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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
...then we can just take a trip down to the moon!
Did you calculate the forces, i think they would still be extremely high giving a very great risk, if this is feasable at all
plus there is no need for a large heavy object just obriting
Think how much easier it would be to get to the moon if we would attach a 'space elevator' from, say, the north pole to the moon...
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.
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.
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
How would we get the materials there?
Oh , I know - a big elevator!
This has to be a vastly better alternative to sitting on our backsides contemplating our navels (or starting wars etc).
Of course, the chance of any nation getting stuck-in is remote due to plain beurocracy. (We're back to contemplating navels)
Ripping an new rectum in the fabric of spacetime.
I thought we were going to use the moon to anchor this to , instead of the typical big bulky sattellite.
.....
Relocating to the Moon won't help the project a bit if the raw materials (whatever) has to be brought from Earth . A mining/harvesting camp on Moon would be at least a few decades away, until then this can wait on the backburner. An orbital platform harvesting asteroids for heavy metals would rock ! (literally) . Would be nearer to earth and it would put solar sails in the domain of practical rather than as Sci Fi book fodder.
Hmm... all the differential equations in Rocket Science confuse the hell out of me . I suppose the space elevator doesn't have the rocket's exponentially growing weight problem ?. (Now I know why they say "It ain't rocket science)
I'd rather vote on the space catapult to launch rockets at Mach 3 (or higher) with something (jet aeroplanes or Maglev rails on mountains) . If the initial acceleration can be supplied by ground based non-moving power equipment, the rocket could go a looong way in reducing weight.
Sadly the word space Catapult brings into mind unnecessary images of North Elbonia and
Quidquid latine dictum sit, altum videtur
Right, it couldn't be attached to the equator because the Earth rotates faster than the Moon orbits it, and the cable would end up twisted aroud the Earth and pull the Moon down. However, the Antarctic would make more sense than the North Pole because there is actually land below the Antarctic ice, and the cable should be attached well to prevent it from flying off.
The Moon end of the cable could probably be attached on the Lunar equator, since the Moon always shows the same side to Earth. Unfortunately, while this makes the Moon lift-off easy, the lift-off from Earth would probably be very tricky when the cable is at a near-horizontal angle (as seen from the pole).
Also, there would probably have to be some slack in the cable since the Earth-Moon distance varies slightly as time goes on. But overall, I think your idea has some merit and NASA should look into it. How do I contact the responsible NASA engineers anyhow?
How about an elevator from Earth to the Moon?
Linux is not Windows
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.
you need to launch the materials for the lunar elevator into space cheaply.
to do that, you need to make the earth space elevator first
Everybody knows this joke is outdated and boring, besides, it's going to be renamed to urectum in a few years time because of that.
But of what use would a lunar space elevator be? Most of the things we want to ship into space are right here on Earth. Shipping them to the moon and then into space seems like a waste of energy.
Thirty years to build at a cost of $600 Billion, and one of the myriad asteroids zipping through the Earth-Moon orbit would take it out in about 1.5 milliseconds.
I'd rather light $20 bills on fire.
Good joke! The cable would pull the moon down... Brahahahahaha... I would love to see *that* cable!
I'm sorry if there is an obvious answer to this but doesn't the moon orbit around the earth. If this lift was even in the relm of possibilities then it would be connected to the earth. Wouldn't the cable wind around the earth. This would probably break the cable or (pull the moon closer lol). The only solution i could see to this is the was an rail running around the earth and the cable was connected to that. This is ludicrious anyway.
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.
Sadly enough, when I first read the title I was like "an elevator from the earth to the moon? Surely that's harder than just one that goes into space?"
Of course, having had this thought and being a geek, I have to take it to it's illogical conclusion:
So, you couldn't just anchor it to a single point. So you'd have to encase the earth in the universe's largest ball bearing, so the the relative position of the anchor remains stationary, rather than creating some sort of twisted celestial yo-yo.
