LiftPort Wants To Build Space Elevator On the Moon By 2020 210
Zothecula writes "When the late Neil Armstrong and the crew of Apollo 11 went to the Moon, they did so sitting atop a rocket the size of a skyscraper that blasted out jets of smoke and flame as it hurtled skyward. For over half a century, that is how all astronauts have gone into space. It's all very dramatic, but it's also expensive. Wouldn't it be cheaper and easier to take the elevator? That's the question that Michael Laine, CEO of LiftPort in Seattle, Washington, hopes to answer with the development of a transportation system that swaps space-rockets for space-ribbons. LiftPort ultimately wants to build a space elevator on Earth, but the company isn't planning on doing it in one go. Instead, Laine and his team are settling for a more modest goal – building an elevator on the Moon by 2020. This is much easier. For one thing, there’s no air on the Moon, so no icing problems. Also, the lower gravity means that no unobtainium is needed for the ribbon. Kevlar is strong enough for the job. And finally, there’s very little in the way of satellites or debris to contend with."
Just build it horizontally (Score:2)
The Earth has an atmosphere, so a space elevator needs to go up to get out of it. On the Moon, there is no atmosphere, so the you can just build a mass driver [wikipedia.org] horizontally, along the ground, and launch stuff in a tangential trajectory.
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Space elevators also allow you to bring things gently DOWN from orbit. How's that mass driver gonna work for ya?
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Re:Just build it horizontally (Score:4, Informative)
Space elevators also allow you to bring things gently DOWN from orbit. How's that mass driver gonna work for ya?
It could work quite well. Mass drivers can decelerate as well, and can recover and convert the kinetic energy to electricity in the process.
Re:Just build it horizontally (Score:5, Insightful)
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Ya do realize planes manuvering to land on an aircraft carrier have wings and tails to take advantage of an atmosphere, and every tiny bit of manuvering to line up exquisitly precisely with your bullet-catcher is going to require fuel...
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Get the trajectory just right and maybe you could 'catch' the object in the end of the catapult and slow it down using the electromagnets in a manner similar to the regenerative braking used in electric cars?
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True, but there are mountains and craters and other geological things that need to be avoided. Its not like its a perfect marble.
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Though if you use convict labor things could get interesting.
Mycroft
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Yep real good for launching grains and such from the lunar colonies, as long as you have a decent computer to run the whole thing. Though if you use convict labor things could get interesting. Mycroft
I see what you did there, tovarisch.
There is one problem... (Score:5, Informative)
That problem is that there is no way to create a lunar-centric orbit where the upper terminus of the ribbon hovers over a fixed position. So any tether can not be fixed to the ground. So lifting anything with that tether will involve something like a skyhook catch, except it will be at orbital velocities.
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Which, at least in my opinion, makes it not a space elevator at all. After all, we could probably make a ribbon strong enough for an ultra sonic sky hook today or at least quite soon. A space elevator is a completely different ballgame. Using misleading buzzwords to get your funding off the ground is a bit of a red flag IMO.
Re:There is one problem... (Score:5, Interesting)
That problem is that there is no way to create a lunar-centric orbit where the upper terminus of the ribbon hovers over a fixed position.
Actually a Lagrange point would do fine for that. L1 is about 58,000 km [universetoday.com] from the moon towards the earth.
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I hadn't considered that, it isn't strictly a lunar orbit.
And the length of cable would actually be as long as or longer than the cable required for an earth-geosynchronous orbit elevator (~36,000 km)
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I hadn't considered that, it isn't strictly a lunar orbit.
And the length of cable would actually be as long as or longer than the cable required for an earth-geosynchronous orbit elevator (~36,000 km)
As others have pointed out here, it would need to be a bit longer still and with a mass at the end, in order to maintain tension on the cable.
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I mean that there is no geostationary orbit within the moons hill radius. And orbits do not exist outside an objects hill radius, things outside the hill radius by definition orbit something else or are on a non orbital trajectory.
Re:There is one problem... (Score:5, Informative)
Having read TFA, this seems to be precisely what they're doing [gizmag.com]; it looks like they deploy at the L1 point and extend the tether in both directions. Of course, this does mean the tether needs to be an extraordinary 250000km long.
Despite being totally awesome (which is reason enough to do it!) and also good practice for Earth (ditto) I am slightly at a loss as to how useful this would be. Space elevators are slow, and a lunar elevator would be really long and therefore really slow. And it's not as if the moon's hard to land or take off from.
