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Helix World

Tropical climate *and* perpendicular gravity for everyone!
  [vote for,

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 a cylinder. As was established by fellow halfbakers, massive celestial bodies tend to morph into a spheroid over time, through the accumulated effects of (self-) gravity.

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, using 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 continents!

Now onto the tropical part! The sun will shine through the helix's cracks and bathe 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 helix will have longer days than the rest, since there is less shadow from the opposite side.

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 be 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

illustration http://picasaweb.go...5049949941651726738
[placid_turmoil, Apr 05 2007]

Vavatch Orbital http://www.alexhold...ider_Phlebas_f.jpeg
Sadly destroyed during the Culture's retreat. Ring shaped with centripetal gravity. Internal atmosphere contained by high walls. [wagster, Apr 05 2007]

Artificial gravity http://en.wikipedia...al_gravity#Rotation
[nuclear hobo, Apr 05 2007]

Ringworld http://en.wikipedia.org/wiki/Ringworld
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)
zen_tom, Apr 05 2007

       Interesting point [zen_tom]. A straight tube connecting both tips may be sufficient to enable a wind loop.
placid_turmoil, Apr 05 2007

       I like it. Are you selling real estate yet?
Galbinus_Caeli, Apr 05 2007

       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.
nuclear hobo, Apr 05 2007

       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.
baconbrain, Apr 06 2007

       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...
emjay, Apr 10 2007

       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.
nuclear hobo, Apr 10 2007

       // 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 days!   

       // 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 obstructing sunlight.
placid_turmoil, Apr 10 2007

       In a sort of two-cups-of-coffee spirit, how about "Double Helix World"?
hippo, Apr 10 2007

       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!
wagster, Apr 10 2007

       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.
nuclear hobo, Apr 10 2007

       [hobo] Were you contractor A, B, C ....or F?
Galbinus_Caeli, Apr 10 2007

       Saturn - a nice starting point for building a Ringworld, the raw materials are all there already.
wagster, Apr 10 2007

       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.
Cosh i Pi, Apr 11 2007


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