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Tech Level: 14

A Rotovator is a spinning orbital tether built on a truly gigantic scale, designed to reach down from space into the lower atmosphere, or perhaps even to the surface of the Earth, pick up and drop off payloads directly. The orbital altitude of the cable’s center of spin is equal to half the length of the cable.

The Rotovator would be orbiting along the equator, perpendicular to Earth’s surface. The rotational velocity of its tips can be matched to the rotational velocity of Earth’s surface spinning under it. Both the forward motion of the tether in its orbit and its carefully timed rotation rate can result in its lower tip "hovering" over a certain fixed point on Earth for a few minutes, allowing smooth transfer of cargo.

It is important to understand that even though the word "hover" is used above, the tether of course never stops spinning, just as the surface of the Earth under it never stops rotating. But the forward orbital motion of the rotovator is synchronized in such a way with its spin that the lower tip "glides" over a fixed spot on the rotating Earth, making it seem stationary for a few moments to observers on the ground. In fact, because of the scale and choreographed motion involved, people on the ground could never tell the rotovator was in fact rotating by eyeball alone; all they’d see is a gigantic column of material reach vertically down from the sky like God’s own arm, pick up its cargo, and retreat back up in exactly the same way.

Robert L. Forward in his novel Timemaster gave extensive details about a rotovator 8000 miles long that "touched down" into the lower atmosphere to pick up cargo and passengers flown up to it on specially-modified jets. This rotovator’s orbit and spin were designed in such a way that it set down three times per 24-hour period. Rotovators need not always be quite on this scale, but a length of several hundred miles is probably minimum.