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While a space elevator is constructable on the moon or mars, making one for earth would needs exotic high tensile strength materials that we don't know how to build.

A launch loop, on the other hand, has many of the benefits of a space elevator; but the nicest feature is that it can be constructed from conventional materials. https://en.wikipedia.org/wiki/Launch_loop

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How about a active structure, like a space fountain?

rockets connected to each other ascending and descending constantly?

Iirc, Robert L Forward's variant was an electromagnetic cannon launching metal pellets, which were slowed down at the top and fired back down.

The pellets would go up and down like a juggler's balls was thrown.

Since you'd regain much of the energy when you slowed them down, it wouldn't be so energy expensive as it seems. And yes, you need vacuum pipes. And a stop in electricity would have side effects ("Timber!"). :-)

some kind of ubend, and the "pellets" are magnetised?

say we drop a rocket into this ubend and it redirects the energy back up into space?

and in orbit there are rockets that lift them the rest of the way, remove the passengers and then drop them again.

I was clumsily trying to explain Space fountains. :-) This do discuss the Forward thing and so on:

https://en.wikipedia.org/wiki/Space_fountain#History

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