I haven't done any calculations but it sounds like you'd need an awful lot of power to lift the fuel pipes. You'd need enough thrust from each of the platforms to keep the pipes in position and they'd have to be heavy to make them safe. A fuel leak or failure in any section would have serious consequences.

Is the thrust needed to lift a very heavy object at 1.5 km/s going to be less than that needed to lift a much lighter rocket at 7.7km/s?

I think a more permanent structure like the space elevator would work out cheaper because you only need to erect it once, not every time you do a new launch.

An interesting idea but it will only be proven by the calculations that you need to back it up with.

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Spike
:)