Space Elevator Going Up 684
Adlopa writes "The
Guardian newspaper reports on scientists' efforts to realise the space elevator, as first described by Arthur C Clarke in his 1979 novel 'Fountains of Paradise'. Advances in materials science mean that 'a cable reaching up as far as 100,000km from the surface of the Earth' is no longer an impossibility and 70 scientists and engineers are discussing the idea at a conference in Santa Fe today."
Error in article: (Score:5, Informative)
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A space elevator would make rockets redundant by granting cheaper access to space. At about a third of the way along the cable - 36,000km from Earth - objects take a year to complete a full orbit. If the cable's centre of gravity remained at this height, the cable would remain vertical, as satellites placed at this height are geostationary, effectively hovering over the same spot on the ground.
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Actually, at 36,000 km from earth, objects take a day, not a year to complete a full orbit. The moon takes about 28 days to complete an orbit, (one lunar cycle) and any object far enough out from the earth to require a year in order to complete an orbit would passed the instability limit, where it would be captured away by the sun's gravity, and would no longer orbit earth.
For more info on Space Elevators (Score:5, Informative)
Not an impossibility? (Score:5, Informative)
Quote from the article:
"Until some of the basic science concerning how to connect nanotubes together and transfer load between them in a composite is understood it will remain elusive, but a lot of progress is being made."
Basically, the state of the art with carbon nanotubes is that you can build them a few centimeters long, of almost/just about the right strength (72 Gpa); but nobody has made or can make a rope even 1 foot long with the right strength (ideally 130 GPa including a 50% safety factor).
State of the art carbon nanotube ropes are down under 3GPa (less than Kevlar strength). To oversimplify the problem nanotubes are very slippery and hard to join with any strength. Splicing rope out of threads traditionally loses 20% of the strength, but nanotubes are too slippery, and not strong enough anyway for that right now.
Still, enormous progress has been made; and it looks surprisingly promising; but it's impossible right now.
Re:For more info on Space Elevators (Score:4, Informative)
Re:Kind of scary. (Score:4, Informative)
The cable is actually pulling up. Catastrophic failure at any point along the cable results in it leaving earth.
Basically, you put the center of gravity of the cable right at geosynchronous orbit (ideally you want it to be a little higher than that)
If it's at geo orbit, then the cable stays still even if you cut it off. A hurricane would push the cable sideways, tidal gravity is enough to keep the cable taut by itself. It's a non-stable equilibrium however; eventually the cable will drift enough to escape earth gravity. Unless it hits a mountain first. But even then, EVERYONE is under it. It'll wrap around the earth at least once before it's done falling...
Correction (Score:5, Informative)
Objects take one DAY to complete a orbit at 36,000 km... and if that orbit is in the same direction as the earth turns, then you can orbit continuously over a spot on the equator. There's actually a minor perturbation, but those forces are minor compared to the other forces a space elevator would have to deal with...
BTW, a nice recent sci-fi novel on the subject of space elevators is _Rainbow_Mars_ by Larry Niven, of _Ringworld_ fame.
Re:this would be sweet (Score:3, Informative)
Guestion for you - what do YOU think would hold this thing up? Maybe you expect a bunch of Indian Fakirs to be sitting around the base blowing on flutes? (reference to Indian Rope Trick for those who were wondering...)
To answer my own question, the fact that one end of the cable is moving faster than the other end makes the part that is moving want to fly off in a straight line - but the tensile strength of the cable keeps the two hooked together. If the cable were at either of the poles, there would be a bunch less difference in speed between the two ends - and the system would be more UNSTABLE.
Re:Kind of scary. (Score:3, Informative)
Would you please document yourself, make the appropriate research [www.isr.us], concentrate for 2 seconds on the topic at hand before you open your hole and spill out the first fearful thought that comes to your mind?
- It would be built in the middle of the ocean on a floating platform
- If it broke, most of the 100,000Km would NOT fall to earth (junior high physics can tell you that), and most of the piece that would, would burn in reentry
- What remains would be much more harmless than your poisonous, unscientific whining.
