Related to the
Space Elevator concept, the rotavator provides easier access to
orbit using a
high-tensile cord, probably made from
carbon nanotubes. There, however, the similarity ends. Principally, the cord is not
geostationary. The cord as a whole orbits faster than the planet spins, but the cord itself spins so that whenever an end is close to the surface, that end is moving slowly in respect to the surface. One can imagine a collossal wheel rolling across the surface of the planet; the rotavator would be a spoke of this wheel.
This design has several interesting features:
- No climber is necessary. To get from the bottom to the top, you grab on and hold on. This makes using it much much easier than on a space elevator.
- If the rotavator does not dip down to the surface but merely to an airplane-attainable high altitude, you do not need to worry about severe near-surface weather conditions damaging the cord.
- On the other hand, getting on board ceases to be trivial.
- The cable will need some force to keep it up, unless the up and down loads are mass-balanced. However, since this is already in orbit it can use high efficiency and high specific impulse rockets instead of high-powered ( and thus necessarily low efficiency, low specific impulse) that a load would need to get into orbit in the first place. Or one can use electrical forces interacting with the Earth's magnetic field, a.k.a. skyhooks.
- The rotavator wanders around the planet and can pick up from a variety of locations, with little surface equipment. This is both good and bad (its omnipresence would make it easier for an adversary to destroy). One can choose a path which will produce a consistent set of stops, so drifting around everywhere needn't be a problem.
- The rotavator can deviate from the equator very easily (unlike a space elevator), though it will work best at one chosen latitude (the latitude at which the surface's velocity matches the rotavator tip's velocity).
- Like a space elevator extending significantly beyond the geosynchronous point, the rotavator can actively hurl things into space.
Several designs have been proposed, using various propulsion methods. One design even has two rotavators meeting periodically to swap loads up like a Jacob's ladder. This provided much faster hurling motions than other rotavator and space elevator designs.
Either way, we're still waiting on a means of making a macroscopic cord with the required strength (yeah, we're still working on a method to get the first meter - let alone the thousands of kilometers needed to make this work).