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Space Elevator May Become Reality
mojotek writes: "The NASA Institute for Advanced Concepts has a study(15Mb pdf) about the feasibility of a "Space Elevator" comprised of a 22,000 mile long cable built out of carbon nanotubes. In theory, it would be able to carry loads of 20 tons to space without using a single rocket engine. Sounded way too sci-fi for my taste at first, but this article at TechTV actually helped fill in the holes."
vacuum gloves, radiation belts, high-velocity hardware...
"Those who have never entered upon scientific pursuits know not a tithe of the poetry by which they are surrounded."
Not to dismiss the elevator out of hand, but wouldn't research into efficient space vehicle propulsion yield better long term results? While the engineering feat of building an elevator would certainly yield advances in science and technology, the elevator's limit would be its height. Non-tethered vehicles have no such limit.
I didn't see anything in the .PDF about armoring the elevator against Vermicious Knids. It's just that sort of oversight that will be their undoing. Mark my words. Or Roald Dahl's.
I am the very model of a modern major general!
I did the math and worked out that if you gibbed the cable (say 1m chunks), you'ld wind up with something like 25-30 thousand km (I don't remember the exact figure) of the cable crashing down on earth and the rest flying off into space. However, I didn't figure out if the cable would fall east or west (west would be better, but I think it's less likely). Either way, that's a little over 1/2 way around the world and while the only land mass likely to be hit is Africa, I don't imagine the impact with the water would be particularly fun (possible tsunami).
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
as shown in full gory detail here. note the counterweight too.
The line might generate a lot of electrical potential if it didn't remain stationary relative to the earth's magnetic field... Also, wouldn't things like wind, static electricity, lightning and auroras cause problems with a 22,000 mile long cable?
"Leave the strategizing to those of us with planet-sized brains." -Tycho
Because if it fell down, it'd be about as destructive as a thermonuclear bomb (kinetic energy's a bitch). And NOBODY would want this in their back yard after 9/11.
On the moon, Mars, any other sparsely-populated/unpopulated body in the solar system? Sure. But not here.
That's the book he wrote about this. Worth a read, it even describes some of the projects by the US and Russia concerning this decades ago, in the appendix.
To transport you (70 kg) up to an altitude of 200 km would take roughly 140,000 kilojoules of energy (you do the math ... first year physics stuff). However, they can't just lift you, they also have to lift a vehicle containing you. Say the vehicle weighs 500 kg for every person it can carry -- this would take rougly 1,000,000 kilojoules. If they do this electrically (which is one of the more expensive forms of energy), at 100% efficiency it would eat up roughly 300 kWh of energy. At 0.30/kWh (say), that's roughly $100.
Of course, a clever engineer would realize that every vehicle going up eventually goes down ... so the vehicle on the way down could be used as a generator, feeding power to the load of a vehicle going up. Equally obviously, we're not considering the amortization of the construction cost, which would be monumental.
Toronto-area transit rider? Rate your ride.
You can't have the orbital part without a counterweight otherwise you have gravity pulling down on the vast majority of the cable and the whole thing falls out of the sky. So you need a mass at the end of the cable so angular momentum holds everything up. Last I heard you needed a lot of mass to do that -- like a trapped asteroid or something -- far more mass than we havet he technology to put into orbit.
they want to have a 22,000Km cable to space, but I can't get DSL because I'm 2.3 miles away...
Grrrr
Chaos, Mayhem, and Destruction: Not
Trouble is, if someone farts in the elevator, it's a damn long wait before you can open the door... ;)
The short answer is: Yes.
Physics works everywhere all the time. When you climb a flight of stairs or walk up a hill it slows the Earth's rotation - and it speeds back up as you walk back down.
No - seriously - just as an ice skater's rotation slows or speeds as they extend or contract their arms the same principles apply to all rotating bodies. Everytime we slingshot a space vehicle around the Earth we are effectively transfering some of the planet's energy to the vehicle and that energy has to come from somewhere.
But the amounts here are so small that the effect is not measurable or "effective" in the scale of anything we could notice. It's like the fact that anything with mass has a gravatational field - but you don't notice the effect of the gravity created by your pen.
=tkk
Bill Gates - Creationist?!?
It's really slow, but it ain't pdf format http://www.niac.usra.edu/files/library/fellows_mtg /jun00_mtg/html/472Edwards/472Edwards.html
I guess this obsoletes my "space escalator" idea then, eh?
This disaster was used (although on Mars) in the plot of in Kim Stanley Robinson's Red Mars (or maybe Green Mars... can't remember). In that case, though, the "beanstalk" was sabotaged as a weapon during a revolution. It wiped out a slice of a city, puncturing the atmosphere of a bunch of buildings, but had no casualties outside the settled areas. Can't have a tsunami in that thin an atmosphere.
"Prepare for the worst - hope for the best."
