Pulley Elevators

for the Launch Loop and the Space Elevator

A pulley elevator is a simple-appearing way to provide both support and lift in a space elevator or a launch loop. The vehicle can be passive, containing no more than some kind of automatically actuated clamp so that it can release from one moving elevator cable and clamp onto another.

Real life is never that simple. The main drawback for an elevator cable is that if it is tall enough and the cables are closely spaced, then they can easily come close enough to abrade each other. The design must prevent this. The other problem is the same as all long cables, where force changes are rapid compared to the speed-of-sound propagation time; the analysis is complicated, and involves not just the static stretch of the cable, but the inertia and mass flow rate.

Megastructure cables and elevators face yet another complication; their interaction with a nonlinear gravitational field in a rotating frame. Very long cables may move in ways not anticipated by a designer focused on elasticity and strength of materials, particularly movements radially from the expected straight-line path. Electrostatic repulsion may also play a role.

Limiting Case - a moving cable without external tension

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Limiting Case - a non-moving cable around pulleys

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Electrostatic Repulsion

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The Steady State General Case - moving cables around pulleys, without velocity change

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The Dynamic General Case, with velocity change

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