Getting at Earth's rotational energy

[Xema]

@sunacres

I’m thinking the Earth end of the cable could be fitted with a steerable, winged fitting that would work something like the hose connector on mid-air refueling booms, allowing it to be “captured” by openings in the track.

This “flying” cable end will probably need to be substantial, to deal with the enormous drag of a cable moving at high speed through the atmosphere.

And anything traveling any appreciable fraction of 1000 mph (i.e. bullet velocity) is going to be a bitch to deal with.

I’m not sure I understand the difficulty of anchoring a cable to the moon.

The difficuly part is not so much anchoring it as getting it there, intact and connected to the earth. (Or lowering it, as you suggest, from some intermediate station.)

There would need to be some kind of winch to deal with variations in necessary cable length

Indeed - and it will need to be an impressive and powerful machine. Every 28 days the moon’s distance varies between about 363000 km and 405000 km. That’s 42000 km each way, for an average speed of 125 kph, with the peak probably twice that. It has to maintain the cable’s tension all the time (and that tension will necessarily be very high, to cope with atmospheric drag and to generate meaningful amounts of power). If this winch is anywhere but on earth, getting sufficient power to it will be quite a feat. One operational glitch at the winch probably means a broken cable.

[Telperion]

@sunacres

I’m not sure I understand the difficulty of anchoring a cable to the moon. Heck, as long as we’ve got plenty of cable we could just loop it around (I understand we’d still need to cut a pretty expensive groove for it).

For one thing, even if we dare to imagine that a strong enough cable could be produced that weighs only one kilogram per meter, we’d still need to devise a way to send some 400,000,000 kilograms of cable to the moon. I reckon that part might be a bit of a problem…

[Mangetout]

On top of everything else, the system has to work without going wrong, pretty much indefinitely. How, for example, do you maintain a winch that is reeling in or out massive, substantial cable at a rate of ~125kph, whilst also travelling at three times the speed of sound?

[sunacres]

@Telperion

For one thing, even if we dare to imagine that a strong enough cable could be produced that weighs only one kilogram per meter, we’d still need to devise a way to send some 400,000,000 kilograms of cable to the moon. I reckon that part might be a bit of a problem…

I guess that’s the bit I’m struggling with. Don’t we just need to get enough cable out there to start pulling up more cable (from the poles where the whole bullet problem is minimal)?

Couldn’t the entire length of cable that is dipped into the atmosphere be fitted with wings to provide continuous lift, steered to a latitude with manageable velocities, then trail windmill generators?

I can see the track has to go. Clearly. That’s right out. But I’m still liking the upside down kite idea.

[WarmNPrickly]

What about a giant foucault pendulum, or a billion small ones?

[sunacres]

@WarmNPrickly

What about a giant foucault pendulum, or a billion small ones?

That’s the idea behind the link posted above. I’m interested in fleshing out the problems of cable-based strategies, and the feedback so far has been terrific. Thanks to all who have contributed, particularly Xema, Mangetout, Talperion, and really, everyone.