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For a functioning space elevator would the top of the elevator be in geo-stationary orbit, or would it be the centre of mass?

Grumble wrote: Thu Apr 20, 2023 8:42 am For a functioning space elevator would the top of the elevator be in geo-stationary orbit, or would it be the centre of mass?

The centre of mass would be just above geostationary orbit in order to keep the system under tension.

What I never quite understood is why the elevator would stay straight. At least it is usually depicted as straight, but maybe that is a simplification.

Isn't that the effect of said tension, to keep it straight?

It wouldn't stay that straight - there'd be plenty of flex in it (which among other things would allow it to move to avoid satellites and space junk, with some amount of control). But the tension would help keep it straightish.

TimW wrote: Thu Apr 20, 2023 9:11 am Isn't that the effect of said tension, to keep it straight?

That is the intention of course. Powerlines hanging between pylons are also under tension but doesn't mean they are straight. An idealised space elevator with a massless wire and no payloads would be straight, but I just wonder what the effect is of the wire mass, and of perturbations to the system like sending up a payload.

That one they built in Sri Lanka was built outwards in both directions from the geo-stationary orbit, wasn't it? So they used the other half as a slingshot, which I couldn't get my head around.

lpm wrote: Thu Apr 20, 2023 10:59 am That one they built in Sri Lanka was built outwards in both directions from the geo-stationary orbit, wasn't it? So they used the other half as a slingshot, which I couldn't get my head around.

There's something wonderfully perverse about building a highway to space that terminates on an island that's far from the usual shipping routes.

Even better would have been to build it from somewhere like West Papua.

dyqik wrote: Thu Apr 20, 2023 11:14 am

lpm wrote: Thu Apr 20, 2023 10:59 am That one they built in Sri Lanka was built outwards in both directions from the geo-stationary orbit, wasn't it? So they used the other half as a slingshot, which I couldn't get my head around.

There's something wonderfully perverse about building a highway to space that terminates on an island that's far from the usual shipping routes.

Even better would have been to build it from somewhere like West Papua.

If the British had built it they'd have decided at some point to just not bother bringing it all the way down to the ground.

dyqik wrote: Thu Apr 20, 2023 10:11 am It wouldn't stay that straight - there'd be plenty of flex in it (which among other things would allow it to move to avoid satellites and space junk, with some amount of control). But the tension would help keep it straightish.

Thank you, this is all very useful for my plans.