Question about space elevators:

Originally posted by twhitehead
The Warsaw Tower was 40 odd times taller than a 30m radio mast. It still didn't need the downwards force to be spread at the base. What changes?

[b]I think what googlefudge is getting at is that the point of an Eiffel Tower type arrangement is that most of it is empty. The idea is to keep the mass down but maintain a strong structure.
And a guy r ...[text shortened]... withstanding that. It is probably more economical to shoot down any aircraft that get too close.[/b]

Ahhh but we already build skyscrapers that can withstand aeroplane strikes.

Also, again, you radio mast doesn't have to carry the same loads as a space
elevator base tower.

And it's also not ONE cable stretching from the top... It's hundreds.

You need redundancy and also to maximise the lift capability per space elevator.

And also the entire collection is surrounded by a mesh of spiralling cables to form
a Whipple Shield around the core cables to protect from micrometeorites and
small space junk.

So you have many cables, spread over hundreds of meters. With several thousand
tons minimum on the elevator at any one time.

And much more in the tower itself.

Huge hydraulic rams used to induce or counteract vibrations in the cable to bend it
around space debris or faulty satellites... ect ect.

Originally posted by Metal Brain
How are you going to put the lightning conductor into place without getting fried by electricity? Are you volunteering? Better you than me.

Yes because skyscrapers are regularly destroyed by lightning during construction...

It's made of METAL, which is a conductor. lightning wont hurt it, just like lightning
doesn't destroy the Eiffel Tower or any other major piece of engineering works.

Originally posted by googlefudge
Yes because skyscrapers are regularly destroyed by lightning during construction...

It's made of METAL, which is a conductor. lightning wont hurt it, just like lightning
doesn't destroy the Eiffel Tower or any other major piece of engineering works.

That doesn't explain how you will put it in place without getting killed. Try reading what I wrote next time.

Originally posted by Metal Brain
That doesn't explain how you will put it in place without getting killed. Try reading what I wrote next time.

How about you halt work during a thunderstorm...

How stupid are you?

Originally posted by Metal Brain
How are you going to put the lightning conductor into place without getting fried by electricity?

Dirr; don't do it during a storm.

Originally posted by humy
Dirr; don't do it during a storm.

That might actually be a problem. Something taller than a mountain is going to affect the weather around it. So it could induce thunder storms. Although it's difficult to see how a potential difference could build up given the presence of a convenient conductor. Have people included effects on weather in their studies of this kind of idea?

Originally posted by googlefudge
Ahhh but we already build skyscrapers that can withstand aeroplane strikes.

Or at least we try to. The vast majority of sky scrapers would not. And achieving that requires an enormous amount of concrete and steel. I just don't think its cost effective.

Also, again, you radio mast doesn't have to carry the same loads as a space
elevator base tower.
What are those loads? If my understanding is correct, a space elevator pulls upwards most of the time. The only significant loads will be wind sheer which I believe is not significantly higher than the Warsaw Tower had to withstand.

So you have many cables, spread over hundreds of meters. With several thousand
tons minimum on the elevator at any one time.
But most of those tons are being supported by the tether, which is pulling upwards.

Huge hydraulic rams used to induce or counteract vibrations in the cable to bend it
around space debris or faulty satellites... ect ect.
Might be better to get rid of the space junk first.

Originally posted by twhitehead
Or at least we try to. The vast majority of sky scrapers would not. And achieving that requires an enormous amount of concrete and steel. I just don't think its cost effective.

[b]Also, again, you radio mast doesn't have to carry the same loads as a space
elevator base tower.
What are those loads? If my understanding is correct, a space elevator ...[text shortened]... debris or faulty satellites... ect ect.[/b]
Might be better to get rid of the space junk first.[/b]

Ok. your radio mast is ~1/40th the height of the tower.

Given that it is a linear structure that means that a tower of similar design
would have ~40 times the weight. [and if we make it wider but maintain the
same structural density we still have the same weight per unit cross sectional
area]

So, without any extra loading from having human habitable airtight structures
at height for example, this tower must have ~40 times the strength of the radio
mast.

For that to be true, and to maintain at least a 2~3 fold safety margin, your mast
must be between 1/80th and 1/120th of the structural strength of the materials [steel]
used.

Given that the failure of one cable caused total catastrophic collapse of the entire
structure I find this fairly improbable.

http://en.wikipedia.org/wiki/Warsaw_radio_mast#Collapse

This is not the kind of instability you want in a 20~25 mile tower.

I would also note that the steel tube thickness varied from 8mm to 34mm [according to
the wiki article]. Now assuming that the thickness increases linearly [it wont] then making
it 4 times taller leads to a thickness of the steel in the tubes at the base of 1.36 meters.

Now as cross sectional area increases as the square of the thickness, but the mass as the
cube of thickness, then we know that we will actually get an exponential increase in thickness
to support the increasing mass. In short you get a tapering structure that looks like the Eiffel Tower.

Originally posted by Metal Brain
How are you going to put the lightning conductor into place without getting fried by electricity? Are you volunteering? Better you than me.

