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Lunar Space Elevator Instead?
koa writes "We have all seen articles on building a Space Elevator on the earth, how about this article about experimenting with the Moon first since the technology we have available to us is sufficient, as the Moon's gravity is 1/6th that of Earth's (the cable weight would require less exotic materials such as carbon nano-tubes). One could make a very good argument for commercialization of Space if getting materials to and from the Moon's surface was vastly cheaper and easier."
This theory has been investigated in depth in a recent book, http://www.amazon.com/exec/obidos/ISBN=014032870X/ 002-2420335-1812868
Business Voyeur
Bah! The idea is pure lunacy.
Earth is where all the people and materials are. Building a space elevator on the moon would be like building a superfreeway from one point on antarctica to another point on antarctica: pointless as there's noone around to use it, nor anything to transport over it.
If you are going to just say "move people and materials from earth to the moon, then go from there" - you still have to escape Earth's gravity, which is the f'ing point of the earth-based space elevator to begin with.
Unless we have a working lunar colony/base, it's useless.
The whole point of the elevator was to make it easy to get out of Earth's gravity well. To get to a lunar elevator, you still have to do that.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
...how about long term stays on the lunar surface? As in months or years.
How about a lunar colony instead of a freaking space station?
Would seem to be a prerequisite for anything approaching a lunar space elevator.
And long term lunar stays would provide valuable practice for something like a martian colony.
Tons of people are complaining that this is a useless gesture, as the ultimate point is to transfer material out of earth's gravity well. But they're missing the point of building on the moon first. Think of it as a proof-of-concept. Once we have a working elevator in place, we can then test its performance and learn a great deal about how to eventually build one on earth.
An effect of O'Neill's proposal is the creation of space settlements which could house thousands of times the land area of the Earth from asteroidal materials alone. The creator of the space-settlement FAQ, Mike Combs, says in that FAQ to the question "Is space settlement a solution to the overpopulation problem?":
This is ironic since O'Neill himself described just such a transportation system and projected depopulation of Earth to require an infrastructure not much larger than that supporting the commercial airlines.Seastead this.
BOO TERRORISTS!
You must be american. Get over it - or take some lessons from countries (Spain, England) that have had "terrorists" to deal with for many years - and you don't see them going bananas over it and mentioning it in all sorts of contexts.
it's in my head
"A lunar space elevator would work differently than one based on Earth. Unlike our own planet, which rotates every 24 hours, the Moon only turns on its axis once every 29 days; the same amount of time it takes to complete one orbit around the Earth. This is why we can only ever see one side of the Moon. The concept of geostationary orbit doesn't really make sense around the Moon.
There are, however, five places in the Earth-Moon system where you could put an object of low mass - like a satellite... or a space elevator counterweight - and have them remain stable with very little energy: the Earth-Moon Lagrange points. The L1 point, a spot approximately 58,000 km above the surface of the Moon, will work perfectly."
In other words, RTFA.
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The comments on this topic make it clear few, if any, RTFA. 90 percent of the comments should be modded "Redundant" since the article answers the very questions posed.
Geekdom sure ain't what it used to be.
Ignorance is curable, stupid is forever.
To everyone that says a lunar elevator would be useless right now, did you read the article? He says we can make this thing right now. With current materials, and launch cababilities. All that it needs is money and people to build the flipping thing and it can be done. Now.
And just because it's on the moon and not earth, doesn't mean it can't be quite useful. Imagine being able to send lunar rovers with return capabilities without having to give them heavy expensive fuel for the return trip. Just hop on the elevator and from L1, just a small thruster push and back it comes.
If Mr. Edison had thought smarter he wouldn't sweat as much. --Nikola Tesla
The moon rotates once every thirty days.
It also orbits the Earth once every thirty days - in other words, it's locked in a 1:1 resonance with the Earth. This is of great benefit in this case!
A little background:
Space elevators need to remain stationary with respect to the body that they'll be attached to. With the Earth, that means you need to be rotating at the same speed as the Earth - in other words, GEO.