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.
orbital_radius^3 = (3,600^2 * surface_gravity * surface_radius^2 * orbital_period^2) / 2*pi^2
...the height of the elevator, therefore; for the moon it's 190000km. In other words, five times higher than one on Earth! That's nearly half-way to Earth; the gravitational disturbances from Earth's much greater mass could well make the whole thing infeasible.
Yeah but who reads the front page any more? RSS wasn't invented for the fun of it.
Forgive me if Im wrong but wasnt one of the aspects they discussed as a gain when making a space lift, the fact that they could use the end point of the lift to launch interplanetary probes, maybe even interstellar ones, without expending any fuel at all? It seems this would work on a lunar elevator, perhaps not as well as an earth elevator but still.
So you have a 1 year transit to the moon with an ion engine, hook up to the lunar elevator and launch to jupiter or pluto or alpha centauri or whatever with a minimal amount of fuel and 99% scientific payload?
Who says its all about lifting crud off the lunar surface...
We go so... "often" on the Moon and it would be so "usefull" ... seriously, if you want to test it, they are other ways such as simulation.
Anyone else noticed the McDonalds wrappers and crap we leave every day on Earth? Do we really want that on the Moon?
The human race as a whole is not ready for population of any planet which can't naturally support us. If only takes some bully to smash another kids space suit or some idiotic kids to think it's fun to throw bricks at a glass dome and we have a major emergency.
This isn't sci fi here, the stupidity involved in the human race would destroy anything we set up.
I like muppets.
...is a thousand millimeters to the meter.
Got time? Spend some of it coding or testing
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.
In "the Moon is a harsh mistress" (heinlein), they used a great big railgun to accellerate boulders enough to get them into orbit. course, this was later used during the revolution as a threat weapon to declare independance from the earth.
meh
I remember when they discovered rings around Uranus, and suddenly it had to be renamed to "You're a nuss".
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
So stay home. Who needs ya?
--- Ban humanity.
Seems to me that the only way to do this cost-effective is to first build a space elevator on earth in order to get the material needed to the moon cheaply...
Funny, really.
I think, therefore I am...I think.
So first we need to learn how to make a replacement for concrete without water and in a vacuume. Oh and refine, cast, and shape metal. Might as well throw glass in there since that's a little easier.
So once we figure out how to lift gigawatts of long term power generation to the moon, and a foundry, we'll be almost there. And don't pin your hopes on a terrestrial space elevator, NASA's overly optimistic time frame is about a hundred years. And I've yet to see one discussion of the ribbon touch on things like the effects of water, ice, intense radiation, air friction charging the ribbon, and even toughness. "Theoretically, it should be strong enough." Famous last words if I've ever heard them.
The space elevator would need to be incredibily solid to resist to small meteorites like they can't disassemble in the atmosphere like they do once they reach the ground. They would reach the space elevator at full speed/intact and destroy a big part of it, then guess what you would get over your head.
Why not just build a long runway and use horizontal takeoff and horizontal landing? At takeoff you could accelerate assisted by some kind of track, and at landing you could just use breaks as normally. There's no atmosphere on the moon, so getting orbital speel (a little less than 2.5 km/s) would be possible at ground level. I admit it would probably not be easy, but getting orbital speel is never easy. It would be a loooong and flat runway! Still it seems to me easier than to build an elevator. Or am I missing something?
There will be no space elevator. Not now. Not 200 years from now.
I am very small, utmostly microscopic.
Earth First - we'll mine the other planets later!
We're not yet done with earth!
Nov 18, 2004 Star Technology and Research, was recently awarded a $75,000 grant from NASA's Institute for Advanced Concepts (NIAC) for a six-month study to investigate the idea further. It seems like NASA "needs to investigate the idea further." Yo can go BYE BYE if you want now.
I wonder how many times I would need to yawn to keep my ears open. Also, will they have bathrooms on this elevator? It seems it would be a long ride.
BIG BROTHER IS WATCHING!