There are some variations on the idea though,like this one, that are close to being possible with today's technology, and can even be provisionally costed. Basically the idea is to construct an elevated runway about 100km up, and use mass drivers to hurl stuff into orbit. At that altitude the saving from air resistance is huge and mass drivers become very efficient
At this stage, NASA speanding serious time thinking about space elevators is probably no more useful than daydreaming. Thinking about this kind of thing is probably more productiove though, becuase something might come of it in the medium term, and its almost as efficient as an evelator anyway - with the decided advantage of not being able to collapse and strangle the planet.
(Since I heard about this from a NASA researcher, maybe Im being a little harsh to accuse them of daydreaming)
Why stop at nuclear waste?
On the way to the sun first should be:
1. The source code and any disks containing Windows 3.11 and Win32s. Puh-leeeez! Pretty Puh-leeeeze!
2. All the AOL CDs on the planet - though that would break the damned thing, wouldn't it?
3. Hillary Rosen. (Just an elevator ride, Hil! Really!)
4. The Microsoft Marketing Department. They've made the rest of the industry go to hell, so....
5. Larry Elliston's ego. Might make the Sun go nova, so we'll have to do some calculations first.
6. Ditto for BillG, SMcNealy and SJobs.
7. All e-mail SPAM. The Internet's equivelent of nuclear waste.
8. Jon Katz stories and Cowboy Neal polls.
Did I forget everything, er, anything?
Soko
"Depression is merely anger without enthusiasm." - Anonymous
But the weight to payload ratio sucks pretty hard. I imagine the up-front construction costs would be a lot higher than the cost of building rockets. So even if it's cheaper after, say, 10,000 uses, we might not see anyone wanting to build it.
You see? You see? Your stupid minds! Stupid! Stupid!
A one-way trip would take about 5 days or so, and your weight would gradually decrease from normal to zero as you reached the geostationary station.
You would not stop at the 200km height, no more than you get off a ski lift at the first tower.
At the 200km height another poster mentioned - you would have a hard time finding any change in your weight. Instead of being something like 6400 km from the center of the earth you're 6600 km away. That's enough for about a 6% change - less than the annual weight change by many people on yo-yo diets.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Has anybody really sat down and worked out the physics of this thing if it were to collapse? How would the atmosphere effect it? How much of the structure would burn up? Most of the models for something colliding with the earth involve something that is one contained piece of mass. How does a big long rope like mass react during a similar collision?
This sig has been temporarily disconnected or is no longer in service
Ok, let's say that the destruction aspect of the tower isn't an issue, that the way this thing works means it could collapse in a (relatively) harmless way. I'm a little concerned with the whole idea of cheaply and easily getting things into orbit. Maybe I've read too much post-appocalypse Cyberpunk (spefically one of the stories in "mirrorshades") but it seems like there needs to be a *large* amount of regulation with what goes, because of what might be coming down... (like huge quantities of EMF blowing out pretty much everything electronic...)
SO YOU'RE GOING TO DIE: The Comic for Dealing with Death
9. Linux users. Puh-leeeze!
I'm a loner Dottie, a Rebel.
I hope I don't get modded down for this idea like I always do but here it goes anyways..
I've read several books which include the idea of a space elevator, and one of the key problems had to do with bringing that much cable to space, and the strength of the cable to stay together. The closer the cable gets to earth the harder the pull, the further out the "satellite" holding the cable in geo-synchronous orbit has to be. Instead of bringing the cable down to earth.. or putting it atop a very high tower, why not create a platform 50-80,000 feet up for planes to land on. This would save very large amounts of cable from being created, the satellite wouldn't have to be nearly as far out either to compensate for the gravitational pull from the cable below. Also, to compensate for the excess weight of the aircraft and payload while landing, the satellite holding the cable could move up and down to balance any weight added or removed to the cable.
Now, having a shortend cable would have added benefits too, in the event of a disaster, normally a cable attached to the earth would wrap around the planet several times causing an incredible amount of destruction. This could be minimized with my platform idea. Imagine something colliding with the cable causing immenant failure... why not create sections in the cable to automatically break off in the event of a disaster, this would minimize the amount of cable falling to earth, and the remaining cable would be either ejected into space, or depending on how an object hit, its possible the upper section could re-establish a geo-syncronous orbit after losing much of the cable.
Any pysicists out there able to agree/disagree with this? The tether would also most likely have to be conical in shape, thicker higher up, and thinner below to minimize the amount of carbon tubing used in the elevator.
One big issue they missed is the fact that a carbon nanotube cable still isn't strong enough to support it's own weight without tapering the cable correctly, at the middle it has to be about 10 times thicker because the stresser are highest at geostationary orbit.
The deployment method they're using doesn't take account of the fact that you need the thickest part to always be at the middle - if you simply unroll it the way they suggest then the incorrect thickness profile will result in the cable exceeding it's breaking point and snapping.