You're like those people that hear the word "nuclear" and immediately thing BAD BAD BAD
Re:harnessing the public interest (Score:5, Informative)
Re:Kind of scary. (Score:5, Informative)
This stuff is pretty light, and they are looking at a RIBBON, not a cable. So the air resistance would prevent a 100 ft piece (for example) from accellerating to a speed that will cause any major damage. At least that is how I understand it after reading the article.
Same reason if you throw a sheet of paper off a tall building, no one is hurt. You throw a marble instead, and you can split a skull.
Sources (Score:3, Informative)
That's in Science vol. 151(3711), p. 682 (1966).
Interestingly, Clarke envisioned the thread leading up (or down) the skytower to be nanodiamond, while these days nanotubes are all the range. The difference in the materials is that in diamond carbon atoms have four neighbours but in tubes they have only three, as in graphite, yet at about the same formation energy. That makes their chemical bonds actually stronger than in diamond and gives nanotubes their extraordinary tensile strength at low mass - perfect for engineering a space elevator.
Re:What about the static electricity it will gener (Score:5, Informative)
Clarke didn't invent this!!! (Score:5, Informative)
According to A. Clarke himself the space elevator was invented by Jurij Artsutanov from St. Petersburg.
(3001, The final Odyssey, under sources)
Re:Kind of scary. (Score:3, Informative)
Re:Kind of scary. (Score:3, Informative)
The cable is only epoxied together, so anything past 100 km or so above the earth would fall apart into fibers during reentry (you'd probably blow it up into sections to help it melt correctly). Nobody knows what effect breathing these fibers in would have.
Incidentally everyone envisages the cable as being made of metal- it actually would weigh on order 1kg per kilometer, so it's not going to hurt you (although I wouldn't want to motorcycle fast at a section for obvious reasons.)
Re:this would be sweet (Score:2, Informative)
Re:Idealism... (Score:2, Informative)
Re:Not an impossibility? (Score:3, Informative)
If you read that article really carefully you'll note that they said it was stronger than steel, but tougher than any material. Steel isn't massively strong (Kevlar is stronger), however toughness is journalistic speak for 'how much energy can it absorb before it snaps'. That's cool, but for an elevator you need tensile strength, not energy absorption; you're not catching flies with it :-)
(And don't even think about catching space junk- it's going way to fast for that!)
Re:Um...... (Score:5, Informative)
The physics are simple: you just have a cord that stretches out beyond geostationary orbit. At geostationary, the cord's mass is in a precise orbit (zero pull towards or away from Earth); beyond that, the cord's inertia pulls it away from Earth. So you don't even need a lead weight at the end -- all you need is enough cord. As a bonus, anything that gets pulled past the geosync point will be accellerated away from Earth; so you can use it as a cosmic slingshot.
Hoist a chickenfarm to the end of the tether, and you can throw eggs at Mars!
-Billy
Re:Huh? Re:What what what (Score:3, Informative)
Oh hell, I will help you:
At about a third of the way along the cable - 36,000km from Earth - objects take a year to complete a full orbit.
You are right, "it takes one day to complete a full orbit at 36000km", BUT THAT IS NOT WHAT THEY SAID!
Re:Waterbeds! (Score:3, Informative)
Re:For more info on Space Elevators (Score:2, Informative)
Also check out LiftWatch [tiki-web.com].
The conference site is (Score:5, Informative)
Re:What about the static electricity it will gener (Score:4, Informative)
They have had tecnical problems when they have tried it but they physics is all undergrad E&M.
Re:For more info on Space Elevators (Score:4, Informative)
Re:Kind of scary. (Score:5, Informative)
Actually, yes, we are. That's why advances in materials science were necessary before they could even think about building this thing. I quote from the article:
The cable's structure will be balanced by gravity -- the center of gravity will rest at the geosynchronous point, meaning that the bottom half will be falling toward Earth while the top half will be moving away at an equal rate.
Being "balanced by gravity" means there's a huge amount of tension here. In fact, that basically says that the top half (by mass - by distance probably a very small proportion of the thing) holds up everything below the center of mass at the geosync point. (Or from the other perspective: the bottom half holds down the top half, which would fly off into space otherwise.) It does that with tension in the cable, and we're talking about a lot of tension in the cable.