2) The moon's orbit isn't equatorial
Because of this, the cable length would vary. You could either have some mechanism to take up the slack, or make it with the size of the longest distance ever needed. In this case, one would need a careful study of how it would behave when not fully stretched. Yes, it could work, I suppose, but, to reach all the way to the point where the Earth's and the Moon's gravitational attraction cancel each other, one would need a stronger cable than if it just went to the Earth's geostationary altitude.
Also good for delivering stuff into the Moon's gravity well... which is something you'll want to be doing from time to time. Delivery vehicle stays well out in space, doesn't have to waste energy getting down and getting up again.
More efficient than parachutes.
The radiation of the sun would have killed them once they left the Earth's various fields. Just like what would have happend to the moon landing crew had they actually gone to the moon and not a film set.
I had an imaginary sig once, he said I was a loser and ran off.
I wonder what they would do if the elevator got stuck somewhere in the middle.. call the elevator guy ? :)
Although interesting, I assume that this isn't pratical, and therefore, a frivolus waste of time, energy, and money. I love the space program, and space itself, however, we do some dumb shit with space and the ideas surrounding it.
Yes NASA awarded some money to the project, but it say that they are "funding" the research is a bit of a stretch. $75,000 over 6 months isn't exactly going to go very far. If you are talking about have a top level scientist on the job, thats the whole budget.
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.
First, the distance to the moon is 30 earth diameters. You would have to travel along the cable at incredible speed to make it to the moon in an acceptable time. Lets assume you could travel on the cable at 60 mph. 237525/60 = 3959 , 3959/24 = 164 days to get to the moon. How are you going to power the vehicle to travel for 164 days? And feed the people in the elevator for that long period of time?
I think the ion engine solution would be more efficient. It takes a long time to get to the moon with that solution also.
Just like the railway opened up the west for settlement, these will open the moon. (Yes, once we stop laughing.)
Also, in the spirit of the X-Prize, I will personally send TEN DOLLARS (Canadian) to the first person who builds a working space elevator from the moon to the Earth-Moon L1 point.
Offer expires, let's say, December 31, 2039.
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.
Publisher, Universe Today - http://www.universetoday.com
Introducing a space elevator on the moon is a double whammy: Not only is the force of gravity much smaller (as a result of which the line is lighter, and a thinner line is ok), but its length needs to be smaller as well, so, it doesn't have to be that thick to withstand the .
If the space elevator is operated on electricity, and if good electricity storage devices exist, it would be possible to drop something on the moon without costing energy (now you have to burn rocket engines (which require fuel to take from earth), but instead even generate electricity which could be used to get payload from the moon back up to be picked up by a spaceship.
And of course, the line may be thinner because it doesn't have to withstand wind, carry ice etc. So, its way more feasible as a first step
I hope some kind of alien doesn't mistake our two planets connected with a cable to eachother, for a giant bola.
Hmm. A horrible idea popped into my head. Somehow this scheme looks like a grand plan to deorbit the moon (grinning). Well, it *is* a satellite, and that *is* a tether, and there *is* a magnetic field.
For sure, it's the solar rather than the earth's field that bothers me, but since the earth-moon system is orbitting the sun I'd expect some kind of generator effect. Not to mention the fact that nobody really has a clue about the dynamics of the solar field.
So, even after somebody does some calculations to check whether electrical effects could dust the idea, it would be a great idea for NASA or ESA to launch a probe to L1 with the intention of spooling out a very long cable, so that any electrical stuff could be measured.
Now, for the really wacko suggestion. Why not connect the Lagrange points to each other with wires? Hmm. Really big LAN that one...
Anyone with enough physics want to do the back of pad electrical calculations?
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.
I suppose my first question is, how do they intend to do this and not fuck around with the moons affect on earth's gravity. after that i would have to wonder why the hell they dont just build a better spacecraft, and then lastly why not just use the technology to, as opposed to building an elevator, build a series of magnetic rings between the moon and the earth that would act as transportation. you get up to the atmosphere with an x-prize plane and get into the tube, you get sucked at ridiculous velocities to the moon, slowed down by the same tube, and then land.
