Giant leap for space elevator tech!

You cannot use the space elevator to give objects that go up an extra push. They have to do that themselves. Because, momentum builds and the space elevator would come down.

 

Well, this comes down to managing the oscillations. Whenever anything travels to the top of the elevator, its momentum gain as it travels up will be transferred to the elevator which, because it is in a stable equilibrium, will set up oscillations. Yes, if these oscillations are allowed to grow, they will bring the structure down. And since most of the elevator will be beyond the atmosphere, it seems that the oscillations will experience very little damping.

A natural way to control the oscillations would be to control the velocity and timing of ascending objects very carefully so that the next launch cancels out, as much as possible, the oscillations set by the previous one. I'm just not sure that it would be very easy to set up in practice. Then, once the object has reached the apex, above geosynchronous orbit, it merely needs to let go to be placed in orbit. It should then have some thrusters to correct its orbit later so that it doesn't smack into the space elevator after a few orbits (it may take a little bit for the two to line up again).

 

That might work if there was only a single oscillation traveling along the length of the elevator. But, that won't be possible, as each launch (and many other things) would create harmonics if they're not a totally exact counter.

Adding elastic elements wouldn't help (if the would even be possible), dampers would have to be extremely massive and so aren't feasible. Which leaves adding rocket engines everywhere to dampen the vibrations. And control centers, fuel pipes, etc.

So, a cable in the form of a simple strand wouldn't work in any case, unless it's extremely stiff and not anchored.

Btw, you could move elevators up and down with impunity, as long as they have the exact same mass all the time. But people walking around would create vibrations, which would build or reduce other harmonics.

 

Right, I expressed this concern back on page 1. We could technically damp the harmonics by waiting until they loop back to the alternate phase they were in when produced before launching the next one, but that could take a long while, and the little damping that does occur may make it impossible. Carefully controlling the velocity on the way up may allow us to launch more often, but even then it's going to be an incredibly difficult engineering problem.

Then there's the issue that the elevator is going to intersect the orbits of nearly every satellite up there eventually. That will make it a mite difficult to keep the thing up once deployed.

 

Look who's now suddenly promoting the idea after dissing it a page ago...

Vibrations must be handled in a way or another anyway, whether we would launch anything from the structure or not. Of course their magnitude will be a whole lot larger if we do, but in time the smaller vibrations from atmosphere and from simply using the elevator would build up anyway - right?

Why would we want to install rockect engines in fixed locations? Can't we haul a large load of crap up with the elevator, and jettison it in pieces out from the crawler at suitable moments to dampen the oscillations while the elevator is moving?

 

I'm not promoting it. You might want to read what I wrote more thoroughly. I still think it's probably unfeasible.

Vibrations from launching off a rigid structure would need to be considered, but aren't even in the same ballpark of difficulty as dealing with them on a space elevator.

Since both structures are almost entirely above the troposphere, no, the weather isn't going to play much of a role.

That seems like it would cause more problems than it solves. You definitely don't want to throw extra junk into orbit that could potentially collide with the elevator at a later date.

 

I suppose it really depends what goals you want to attain. I don't think you'd want to have those fixtures up there for extended periods of time anyway.

You could imagine contracting the fixtures mechanically to lower altitudes when its not needed.

In fact, depending on cost (whoever that works out), it might be a sort of one and done deal. You build the elevator, send up a bunch of satellites cheaply, and then bring it down (violently if need be, you could just let the thing collapse into an ocean or something, since it makes sense to build it in the presence of water anyway).

 

I was referring to the elevator all the time. If it is to be built, vibrations need to be taken into account, whether we use it for launches or not.

[Dr.Evil tone]
Well let's have some friggin' laser beams vaporizing the jettisoned junk then. Do I really have to think out everything for you people? Throw me a bone here.
[/Dr.Evil tone]

Or for less cool option, burning the junk in atmosphere.

 

Right, but new vibrations aren't going to be generated except when we do send things up the elevator.

This is how it'll work for junk that's released much below the geosynchronous orbit point. But too high and they just won't hit enough atmosphere to decay before coming around and smacking the elevator.

 

Would it be outrageous to suggest that if the elevator gets built, it should be used for its intended purpose?

 

You said "whether it is to be used for launches or not".

 

And you said "vibrations aren't going to be generated except when we do send things up the elevator."

Both comments imply that simply using the elevator to lift things into orbit will cause oscillations.

(A case of misinterpreted terminology, I suppose. By launching, I mean launching to escape orbit, which we were discussing earlier. As in using the elevator as a fling. Not just lifting stuff from surface to geostationary orbit.)

 

Okay, that's fine. But my earlier statements on this regard were that a single launch might potentially cause such significant oscillations as to put the elevator in jeopardy, whereas a lazier lifting to orbit shouldn't be so bad (this is more intuition without doing any calculations, though...).

 

Maybe the =y could change the rate of ascent so harmonic oscillations do not set in.

 

Well, the oscillations will set in no matter what. The issue, however, is how big the amplitudes are and which modes are excited. My suspicion that a faster launch is worse stems from the fact that there will be less time to "correct" the velocity of the launched object, so instead of going along the elevator, it'll just drag the elevator along with it as it attempts to ascend in a straight line (note: an ascent along a straight elevator is *not* ascent in a straight line, as the Earth is rotating). But I suppose I'd need to do some calculations to figure out exactly how it works.

By contrast, if it went up more slowly, the elevator would have some time to oscillate back and forth during the ascent, meaning that the increase in amplitude wouldn't be monatonic: sometimes the object would be increasing a mode's fluctuation, sometimes decreasing it. With a launch it'd be all one way.

 

I meant you might be able to change the velocity to cancel out oscillations or something. It might be one of those unsolvable problems though where it gets so complicated so quickly you cant really hope to mathematically solve it let alone in real time.

 

Well, you could probably partially do this for the medium-wavelength oscillations, as long as your vehicle wasn't traveling too fast. But the longer-wavelength oscillations, I think, would require a second launch, and the shorter-wavelength oscillations probably couldn't be actively canceled.