What they need to do is unfurl a cable like this from geostationary orbit simultaneously up and down at the same time. The Mechanism to do this would have to be very delicate at unfurling the last kink or the cable will again snap.
The cool thing about this is if you figure out what kind of weight you want the cable to support then you can come up with an idea of the amount of energy stored in the tension. If the cable snapped at any point then the amount of energy released would be pretty phenomenal. From each end of the snap you'd generate a compression wave which would get stronger as it travelled along the cable, after a while of picking up energy it may turn into a shockwave and snap the cable again (essentially shattering the cable). If it doesn't then the wave will have energy equivalent to nuclear weapons when it reaches the endpoints and the waves transmit themselves into the supporting structure....
Besides, this "space elevator" would be a giant, provactive, easy target for terrorists.
If we let that stop us, then the terrorists have already won!
___
The way to see by faith is to shut the eye of reason. --Ben Franklin
Oh, please, go back to your caves and freeze to death why don't you!
You do realize we HAVE to leave earth or we die here! What, you think the Sun is going to burn forever? Long before that, we will get hammered by some multi km asteroid that will barbecue most of life here anyhow! Wake up, get your act in gear, it's time to colonize space while we still can.
The solution to this problem is also simple. Each piece needs to be aerodynamic anyhow, so add some flight control surfaces so it can "fly" apart under control...
...or "beanstalks" as the insiders like to call them, read the scifi/humor novel Rainbow Mars by Niven. It features beanstalks in many places, including what happens when one pulls loose from Brazil.
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
If you'd like to see a surprisingly realistic sci-fi version of this, I suggest you take a look at Bubblegum Crisis 2040, an anime series that most geeks would really enjoy anyway, even if just for the interesting sci-fi ideas and the references to American sci-fi movies like Blade Runner and Alien.
It would totally depend on how far from the earth you were. If you are exactly on a geosyncronous orbit then you would definetly feel weightless no matter what. I'd assume that such a space elevator would be "anchored" on a geosyncronous orbit since otherwise it would drift and probably break the whole assembly.
If you are below the geosyncronous orbit you'd feel slight gravitational pull and above it you'd feel the effect of sentripetal force of the elevator keeping you attached to the earth - you'd actually be standing on the roof then.
Shuttles are normally orbiting the earth at a speed and height (mv^2/r=GmM/r^2) where earths pull is just enough to keep them on a steady circular course around earth - so they are technically free falling but never approaching earth. Geosyncronous orbit is just a special case where you're going at the same angular velocity as earth.
Something like this wouldn't be built for at least 20 years from now. By then simple nanomachines should be available, since much of the construction of this would probably be done at a nanoscale. If there were swarms of nanomachines all up and down the cable and if they were made to detect any abnormalities in the structural integrity of the elevator, they could simply deconstruct it. Billions of micron length strands of bucky tubes should not have that much of an impact on the ground due to friction in the atmosphere. It would simply be dust particles floating around. I'd think the deconstruction of the cable could be done in a relatively short amount of time as well. The only problem with this would be false alarms, but then again with that kind of technology it wouldn't take too long to reconstruct a new cable.
Just some thought anyway..
And it is exactly that, sci-fi. Sure, carbon nanotubes are incredibly strong. And they're also on the order of a few microns long. Now, this cable needs to be a few hundreds of thousands of meters long. You do the math.
The semiconductor industry figured out how to make large single crystals of ultra-pure silicon, then pattern the surface down to a ridiculously fine resolution. The fiberoptic folks figured out how to make glass so clear that a light pulse can go through many many miles of it and still be recognizable at the other end. Molecular biologists can "amplify" single molecules of DNA into macroscopic quantities.
I wouldn't be so quick to say that we will never be able to make carbon nanotubes that are long enough to be useful as structural materials.
This reminds me of a comment my parents made after taping Atomic Train (NBC) for me since NBC felt Coloradans were too feeble-minded to deal with the plot.
A train containing an atomic (not thermonuclear) bomb crashes in the mountains 40 miles west of Denver. It detonates! What would I do?
I told my mom I would go outside to watch. An atomic detonation at 40 miles away doesn't bother me. An accident at Rocky Flats (5 miles south) when it was operational is a bit worrisome, but not a fission explosion 40 miles away with several mountain ranges between us. Even a thermonuclear explosion at that range is not the instant death portrayed in that movie.
The point is that nuclear weapons, as destructive as they are, are still largely local events. The cable smacking into the equatorial oceans would dump a lot of energy into the water, but that energy would be spread across coastlines worldwide. Millions may still die, but not billions. And that risk may well be considered acceptable if the alternatives are far worse.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Actually, there's strong evidence that the number of large dams constructed over the last few decades have changed the length of the earth's days. Not by a huge amount, but I think it has started to affect the introduction of leap seconds.
