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# polar_beanie

Polar space beanie - smaller than a space elevator
 (+3, -2) [vote for, against]

Space elevators are cool, but way over-sized. We just need something that gets us out of the atmosphere and up to orbital velocity - not all the way to geo-synch.

What if we put a huge spinner just over the south pole. Maybe "only" around 1000km in diameter. Spin it fast enough to hold itself out. The spinner's outer tips could be going at orbit velocities - around 7km/sec - just slide out and let go, then adjust your orbit with rockets - or spin it a bit faster and you can head off to Mars.

We just need a way to keep it's center of mass elevated, and a way to get up to the center.

1) A massive and tall tower holds it up. Need to compensate for massive atmospheric drag. Perhaps solar power on the outer spinner arms, and use the earth's magnetic field to keep spinning it up?

2) Use airfoils on the spinner to hold it up. Magnetic acceleration to make up for the power losses, but it'd be higher in the atmosphere so less drag overall.

3) A really big ballon holds up the spinner and optionally an elevator (the balloon would be so huge you could just put an airstrip on top of it instead). Miles up, where atmospheric drag will be less of an issue. This would still use magnetic acceleration, but might take less power. Maybe combine with 2.

If magnetic acceleration won't work, maybe a nuclear power plant right at the pole, feeding power up to the spinner on the elevator.

And if it happened to spin down, at least it's over mostly unpopulated areas. (In an emergency, it'd be far wiser to split the spinner and let the two halves sail off into space - either flung away completely, or more likely moved into stable orbits before they crash back to earth.)

 — TomRC, Aug 23 2002

Stairway to heaven http://www.halfbake...irway_20to_20heaven
[phoenix, Aug 27 2002, last modified Oct 04 2004]

 Damn. I thought someone had designed some kind of headgear for me... a la fish beanies. Perhaps we could fashion the tower out of ivory?

I think this is a good idea, but I don't know anything technical enough to decide whether it is a sound or feasible idea.
 — polartomato, Aug 23 2002

<Tonto>What you mean, "we" - white man?</Tonto>
 — thumbwax, Aug 23 2002

Q: How does a static magnetic field keep it spinning?
 — RayfordSteele, Aug 23 2002

 //Just slide out and let go//

huh?
 — dag, Aug 23 2002

RayfordSteele: The spinner would run current through coils, much like an electric motor (which also has static magnetic fields).
 — TomRC, Aug 23 2002

earths magnetic field a bit weak to spin a 1000km disc
 — chud, Aug 23 2002

[chud] While the magnetic field is weak, we're talking about a huge length and area of spinner that could accumulate that force, and the amount of spinner experiencing atmospheric drag is relatively small. And it'd be more of a cable than a disc by the way.
 — TomRC, Aug 23 2002

but enough coils to turn it will weigh a lot, use lots of power and mess around with electrical equipment on spacecraft
 — chud, Aug 23 2002

[dag] Unlike an elevator car on the "beanstalk" space elevator, a vehicle on the polar beanie wouldn't need to pull itself up against the force of gravity. Centrifugal "force" will rapidy accelerate it out more or less horizontally. At the end of the cable, it should be well above the atmosphere, so it can just let go and fly off with the same velocity as the end of the cable and into orbit.
 — TomRC, Aug 23 2002

[chud] Yep, this thing will weigh a LOT - but once you get it spinning, mass is actually an advantage - gives it stability. I don't have a handle on the power issue - but it "feels" like enough solar power could be collected along its length to overcome the drag of the atmosphere near the center of the spinner. There are proposals out there for solar powered ultra-light aircraft - and that's just using the power collected on the wings, all of which are in the atmosphere.
 — TomRC, Aug 23 2002

they arent powered by magnetism, though the idea is slightly more possible using similar design to those planes (like a whole load of them in a circle joined by cables)
 — chud, Aug 23 2002

No, they aren't magnetically driven - but they are apparently able to derive enough power from sunlight to overcome atmospheric drag to keep up to speed. It just suggests solar power collection on the 95% of the spinner out of the atmosphere might be able to provide enough power to overcome the atmospheric drag of the 5% in the atmosphere.
 — TomRC, Aug 24 2002

i think this could work but i just remembered reading about an idea similar to this from the fifties that was vertical at the equator
 — chud, Aug 24 2002

[chud] You're probably thinking of the pin-wheel concept - spinning as fast as it is orbiting, so that when an arm comes down close to earth, it's almost at zero velocity relative to the ground. You must fly up to rendezvous with it. It's probably more practical than the polar beanie, but lacks the convenience.
 — TomRC, Aug 27 2002

How fast does this thing spin at ground level?
 — phoenix, Aug 27 2002

 [Phoenix] You'd want it to spin at under the speed of sound inside the atmosphere. So maybe 800kmph where the air is thickest. Adjust the length of the spinner as needed to accomplish that - the longer the spinner, the lower the rotation period needs to be for a given "end" velocity.

E.g. if it must go no more than 800kph at 100km out, and needs the ends to be moving at 20000kph, the spinner would need to be about 5000km in diameter.
 — TomRC, Aug 27 2002

Do we have material to build a spinner that big that spinds that fast that won't rip itself apart?
 — tedhaubrich, Aug 03 2004

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