A bullet may have your name on it but splash damage is addressed "To whom it may concern."
$100M for the first kg of lunar material moved, without rocket propulsion, to a Lagrange point.
Seastead this.
It's nice that this fellow is informed on the topic and he paints a correct picture on the generalities of the process. I can assure you, though, that he is not the original author of the article.
Okay, so lets say that we now have a working
space elevator technology. What possible
reason could there be for such an elevator
on the moon (at 1/6th Earth gravity)?
The whole idea behind such technology is to
cheaply lift material into orbit. The only
thing the moon has (right now) is moon dust,
and once those first samples came back at
tremendous cost, what's the point? Just how
much moon dust would be necessary to satisfy
the demand on Earth? Even marketing the stuff
on eBay has got to have some limit to demand.
The space elevator, then, is intended to lift
"valuable" cargo into orbit -- not just junk.
A permanent moon colony that uses solar smelters
to create (mainly aluminum) building materials
would still be more expensive than lifting from
Earth -- there is no water and no air on the
moon, and a space elevator would still be needed
here to supply moon colonists/miners/refiners
those life-sustaining resources.
A better scenario would be the use of Earth's
resources, space elevators, and NEO spaceship
construction to go where the real resources
are in the solar system -- the asteroid belt
and (possibly) Mars.
Read the fucking grandparent, bitch.
If we can dangle a length of string from the visible face of the moon towards earth and put a brick on the end, making sure that the string is short enough so the brick dangles just outside the atmosphere:
1. The earths gravity will pull on the brick and keep the string taut.
2. The brick will skim the outer atmosphere at about (pulls figures from ass) 1500 to 2000 mph.
3. Any craft that can do 2000 mph at very high altitude can grab the brick and then climb to the moon.
I will leave others to spec the string and brick. And do the calculations. And which way to the patent office?
They whose government reduces their essential liberties for temporary security, receive neither liberty nor security.
This is like trying to build a serious engineering project like the Gibralter bridge by sending small fishing boats to carry the materials.
Technically impossible, incredibly unfeasible.
No! It's a *SIG*. Keep the Special Interest Groups away! (Con joke!)
Personally I'm a little iffy about altering the mass of a giant object that orbits the Earth. I don't know about the physics here but how would it affect the orbit of the moon if we started increasing its mass by bringing materials from earth up there?
Not since Marie-Antoinette played milkmaid has looking simple and honest been so fake and complicated.
RTFA moderators, or at least RTF summary. Obviously it's not about an elevator between earth and moon if the advantage is that less exotic materials would be needed due to lower gravity... duh... if it linked earth & moon it would be *even harder* to make, not easier.
Mod parent +1 and grandparent overrated.
You will need to accelerate the counterweight to preserve balance. Other then massive job creation i don't see any real benefits.
Sometimes someone mentions an idea and a million people kick themselves for not seeing it's logic and beauty earlier. Great idea!
"Curiosity killed the cat, but for a while I was a suspect."- Steven Wright
Once again I find an example of the confusion between gravity and acceleration, or energy and force.
The Moon's gravity is 1/81st that of Earth, because it masses 1/81st as much. It's that simple. Gravity is the result of energy, energy in this case is basically entirely contained in the rest mass, so presto, 1/81st the mass means 1/81st the gravity.
So what about the whole "lunastationary elevator" idea? If there's less gravity, isn't that going to make it much easier? Not really. Think about a line extending from a feature on the moon out into space until it reaches the stationary point -- that is, the point that an orbit remains over that feature on the moon. Where is that point? The Earth. Think about it for a second...
There are other places it could be anchored, the L1 point is often talked about. Yet that is still 58,000km, even longer than Earth's geostationary points at 36,000km. So as am experiment all it does is let you use some other material that's not impossible to make -- but that hardly seems like a good reason to try.