(The main reason the earth is slowing down, IIRC, is the tidal forces from the moon and sun. If the moon was gravitationally bound to the earth it would be falling, but since it's not it's slowly drifting away.)
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
The CBC Radio science program, Quirks and Quarks had an article about the space elevator on November 3rd, 2001. An MP3 of the article is available. Check it out!
They're talking about a tube with ~paper-thickness walls (single layer of Carbon-60?). If something like that broke into small sections, I wouldn't think it would really crash, but just drift down sort of like a bunch of kites that lost their strings. It would be expensive to replace, but no catastrophe.
I don't have any idea what would happen if it broke free while mostly intact, but we could always make sure it breaks up in that case. If nothing else, the defense force could just shoot at it.
I think those few ships would probably just be a few missle cruisers in a ring. If there is no legitimate air traffic in that area, they have a lot more leeway to defend the elevator. Anyway, it's not like Aegis cruisers have never shot down airliners before... (U.S.S. Vincennes, late 80's)
"Where do you put the extra length? In the ocean? "
The other end is in orbit, it can easily move nearer or further the earth
---
Oregon
Bungee jumping off the Space Elevator
... woah!
...
Hacking the Space Elevator "this is the down signal"
Getting Greenpeace to fly a very large flag from the Space Elevator "better than a smokestack"
Getting a bunch of friends to ride up with you and all sway together so it rocks
Tossing pennies over the railings and watching them burn up on reentry
Paragliding from the space elevator
Paragliding onto the space elevator (not for the faint of heart)
Downloading images from the Space Elevator Coffee Pot webcam
Taking a dump - has to go somewhere
-
--- Will in Seattle - What are you doing to fight the War?
I was just out of college (iirc) when the first popular discussion of beanstalks came out (Charles Sheffield, in some long-dead Baen book-zine).
The numbers were so ludicrious that he repeatedly apologized for wasting our time. Of course this was a flight of fancy, the numbers were orders of magnitude larger than the strongest known materials. Yet, if "ultronium" could be developed from some exotic material....
Then buckyballs were discovered. Then buckytubes.
The fact that this is even "just" possible with known materials less than 20 years later is mindblowing. I can only compare it to the confident RSA predictions in Scientific American (which I also remember when it first appeared) that RSA-128 would take millions of years to crack. We all know how well that prediction held up.
Given this perspective, I don't think it's unreasonable for NASA to spend some serious money considering its options if/when stronger materials become available. It's easier to believe that even stronger materials will be discovered (e.g., perhaps by putting foreign elements within the tubes to manipulate quantum properties) than that we've suddenly hit the ultimate barrier.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Would you really be weightless, or would the centripital force created by the rotation of the Earth (and hence, transferred to the cable) be enough to keep you pinned to the cieling when you get to the top?
"Alcohol, Tobacco, Firearms, and Explosives" should be a convenience store, not a government agency.
Argh! Damn elevator! Here, let me pry open that door so we can climb---" (Big sucking noise)
I meant to insert "the apparent centrifugal force caused by the inertia of the cable due to", but hit submit before I did that.
"Alcohol, Tobacco, Firearms, and Explosives" should be a convenience store, not a government agency.
Good point. Imagine the danger of strapping a few idiots to the top of a cylinder full of insanely flammable gasses to escape the Earth's atmosphere. This "rocket" could blow up and kill everyone aboard. Or it could crash and take out many other innocents. It could be shot down by missiles, bullets, bombs, etc. And worst of all, it might ignite the upper atmosphere and end life on Earth as we know it!
People go nuts when you suggest building a new nuclear reactor. What do you think would happen if you tell them you're going to multiply the potential destructive consequences of that by many fold, and suspend it over their heads? And the potential for an accident pales in insignificance if you consider how attractive a target it would make for someone to take down on purpose. I'm as big a techno-freak as anyone (hey, bring on those nukes, we need the power), but this would worry even me.
A sci-fi/sci-fact magazine in paperback form called Destinies had a story about this in their Aug-Sept 1979 edition. The story was called "How to Build a Beanstalk" by Charles Sheffield. He did some research into the material strength required, and to get the stalk to reach down to earth, or somewhere near it required a material with a tensile strength of 2 000 000 kg/cm^2, which was 10 times the current known tensile strength of known materials at the time.
"Beanstalks, originally called skyhooks, are an idea of the 1960's whose time may at last have come. They are used as important elements of at least two novels published in 1979, Authur Clarke's 'The Fountains of Paradise' and my own 'The Web Between Two Worlds' "
http://pcblues.com - Digits and Wood
I've read this paper in full, a couple of months back. According to the paper the actual, demonstrated strength of the carbon tethers is only as strong as Kevlar- it's about 1/10 of the needed strength. The overall weight of the fiber is exponentially related to the strength, so the tether works out maybe 20,000 times heavier than his design- which makes it completely uneconomic.
