Lunar Space Elevator

GCNRevenger · 2006-02-21 15:12:42

Okay, back to business...

"attached by cables and these will be tight"

Attaching these cables will be extremely difficult on a moving asteroid, and you will have to connect alot of them. Say, one every ~5m on a 250m asteroid is going to add up to quite a few kilometers of cable. Possible, oh sure, but practical? You will have to "follow" around the rock with rockets, which will be extremely difficult flying.

"Mass driver use of slag? Got a use for it now"

No, its not a problem of having a counterweight big enough, its that the Lagrange point moves around slowly, and your space station or elevator station will have to chase it from time to time.
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"Even with lots of impact sites on the moon, its still a finite resouce, and your going to have to sift through a lot of other stuff just to get whats concentrated in a asteroid. And oh by the way, your then going to have to get it of the moon. The moon will come first, but your always going to be looking for a smaller gravity well."

No. All it takes is one big rock, and that would keep miners busy for a long time. They won't be deeply buried either, since ejecta will sit nicely on the surface under a little dust. Remember, that the rocks we want on the Moon are asteroids, so they should be just as rich in PGMs as free floating asteroids. Except, of course, that they will be easier to process on the Moon with the bennefit of gravity.

And getting stuff off the Moon won't be that bad. We won't be launching raw materials any place, and PGMs aren't that heavy considering how much of them we need. Five sixths of all the propellant needed can come from the Moon too, the oxygen, and maybe all of it if ice is available.

"At that size you can have prebuilt scaffolding built on the moon and assembled in orbit. By wrapping the scaffolding around it you can spread out the stress of pushing against it by attaching it to the asteroid at multiple points.

You arent' listening. You can't do that because the rock is spinning, there is no way you are going to build around it with a "scaffold" or something. Its just not practical.

If we can field the power sources, I think high powered lasers will be more effective than drills. The scaffolding could support any number of scoops to clean off loose material, as well as arms to grab peices, as well as cutting lasers, perhapes drills, and personal platforms... Processing probably won't do much more that grind up raw peices and seperate them down to base minerals and melt them into hulks of whatever minerals are useful. These would have be clumped together for storage."

Lasers are horribly inefficient watt-for-watt, and the size of the laser you would need would be immense. There isn't going to be any loose material on Fe/Ni asteroids, since the things are basically just solid chunks of metal alloy. The PGMs are intimatly mixed with the Fe/Ni alloy, and can't be seperated except by smelting or chemical means, so there wont' be any easy breezy "preprocessing" or whatever. Again, this is not like Earth mining.

"Crew quarters would basically be just like any other interplanetary craft in terms of life support systems ranging from simulated g to food production."

Which will be much harder to build and maintain then a Lunar setup, which will not need food production or as many comforts, since Earth is so close.

"Crumbly ones would be much harder. It might be possible to melt the top few inches of soil using microwaves (someone described a way to melt roads on the Moon, however that was done)"

Nope. The microwave trick only works when you have ultrafine iron powder in the soil, which only the Moon likly has the gravity to retain when it is formed by collision. Plus, since ice absorbs microwaves, you might just blow off all the water you want to mine.
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"laser drill rigs spotted and anchored about the surface and aimed so their powerful beams will intersect at the centre-of-mass would create the hollow site from which to start--using remote presence from nearby without actually having to land.

What? You aren't making any sense, "intersect so they create a hollow site?" All you would accomplish would be to make a number of mine shafts that just happen to intersect.

And, you aren't seriously talking about burning through hundreds of meters of solid metal with a laser are you? Nobody has even contemplated a laser of that kind of power, much less have any idea how to power the thing. In space no less!

"Solar-thermal steam rockets, driving water-ice encapsulated product at regular intervals, at the same temperaure as H2/O2 electrolized chemical rockets would have equivalent specific impulses--trading the complicarted electrolyzing and gas storage gear for a much simpler to maintain solar collector mirror arrangement--for transporting product to any destination in space where it is needed.

Not quite... First of all, I don't think you can reach those kinds of temperatures with a solar arrangement while still having any real thrust. We're talking 6000F here, the mirror would be just plain too big, it would bend from even the meager gravity of the asteroid, much less be able to point the thing. Plus, modern engines run fuel-rich, which gives them an extra kick of Isp yours won't have.

"Power for the drilling would be transmitted to the anchored surface laser drill rigs by a (to be determined) self-orienting laser power transmission/receiver/heat conversion system, which would double as a means of slowing rotation in various ways by means of conservation of angular momentum in various ways mentioned in some of the other replies."

No. This might be possible, but it will never be practical. And, do you have any clue how much energy it would take to stop the rotation of a half-mile sized mountain made if Iron? The fact that you proposed it pretty much shows that you don't I suppose. You cannot forget the thermodynamics, it takes as much energy to make it stop spinning as it takes, there is no way to cheat and reduce it.

"The mined material, via control of the centre-of-mass oriented shafts, would be retained inside the asteroid until rotation rate is no longer a factor, and perhaps even manipulated to help slow the rotation, before being ejected from the shafts to the foundry/refractory facility to be processed. "

Again, the volume and practicality of these shafts for doing much of anything is zilch. The energy required to burn them in the first place increases with the square of their radius, which is already going to be astronomical. Assuming you can put 10% of the energy generated into heating of the metal, which is fairly generous considering how poor lasers are, you are talking about 5.61x10^(12) Joules per cubic meter to heat and vaporize the metal... assuming you don't lose any in the heating prrocess. (thats a big number)

Rxke · 2006-02-22 03:10:46

GCNRevenger, You keep coming back to how the Lagrange point being unstable poses a serious problem, but it isn't, the counterweight is *way* beyond Lagrange, towards Earth, which is a self stabilising setup. If the countermass were at Lagrange itself, it would come crashing down immediately.

(Googles for picture... Tadaam:)

Hmm... I see someone has a 'tramway' (???) installed, doesn't make much sense, but ignore that part of the drawing)

(Edit: that's probably to easily get from the poles (water etc.) to HEO etc. (I guess HEO is High Earth Orbit?)

GCNRevenger · 2006-02-22 09:09:34

Hmmmm putting the counterweight waaay beyond L1 would help, but L1 is not so much an orbit, its a spacial location where the Earth and the Moon's gravity essentially cancels. The trouble is, this location is not really fixed as I understand it, so some stationkeeping will be needed.

Rxke · 2006-02-22 09:48:41

But... That's not the point. The counterweight will be beyond L1,2 to be towards Earth, so the countermass will be attracted by Earth. L1 has little to do with the whole thing for starters (as far as I've made out of stuff I read.) So in fact, if this cable were built, and there were some stations around Lagrange points, it would be a damn nuisance, getting in the way and all that

But to be frank: that looks like a looong cable, then if it has to make use of a significant amount of pull from Earth... More than Luna. (Googles: mkay: 'more than twice as long as an earth variant)

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#26 2006-02-21 15:12:42

Re: Lunar Space Elevator

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Re: Lunar Space Elevator

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Re: Lunar Space Elevator

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Re: Lunar Space Elevator

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