So you need some excuse to make one, and the answer is "there is no reason whatsoever". All of the materials available on the Moon are available for a lot less money here on Earth. Sure, if you have a massive space infrastructure perhaps there is some point at which there is an economy of scale in its favour, but that already presupposes lifting all that stuff off the Earth already.
You can buy, off the shelf, tens of thousands of miles of fiber that does this job.
The scale of the lunar elevator can be much smaller.
It is vastly less vulnerable to terrorism or other mishap.
This really could solve the Earth's energy problems and lead to a dramatic reduction in ecological pressures.
This is a great idea.
I'm surprised and a bit ashamed that I haven't heard about it before.
It should be the next big space prize after America's Space Prize.
Seastead this.
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.
The benefit to the souvenier moon rock industry alone would be enormous.
Some thoughts on unstable orbits:
First, the notion that the tether from the moon to the top of the elevator would seems a little shaky. If I understand correctly the cable can provide tension but is not rigid. As such, if it were strong enough (probably not unreasonable) it could prevent the elevator from drifting to the Earth side of L1. But L1 is unstable in the Lunar direction too, and the cable's tension would do nothing to prevent it from drifting to the Lunar side of L1; so, the cable alone couldn't keep the elevator centered on L1.
From TFA: "Without any kind of thrusters, you'll eventually drift out of this perfect balancing point, and then start accelerating towards either the Earth or the Moon."
Now, there are tricks you can play with the orbit to bias the instability in one direction or another. Specifically, if the elevator is positioned slightly on the Earth side of L1 then its tendency will be to fall Earhtward, and the tension of the cable could be sufficient to hold it in place. TFA is slightly unclear, but it appears they might be considering this plan: "Once the cable was anchored to the lunar surface, it would provide tension, and the entire cable would hang in perfect balance, like a pendulum pointed towards the ground. And like a pendulum, the elevator would always keep itself aligned perfectly towards the L1 point, as the Earth's gravity tugged away at it."
At first glance, this approach appears to have a problem too: if your center-of-mass isn't exactly aligned with L1, you don't stay aligned with the moon! In this case, where the center of mass would be slightly Earthward from L1, the elevator's orbit around Earth would be faster than the Moon's. It's not clear what effect this has, though. Anyone?
Second, the orbit of the moon is (slightly) elliptical, so the L1 point should oscillate in distance from the moon. I'd think that would also aggravate the problem of trying to sit on the already-unstable equilibrium point. All in all I don't see how they can avoid having to use thrusters to keep it in the right place.
I am not a physicist or rocket scientist, but a few questions pop out:
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.
Wouldn't the cables center of mass need to be at L1 or slightly above (relative to the Moon), rather than the end of the cable? If one end of the cable were at L1 and the other end on the moon, the moon's gravity would have a greater effect than the Earth's gravity, so the cable would be pulled back down to the moon, correct? Or am I missing something?
Eventually, the cable would wrap itself around the Earth due to the moon's orbit.
First, the notion that the tether from the moon to the top of the elevator would seems a little shaky. If I understand correctly the cable can provide tension but is not rigid. As such, if it were strong enough (probably not unreasonable) it could prevent the elevator from drifting to the Earth side of L1. But L1 is unstable in the Lunar direction too, and the cable's tension would do nothing to prevent it from drifting to the Lunar side of L1; so, the cable alone couldn't keep the elevator centered on L1.
If the elevator starts falling (moves towards the Moon), it starts to lean to the east. To keep it stable, you pull to the west at the anchor point, and it doesn't move.
GEO isn't stable either - it's not a minimum in the potential at all. But the competing accelerations keep the cable taut. It's exactly the same in this manner.
You need thrusters to remain at GEO, too - obviously any slight acceleration pushes you away from it. But a space elevator doesn't need thrusters to sit at GEO, because slight perturbations cause fluctuations in the tension (which are compensated at the anchor point), not in the orbit.
The dynamics of an L1 elevator are pretty much identical to that of a GEO elevator. It's just simple orbital mechanics.
