
Inflatable tower could climb to the edge of space - raju
http://www.newscientist.com/article/mg20227117.000-inflatable-tower-could-climb-to-the-edge-of-space.html
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stcredzero
A series of towers that could suspend a magnetic accelerator about 300 miles
long above the bulk of the atmosphere would be almost equivalent to a Space
Elevator. (A space elevator transfers angular momentum from the Earth's
rotation into the orbital velocity of the cargo. Most of the work needed to
attain orbit is involved in the lateral acceleration, not in gaining
altitude.) It would be about as heavy as one, though.

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rbanffy
"A series of towers that could suspend a magnetic accelerator about 300 miles
long above the bulk of the atmosphere would be almost equivalent to a Space
Elevator."

The problem is that during acceleration you would push the tower back with a
force greater than the weight of the craft being accelerated. I am not sure
how much load those inflatables would bear, but I would guess that it's in the
"not much" range.

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stcredzero
This is why you'd want a series of towers, so that the force would be
distributed. Also, you'd have the accelerator start at the ground, so the
structure could be tethered there.

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Semiapies
Is there even enough commercially-available helium in the whole world to
support this structure, much less a 100+ km tall version?

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randallsquared
When you're talking about floating structures measured in miles, it doesn't
matter. You could do it with small temperature differences. You could float a
half mile geodesic sphere with only a degree or two of temperature difference
and ordinary air.

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Semiapies
Hmm, good point.

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mnemonicsloth
This is a bigger deal than it looks. The space elevator cable has to support
its own weight, so the stresses on it increase exponentially with length. Not
having to support those last 20 miles of cable could take the space elevator
concept a big step closer to reality.

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rbanffy
A tower extending 100 Km up would be a great point for scientific observation.
But to be a space elevator replacement you would need a tower that could bear
load up to geosynchronous orbit.

That's not easy.

I have read about using a series of balloons for lifting - a more rugged one
for low atmosphere, then switching the cargo to a lighter one designed to
operate in the high atmosphere and then propelling the cargo with something
like an ion engine to orbital speeds and increasing heights where the balloon
would give less and less lift (and offer less and less drag).

Looks like an interesting idea.

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mnemonicsloth
_But to be a space elevator replacement you would need a tower that could bear
load up to geosynchronous orbit._

That's not what I'm suggesting.

Build the tower as high as is practical, say 100 km. Then launch your space
elevator satellite and lower the cable down to the top of the tower.

The cable has to support its own weight, so it has to be thicker at the top
than at the bottom. It turns out that the cable thickness has to taper
_exponentially_ (basically, this amounts to a rotation of the catenary
problem).

So not having to support the last 100 km of cable at the end translates into a
weight savings along its entire length.

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rbanffy
"He calculates the tower could be extended up to low Earth orbit at 200
kilometres."

200 Km standing on top of an inflatable toy is not low Earth orbit! Who writes
this stuff?

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stcredzero
Getting to the height of low earth orbit could still be useful. Once you're
that high, it's much easier to accelerate something to orbital velocity.

