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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."
I thought the point of an elevator was to provide a launch platform removed from the restricitons of Earth's gravity and atmosphere. These don't exist on the moon, so what's the point?
Waste of money IMO.
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.
So you'd also need to built a transport route between the northerly moon base and the equatorial lunar elevator. I suppose that would be a lot less effort than building a bloody lunar elevator though, given that we haven't even been to the place in around 30 years.
There's a good reason to build a terran elevator. For a start, we live on this damn planet! I think that the logistical problems of building an elevator on the moon will outweigh the material problems of building one on earth.
Of course, it could be that it becomes cheaper and easier to simply launch ships from Earth in the future, making an elevator redundant.
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.
The mass of material required for such an elevator (while smaller than an Earth-centric one) must be pretty large compared to the mass that 1 rocket could launch to the Lagrange point.
I'm glad I haven't heard many fearful and wildly speculative comments about space elevators. The most obvious one would be 'what if the cable breaks?'. Any Chicken Littles in our society would assume that lengths of the cable will fall, crushing sections of cities.
A lunar elevator would show that such fears are unfounded.
It would also be good to work out design bugs.
Sounds like one of those ideas that are theoretically possible but utterly impractical to implement.
Yes the elevator could be built. What exactly are we so desperate for we can only get from the moon? Oh thats right, nothing, at least nothing that makes the expense of this endeavour currently worthwhile. The cable may be inexpensive but who wants to pay to put the lunar base in place and get the heavy mining equipment up there, cos that aint gonna be cheap. Also it conveniently fails to explain how we actually get material back to Earth from the L1 point. Maybe it is to be pushed into a decaying orbit by the climbing robots and we take our chances?
Do not try to read the dupe, thats impossible. Instead, only try to realize the truth
What truth?
There is no dupe
The moon application is just a test case, of course. But when it comes to the earth application, what if someone cuts the cable mid-way, so that a strong cable plummets to earth? Instead of "do what I want or I'll cut off this head" it might be "do what I want or I'll throw this 36,000 kilometer cable at your hemisphere.
Now that our worrying caps are on, let's think about why the Bush administration is keen on weaponizing space.
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.
next time RTFA /.
oh, right... this is
120chars for a sig is teh suck
The masscentrum of the elevator must lie in the geosynchronous orbit. Does the moon have a geosynchronous orbit around itself (due to the slow rotation, 1 rotation in 20-something days)?
:) (likewise if the elevator is placed on the other end of the moon). Seemes like it is best to start with earth after all?
I guess earth lies in its geosynchronous orbit, since we always see the same side of the moon, but an elevator from earth to the moon would be a little bit long, eh?
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
There will be no space elevator. Not now. Not 200 years from now.
I am very small, utmostly microscopic.
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.
Have you considered actually reading the article? No part of this thing is attached to the Earth. It is a space elevator on the moon, and the moon only.
If it's not on fire, it's a software problem.
$100M for the first kg of lunar material moved, without rocket propulsion, to a Lagrange point.
Seastead this.
The cable would have to be much longer than that. As the cable is extended toward the surface of the moon, a counter-weight would have to be extended toward the earth so that the elevator's center of gravity would stay at L1 (or else the whole structure would fall to the moon's surface). Once the elevator reached the curface of the moon, the counter-weight would have to be extended yet further in order to offset the weight of the objects traversing the cable. The total length would have to be more than 120,000km.
The concept also doesn't mention coriolis force. The shortest cable would be one that anchors to the lunar surface direcly below L1, however objects travelling on the cable will impart a force onto the cable at 90 degrees to their direction of travel. The base would therefore be best located east or west of the ideal point depending on whether the net traffic on the cable is upward or downward.
L1 is unstable... I'm not sure if the perpendicular direction is unstable as well
The instability is only directly along the earth-moon axis. Imagine a triangle based on the earth, moon, and the object. The earth-moon axis is the base of the triangle, and the other two sides of the triangle represent the earth's and moon's gravitational pulls. The two sides of the triangles nearly balance except that they both pull in the same direction back towards the axis.
So a counter weight on the earth side of the point will pull towards the earth (and be stabilized by the moon anchorage) and be stable in all other directions.
Releasing a payload from either the counterweight on one side of the L-point or from anywhere on the cable itself on the other side of the L-point gives you a choice of which way to "fall away". And during that "fall-away" any any off-axis thrust would be amplified. A very good place to start from making it easy to "fall" off into different orbits in any direction.
And if you are willing to accept travel times on the order of months you can use the chaos points of the three-body system to loop around the earth and moon and get a major gravity-kick towards almost any orbit you like, almost for free.
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.
I believe L2 is also off-axis-stable, only instable along the axis. Assuming so:
Once you are out of the gravity well and into lunar orbit it really doesn't much matter which side of the moon you're on. In orbit you can naturally coast from one side to the other. Any thrust involved would be negligable compared to kicking mass over to an earth-centered orbit. But as I mentioned above, if time is not a factor you can use three-body chaos to manage that orbit tranfer almost for free.
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Actually you would want the center of mass to extend just past the L1 point. Assuming the tether is secured to the Moon, then the tether will hold taught because the saddle equilibria about L1 will always being pulling towards the Earth. Surprisingly, this extra tension is all that is necessary to make L1 a point of stable equilibria because the other two dimensions were stable to begin with. I had done very similar research a few years ago on my own and was unaware of Pearson's work, but came to the same conclusions. The Corialis force has to be taken into consideration but so long as this force is kept below certain limits then it has no effect on the overall stability of the system.