I shouldn't've mentioned that the tether "cancels the radial instability" - that's unimportant, as any orbital perturbations get translated into tension perturbations.
The interesting part is that since unpowered orbital paths naturally lead away from L1, debris will have a harder time hitting that portion of the elevator. The other portions will still be vulnerable, though.
On improving reading ability, analytical and logical thinking amongst the general population?
:)
Looks like a more urgent issue.
The article discusses why this elevator would be useful.
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
But if we build a space elevator to get stuff off the Moon, instead of a mass-driver or similar electromagnetic catapult, then how will our eventual Moon colony throw rocks at us in order to gain its independence? Someone needs to be considering the future ramifications, dammit!
Kai MacTane: Web developer for hire in San Francisco
You want to ride an elevator into Space? Man, do you know how much Muzak you would have to listen to on a ride that long?!
Would it help if we went out and shot everyone who was still laughing?
One line blog. I hear that they're called Twitters now.
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.
Sig:Why copyright isn't a fundamental human right
Would the tether be passing through any magnetic fields such that it could be used to generate power for its own operation? Failing that how about the possibilities of generating/capturing energy as the load is accelerated by the Earth's gravitation? If generated and fed back through the tether it could supply power for the operation of the tether/support base. If captured in a flywheel it could be used to supply power on the receiving end at the L1 point.
Put down your bones and stones while your at it!
We have been technological creatures for a few
tens of thousands of years now - get over it!
Let's hope no one allows children who love to press every floor button on that elevator. Otherwise lunar travelers will have a long, long wait...
This is the way: http://jv.gilead.org.il/evans/illustr/pics/25-rokt .jpg
Pay no attention to that man behind the curtain.
The paper the article was based on is here: (276k pdf)
But you would think that to "commercialize" the moon, you would first need an economically viable way to get stuff up and down to the earth, something far more economical than blasting it up on an Arianne 5, SS-18 or Delta IV, and letting it drop into the ocean from LEO.
This analysis is WAY beyond putting the cart in front of the horse.
Books, whatsa book? Oh yeah I read about them on a blog once before the cosmic-bit-shredder bio-weapon destroyed them all.
So sled launch enough mass to hang the L-vator on, do the same thing for an Earth E-vator and connect the two with a couple of giant universal joints and some nano-cable.
Then U-can ride your transport pod from terra-firma to tranquility for a quick visit to Armstrong Park... U-can also generate enough power to make it a free ride. Of course that will take all the fun out of hot-sleding through the atmosphere - oh well the price of progress.
It occurs to me that a luner elevator might be a better deal for landing things on the moon than takeing them off.
For lunar launches, the Moon's lack of an atmosphere makes mass drivers practical. No fuel required, just energy. And isn't that the prime selling point for a space elevator?
On the other hand, coming down, the lack of an atmosphere is a problem. No free aerobraking like on Earth. You have to expel propellent. A lunar elevator would fix that. But is it enough to justify building and maintaining the structure?
The article mentions this: Space elevators are for cargo and freight, which aren't in a hurry and don't need heavy radiation shielding. And yes, there are plenty of useful materials on the moon, probably just as many as on Earth, and maybe more. We'd be stupid to lift stuff from Earth if we could get it on the moon and not have to fight with our gravity and atmosphere.
Although ... I'd prefer a magnetic rail launcher that accelerates things to lunar escape velocity and shoots them into orbit.
This concern has been brought up before. Current space elevator designs are not likely to cause damage when falling, since they have low mass compared to their cross section, much like a ribbon or a sheet of paper.
Because the moon is airless, there is a cheaper alternative, in my opinion. Picture a space station that circles the moon in an eccentric orbit that dips down to within a kilometer or two of the surface at apogee. It twirls a long cable in a direction opposite to its orbital path. That is, when the cable is closest to the moon, the lower end of it is moving in the opposite direction to the station's orbit, cancelling out the orbital motion of the station. With a little agility, it would be possible to have the end of the cable come to a point of zero motion relative to the moon at the moment of contact with the moon's surface, making it possible to set down a load gently. Loads could be picked up in the same way. The station varies its orbit by shooting rocks with a mass driver. Each upcomming load would include some more rocks.