I'm wondering if there's something useful to do with the other end. The high end of the tether is only 135000km from Earth. Is that far enough into the ionosphere to use for power generation?
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And where is the counterweight going to go in case of an accident that severs the elevator?
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er.. does the moon rotate fast enough?? (Score:2)
Re:er.. does the moon rotate fast enough?? (Score:4, Informative)
The moon does not rotate. When you look at the moon the same side of the moon always points to the earth. So, the ribbon would need to be held stable by Earths gravity to some extent (it seems).
Our moon does rotate, with a period equal to its revolutionary period about the earth. This kind of synchronization is common with moons of planets, and is caused by tidal forces between the moon and the planet.
One other thing a Space Elevator needs... (Score:5, Insightful)
They're forgetting the single most important part of a space elevator: It needs to actually be useful.
What are we going to do with a space elevator on the moon? We don't go there for a very good reason: Its expensive as hell. Making the cheap and easy part a little cheaper an easier isn't going to change the fact that the entire rest of the trip is prohibitively expensive.
It's like your friend moving across town to be closer to you, but he lives in Seattle and you live in London.
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They're forgetting the single most important part of a space elevator: It needs to actually be useful.
But we can use the ribbon to hurl the moon at Melancholia and save ourselves!
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We don't go there because we're shortsighted and stupid. There's plenty of things the Moon would be good for, such as astronomy, and especially mining. There's a lot of He3 there, which would be very valuable for fusion reactors.
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Re:One other thing a Space Elevator needs... (Score:5, Funny)
If we had helium fuel, we could have helium-fueled fusion energy, if we had a fusion reactor.
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The moon sucks for astronomy. It's covered with a particularly nasty form of dust, the temperature variations are extreme, and your telescope is in the blazing sunlight for two weeks at a time, so your duty cycle is horrible.
What can you mine on the moon that you can't mine on Earth for much cheaper? And by "much" I mean astronomically.
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I'm sure the dust problem can be overcome with engineering. How much worse can the temperature extremes be than what our orbital telescopes have to deal with? As for sunlight, isn't that already a problem on Earth?
For mining, it's hard to say without actually going there and looking more closely. There's tons of stuff we mine now that it very rare and we could use more of. Even copper is getting more and more rare, as the prices for it keep rising greatly, and it's of critical importance to our technolo
Re:One other thing a Space Elevator needs... (Score:5, Informative)
Why deal with dust at all? Put your scope in space.
The temperature extremes are much worse on the moon - close to absolute zero to hundreds of K if my memory serves right . In space, you just put your scope at L2 or Earth-trailing, build a passive solar shield (or use a cryopump if you need really low temps), and point it away from the sun. Voila, constant temperature and 100% duty cycle. Put your scope in space.
There's also the fact that during the two weeks of duty cycle where you can operate the scope, you don't have solar power, so you have to have some way of storing energy. A telescope in space just uses solar panels and gets power 24/7. You'll have to cool your electronics half the time, and heat them the other half, so again, power, and storage. Go ahead, say nuclear. My understanding is that the moon has very few heavy elements, so all that has to come from Earth. So add a nuclear reactor, RTG, or batteries to your expenses.
Telescopes on the moon have to have pointing mechanisms, and the moon has gravity, so it's more mechanically complex (dust, vacuum). Telescopes in space have reaction wheels and thrusters to control pointing. No dust, and also few moving parts in vacuum. Much simpler. Put your telescope in space.
That is, in fact, why we are putting our telescopes out at L2 or Earth-trailing. Hubble would have been there had it not been for the mandate that it ride the shuttle. Have you noticed that we're not putting telescopes in Earth orbit anymore? It's not because we don't have the shuttle. It's because Earth orbit is sub-optimal, and not just a little bit.
As far as comparing astronomy on the moon to astronomy on Earth, well, Earth has a lot of advantages for telescopes, and that's why there are lot more of them here on Earth than there are in space. Not least that you can breath the atmosphere and find cheap places to sleep and have grad students pull the late night shifts. There are of course disadvantages, and you could never have JWST on the ground, but the moon is just not a great place for telescopes. I'm not entirely talking out of my ass here. I've sat in the rooms where these tradeoffs were made, and the moon gets put on the list. Then we start ranking. The moon ranks low in performance (duty cycle, power), high in cost (humans in space suits have to build it, everything has to be shipped from Earth), and high in risk (you have to ask why, srsly?). Then by the wonders of Excel, the moon drops to the bottom of the rankings.