OTOH, single fibers are almost strong enough, but only if you allow absolutely no 'safety factor'. Most normal engineering uses atleast 2 safety factor, and usually many times that. But as nobody knows how to splice them together into a rope, and doing so would lose atleast 25% strength, it's not enough.
He's got the best architecture I've seen for this by a long way, nice paper study. Not practical right now. Hope somebody sorts out the fibers very soon.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Nasa already tried a long cable experiment. This one was probably made of metal though. They deployed a long cable from the space shuttle (i forget how long, but it was pretty darn long) and let it 'drag' behind. The idea was that as it dragged across the Earth's magnetic field, it would produce an electric current that the shuttle may be able to use.
Well, they goofed up the math somehow. They underestimated the stresses on the cable and the thing snapped shortly after deployment, flinging it away from the shuttle. They did not retrieve the cable; one more piece of space junk.
"Never, never suspect the dreams within the dreams of dreaming children." ~The Amazon Quartet
Translation: "I can't imagine any solutions for these problems, therefore no solution could possibly exist".
I don't care if it's 90,000 hectares. That lake was not my doing.
Is that you could no longer have satellites in any orbit other than geosynchronous unless their orbits were very carefully tuned to avoid hitting the cable.
BTW: A space elevator will never really fall, if you put a rocket on one end you could get it to pinwheel, but I don't think any terrorists would have the time to attach a rocket motor with sufficient thrust to get it to do this.
No really, think about it, the space elevator would be rotating about GEO at exactly one rotation per day clockwise, while the earth rotates about its center at one rotation counterclockwise. Nothing you could do at the end would allow you to make the elevator fall.
If you really wanted the elevator to fall, go to the center of mass and cut it in half. That'll bring it down quickly.
BTW, read Rainbow Mars by Larry Niven, even if it is fantasy. You'll probably agree that we really don't want a space elevator :)
marotti.com
No, really. While we're building a 22,000 mile long cable strong enough to hold 20 tons, where are we going to put it? It's probably too big to actually
We can't start stringing it off into space as we build it, because it'd keep tending to fall back towards earth until it were about.
And, once we've figured out all that, how do we get it
That said, it'd be a damn cool thing if we had it, and if a team ever succeeds in constructing one, I'll personally buy a beer for every member of the project.
The tape IS wider in the middle than the ends, the tape is very skinny at either end. And his deployment strategy works fine. Read the paper.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"30c per kWh is a lot. I usually pay about 10c. Plus, access to space would give very cheap access to 24x7 solar energy, which would further reduce energy costs.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"I bet that's one cool frisbee.
Insanity is the last line of defence for the master diplomat. But you have to lay the groundwork early.
The tether is expected to get chopped down occasionally by meteorites or space debris. It would be designed to burn up during reentry. It would not harm the earth in any way. The remaining lower length would end up in the ocean, and can probably be collected up and incinerated.
Besides. it's only 20 tonnes initially, an earth killer? I don't think so.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"The idea would be to send mining and manufacturing equipment and set up some sort of mars base. Once you've got everything right on Mars then you look at building one on Earth.
NASA should really consider this. There is nothing, NOTHING that can motivate a nation and a world to tackle the endeavors of space than a 22,000 mile glittering testament to our power and ingenuity rising into the heavens.
"Your superior intellect is no match for our puny weapons!"
On the island Gan, in the Maldives, as noted in the NASA research and AC Clarke. But, I doubt the gov of Maldives would let that happen. NASA says it might build a rig outside the 200 nautical mile zone of Maldives, but since Maldives is such a vocal environmentalist country, this might not fly too. But on a happy note, the people of Gan would welcome this, just as they welcomed the RAF base GAN in the 50's.
It's the most feasable place due to abscence of any real deadly storms and other stuff, not to mention it's on the equator.
Trust the source!
The concept in Rainbow Mars was a pinwheel, not a space elevator. The difference is that instead of having the cable just hang there, it instead rotates around its center of mass. However, you weren't far off thinking about the Dream Park novels. You're probably thinking of another novel he did with Steven Barnes, Descent of Anansi. In that book, a space shuttle trapped in orbit with nothing going for it but a cargo pod containing a spool of "Sinclair molecule chain" manages to engineer manages to engineer its reentry by connecting the shuttle to the pod using the cable and letting the cable spool out. I'm not clear on the physics, but it was something about the shuttle dropping into a lower orbit while the pod ascended into a higher one.
--Fesh
Kill -9 'em all, let root@localhost sort 'em out.
Note, however, that I didn't take air friction into account other than deciding on a safe/unsafe border for chunks to fall to (if they miss the atmosphere, they're not coming to the surface any time soon (days to years)). And then, most of the euator is water, and the cable would likely come down relatively gently. I still wouldn't want to be anywhere near it, but forget the world wide disasters other than maybe some minor coastal flooding and some unpleasantnes in the vicinity of South Africa (hmm, or os that north? My African geography is rusty when it comes to the equator).