Solar panels charge a big honking capacitor bank. Put the ore/water/whatever you want to get off that lousy rock on the railgun, and let 'er rip.
There are no materials on the moon. What's the point?
Fine, but why is this better than just a railgun to fling stuff off the moon? There's no atmosphere, so there's no reason why you can't accellerate stuff into beyond orbital velocity from the ground.
It's possible that shipping large quantities of lunar raw materials to L1 will be cheaper with a cheap Lunar elevator than shipping large quantities of cheap raw materials from Earth on a relatively costly Terran elevator.
But, once you need to process any materials, you will need more complex equipment than a fleet of rovers picking up loose stones from the lunar surface, for delivery to the climber (although this may be good enough for building up a counterweight).
In order to keep from continuously launching complex processing equipment from Earth, you need to deliver a factory, initial mining equipment and rovers to the Lunar surface that can spit out more rovers, miners, cable, spare parts, factory assemblers, solar panels, smelters, factories, etc. Then, you must have people there to repair the equipment, or don't repair, just make sure to produce lots of spares. If people are there you need to worry about shielding while they're not out repairing stuff, and you would need continuing launches from Earth, the expense of which would kind of invalidate the whole point of a Lunar elevator.
So, for this to work at reasonable cost, a very complicated ecology of factories, robots and parts needs to bootstrap itself on Luna, or those things will have to be sent from Earth at high (non-elevator) expense. If anything you save the fuel of doing a powered landing on the moon for those items.
It looks like most of the work here is in developing complex robotic equipment, not so much figuring out the problems with a spool and climber setup.
Good point. The criteria should probably include a repeat rate and number of repetitions -- sort of like the X-Prize's repeat rate -- to eliminate systems that aren't durable. Rail-guns are notoriously self-destructive.
This will likely be decades before a space elevator is placed on the Earth
If not longer.
probably centuries before one is on the Moon.
RTFA
A single launch with an existing commercial vehicle using existing off-the-shelf fiber could put the tether for a lunar elevator at the Lagrange point.
Seastead this.
Who says it has to be robotic? What's wrong with remote controlled?
Three seconds to get a signal to the Moon and back. Okay, your reaction time is going to be crap, but as long as you are patient and take it easy, remote control would be fine.
Heck, with some VR and computer power, you could probably simulate the three seconds ahead required to effectively eliminate the delay for most routine tasks.
This would be sufficent to establish an industrial complex whilst a more self-sufficent base is established.
"Software is too expensive to build cheaply"
Why not give that one more thought. You may find it just as useful.
I prefer the "u" in honour as it seems to be missing these days.
First, How much would it cost to build a railgun on the moon? You have to get the parts to the surface in a safe fashion. Can't just parachute in ( too little of atmosphere ). So now, you have to rocket in and land. Or is there a cheaper way to get cargo to the surface?
The space elevator lowers the costs of going to the moon in wonderful fashion. If we increase the elevators length towards the earth, then we only have to go far less than 1/2 the way to get cargo on the moon. Simply hook on, and then send the cargo.
I prefer the "u" in honour as it seems to be missing these days.
First, the L1 point rotating around the moon every 28 days at a distance of 60,000 km from the center of the planet (someone said the distance from L1 to lunar surface was 58,000 km, so I'll just guess that L1 to center of the moon is 60,000 km) can be calculated this way: 2 * pi * 60,000 km / 28 days = 13,506 km/day = 562 km/hour. I believe this should be about 1/14th the tangential velocity that the balance point of an Earth space elevator would have, because the rotation is happening every 28 days instead of every day and the distance to the balance point is about twice as long in the lunar case.