Sure do seem to be a lot of 1000+ foot towers up all around the planet. I get the feeling, just a guess, that they have that part figured out. Perhaps doing major work when they know there won't be a storm? Literally millions of 1000+ foot buildings up all over the planet too and I don't hear of any of them destroyed by lightning.

Why do you think that would be a problem? I have a lightning rod on my house and it is only a 1/2 inch diameter going to a similar sized cable to ground. My house hasn't gotten destroyed yet and we have had some wicked thunder/lightning storms, starting in August through November here in the Pocono's. Copper conductors 1/2 inch in diameter can handle lightning just fine and the buildings made of steel are way thicker than that and very wide and deep so they are very conductive and go all the way to ground by their very construction .

I also have a ham tower up about 60 feet and it survives just fine.

Are you thinking just getting a tower high in the air by itself is going to attract lightning?

Originally posted by DeepThought
That might actually be a problem. Something taller than a mountain is going to affect the weather around it. So it could induce thunder storms. Although it's difficult to see how a potential difference could build up given the presence of a convenient conductor. Have people included effects on weather in their studies of this kind of idea?

Yes, although if you're actually going to build one you would need to do the
more detailed kind of planning that requires super computer modelling.

The weather effects would certainly have to be taken into consideration,
just as earthquakes and all the other factors would.

The point is just that none of these problems are in any way insurmountable.

Originally posted by twhitehead
Or at least we try to. The vast majority of sky scrapers would not. And achieving that requires an enormous amount of concrete and steel. I just don't think its cost effective.

Not true.

The twin towers withstood being hit by jetliner's, the impact didn't knock them
down.

What brought them down was the steel being cooked by the fire from all the jet fuel.

Those towers turned out [un-fortuitously] to be particularly bad for this kind of thing.
Simply properly insulating the steel from fire would have kept the towers up.

And buildings made mostly from concrete don't even have that problem.

Originally posted by googlefudge
How about you halt work during a thunderstorm...

How stupid are you?

How stupid are you? Skyscrapers don't reach the ionosphere. Humy is equally ignorant. An astonishing electric charge from the ionosphere is not chance like thunderstorms, it is certainty. You are all idiots.

Originally posted by googlefudge
Given that the failure of one cable caused total catastrophic collapse of the entire
structure I find this fairly improbable.

Well they can add a few more cables.

I would also note that the steel tube thickness varied from 8mm to 34mm [according to the wiki article]. Now assuming that the thickness increases linearly [it wont] then making it 4 times taller leads to a thickness of the steel in the tubes at the base of 1.36 meters.
I doubt that would be how it would be done. I also doubt that the thickness of the tubes must increase linearly. The radio tower had just three main poles. When the thickness of the tubes gets too great it would make sense to use more tubes.

Now as cross sectional area increases as the square of the thickness, but the mass as the cube of thickness, then we know that we will actually get an exponential increase in thickness to support the increasing mass.
Odd then that we don't see any such shape when it comes to a 600m radio mast.
If we applied your arguments to a 30m radio mast, we would never expect to be able to build the Warsaw Radio town as it was.

Originally posted by Metal Brain
How stupid are you? Skyscrapers don't reach the ionosphere. Humy is equally ignorant. An astonishing electric charge from the ionosphere is not chance like thunderstorms, it is certainty. You are all idiots.

The ionosphere starts above 85km, we are talking about a 20~25 mile high tower,
it will never reach the ionosphere, so even if you were correct [you are not] you
would still be wrong and an idiot [which you are].


EDIT: and as for the cable...

http://www.mill-creek-systems.com/HighLift/chapter10.html

Discharging the Ionosphere

The charge production rate in the ionosphere ranges between 2000 and 6000 q/cm3/s. For an area around the cable of 1km x 1km and 500km in vertical extent this relates to 1x1025 q/s or 625,000 C/s. With a resistivity 10-4Wm for carbon nanotubes, a 20-ton capacity cable (2 mm2 cross section) would have a minimum resistance of roughly 5MW. For the cable to discharge the ionosphere at the same rate as charge is being produced would require a current of 625,000 Amps to flow through the cable. To produce this current a voltage difference of ~3 x 1011 Volts would be required between Earth and the ionosphere. The measured electric field under thunderclouds just before a lightning strike is 10 - 20 kV/m. If we extend this electric field up to the ionosphere (which does not occur but should be a worst case) we find the static voltage potential would be less than 2 x 109 Volts. At this voltage difference with no redistribution of charge in the ionosphere we could discharge an area 100m around the cable. Since we have assumed the most conducting cable possible (in reality it would probably be down by orders of magnitude due the epoxy sections) and the highest potential difference conceivable it is more likely that only a small volume of centimeters radius would show any affect from the cable's presence.

Originally posted by Metal Brain
How stupid are you? Skyscrapers don't reach the ionosphere. Humy is equally ignorant. An astonishing electric charge from the ionosphere is not chance like thunderstorms, it is certainty. You are all idiots.

Piece of advice, totally for free, take it or leave it. Calling the entire forum idiots is not going to advance your argument. Besides, after modifying it a little I actually supported that point about weather.