Let's put concrete numbers on it: carbon nanotubes are pretty light, but we're still talking about 35,785 kilometers in the bottom half (by mass) of the elevator - that's geosynchronous orbit around the earth. Say the elevator is 1 kg / m (very conservative, I think), which we'll call lamba (normal for linear density). Now gravity changes along the length of the cable (that's sort of the point), so we need an integral to calculate the force of gravity pulling the thing down:
F = \int GM dm/r^2 = \int GM \lambda dr / r^2
(where dm = \lamba dr). From my Physics I book, r_e (the mean radius of the Earth, which is a bit higher than sea level but not too bad) is 6.37 * 10^6 m. M (the mass of the earth) is 5.98 * 10^24 kg. And G is 6.67 * 10^-11 N*m^2 / kg^2. So the integral becomes:
F = \int_{6.37 * 10^6 m}^{6.37 * 10^6 m + 3.58 * 10^7 m} (6.67 * 10^-11 N*m^2/kg^2) (5.98 * 10^24 kg) (1 kg / m) dr / r^2 = 5.3 * 10^7 N = 53 MN (mega-Newtons)
...which I think is the require tension right above that point. I can't think off-hand exactly how geosync works, but essentially the stuff above that is being sped up and the stuff below (and the Earth itself, though not significantly) is being slowed down by that tension.
Disclaimer: I'm an undergrad physics student with a headache. I very well may have made a mistake above, but I guarantee it's closer than the parent post.
Re:Not an impossibility? (Score:3, Informative)
And waldoes (Score:3, Informative)
Re:Kind of scary. (Score:2, Informative)
For one thing - this is strong stuff we're talking about - incineration is garuanteed. If it breaks up that might sound like an imporovement - but the it's like being shot with a shotgun. It may be loaded with pellets, or it may be loaded with solid rounds. You may spead the impact a little, but its the kinetic energy that'll kill you - and you still get all of that.
Not scared yet? Let's put this in perspective.
according to its website the Golden Gate bridge [goldengatebridge.org] weighs 380,800,000 kg and spans 1966m. That's probably comparable to the weight/length ratio for a space elevator. It uses hi-tech materials, but it has to support its own weight across its entire length, and its going to be long! According to Nasa (google cache) [216.239.59.104] the elevator is likely reach 36,000,000m. That's 18,311 times the length of the GGB
So taking the golden gate bridge as a guide, we can estimate the total weight of the cable at 18,311 x 380,800,000kg = 6.97 x 10^12. Seven gigatonnes - lighter than I expected.
How hard is it going to hit? Well, at least terminal velocity. I say "at least because the upper reaches will be going faster and have to be slowed by the atmosphere. Also the cable will be considerably denser than a human, so we can reckon it's terminal v as being rather more than a human's. Human terminal v is about 50m/s [slashdot.org] so let's go with that for the time being. We're being conservative..
Kinetic energy = 0,5 x mass x velocity x velocity
= 6.97294 x 10^12 x 50 x 50 / 2
= 8.716175 x 10^15 joules
And to put that in perspective, one megaton [everything2.com] comes to about 4.184 x 10^15 Joules.
So if the cable came crashing down it'd release about 2 Megatons of kinetic energy - either as heat as it burnt up, or as shockwaves on impact.
Doesn't sound like much? Well, the Hiroshima bomb is reckoned as being 20 killotonnes yeild. So 200 hundred hiroshima bombs going off in a ring around the equator in fairly rapid succession.
and it it hits faster than that... well that's a square term. 100m/s give you 4 time the energy or 800 hiroshima bombs. 200m/s (not unreasonable) gives 16 times - 3,200 x hiroshima.
Don't get me wrong - I'd love to see a space elevator. Just let's bear in mind that this is dangerous
Give some credit to the inventors (Score:2, Informative)
The concept had been invented independently both in USA and the Soviet Union long before the book was written -Arthur C. Clarke's great contribution is bringing the concept to a wider audience. (The cosmonaut Leonov had actually made a painting depicting a space elevator, but westerners -ignorant of the concept studies being done- thought he was nuts)
BTW, I was in contact with ACC two yeras ago and asked him about this novel. He mentioned that the scientist who helped him with the facts was non other than Buckminster Fuller, the discoverer of "buckminsterfullerene".