But it is considered.
That's even assuming we had the capability to build a telescope on the moon. Which would be insanely expensive. Humans building telescopes, launchable or not, where they can breathe is always going to be way cheaper than building them on the moon.
Care to link to any peer-reviewed documentation that shows the abundance of He3, or any other interesting mine-able elements on the moon? I am ignorant of the geology of the moon, so if there's evidence that there are mine-able elements on the moon (including He3), I'd be happy to have my ignorance lessened.
You haven't really addressed the question of you know, actually having a working fusion reaction that needs He3. We don't. And probably won't any time soon. What are the economics of mining something we don't yet need and is difficult to store?
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Holy cow. Never mind, I just read the Wikipedia page for He-3. It's even more far-fetched than I thought. 150 MT of regolith to get 1T of He3 (1.5e8:1 !!!), and He3 fusion might not even be realistic?
Sigh.
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"Hubble would have been there had it not been for the mandate that it ride the shuttle."
Hubble was serviceable, hence it needed to be in LEO. It had nothing to do with being launched on the shuttle. Plenty of probes have been launched beyond LEO from the shuttle, they just use an upper-stage (just as they would if launched from anything else.)
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A radio telescope? Naw, put it on Farside. It'll have a small planet between it & all that radio noise from Earth to block it, should make for some sensitive scopes. As for an optical telescope, just put a barrel around the mirrors to keep out the daytime sun. The big problem is going to be thermal expansion of the optics. It'll seriously warp 'em.
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What are we going to do with a space elevator on the moon? We don't go there for a very good reason: Its expensive as hell. Making the cheap and easy part a little cheaper an easier isn't going to change the fact that the entire rest of the trip is prohibitively expensive.
For the Apollo missions, they needed their rockets to use fuel to lift the fuel that carried the payload that was fuel for the lunar descent to retard the fuel needed to lift the fuel for the ascent. It gets complicated pretty quickly.
Absolutely none of this was of course free, and the most expensive substances were those at the lunar end - every gram has a much larger fuel equivalent at the start of the process.
It will still be expensive to go there even with the elevator, but any reduction in price will i
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It is significantly easier and cheaper, much more than you are making it out to be.
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This is Micheal Laine you're talking about here - useful is optional and definitely secondary to his Vision of a Glorious Future.
Did they ever get around to repossessing his 'factory' in (IIRC) New Jersey? He's come a long way from shilling for dodgy tech based initiatives, but that's long been his pattern - when one scheme falls apart, move on to another even more dubious one.
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..ok, how? (Score:5, Interesting)
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Seems like the biggest challenge would be building the cable and satellite; the work you have to do on the Moon should be minimal, mainly just anchoring the cable after it's dropped from the satellite. Of course, afterwards you'd want to build a base or something, but just to get the elevator working that isn't strictly necessary. The cable would be built on Earth. After this is all done and in place and a base is established, and mining operations started up, then we can start building up infrastructure
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Simple! They build the elevator on Earth, then strap it to a rocket that they fly directly into the moon. Fortunately, they have turned the elevator upside down, so when the rocket crashes into the moon, the elevator stands upward.
This is kinda like how they build skyscrapers: Build it lying down, then straight it up when it's done. Much cheaper and safer.
Re:..ok, how? (Score:4, Insightful)
You're reading this wrong. 8 years is exactly the right amount of time.
It's less than 10 years, which is sufficient to attract VC funding
But it's also greater than 5 years, which is long enough to avoid any expectation of progress or success.
Lunar Musaz (Score:2)
moon-stationary orbit, correct me if I'm wrong (Score:2)
google: ( ( lunar cycle / 2*pi)^2 * mass of the moon * gravitational constant )^(1/3) .. 1.12x the earth moon distance. Uhhh
That's 429,000km
Good luck (Score:3)
Did someone just use the words "settle" and "building on the moon" in the same sentence? Who are these people?
Where are the billions of dollars this is going to take? How the hell are they going to prototype it?
Do they realize that 2020 isn't some lofty far off time these days? That's a bit more than 7 years.
If NASA, Russia, or China (or Elon Musk) said they were going to try this, I'd be excited. But this shit is not going to happen like this, lets just be honest.