Maybe I should have stated this in my post, but I'm actually for a space elevator.
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
I studied this concept as part of a commercial space development group back when I was in college. It's quite compelling.
;)
/. - I may have messed up initially and buried this as a reply deeper down the treads.]
There're two significant challenges in implementation, though.
The fundamental flaw in the concept lies in conservation of rotational inertia. Think about a spinning ice skater - as she draws her arms in, she spins much faster. The opposite is also true - as a rotating mass extends from its center, its rate of rotation decreases.
The space elevator rotates at a constant geosynchronous rate, but as its payload is raised along that axis, the difference between its linear inertia at the surface of the earth and its linear inertia around the circumference at geosynch altitude (or any significant altitude along that axis) is absorbed by the elevator's structure.
Unless the payload applies some sort of thrust perpendicular to the axis of the elevator, that difference in inertia only works to pull the whole system back down to earth. Effectively, the amount of energy you'd have to put into the system to keep it up would equal the thrust expended to send the payload into orbit by conventional means.
Then there's the whole issue of vibrational harmonics. Accumulated shocks from winds, payloads, and even space dust would propagate up and down the string (any human structure of that incredible length would effectively be a string in tension) and create severe vibration problems. That'd take some *seriously* epic engineering to dampen.
NASA has done some experiments with tethered satellites which address the vibration issues (as well as accumulated electric charge from atmospheric drag), but they were intended more for spinning-wheel satellite applications than for space elevators.
It's a really cool idea that unfortunately is a something-for-nothing scheme. If there were some kind of cool electric thruster system which didn't rely on reaction mass, it'd be feasable, but then we're straying into Area-51 technology.
[This is my first post to
NASA is currently recruiting a team of flute-playing Snake Charmers to coax the cable into the air and keep it there. Send your demo tapes now!
Often in Error, Never in Doubt.
LOL, Found this article at Weird NJ
WeirdNJ.com
ONE OF NEW JERSEY'S MOST BAFFLING MYSTERIES came in the form of a silver "thread" that was suspended for days over the house of Mr. and Mrs. A.P. Smith of 85 Forest St. in the quiet suburb of Caldwell in Essex County.
--Jon
Let's hope that dubya's goons won't be deployed to Taprobane to level that old temple and kick some monk-ass...
Only 50 years ago, it was a tens of cubic centimeters per tube. Now, you can have 100 million in something lightweight enough to put on a finger. You can fit a billion in your pocket. They're already talking about billion-transistor chips in 10 years.
Other 'impossible' things have happened. Humanity can marshall immense resources. The interstate highway system built tens of thousands of km of highway, moved mountains, built bridges, over a country with millions of square km.
In 50 years look at the communication system we've built. Its millions of times higher bandwidth.
And, with modern productivity, you can do orders of magnitude more stuff with less effort.
THings aren't geting faster and better.. THey're getting faster and better at an ever increasing rate. There has been more change in the last 60 years than all of history put together. Some would say 30 years.
NASA began considering the concept in June 1999 at the Advanced Space Infrastructure Workshop on "Geostationary Orbiting Tether 'Space Elevator' Concepts" held at the Marshall Space Flight Center in Huntsville, Alabama.
GOTSEC? Can this be real?
Living better through chemicals
You forgot about the 10000 people in the hotel and casino at the top of the elevator...
On a side note, how fast would something like this actually fly into space? Even if you could hit it at 30,000 ft with something like an airplane, roughly 99.97% of the cable's mass should still be hanging in space.
Given that the cable was held in place by its own mass originally (not by being welded to some island,) and that it was already in geosynchronous orbit, just how quickly would it start to move? Would we have time to re-anchor it before we lost the whole thing?
Living better through chemicals
Questions for the astro peeps here...
What would the g-forces be like on the end of this thing going around so fast at that distance? Wouldn't it be like one of those machines they stress test pilots on?
The document describes it like swinging a ball around your head, but that means you've got an oscillating force. Would it be enough to make the Earth wobble a bit? Would that be comfy? Would we need two elevators, one in each hemisphere?
Then there's the whole issue of vibrational harmonics. Accumulated shocks from winds, payloads, and even space dust would propagate up and down the string (any human structure of that incredible length would effectively be a string in tension) and create severe vibration problems. That'd take some *seriously* epic engineering to dampen.
To some extent those two are each others' solutions.
The low-frequency vibration solves the pull-back problem. Thinking discretely: The weight of the payload on the thether and the taut teather form a loaded "stringed-instrument" string:
Go up a bit, you pull the string back.
Stop and wait a bit, the string accellerates you forward.
Now go up some more while the string is still going forward, providing a "pull" backward that damps the vibration, stopping the string at the vertical position.
