I was watching the sun come up the other morning and started wondering about how we might tap into some of that huge rotational energy.
A bit of Googling revealed some actual work being done to use gyroscopes to provide a “base” against which that rotational motion might be exploited, but the gearing has to be so extreme that losses overcome the gains.
My math and physics abilities are too limited to assess another idea, maybe you can help:
What if we anchored a cable on the Moon and tied it to a sled running on a track at a convenient/economical latitude around the Earth? At the equator such a sled would be moving at about 1000 miles/hour, which should be able to kick up a fair amount of energy.
Would the limiting factor be cable strength? Would a cable strong enough be too heavy to support it’s own weight? Or what?
It occurs to me that the track wouldn’t even need to completely circle the Earth, since we could put some sort of aerodynamically steerable guide on it for leaving land masses and jumping deep oceans.
Yes, I should have also mentioned tidal power schemes in addition to the gyroscopic ones in the OP. But my question is aimed at identifying the practical problems associated with the moon cable proposal.
One big problem with the moon cable idea is that there isn’t any point on the Earth that remains at a contstant distance from any point on the moon, neither is there any track you could trace around the earth, to which you could attach a cable of constant length to any point on the moon.
From the POV of the moon, the Earth rotates and wobbles - your cable would have to be capable of adjusting its own length so as not to snap or go slack throughout the day or year.
Here are a few:No cable of anything like suitable length, strength and mass now exists.
If one magically appeared, attaching it to the moon would probably exceed the total difficulty of the 20 biggest engineering problems yet undertaken by mankind.
A sled running along a track at 1000 mph would demand some sort of maglev system far beyond any current technology.
If the track isn’t continuous (and making it so would be fantastically difficult) then you have the problem of “landing” your sled at 1000 mph and re-attaching it to its (necessarily high-tolerance) track.
The power generated would be diffused over 25,000 miles, making it tough to distribute in a useful way.
Most repairs would be enormously difficult (can’t stop - or even slow - this machine).
The cost of solving any one of these problems would be beyond enormous. The total cost of this project would so far exceed the value of the energy extracted as to defy calculation.
Thanks Xema, that’s what I’m looking for. But I’m not sure all of those are really that insurmountable.
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.
And the groundspeed could be anything, couldn’t it? Just build the track at non-equatorial latitudes. And the boom could be flown to the poles for maintenance, making it essentially stationary.
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).
There would need to be some kind of winch to deal with variations in necessary cable length, but those would be necessary to lower the cable in the first place and would seem like good candidates for being located somewhere between the Earth and the Moon.
I’m not sure I understand what the limiting factors on cable strength are, but it may be that gravity alone is enough to pull apart all known materials being dangled from space. Is that true?
Having a moving generator certainly limits the application of the power though. That’s a problem.
Maybe with the development of low-loss transmission media we could use the cable to tow a huge wind farm through the upper atmosphere and run the power down to a distribution station at the poles. That would avoid the problems with the track, too. Now we’re talking!
A space elevator could do it. You simply extend the thing out beyond geosynchronous orbit, and you can use the rotation of the Earth to fling ships or cargo at great speed. The Earth spins a ( VERY ) little bit slower, and the vessel goes much faster. You could tap into this energy and turn it into electricity if you wanted I guess, but it would seem to be beside the point of building a space elevator in the first place.
This guy calculates that tapping Earth rotation for the equivalent of current US energy consumption for 1000 years will lengthen the day by .0007 seconds.
Granted, you can see the flecks of spittle coming off the page, but I’m sure the available energy is pretty enormous.
Trouble with that is: if we had the ability to do it, our energy consumption would not remain constant for the next 1000 years - a notionally unlimited source of power would encourage runaway increases in consumption.
Let me see if I’m understanding this. We are talking about a track that encircles the Earth, with some sort of platform on it, from which there is a cable that stretches to the moon and is attached to a similar set up there? Is that right, and if so, how would that generate energy?
Rather than having a 250,000 mile long cable then, couldn’t it be attached to a fixed artificial satellite, allowing the Earth’s 1,000mph rotation to move the track beneath the generator platform?
Ain’t no such thing. Satellites stay in orbit because they have momentum. As soon as you start pulling on them with cables, they lose that momentum, fall down and go boom.
The Earth’s rotational energy is being transferred to the Moon, through tidal coupling, causing it to recede from the Earth. We can extract a lot of energy without bringing the Moon closer.
An artificial satellite would have to be further than geosynchronous orbit to not be (eventually) pulled in (which would be bad). Also, it would need to be massive enough to raise its own tide, to extract Earth’s rotational energy. Obtaining this satellite, and moving it into position, would itself require a lot of energy.
I propose we replace the track and platform with fluid in some kind of channels, then use gravitational coupling to replace the cable to the moon, then harness the resulting movement of the fluid by means of turbines, or something.
If only we didn’t have to build it all from scratch, though.