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I think it makes more sense to make a space elevator from LOE. All the advantages of a lunar elevator, but actually in a useful location,
Somehow relevant... (Score:2)
Kickstarter campaign! (Score:5, Informative)
You put LiftPort on the front page and forget their KickStarter campaign?
It started on the 23.08, and in 5 days it's raised $27.514 of the 8000 goal.
http://www.kickstarter.com/projects/michaellaine/space-elevator-science-climb-to-the-sky-a-tethered [kickstarter.com]
they forgot to do somet math apparently (Score:2, Interesting)
Re:well that's just silly (Score:4, Insightful)
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"make it more economical to conduct mining operations on the the moon"
OK, but I'm having difficulty imagining massive mining machines working their way along the tether. And how to begin the process from an orbiting craft. And then, once landed, how will these machines get the energy necessary for mining operations?
I'm obviously missing some essential information about why this might be practical.
Re:well that's just silly (Score:5, Insightful)
The mining machines wouldn't necessarily need to be: massive, transported via the tether, and/or come down fully assembled. Not everything has to start out on massive scales. For instance consider the state of global shipping back in the 18th century then compare that to the early 21st. Or farming in the 18th vs. 21st. Normally things start out small and gradually build out as technology and resources develop. Staging things is simply an engineering problem which if Curiosity is any indicator we seem to be getting pretty good at. Even during the Apollo missions we were dropping some pretty serious hardware down onto the moon. Powering these machines can come from any number of technologies from mundane to exotic. We already have well proven solar and RTG technologies, there are a few rather interesting possibilities using in-situ resources as well. For instance using the newly discovered water with the aluminum in the regolith to produce hydrogen for fuel [smartplanet.com]. The Aluminum Hydroxide byproduct has its own interesting uses. The obvious one is of course simply using the mined He-3 for fusion power (whenever we get that one figured out).
Few grand adventures into human frontiers are ever "practical" initially and that unfortunately prevents people from seeing what humanity's pioneers and explorers see. In the 1800's no one got what Charles Babbage saw. During the first half of the 1900's very few saw what Konrad Zuse saw. Today no one can miss it and everyone demands it. People too often are quick to see problems as "too hard", too near-sighted to see possibilities, too self-centered to appreciate the benefits to others. You might not get to holiday on Utopia Planitia, or sail the methane seas of Titan but wouldn't it be awesome to initiate the projects now that make that a reality for your progeny? Both incomprehensible business opportunities and human delights await us on this next frontier. What are we waiting for?
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Except that it's not economical: all current plans for fusion power intend to breed the required fuel isotopes from lithium, which is several orders of magnitude cheaper than mining anything from space.
So, that leaves what? Nothing. There is nothing on the Moon even remotely worth the multi-trillion-dollar expense. It's just rocks in a vacuum. We've got plenty of rocks here!
Re:well that's just silly (Score:5, Insightful)
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He-3 is preferable for a fusion fuel since it's aneutronic--no radiation to deal. It comes that way from the moon, the path to producing it on earth does everything but avoid radiation.
Even the "aneutronic" fusion reactions have side-reactions that produce neutrons [wikipedia.org]. While a lower neutron flux helps with materials engineering from a longevity standpoint, it still makes the reactor wall materials radioactive. That's the real problem, and He-3 doesn't fix it.
He-3 is useful as an advanced fuel in rocket propulsion
a) Requires technology that is currently at the wishful-thinking stage of development.
b) Rockets don't require aneutronic fusion, because fusion engines would be most useful in deep space, where radiation is not a problem.
c) He-3 fusion
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Reaction mass.
If we're going to send more probes / spaceships out into the universe, collecting reaction mass from the moon would be more energy efficient than lifting it from the earth. Even if we can't use that mass directly as an energy source.
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- Real estate covered in solar flux = energy
- Temperature differences = energy
- A shallow gravity well = easy to ship things out
- Low gravity may = easier life for those weak due to medical conditions = retirement
- Dark side = potential astronomy sites
- As closest planetary body from which vacuum based engineering such as asteroid mining and space habitats could be tested and based.
- Close enough that robotic operations can be monitored and directed in real time
- Far enough that it is a good place for dange
Re:well that's just silly (Score:5, Insightful)
Seriously, name one thing that's on the moon that you think is worth trillions of dollars, keeping in mind that its surface is entirely covered in rocks.