Repeat.
In fact you do this continuously, modulating your ascent slightly so the net result is the string stays nearly vertical. When a vibration starts to build up you adjust your speed in sync to damp it.
Similarly the tether and the weight at the end (large compared to the payload) form a pendulum. It's a much more complicated pendulum than one near the surface, due to the varying gravity and the rotating coordinate system, but that's the basic idea. Again thinking discretely:
Go up a bit. The couterweight pulls back.
Stop and hang around. The counterweight starts going forward.
Go up some more. You decelerate the counterweight and bring it to a stop near the top again.
Repeat.
Again you do it continuously, this time keeping the weight at a constant displacement behind the point over the tether's base. The slant of the tether corresponds to a forward accellerating force from the rotation of the earth, providing your angular-momentum transfer by accellerating your payload and decellerating the earth. (Coming down you push the counterweight forward to accellerate the earth and decellerate the payload.)
Now there may be one or more locations along the tether where what you have to do to damp the two modes is exactly opposite. But if you've kept it damped on your way to those spots you should be through before an oscilation builds up. Or run two or more payloads simultaneously and coordinate them so you can always damp both modes. (Multiple coordinated payloads can also provide better damping and trade off each others' effects on the tether to achieve faster travel.)
Of course you have to put your counterweight a bit further above geosync, so lift losses when it is displaced downward slightly don't turn into a positive-feedback collapse.
If you don't have enough payloads in transit you can damp higher-frequency modes against the atmosphere with a few active airfoils spotted along the tether. (REALLY high frequency stuff - like seconds-to-audio - you can damp with a couple small structures attached near the geosync level.)
Effectively, the amount of energy you'd have to put into the system to keep it up would equal the thrust expended to send the payload into orbit by conventional means.
No.
The amount you have to put in is only a small delta above the amount that you would have had to put in to run an electric elevator up an idealized stiff structure of the same height - and the delta approaches zero as your damping approaches perfection.
But once it's up you don't need to power it AT ALL, which I'll get to in another posting.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Something I haven't seen mentioned here (is the idea forgotten, or has it been proven to be flawed?) is the "construction ring" method.
Basically you launch your cable fabrication facility and create a *huge* loop of cable. Something long enough to encircle the earth at geostationary orbit. This loop is initially unstable and will require temporary station keeping engines. You don't care about north-south twists, but don't want in-out twists to grow to large. (Read any analysis of _Ringworld_ for details...)
You then turn the cable machines on their side and start laying cable towards/away from earth. The cables will follow local geopotential fields down and up, and eventually you'll have a starter cable touch down. This can be a temporary cable, designed to be discarded, that does nothing but throw mass up the cable to build the ballast and feed additional cable machines that are producing the production cables.
Eventually you have ring in geostationary orbit, plus numerous anchors along the equator. You supplement the ring at geostationary orbit with another ring a bit inside (or outside) of it so that it's always under tension.
Besides solving some construction issues, it eliminates many of the collapse modes. If the cable snaps, the upper portion is kept in place by the ring. Even if all cables are snapped, the ballast weights will keep the ring under tension and survivors can manage station keeping by dumping ballast. (Unfortunately, if all cables snap the rest of the system will have a different net orbital velocity and there could be a big jolt.) Since there are multiple anchors, there's little value to terrorists in destroying any single anchor.
I know that _3001_ mentioned a ring as an endstage after building the first beanstalk, but I thought I've seen papers suggesting they be used as a construction platform.
And the secondary benefits are huge. Let's say the ring is 250,000 km long, and there's a 500m wide band of solar cells attached to that ring. The solar constant is around 1370W/m^2, that's potentially 171 GW of pollution-free power than can be fed down superconducting cables - 540 trillion kWh/year. According to the USGS the US consumed about 9 billion kWh/year of power from all sources in 1998, so even if the ring has only 1% efficiency it would still provide every person in the world 300x more power than the average American consumed in 1998!
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
Here's how to do it for zero energy cost, once the tether is up and the first set of vehicles are "charged".
(By the way: I haven't seen this anywhere else so I may have just invented it. Dibs! B-) )
Build your tether so it goes out FAR BEYOND geosynchronous orbit.
Your vehicle consumes energy as it climbs to geosync orbit.
But as it goes further out, it is going DOWNHILL against the local apparent gravity again, experiencing increasing centripital force from the tether. It collects energy by DEcellerating itself against the tether. When it has collected enough (and released the payload at a desirable velocity) the vehicle decellerates to a stop (collecting still more energy) and starts back toward earth.
It uses part of its stored energy to "climb back down" to the geosync point. Then it continues to ground, accumulating more energy by regenerative braking against the tether (just as it did above the geosync level). It arrives at the ground with as much power as it started with, or more.
