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Anonymous Poster

Is anyone interested in a stepped space elevator?

01/14/2009 2:19 PM

Has anyone considered what I am terming a stepped space elevator? It seems to circumvent the current problems related to the space elevator.

Instead of a single tether (like an express elevator that only runs from the ground floor to the upper floors of a building), what is the problem with stopping at an intermediate platform or platforms? The platforms act as huge airfoils/kites and steps so that the tether doesn't need to support its full weight at any point. It does need to be strong enough to anchor the kites.

As kites get higher, there is less air to provide lift, but this is also offset by less gravity to overcome. At the point where there is not enough atmosphere to provide lift, hopefully there is minimal gravity so that the tether can support its own weight at this point to extend into space.

A possible assist to forward motion could be provided by solar panels to power electric drive motors, lessening the tension on the anchor tether.

If the rotational speed of the Earth is too fast, one could position the ground anchor neare the poles (which would also increase sun exposure.) Another possibilty would be to not anchor the tether to the Earth, but this would require the platforms to be powered and/or lighter than air (or only as heavy as the propulsion could keep airborn. Then the lowest platform would act as a small landing pad/strip for cargo to be transferred to airplanes/helicopters as the Earth passed beneath it. Or from a ground perspective, the platform passed overhead. This raises the possible problem of political permission to use airspace, but hopefully the having access to the elevator would be incentive to allow it.

Does this make any sense? Am I missing something obvious?

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The Engineer
Engineering Fields - Engineering Physics - Physics... United States - Member - NY Popular Science - Genetics - Organic Chemistry... Popular Science - Cosmology - New Member Ingeniería en Español - Nuevo Miembro - New Member

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#1

Re: Is anyone interested in a stepped space elevator?

01/14/2009 3:00 PM

You Wrote: "what is the problem with stopping at an intermediate platform or platforms?"

I believe the problem would be gravity. Gravity doesn't change much from the surface of the Earth to where you are proposing these platforms. Think about it, the Moon is in orbit around the Earth due to the Earths gravity. You have a serious misconception regarding gravity.

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Power-User

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#2
In reply to #1

Re: Is anyone interested in a stepped space elevator?

01/14/2009 4:48 PM

Mr. Pink is correct, but using the moon as an argument isn't appealing. After all, Newton had to invent the calculus in order to prove that the earth attracts the moon the same as it attracts the apple that dropped on his head.

Here's the equation for gravitational attraction:

F = GMm/r^2

where,

F = the force of gravity

G = gravitational constant

M = mass of the earth

m = mass of object in gravitational field

r = separation of object from earth's center.

The point of Newton inventing the calculus was to demonstrate that a distributed mass such as the earth attracts a mass near its surface the same as if all the earth's mass was concentrated at its center.

Now the radius of the earth is about 4000 miles. If you are 100 miles above the earth's surface, the equation tels you that gravitational attraction will be that at the surface, adjusted by the factor:

factor = (4000/4100)^2 = 95%

So as Mr. Pink said, the force of gravity has not diminished significantly in low earth orbit.

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Anonymous Poster
#3

Re: Is anyone interested in a stepped space elevator?

01/24/2009 11:24 AM

So the problem is lift is going to run out way before gravitational forces are diminished.

Thanks for explaining.

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Commentator

Join Date: May 2009
Posts: 75
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#4

Re: Is anyone interested in a stepped space elevator?

06/02/2009 11:35 AM

Also, that last 100 miles does not contribute that much mass to the tether.

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