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Fans of sci-fi and fringe tech may already be familiar with the idea of the "space elevator," which is pretty much exactly what it sounds like — and totally impossible with today's technology. But a pair of scientists think they've found an alternative: a Moon elevator. And it's slightly less insane... technically.
The idea of the space elevator, first explored in detail by Arthur C. Clarke in his novel "The Fountains of Paradise," is essentially a tower so tall it reaches space. Instead of launching ships and materials from the surface of the Earth to orbit, you just put them in the elevator of this tower and when they reach the top, somewhere about 26,000 miles up in geosynchronous orbit, they're already beyond gravity's pull, for all intents and purposes.
It's a fun idea, but the simple fact is that this tower would need to be so strong to support its own weight, and that of the counterweight at the far end, that no known material or even reasonably hypothetical one will do it. Not by a long shot. So the space elevator has remained well on the "fiction" side of science fiction since its first proposal. Hasn't stopped people from patenting it, though.
Source: https://techcrunch.com/2019/09/12/scientists-propose-spaceline-elevator-to-the-moon/
(Score: 1) by sfm on Sunday September 15 2019, @05:05PM (2 children)
The main article states "From the surface of the Moon to geosynchronous orbit ..."
This would mean the docking end of the cable "moves" around the earth with
the same period as the moon, which is a significantly different speed than that
of an earth geosynchronous satellite.
Bottom line, it will be a real pain in the neck to rendezvous with the earth end
of the cable.
(Score: 2) by Immerman on Sunday September 15 2019, @06:24PM
I think "geosynchronous" was a mistake. It is relatively easy to have the Earth-end of the cable terminate at an altitude where it's matching tangential (linear) speed with the Earth, even though the angular speed is synced with the moon. Basically, it'll still move overhead as seen from Earth's surface, but if you launch perfectly vertically and time it just right, you'll match speeds when you rendezvous with the end of the cable without having to do any horizontal accelerating at all.
(Score: 3, Informative) by Immerman on Thursday September 19 2019, @02:20PM
After reading the original paper, you're correct - the bottom end of the elevator is at geosychronous orbit, but moving far too slow.
That's not actually a big problem though - in general, any object climbing to a new orbit is going to be going far to slow to stay there. You give yourself a boost of speed from a low orbit, which sends you on an elliptical orbit whose high point grazes the desired orbit, and then give another boost to get the speed to stay there (see: Hohmann transfer orbits).
To rendezvous with the tether, you just wouldn't give the second boost. There is a question as to whether something dropped from the end of the tether would actually be in a stable (highly elliptical) orbit, or on a collision course with Earth. Given that kinetic energy is only 1/6th of the total specific orbital energy at geostationary, I strongly suspect that the orbit would be stable - or would become so with only minor additional thrust, which would make things much easier.
It would make for a much more precise docking maneuver than matching speed with something in a shared orbit - you have to be in exactly the right place at exactly the right time, going exactly the right speed. It would still be a lot more forgiving than docking with a skyhook though, and some sort of "docking harpoon" mechanism could add a lot more room for slop to the maneuver.