Denial or Ignorance Amongst NASA Scientists?

The designers of the Tacoma Narrows Bridge , here in Washington State, USA, were pretty confident in their design, too. Surely you've all seen the video of what happened when the wind blew.

It's a good thing I'm not a terrorist, because I know just how to attack that ribbon for very little cost—and without committing suicide. I think a three-rope design would be slightly less vulnerable, but look what happened to the twin towers; any kind of space elevator will be a whole lot easier to take out than they were. Round-the-clock security will more than double the cost of the project. Damn! I wish I were wrong about this; it was such a wonderfully elegant idea!

PhilJ wrote: ". . . it was such a wonderfully elegant idea!"

Don't give up on the space elevator idea so easily. Terrorism will not be around forever. The world will become peaceful again. Indeed it has been becoming increasingly peaceful.

Terrorism is specific to perceptions of particular extreme injustices, such as many muslims feel at the present time of apparent American and Israeli occupation of Islam's holiest sites in: The Arabian Peninsula, Iraq, Israel.

Throughout my lifetime, there have been terrorists kicking Europeans out of their colonies around the world. Now we see the same happening to Americans, only because they appear to be doing what Europeans were doing earlier.

It will eventually blow over for Americans, just as it did for Europeans, hopefully . . .

Also, I wasn't knocking the space elevator idea, only the quoted generalisation, and the Space Shuttle, from a vibrational point of view.

Vibrations may not be an insoluble problem so far as the space elevator is concerned. For one thing, unlike the Space Shuttle, it is not attached to "a controlled explosion". For another, it does not have to resemble a tuning fork, again unlike the Space Shuttle.

The same material providing the space elevator's tensile strength would also make it extremely stiff and resistant to vibrations. There would be many design possibilities for dampening any space elevator would vibrations also, just as we do for cars and other structures.



Peter Nielsen

Email: uusi@hotkey.net.au
Post: 12 View St, Sandy Bay 7005, Australia

I do believe it would be possible to control vibrations of a 3-rope space elevator, but the proposed ribbon would present many times greater surface to the wind. It would go the way of the Tacoma Narrows Bridge. The dynamics of a ribbon in the wind are such that a small eddy develops on one side of the windward edge. The eddy grows, twisting the ribbon toward the eddy. When the eddy reaches its maximum size and strength, it breaks free and travels downwind of the ribbon. The ribbon then recoils past center, and an eddy forms on the opposite side. (I have experienced a similar oscillation while riding a motorcycle in a sharp turn with a full fairing windshield (attached to the handlebar); my shoulder still hurts when I think about it.)

This oscillatory motion may start on one small section of the elevator and grow until all of the ribbon that is in the atmosphere osillates in unison, sending waves up toward the top of the elevator. Any active devices that might be added to dampen the oscillation would add significantly to the weight and cost of the elevator.

A rope in the wind produces audible frequency eddies in its wake, as evidencesd by the way power lines howl in a gale. Despite the high frequency, such vibrations are an energy source which may drive a much slower resonant oscillation along the length of the rope. I believe such oscillations may be controlled affordably by passive dampeners at wide intervals.

As for that half-baked idea that I mentioned on August 14, I believe it could work. Instead of discarding tons of carbon fiber rope with each satellite, the rope can return to the bottom of a contiunous loop. Geosynchronous orbit is about 36,000 km above Earth's surface. If the top of the loop were a bit more than twice that high, a 1 tonne satellite at the top of the loop could lift another 1 Tonne satellite off the ground. Make the loop a few thousand kilometers longer still, and you could launch a continuous string of 1 tonne satellites with no significant power input except what the Earth generously furnishes.

Of course the price tag for the first space elevator is high enough, already. The self-launching loop would involve four or five times as much carbon fiber. Besides, orbits that high are less in demand than geostationary orbits---at present. But they might be very useful as preparation for trips to the moon and beyond. Make the loop just a little longer, and you could launch satellites directly to L5.

P.S.: Make that endless-loop space elevator just a little taller and not only will it launch satellites with no energy input, but it can actually generate electric power as an added bonus!

I've been reading the Space Elevator forum . My ideas, above, are old hat.

Oops! The math says the Space Elevator (SE) would have to reach far beyond the moon before satellites at the top end could balance the force needed to lift those near the bottom. Obviously, the moon would collide with the SE periodically; so that scenario is impossible.

It is still likely that some future SE might be a continuously moving conveyor belt. The first one, though, will be thicker or wider near the geosynchronous orbit height, where the tension will be greatest. A loop would need to be uniform strength all around, which requires stronger materials. Manufacturers are still struggling to achieve the material strenght needed for a one-way strand to support its own weight.

I have not yet found any discussions about advantages of a ribbon instead of a rope.

The page listing topics under "Artificial Structures on Mars" indicates the last post on this thread was by xterrester, 25 Aug 2005 05:16:42.
But the latest post that displays when I view the thread is my post, 22 Aug 2005 : 17:00:37. I had the same problem a couple of days ago on a different thread.

[edit]After posting this msg, it appears after my 22 Aug post; xterrester's 25 Aug post is missing.