Make the tether long enough and your payload can achieve solar escape velocity and still leave you with more "charge" in the vehicle's storage than you started with. (Launch some cheap rocks to power the space terminal's parking lot lights. B-) ) Of course the tether might end up so long that, even using the extra length as the entire counterweight, you have to strengthen the lower end a bunch. (This I haven't worked out.)
With no-cost (except storage) energy, your trip only costs the ROI on the equipment. (Probably reasonably large. But still LOTS cheaper than rocket-based space shuttles.)
It's not perpetual motion: Like tidal power, you're getting your energy from the spin of the earth, slowing it down to power your system.
But if the envirowackos complain, a millenium or two later, that their watches say sunrise is a couple nanoseconds late, you can bring down some ore from an asteroid mine and balance things out.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Space Elevator: Another project brought to you by NASA after a few hours with the SpaceBong 4000.
pr0n - keeping monitor glass spotless since 1981.
#2 Balancing this thing so that it doesn't wobble. For every pound that goes upward, we need approximately as much going down, right?
No. (See my previous post. You just need to have the center of gravity a bit high and be careful about how fast you go up at any moment.)
#3 Can we sit a free floating space station just a few hundred yards outside of it?
Yes, at the geosynchronous level. (Though climbing and lowering loads will move the tether forward and backward a LONG way as they are moving up and down.)
#4 If we can do that, can we build a bridge to it (of course, you'd need to do this in both directions) ?
Yes. But if you connect them your satellite will move forward and backward as the tether is displaced by payloads moving up and down. Or else your bridge will fold up.
#5 If the bridges get long enough, could they meet up with another strategically placed beanstalk?
Yep. But this is REALLY long. (Of course it also lets you have a "slip joint" so each tether can "slide along" the bridge.)
And be careful about stability: A long thin object in orbit is in an energy valley when pointing along the line to the primary and on a ridge when at right angles to it. You need active compensation or you lose your orientation the first time anybody scratches his nose.
#6 Could we wrap a bridge around the entire earth?
Now that's REALLY long. Yes you could. But now the instability gets worse and quickly breaks up your ring or crashes it into the primary. (See "The Ringworld Engineers" by Larry Niven.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
I'm pretty sure the Rainbow Mars elevator was fixed in place. It was destroyed when terrorists severed it from the (large) satellite used as a counterweight, destabilizing its orbit.
Gimme a break. How do you prevent terrorists from suicide bombing the Space Shuttle? The Superbowl? Nuclear plants? The [fill in your favorite target]? It's all about security, and in the end, about acceptable risk. You can't completely eliminate all threats, just minimize them. Letting fear of a terrorist attack getting in the way of projects like this is letting the terrorists win.
MSN 8: Now Microsoft even has bugs in their ad campaigns.
yeah dude, you got robbed. I love the idea of making it to a geosynchronous platform, then loading your maglev podule onto the track on the other side, pressing "GO!" and flinging yourself at Mars! That would ROCK!
"If you create user accounts, by default, they will have an account type of Administrator with no password." KB Q293834
Actually, it's not that a nuclear rocket would normally release anything radioactive, it's what happens if it blows up. Theoretically, the exhaust is just super heated gas. If you could be sure that the nuclear fuel would survive an accident intact then you could probably use them (convincing Greenpeace would be another matter). It's not entirely relevant because it's talking about deep space missions but here's an article on nuclear rockets.
A beanstalk needs to be anchored in geostationary orbit. There's no such thing as a geostationary orbit around a body that doesn't rotate on its own axis. So no, you can't build a space elevator on a tidally locked world. And it would be really impractical on worlds that rotate very slowly, like Mercury; you'd need an absurdly long cable.
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or...
Expect nothing - hope for the best.
-Kraft
Live and let live
At that scale, it must affect the weather. It would act like a giant sail and catch the wind. I know it would be mostly parallel to the West-East winds but 30,000km^2 is a hell of a big sail. It would be a pretty strong force on the side of the wall. If it's tapered, you're going to be deflecting wind upwards. I haven't done the math but this *will* push down on the structure. How much? I don't know. What happens if you get a cyclone (hurricane) in the area?
Also, do we really know the effects of deflecting that much air upwards? Until we *really* understand the weather, we should probably avoid building stuff on a geological scale.
The space elevator, being thin, wouldn't have most of these problems. Has this guy really thought everything through? I'm ignoring the obvious problem of how to get half a million tonnes of diamond.
This cable is going to be pretty thick right? It's going to be 1000s of km long right? *You* do the math and tell me how it's going to fit in a shuttle!
That doesn't help; it means that a geostationary lunar orbit would intersect with the Earth. Minor problem, that.
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Errrr, moon is in orbit around the Earth that is. doh!
-- Never make a general statement.
Do carbon nanotubes burn? Carbon does.
There is absolutely no reason to panic.
Was Rainbow Mars the one he wrote with the space elevator trees?
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