Rocks in space.
Seriously, look at the price of titanium on earth - about $7 US per kg for commodity ferro titanium. Look at the price of titanium in low earth orbit - according to Wikipedia [wikipedia.org], it costs about $4300 US per kg using a Proton rocket (the cheapest non-subsidized launch method listed). There's quite a lot of titanium on the Moon, as well as aluminum, iron, and magnesium.
That's why we want to mine asteroids and the Moon - getting material out of the Moon's gravity well is a lot easier than getting it out of Earth's gravity well (and of course asteroids generally don't have an appreciable gravity well).
If we want a space station that's more than just a few tin cans glued together and can protect its inhabitants from radiation, we need building materials. We can get many of those materials from the Moon. We'd have to learn how to process and smelt them there first, of course, but you have to start somewhere.
He3? Well, maybe later. You don't build a gas station before the invention of combution engines. Water is more valuable, if it can be collected in any serious amount, which we still don't know.
That said, I have my doubts that anyone could put a space elevator on the moon in 8 years. It's just not going to happen. The design phase would take at least half that time.
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I think you've missed bertok's point.
He3 is a waste product from D-D fusion. And D-D and D-T fusion are much easier than He-3 fusion. So if we ever achieve commercial He3 fusion, we'll have already had D-D fusion for decades. And since He3 fusion requires higher temperatures/pressures (ie, better confinement), the same technology would make D-D and D-T fusion more efficient/compact. Which means that even as He3 fusion displaces D-D/D-T for big power-stations, they'll move into entirely new markets (such as
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The reason that the elevator can work without unobtainium is that its EASY to get off the moon. The delta-v required is withing the range of all sorts of technologies (rockets - don't even need H2, could probably use O2 or N2 exhaust), mass drivers, etc.
This project would be insanely expensive - need to get the elevator (still a multi-thousand km structure) to the moon, set up etc.
Insane to think it could be done in 8 years.
Once you've done all that, there just isn't that much you really want from the moon
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One, there is almost no He3 on the moon, sure the ratio compared to He4 is massive... but that is not the same thing as a decent amount of He3. Its about 50ppb or less, the average is more like 1ppb. You would use more energy mining it that you get from the He3. Note this more than 1000 times more dilute that commercial quantities of Uranium.
The second big problem is that He3 fusion is ~50 times harder to do than DT fusion which we can't do! So even if you get
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Yeah, I don't see the point. The moon has a lower escape velocity and no atmosphere. Lunar material can be put in orbit with a catapult. (Just make sure the free luna movement doesn't take it over.
Re:Space elevator orbiting the moon? (Score:5, Informative)
They said Space elevator. Space elevator "orbiting the moon" are your words. This link shows exactly what they are attempting to do: http://www.gizmag.com/lunar-elevator/23884/pictures#2 [gizmag.com]
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They said Space elevator. Space elevator "orbiting the moon" are your words. This link shows exactly what they are attempting to do: http://www.gizmag.com/lunar-elevator/23884/pictures#2 [gizmag.com]
By definition a space elevator orbits whatever you attach it to. Otherwise, it falls.
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A space elevator cannot orbit what it's attached to. Otherwise, it's not in "orbit".
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Astonishing!
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As the earth rotates approx 28 times the rate of the moon's orbit, said string would be winding around the earth like a spool. So either the string will break as the attachment point on the earth moves away, or given infinite strength it will reel in the moon to impact in approx 9 days.
So if the imaginary string is fragile it will snap. If it's sufficiently strong then no, the moon would no longer orbit the earth.
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The problem with that is that the Earth rotates (in angle) faster than the moon orbits. Thus the string would end up being wound up around the equator (and pull the two together (assuming and infinitely strong string and anchor points...
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By definition a space elevator orbits whatever you attach it to. Otherwise, it falls.
By definition, a space elevator is in a super-orbit.That is, it's centre of mass is moving faster than the natural orbital velocity for the centre-of-mass' distance from the parent mass. It would move into a higher eccentric orbit (or escape) were it not for the application of a force in addition to gravity. Specifically being being attached to the ground by a insanely long cable. Which keeps the whole system stable, under tension.
