Space elevator stability

Andrew S

Hi.

This may be really basic, but would appreciate your help. Is a tower whose height reaches a geostationary orbit at 35,000km's altitude or so more stable that one which doens't quite reach that height? So, say you are building a tower, decide you'd like it more stable, so should you go to the effort of making it a bit taller in order to take advantage of some sort of low gravity pull from the top?

I guess the question is whether there is such a 'pull' from orbit, or if the downward pressure is just less on the higher portions....

Thanks heaps.
Andrew

Clausius2

Are you taking into account ground vibrations and wind force? A number: The highest skyscraper in Madrid is 200 m high (not too high by the way), but its top part oscillates about 1 m in a normal wind day. Definitely I think that building such an "space elevator" is "engineerably" impossible.

LURCH

Yes, the tower would be much more stable if you built it out to geostationary orbit. Just keep in mind, though, that the top of the tower would have to be built beyond GSO to achive this added stability. Whatever portion of the building's weight is above that altitude, that's the portion that will help steady the tower (kind-of the way a string gets steadied when you pull on both ends). Also, this only works if the tower is spot-on the equator.

Andrew S

great, thanks.

Understand this is impossible with today's technology - it's a sub-plot in my book.

The figures I'm thinking are that they were building the tower to 25,000km, found that it would be more unstable than they thought (due to frequency of hurricanes and Tsunami in the projected future), and therefore decided to build it up to 40,000km, to stabilise in the way described.

Does this figure out okay?

Thanks for the equator tip . . . will have to locate it in Africa or something, as I'm planning on most of the Pacific islands having sunk....

cheers,
Andrew

enigma

If the tower is only to Geosynchronous orbit or lower, then it will collapse. Every part of the cable which is at an orbital period of 1 rotation/day (like the entire elevator would be) and an altitude less than Geo-synch will eventually fall to earth. You need a counterweight past GEO to hold that part up.