Item — HN Reader

A tower extending 100 Km up would be a great point for scientific observation. But to be a space elevator replacement you would need a tower that could bear load up to geosynchronous orbit.

That's not easy.

I have read about using a series of balloons for lifting - a more rugged one for low atmosphere, then switching the cargo to a lighter one designed to operate in the high atmosphere and then propelling the cargo with something like an ion engine to orbital speeds and increasing heights where the balloon would give less and less lift (and offer less and less drag).

Looks like an interesting idea.

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But to be a space elevator replacement you would need a tower that could bear load up to geosynchronous orbit.

That's not what I'm suggesting.

Build the tower as high as is practical, say 100 km. Then launch your space elevator satellite and lower the cable down to the top of the tower.

The cable has to support its own weight, so it has to be thicker at the top than at the bottom. It turns out that the cable thickness has to taper exponentially (basically, this amounts to a rotation of the catenary problem).

So not having to support the last 100 km of cable at the end translates into a weight savings along its entire length.