The Moon is Blue (Score:4, Insightful)
My orbital mechanics sucks, but apparently smarter people have thought this through. It's not as intuitively simple as a tether between the Earth's equator and a geostationary satellite, but the physics does work:
http://en.wikipedia.org/wiki/Lunar_space_elevator [wikipedia.org]
My issue is that this is yet another fancy space project that presupposes an earth to high-orbit launching capability we don't have, nobody is seriously working on, and would seem to require more financial support than anybody has the will to deliver.
If somebody can crack this nut, then we can start talking about lunar space elevators, missions to other planets, and other fun stuff. But until that happens, all these fancy proposals are just so much hot air.
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Two of my imaginary friends reproduced once ... with negative results.
I'm confused. Wouldn't the result be positive?
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Two of my imaginary friends reproduced once ... with negative results.
I'm confused. Wouldn't the result be positive?
Replace "reproduced" with "multiplied" and it might be a bit clearer.
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The only way I can see that working out mathematically is that their offspring ate them both.
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Pedantically (which is all I seem to be doing lately), the anchor would be beyond L1/L2. There needs to be enough mass past the stationary orbit to balance the weight of the down-cable, and the payloads, plus a bit more to keep the system under tension.
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The problem with propulsion is that it must be continuous - shut down the engines for a couple hours and your billion-dollar elevator comes crashing down. As for a solar sail, the moon rotates relative to the sun so you can't get stable thrust that way, not to mention that the necessary forces would likely be far larger than could be attained. Solar sails are great for supplying continuous tiny thrust to small ships, given some highly reflective, ultralight unobtanium for your sail. Not so much for suppl
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The moons rotational period is its orbital period. There is no orbit around the moon that is "geosynchronous".
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No, you hang it from a satellite that is in geostationary orbit around the moon. No lagrange point needed.
The moon rotates once every 28 days, not 24 hours. Too lazy to calculate the numbers, but I think a lunastationary orbit would have a ridiculously long radius. Not practical. Better do do what the GP suggests: put the upper part at Lagrange point.
There is some additional information in this article [universetoday.com].
Re:Space elevator orbiting the moon? (Score:4, Insightful)
A lunastationary orbit would have a radius of ~384400 km (the distance from Earth to the Moon).
If you put the upper point at L1 or L2, you'll still have to put an anchor farther out to keep tension on the cable. Which may or may not be really useful, but it's an interesting idea, anyway.
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If you anchor the elevator on the far side, wouldn't it be "flung out" by the motion of the moons orbit, thus reducing the lunarstationary radius?
There's another Lagrange point on the far side of the moon [wikipedia.org] known as L2. The short explanation is that any object at L2 does have a tendency to get "flung out" but the gravitational force from the earth and moon balance that out. As long as the object stays at L2, it orbits with the same period as the moon.
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No, you hang it from a satellite that is in geostationary orbit around the moon. No lagrange point needed.
Make this "lunarstationary orbit", and you are correct.
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License it from Oakley [wikipedia.org], and you can try it out.
Doesn;t seem suitable, but it has so many different properties and uses in eyeglasses, who knows? Might work.
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I assume the latter. I mean, when I'm programming a new component, I often start with the easier component while I'm figuring out the harder stuff, even if the harder stuff could be useable by itself and the easier stuff requires the harder stuff to work (at which point I would just put up a placeholder for testing purposes). Granted, I'm talking about days of one developer's time rather than years of a whole company's, but the principle is similar. Once you had a terrestrial space elevator, you'd want a lu
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Liftport has been around for a while, but they've run into a number of troubles. I don't know what your age or life expectancy is, but if you take their roadmap seriously, it's quite possible that there will still be a space elevator in your lifetime.
Of course, if you take their roadmap without a pretty serious grain of salt, you probably haven't been following them for the last six or so years. It's been adjusted backward many times.
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It's not for profit, because there's nothing worth lifting off the Moon.
It will not work as a proof of concept, because what we learn from it will not apply to a space elevator anchored on Earth.
Maybe I should elaborate on the this. The Moon rotates slowly. Remember, the same side always faces the Earth, thus its rotation period is the same as its orbital period. So for a space elevator to stay up, it would have to be quite long, anchored at an equatorial point facing Earth, and the higher end would have
Re:The goal of the project? (Score:5, Insightful)
Re:The goal of the project? (Score:5, Funny)
3He will power the world!
It will certainly be a much cleaner, albeit hugely expensive, non-feasible fuel for the fusion reactors we won't be able to build in 2050 than the cheap and readily available non-feasible fuel we can't extract from ordinary seawater for the fusion reactors we can't build right now.
