of the helix for a bit less than
half of the day, at an exposure equivalent
to the earth's equator, thus giving
everyone nice tropical conditions. Some
prime real estate at either end of the
will have longer days than the rest, since
there is less shadow from the opposite
The outer surface -- lacking useful
gravity, but nicely out of everyone's sight
-- can be used for industrial purposes.
Gravity-agnostic vegetation can also be
planted there to generate oxygen.
Design problems include retaining an
atmosphere on the surface, which may
solved by adding high walls on the edges
of the strip (on the habitable surface,
inside). If the centrifugal effect is
sufficiently strong, a breathable
atmosphere may not even need to be
trapped with glass or other barriers.
[placid_turmoil, Apr 05 2007]
Sadly destroyed during the Culture's retreat. Ring shaped with centripetal gravity. Internal atmosphere contained by high walls. [wagster, Apr 05 2007]
[nuclear hobo, Apr 05 2007]
Around a sun. [baconbrain, Apr 06 2007]
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||Nice take on the idea - by having a helix configuration, and spinning it, you should be able to stimulate a wind effect (kind of archimedian screw-like) which you'll have to manage, since after a while, the air will tend to blow towards the lea-end of the helix - perhaps a secondary, intertwinging helix could be used, to create a loop (I have no idea what this shape would look like - except that it might exhibit a pretzelesque topology)
||Interesting point [zen_tom]. A straight
tube connecting both tips may be
sufficient to enable a wind loop.
||I like it. Are you selling real estate yet?
||Preliminary calculations indicate that to maintain an Earth Day of 24 hours and equivalent gravity, the radius of the cylinder would be 1.85 million kilometers (1.15 million miles). The cylinder would be 3.7 million kilometers in diameter. If it were a mere 137 kilometers wide, it would have an area equivalent to Earth's 510 million square kilometers. This is about 1.5% of the distance from Earth to Mars or 9.6 times the distance from Earth to the Moon.
||You could maintain equivalent gravity by increasing the speed and reducing the diameter at the cost of shortening the day. Reducing the diameter without increasing rotational speed would result in less simulated gravity.
||The outer surface would make a terrific solar photovoltaic collector.
||Centrepital means "toward the center", centrifugal means "away from the center", and "centrifugal force" refers to inertia in a rotating system, which can substitute for gravity by holding things away from the center. This post has it wrong near the middle, and right at the end.
||The helix world looks a bit like Larry Niven's Ringworld, which looks like the Vavatch Orbital.
||There's no reason that the air should blow to one end, so that isn't a worry.
||If you want to raise crops on the underside, make upside-down greenhouses with hanging-basket planters and mirrors to reflect the light.
||In regards to day and night, wouldn't the helix be in an almost constant state of self eclipse? Thus, the length of day/night doesn't seem to make much of a difference.
||High walls to keep in atmosphere wouldn't help the day/night issue either...
||If it's dark more often, we use more fuel for lighting/heat and end up destroying that planet faster than this one :P Unless you layer the outside with solar cells I guess...
||One of the problems with a ring-like structure is it's fragility. A moderate meteor hit, one that would easily be absorbed by a planetoid, would resulting in the complete destruction of the ring.
||// the radius of the cylinder would be
1.85 million kilometers // Hmmm I
haven't checked your numbers yet but I
was afraid that might be the case. The
good news is, less gravity and shorter
||// centripetal/centrifugal // It feels
centrifugal to a helix world inhabitant,
but the net force is centripetal since he
stays in a circular motion. I'll check out
Ringworld, thanks for the tip!
||// constant state of self eclipse? // You
can essentially choose the light-to-
shadow ratio (arbitrarily close to 1) by
tweaking the width of the land strip
against the width of the void.
||// moderate meteor hit // A civilization
that has mastered the terraforming
technologies required for this concept
will probably have worked out some
method of meteor deflection. However
you are right in saying that the
structure is not very stable. Strong, thin
bridges, maybe nanotube columns,
could be used to reinforce stability
(think bird bones) without significantly
||In a sort of two-cups-of-coffee spirit, how about "Double Helix World"?
||Hi guys! I'm currently building a pseudo-planet composed of an external helix surrounding a smaller, opposing, counter rotating helix which will be orbiting Jupiter.
||Just wondering if anyone here has tried this before or could give me any help or advice? What did you use for the bearings? Did you recreate the troposphere or use another method of cosmic ray absorbtion?
||I tried asking at alt.rec.terraform but they're all hung up on the spherical model. Thanks in advance - respect to you halfbakers!
||I tried building a stable ring around Saturn but it broke up. You can see the result with a small telescope or even a good pair of binoculars. I think using carbon nanotubes from the lowest bidder was a mistake.
||[hobo] Were you contractor A, B, C ....or F?
||Saturn - a nice starting point for building a Ringworld, the raw materials are all there already.
||Sadly, the mechanical forces on this structure are of the same order as those on a single span suspension bridge 1.85 million km long under gravity the same as that at Earth's surface. Which requires a material with a strength:weight ratio about four orders of magnitude greater than the theoretical maximum possible considering the strength of interatomic bonds.
||Otherwise, very nice concept, and okay if you relax the day length and gravity expectations a bit.