With the Moon, however, you can either be rotating as fast as the Moon, or orbiting as fast as the moon, because the moon rotates at the same angular speed as it orbits! And there are 5 places where that occurs - the Lagrange points.
From any one of those points, the Earth and the Moon are stationary in the sky - that is, you don't see either of them moving with respect to each other. Since the Moon's rotation is defined by its orientation with respect to the Earth, therefore, you don't see the Moon rotating. That is, you're in something that's exactly the same as GEO.
Of the 5 Lagrange points, obviously L3 is silly - it's on the opposite side of the Earth as the Moon. So that won't work.
L2 is similarly silly - it's on the opposite side of the Moon as the Earth. Could be useful for sending things to interstellar space, but not for Earth-Moon transits.
So you're left with L1, L4, and L5. Obviously if you're talking about getting things from the Earth to the Moon, you'd want the one that's deepest into Earth's gravity well - and that's L1, "gravitationally halfway" between the Earth and the Moon. And that's what's being proposed.
One helpful thing is that L1 is unstable - orbits tend to drift away from there. However, an elevator tethered to the moon at least anchors one of the unstable directions (radially towards the moon/away from the moon), and I'm not sure if the perpendicular direction is unstable as well. So it may be that an elevator in that position is stable, and that unpowered objects will tend to move away from the elevator. You'd have a natural deflection mechanism. Pretty interesting!
Actually, a combination of an L1 and an L2 elevator could be quite interesting, though you'd have to build something like a railway around the Moon. Once you do that, though, you could go out past the L2 point, and you could sling yourself into interplanetary space. I'd have to work out how much of a boost you could get, but Mars orbit seems quite reasonable.
It's not as good as a terrestrial elevator (because the Earth rotates so quickly, so you can steal more of the Earth's angular momentum), but it's certainly currently feasible.
But you are absolutely right. Having no atmosphere, the Moon is the ideal place to put a railgun. Besides Heinlein, many other authors have used that concept, among them Gerard K. O'Neill, who popularized the L5 orbit concept.
RTFA. The logistical problems consist of launching 7 tons of kevlar cable to the L1 point 250 000 km from Earth. I am not saying there are no technological obstacles to overcome, but compared with Cassini probe or Mars rovers this is a piece of cake. There are existing rockets with that launch capacity, it doesn't take long to get there, it's cheap, easy and we get to test the space elevator prototype. There is simply no reason not to do it in the next few years.
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I wrote the article, and now I'm reading through the Slashdot comments, and they're killing me. Didn't anyone actually RTFA?!?
Let me clear these up...
1. The cable would be 58,000 km long. This is the distance from the Moon to the L1 point, which is the balance point of gravity between the Earth and Moon. The Earth pulls the elevator straight using its gravity. If you looked at the Moon from the Earth, the space elevator would always be at exactly the same place on the Moon, always pointed directly at us, like we're tugging at it with the Earth's gravity. This has nothing to do with centrifigal force, like an Earth-based elevator where the counterweight keeps the cable taut.
2. Because of low gravity on the Moon, you could build the elevator with commercially available materials on the market today, like Kevlar or M5. The cable would be light enough that it could be launched on a single heavy lift rocket available from Arianespace, Boeing or Lockheed Martin.
One launch = one lunar space elevator
3. You could connect a second cable to the Moon's south pole, so the two cables form a V, and then bring up water ice from the south pole. This would put water, air and rocket fuel into high Earth orbit at a fraction of the price of bringing it up from Earth.
4. As you make the cable longer, it allows you to kick objects into high-Earth orbit. You could transfer materials from the Moon into orbit for relatively little fuel.
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Almost the entire highlands surface is composed of plagioclase. You can extract glass and maybe aluminum from that. You might be able to create dopes silicates for electronics, but you'd probably need to bring trace elements from earth. The Mare are a little better: they're basalt. You can probably get Iron there, maybe some other metals as well. Maybe not. In general, there won't be much in the may of heavy metals, because the moon doesn't have mantle convection and volcanism to make them accessible. It certainly doesn't have hydrocarbons, which we need a lot of.
We could probably mine the moon for a few things, but most of our materials would still come from Earth.
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