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It will not work as a proof of concept, because what we learn from it will not apply to a space elevator anchored on Earth.
The biggest issues to work around in most projects are the ones nobody thought of at the beginning. Even though many of the variables will be different for the moon vs Earth, it'll be useful to know that a) it can be done, and b) what the unexpected problems were.
Re:The goal of the project? (Score:5, Interesting)
Indeed, to be stable the elevator would have to be "stationary" within the rotating Earth-Moon frame, with the top extending past either the L1 or L2 point (towards or away from the Earth) far enough that the force of it "falling away" from the moon would be sufficient to counteract the weight of the cable itself.
Calculating the exact distance of the L1 and L2 points can be difficult, but so long as the masses are significantly different they are at approximately the Hills Sphere radius from the smaller mass M2 at r = R (M2 / 3*M1)^1/3. For the earth-moon system that is about 60,000km from the moon, versus the 36,000 km from Earth that constitutes geostationary orbit. So the elevator would have to be about 60% longer than on Earth, but the much lower gravity means it could be far thinner and weaker, and thus easier to build. Even perfect carbon nanotubes barely have the strength-to-weight ratio necessary for an earth-based elevator, with no room for a safety margin.
Plus for the immediate future at least the liability is much lower on the moon - a failure that drops 60,000 km of cable onto the moon from orbit is unlikely to be a problem beyond the fact that your very expensive elevator is now scrap. Drop 36,000 km of cable onto Earth, enough to to wrap almost all the way around the planet, and you're going to have a heck of a lot of secondary damage.
Personally I prefer the idea of the "tumbling cable" elevator - take just a few hundred kilometers of cable orbiting while tumbling end-for-end with the tips coming down almost to the surface like opposing spokes on a wheel rolling along the Moon's equator and you've got an elevator that will match speeds with various points on the equator on a regular basis, coming almost straight down before momentarily stopping and then hauling snagged payload up at roughly 1/4g. By the time the payload reaches it's highest point it will be moving sufficiently fast to easily escape the Moon's gravity, and depending on the particular orbital trajectories of the cable and Moon at the moment of release, moe than enough to escape the Earth's as well, even to put it on a Hohmann transfer orbit to Mars or Venus. Granted all that extra energy means it's not ideally suited to Earth-Moon transfers, but it sure would be a lot smaller and easier to build (except for the necessary drive system to recharge the angular momentum transferred to the payload), as well as making the Moon a major waystation to our much more interesting planetary neighbors.
Re: (Score:2)
Re: (Score:2, Interesting)
I would imagine so, I can't think of a "killer app" that isn't easier to do with an electromagnetic mass driver, and for exactly the same reasons (near vacuum, low gravity), except for possibly the power requirements.
The 'kicker' of course is that an elevator can't launch heavy rocks at high speeds the way a mass driver can. This protects the Earth from possible terrorrorrorrist takeover of any prospective catapult.
Re:The goal of the project? (Score:5, Interesting)
Who needs speed? The elevator would still let you drop big rocks on Earth - sure they're moving slow relative to the top of the elevator when you let them go, but the entire moon is moving at about 1,000km/s relative to the Earth, and once those rocks have fallen the remaining couple hundred thousand kilometers to Earth they'll be moving even faster, more than enough to do massive damage wherever they're aimed. We *might* be able to shoot them down, assuming were willing to expend a space-capable nuke against it, were able to hit the thing given the massive speed it's traveling at (shouldn't be *that* hard to basically stand in it's path), and preferred to have radioactive slag come raining down over a wide area rather than letting the rock vaporize it's target. Of course if several rocks were dropped at once that would be far more difficult.
That's the one big problem with a space-based economy - once you're moving heavy stuff around in orbit *everything* becomes a high-yield weapon, and there's not much anyone on Earth can do to defend against it. It's like the ultimate version of trapping your enemy in a narrow canyon where you can fire down at them from all sides. And if an Earth-moon war should ever break out, well the Moon is almost guaranteed victory - both sides will see any incoming weapons a long way out with plenty of time to intercept - but hitting the Moon requires high-energy launches, while launching from the moon requires only ~1/25 the energy (~1/5 the escape velocity) so they can just throw rocks all day long for the cost of launching one missile, and any debris from intercepted weapons in either direction is far more likely to fall back to Earth than hit the moon.