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Old 05-09-2012, 09:56 PM
 
Location: Westwood, MA
3,608 posts, read 4,774,914 times
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Quote:
Originally Posted by MrClose View Post
I understand that!

I am pointing out the 'error' in the other post stating that the stairway would 'rise' 25,000 MILES UP! (That's what 25k is .. Is it not?)

It would only 'rise' 2 or 300 MILES at most!
Two different ideas at play here. A static staircase to low earth orbit would only need to be about 200-300 miles high, but would have to support its own weight. No known material has a strength/weight ratio to support such a structure and such a design, while conceivable, is not believed to be possible.

A space elevator, on the other hand, balances the weight of a tether against the centrifugal force of a mass beyond geostationary orbit (at 25k miles) and does not need to support its own weight. It does, however, have to support the tension generated by the gravity and centrifugal forces created near and away from the surface, respectively. That's an easier task and some materials have been identified that could conceivably be used for such an application (they aren't good enough yet, though).
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Old 05-10-2012, 10:02 AM
 
28,607 posts, read 40,593,270 times
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And as I read these posts I realize that 264,000 is indeed wrong since the fact that it's a spiral staircase is being ignored. A straight flight is what our calculations are based on. A spiral staircase would be much longer!
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Old 05-10-2012, 11:04 AM
 
Location: God's Gift to Mankind for flying anything
5,371 posts, read 11,277,103 times
Reputation: 4202
Quote:
Originally Posted by jayrandom View Post
No known material has a strength/weight ratio to support such a structure and such a design, while conceivable, is not believed to be possible.
What ???
You haven't seen the latest Sky-Hook yet ???
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Old 05-10-2012, 11:09 AM
 
Location: Texas State Fair
8,565 posts, read 9,804,039 times
Reputation: 4230
Quote:
Originally Posted by jayrandom View Post
Two different ideas at play here. A static staircase to low earth orbit would only need to be about 200-300 miles high, but would have to support its own weight. No known material has a strength/weight ratio to support such a structure and such a design, while conceivable, is not believed to be possible.

A space elevator, on the other hand, balances the weight of a tether against the centrifugal force of a mass beyond geostationary orbit (at 25k miles) and does not need to support its own weight. It does, however, have to support the tension generated by the gravity and centrifugal forces created near and away from the surface, respectively. That's an easier task and some materials have been identified that could conceivably be used for such an application (they aren't good enough yet, though).
Link from an entry by Instapundit, the Foresight Institute addresses the issue of material strength with nanotubes...
Quote:
Scientists from Cambridge University have developed a light, flexible, and strong type of carbon nanotube material that may bring space elevators closer to reality. Motivated by a $4 million prize from NASA, the scientists found a way to combine multiple separate nanotubes together to form long strands. Until now, carbon nanotubes have been too brittle to be formed into such long pieces.

And a space elevator — if it ever becomes reality — will be quite long. NASA needs about 144,000 miles of nanotube to build one.
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Old 05-10-2012, 11:25 AM
 
Location: Itinerant
6,787 posts, read 4,375,882 times
Reputation: 5108
Quote:
Originally Posted by MrClose View Post
I understand that!

I am pointing out the 'error' in the other post stating that the stairway would 'rise' 25,000 MILES UP! (That's what 25k is .. Is it not?)

It would only 'rise' 2 or 300 MILES at most!
Quote:
Originally Posted by jayrandom View Post
Two different ideas at play here. A static staircase to low earth orbit would only need to be about 200-300 miles high, but would have to support its own weight. No known material has a strength/weight ratio to support such a structure and such a design, while conceivable, is not believed to be possible.

A space elevator, on the other hand, balances the weight of a tether against the centrifugal force of a mass beyond geostationary orbit (at 25k miles) and does not need to support its own weight. It does, however, have to support the tension generated by the gravity and centrifugal forces created near and away from the surface, respectively. That's an easier task and some materials have been identified that could conceivably be used for such an application (they aren't good enough yet, though).
That was my assumption for the distance which in itself is a little on the low side, GEO ranges are fixed at ~22,236 miles since they're set by the gravitational pull of the earth, and the earths period of rotation. But 25k was a round ball park figure.

Quote:
Originally Posted by Tek_Freek View Post
And as I read these posts I realize that 264,000 is indeed wrong since the fact that it's a spiral staircase is being ignored. A straight flight is what our calculations are based on. A spiral staircase would be much longer!
Why?

If you have a straight staircase that climbs 10' with 6" risers it requires 20 steps. If you have a spiral staircase that climbs 10' with 6" risers, how many steps do you think it needs?

Here's another question, if you have a 10 step staircase, where the top step is also a landing, that turns 90 degrees to another 10 step staircase, then to climb 10' would require 9 steps (typical stair step) a landing (step up to wider area than a step), 9 steps and a landing to the 10' mark. Is the height of the riser 6"?

Ok if we half the number of steps and the angle, we get 4 steps a landing with 45 degree turn, 4 steps a landing, 4 steps a landing, 4 steps a landing. Still a total of 20 steps up (4 flights of 4 steps, and 4 landings). Is the height of the riser still 6"?

OK you can see where I'm going with this I hope. A spiral staircase is identical to a straight staircase if you offset the steps at a consistent angle to one another, so say you had a 6" riser, and a 10 degree offset (step to step) one complete rotation would need 36 steps, and would climb 18'. To climb the same height on a ladder would require 36 rungs with a rung spacing of 6", and for a straight staircase would need 36 steps of 6" riser, although in that instance if the steps were 12" tread depth then you would have traveled 36' in the direction of the straight staircase.

I might be wrong there might be some weird structural difference between a practical spiral staircase and my theoretical concepts. I've never built a spiral staircase I must admit, but I have build a 14 step quarter landing set of stairs in my house from lumber, and the math worked out for that .
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