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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."
Northerly moon base? The best-argued location I ever saw was for the lunar south pole; permanent sunlight, water, and constant ambient temperatures of -20degC.
But, yes, a lunar space elevator would have to have an equatorial ground station, and the lunar equator is far from the best place for a moonbase.
"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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Sorry to nitpick, but you should really call it the "far side" of the moon. The far side is not permanently in shadow any more than the near side is, so "dark" is a misnomer.
"However, the moon does not rotate on its axis, the tidal forces because of its interaction with Earth mean it is always pointing towards earth, hence, we always have a dark side of the moon."
No, it rotates once per revolution. If it didn't rotate at all, there WOULD be a dark side to the Moon, rather than just a far side.
No, the idea has never really been to put people into space; there are too many problems with this. As noted in the article, the time of the travel and cosmic radiation is a large problem with human transport in elevators. Even more so in the earth case, where we have the van Allen radiation belts. With the elevator in place at the earth, we'd have a tremendous goods shipping facility. Human travel comes much later.
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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The elevator does not go from the earth to the moon.
The moon is not in geostationary orbit around anything. It rotates to keep the same side towards us.
The top of the elevator would be at Lagrange point L1, which is the point at which Lunar gravity and Earth's Gravity are balanced. It is balanced, but unstable. Stationkeeping would be necessary.
People would rarely use the Lunar Space Elevator for personal transport. It would be only for cargo. (Similar to the long awaited Space Elevator from Earth)
No, you can't ride on it.
No, you can't ride on it.
Getting materials off of the Moon is useful. People can explain how it's useful, but it's like lasers when they first came out. They were described (In National Geographic I think) as a solution without a problem.
It would probably be expensive.
It will, however, help make space exploration/development possible.
If we try to justify it economically right away, we will talk (or laugh) ourselves out of it.
Yes, some of these are editorial.
No, that doesn't bother me.
And for those of you who missed it, the article was good too.
Actually, per the article, the point would be to have a no-propultion way to get materials off the lunar surface and into an earth orbit where we can use them for construction.
The Spoon
Updated 6/28/2011
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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