It so happens that the carbon nanotubes which have the tensile strength to make the cable possible are simply tubular versions of buckminsterfullerene. Fuller himself was not aware of this ironic fact, the nanotubes were only produced in the lab and had their strength measured in the nineties, after Buckminster Fuller's death.
Yours Birger Johansson
Re:OT pentagon structure (Score:1, Informative)
From http://www.snopes.com/rumors/pentagon.htm
Anything else I can help you with?
Re:restricted airspace OT (Score:2, Informative)
From http://www.snopes.com/rumors/pentagon.htm
Anything else I can help you with?
Re:restricted airspace OT (Score:1, Informative)
From http://www.snopes.com/rumors/pentagon.htm
also:
Also:
Aww, hell, just read the whole fricking page yerself!
Re:harnessing the public interest (Score:4, Informative)
The envisioned plan doesnn't have two "shafts". Nor do I believe such a arrangement would be possible.
Rather the designers have envisioned a laser based power transmission system. The moveable platform would likely contain a nuclear reactor to power a very powerful laser. The laser would be beamed to the climber which would contain a receiver that converted the intense laser light into elecotricity.
Of course adaptive optics used by the miliatary for exotic anti-missle systems would probably be necessary to hit the spot accurately on a rapidly ascending climber. Additionally, the ribbon cable would also likely be "flapping" in the air so a sophisticated tracking system would be necessary.
As you've pointed out, the descent stage needs no power. However, apparantly venting heat will be a problem at high speeds.
The material science will likely need a lot of work. However, I don't believe that the auto industry will invent the necessary processes. Rather, I believe that the defense industry will invent the processes to turn raw carbon into super-light, super-tough armor for aircraft, ships and tanks.
The last century was the century of steel. The next century will be the century of carbon. Remember the new diamond sythesis techniques that are currently practical. Expect a lot of work in these areas.
Re:Kind of scary. (Score:1, Informative)
Re:The idea is good the article is bull@#$%. (Score:2, Informative)
We all groaned at that mistake in the Guardian article, though you might be able to argue that a "year" for a given body is the period of time it takes to make one orbit around its primary. That is, everything orbits once a year. Pretty weak.
1. Tracing space junk ~0.01-1mm in size which flies around with a speed ~10km/sec.
The ribbon will be about a meter wide, 20 microns thick, and curved across its width. Stuff that small will punch right through it, sure, but won't sever enough of it to cause it to break. Every couple of weeks a maintenance climber will go up looking for little punctures like that and patching them.
2. Moving platform fast enough on the ground to avoid collision at the altitude ~200 -1000 km . At those altitudes junk has the maximum density.
Almost all of the junk big enough to hurt the ribbon is in orbit, is and will continue to be tracked on radar. There'll be plenty of warning; analysis says that the ribbon anchor will have to move about a kilometer once a day.
Edwards, who estimates it would take about $7bn to turn the concept into reality. This thing should weight no less then ISS. Most of it flies much higher orbit: 36,000-100,000km compare to ~500km for ISS,- READ: more expensive to get there.
The initial ribbon, weighing about 40 tons, will go up in two Delta IV launches on spools. (Two more Delta IVs will take up the GEO transfer vehicle and the deployment mechanism.) The initial ribbon will be unreeled from GEO, one end flying down to the surface and the other climbing above GEO to serve as counterweight. We will then send a little tiny climber up this initial space elevator, splicing just a little bit more material to the ribbon along its entire length. Then another one, slightly larger because the ribbon is now a tiny bit stronger. Then another. After 210 climbers, the ribbon will be able to hold a 20 ton climber and we can start building a second ribbon.
So, you see, the Space Elevator is bootstrapped up to a usable size. We don't need to launch it with rockets; most of it goes up on itself. We only need 4 Delta launches, at an estimated price of $500 million each.
Sorting Carbon Nanotubes Will Help the Space Eleva (Score:3, Informative)