Let's say the climber is going to climb the cable at 10 km/hour, meaning that it will take 6000 hours (250 days) to climb to the top. In other words, the tangential velocity of the climber will increase 562km/hour during a 6000 hour period. It's tangential acceleration will be: (562 km/hr)/(6000 hr) * (1 hr/3600sec) * (1hr/3600sec) * (1000m/1km) = .0000072 meter/sec/sec, or less than one one millionth of earth gravity. A single 200kg climber would exert an eastward force equivalent to the weight of 1.44 grams on earth (about the weight of a piece of paper).
In comparison, the downward force from the 5800 kg cable will be some substantial fraction (half?) of the weight of that cable at lunar surface gravity (about 1/6 earth), so, it would be equivalent to a weight of perhaps 500kg on earth, or about 350,000 times greater, so the slope would be about 1:350,000. So, at the balance point, the cable would probably oscillate around some position and average of about 165 meters east as the climber ascended, and oscillate about some position about 165 meters west during the descent.
So, with one climber in the lunar case, the slope needed would be infinitesmal. I think that when I figured the ~1% slope in the Earth case, I was assuming a many climbers travelling up the cable faster and little mass travelling back down.
I wonder about one political question with respect to lunar elevators. Are the Lagrange points really the only areas where one could build a space elevator on the moon? If so, cost effective access to the lunar surface could be easily controlled by a single political power.
that ACs are humour-impaired?
Oh, and wrong, in this case.
(a) it all depends on your frame of reference. If you cut a rope that is supporting a whirling object, and try and hold the cut ends together, you will have to supply both an inward and an outward force to keep the whirled end going round. I don't think it is unreasonable to think of one of those as centrifugal force.
or
(b) let's call "the combination of angular momentum and centripital force" centrifugal 'force'.
an odd definition of fast driving. Towing a 1.5 ton horse trailer behind a V8 Ford Falcon we managed 36 hours door to door, for 3500 km, from Melbourne to Darwin.
Remote controlled devices will work fine, you just need more operators and more bandwidth that way, especially once you are starting to send serious quantities of materials up. But even those should have an automated mode of operation or something so that repetitive tasks like digging don't become too tedious.
"Pick UP. Pick DOWN. Pick UP. Pick DOWN..."
Don't get me wrong, this might actually be a quicker path to energy independence than the Earth elevator, but it will take a lot more thought than worrying only about the physics problems.
Clarke played with yo-yos as a kid.
Cake or Death? Cake Please!
Space-going blimps can't get closer to any planet without at least a thin atmosphere than a parking orbit.
Cheap bidirectional traffic to the Moon is the key to industrialization and colonization of the Moon. Which is the only way we're likely to be able to get jobs or live there.
Safety considerations aren't as hard to deal with where the population dessity that can be affected by chunks of an Elevator and its payload landing on their heads is vanishingly close to zero. Earlier generations of nanotube technology will produce the less strong cables required to build these initial efforts.
This is worth doing, and using the launch techology mentioned above to deliver it to lunar parking orbit, perhaps a lot less expensive than previous cost estimates based on heavy-lift booster rocket launches from Earth.
Tech Public Policy stuff
There has been another suggestion for launching things using long cables, which does not work quite the way as the space elevator: Put a moderately long cable in low-earth orbit and spin it in such a way that the lower end just touches the stratosphere and does not move a lot relatively to the earth's surface. Attach an object to that end (by means of a high flying plane or the like). The object will be thrown into space.
The bad thing about this design is that the spinning cable will loose height in the process and must be powered up using rockets. So in the end, you gain very little. But if you could send in mass from the moon cheaply, you could use that to power up the wheel by catching the packet with the spinning cable when it is high up and releasing it near earth.
This requires extreme precision, but at least the law of physics do not stand in the way. You would have to plan for missing the material from the moon, making sure that it will burn up in the atmosphere or dive in the ocean. You will have to make huge advances in egineering, but it is an option if we cannot get at material that is strong enough for a real elevator.
My only question is .. what's the ROI on this?
No, it's a good question. Who builds it and where does their profit come from?
Display some adaptability.