Slashdot Mirror
Notes From 3rd Annual Space Elevator Conference
colonist writes "The Space Elevator: 3rd Annual International Conference was held recently. Blaise Gassend, a PhD student at MIT, took notes. The main obstacle is still the material: transferring the strength of the nanotube to the ribbon. Other topics include: the nanotube tether Centennial Challenge; Elevator 2010, a challenge for a 250 kg climber to climb a 16 km tether; objections and refinements to Bradley Edwards' design; non-equatorial space elevators; replacing the term 'space elevator' with 'space bridge'; testing the space elevator material on cable cars; science; defense and economics."
This page seems to have some good links. Just check out the bottom of the page as it indicates if you're new to the idea of space elevators.
Wikipedia have a very good article on space elevators
Normal GPS satellites are not in geosynchronous orbit.
Some augmentation satelites are though.
Jeroen
Secure messaging: http://quickmsg.vreeken.net/
The point is that it's an extremely energy efficient way of hoisting stuff into space (in theory).
Better to have a comparably near zero cost elevator than spending gadzillions launching a moonbase into space piece by piece using rockets.
I believe the point is to make access to space economically practical. Burning massive amount of fuel is pricey and pretty bad for the environment. If we really want to be doing stuff in space we either use space elevators or wait for someone to invent anti-matter drives or something.
---
We spoke for about a half an hour. I don't recall a thing we said. - Colorblind James Experience
It's a really long cable that's held up by the centrifugal force created by the Earth's rotation. An elevator theoretically climbs this cable into space. Unaddressed are the problems with it batting down any non-geosynchronous satellites or the way it would wrap around the equator when it tries to lift any significant mass (most of orbital launch acceleration is horizontal, not vertical).
Not in the fairytail....
But there is archeological evidence for a lot of towers in what is now Iraq and Iran.
Among them some very big ones in babylon.
Jeroen
Secure messaging: http://quickmsg.vreeken.net/
Funnily enough, I knew that. Damn.
GPS info available here
T.
Well, actually, a little further out than GEO, so that the center of mass is at GEO.
As for wind -- well, you situate it where the wind is minimal. Remember, since it's synched, it's not generating "wind" by slicing through the air. All you'd have to worry about is the wind that is actually blowing past the (stationary) Earth.
The Mongrel Dogs Who Teach
That's why you need a really strong material for a space elevator - if it wasn't for the weight of the "rope" itself you'd only have needed a material strong enough to handle the weight of whatever you wanted to transport up it, but that is a miniscule amount of the total strain on the elevator.
If we suddenly have 100 miles of superstrong material slamming down at hypersonic speed, it's going to be extremely bad - somebody ought to calculate how many Teratons of TNT that corresponds to.
Just about 0 Teratons of TNT IIRC. The carbon nanotube ribbon proposed doesn't weigh much and has awful aerodynamics, and for the most part would just flutter down. And that's only the part below the break point, which is going to be pretty low, if it's planes were worried about.
Ignoring the weight of the rope itself, probably the main reason for this rule-of-thumb is the difference between dynamic loading and static loading.
If you (accidentally) get something bouncing on a short rope, the bounce will damp out pretty quicky and the period of oscillation is short. If you get something bouncing on a long rope, it will bounce for a while, and the rope is stretched for much longer with each bounce. It doesn't take all that much of a bounce to double the load on a rope, and perhaps take it past its elastic limit.
I'm guessing, but I think that pre-synthetic ropes probably can be briefly overstretched without losing strength because they knit back together again. If you continuously overstretch them, the fibres probably don't get a chance to recover before the slide past each other a little more, and so on.
So my guess is this doesn't apply nearly so much to modern synthetic ropes. In the case of a space elevator, I'd hope they'd try really hard to avoid excess dynamic loading.
Your example of a chain is flawed and doesn't match what you suggested for the rope - A chains strength doesn't weaken for each extra link because of "small flaws", it stays the strength of the weakest link regardless of number of links.
But the moment you start hanging it down you need to take into account the weight of the chain itself, and the chain, just as a rope, will be able to lift less additional weight the longer it is because the strain on any point of the chain/rope is equal to the weight attached PLUS the weight of all of the chain/rope below it.
The text of Tank Farm Dynamo is online.
I wouldn't worry about being killed by a carbon fiber making meteoric reentry. It wouldn't be like the disaster in the Mars trilogy, or even like shadow square wire... by the time it hits it'll be more like laser toner, the stuff is strong in tension but it burns quite nicely: Nanotube Explosions
To correct a couple of other responses...
Since the story's in Genesis (OLD testament), it's not just Christian but is also in Jewish scripture. There's probably a version in Islam as well.
However, the SBAS satellites (known as WAAS in the US and EGNOS in the EU) are in geosync orbit - they broadcast differential corrections to compensate for the errors introduced into the GPS position by the ionosphere, etc. If you can get a good view of the southern horizon in an area that has SBAS coverage then you can get accuracies of under 6 feet.
http://blog.nexusuk.org
While Arthur C. Clarke certainly popularized the idea of a space elevator in his science fiction novel "The Fountains of Paradise", the original concept is credited to the Russian engineer Yuri Artsutanov, who published it in 1960. See, for example, here
Ubi dubium ibi libertas: Where there is doubt, there is freedom.
1 rotation/day = 7.2e-5 rad/sec
120mph vertical rate = 53 mps
So the change in horizontal velocity is 0.004 mps/sec
Not a noticeable acceleration compared to the other forces on the car and the cable.
I think you mean a huge "mass" in space. Since the real problem with teathering a large mass is overcoming the object's intertia as it is pulled along with the earth in a somewhat circular orbit.
The energy is provided by the climber, which in the current designs is powered by a beam of light coming from a ground station.
The angular momentum for the orbit comes from the rotation of the earth. If you would launch billions of tons of rock using a space elevator, the rotation of the earth would slow down noticeably.
Private property is the central institution of a free society (David Friedman)
Waltz, nymph, for quick jigs vex Bud.
It's easier than most people think, you don't need to capture an asteroid. You send up a small counterweight along with the initial spool of cable, and as the first cable unspools downward from geosync, the counterweight moves up. You end up with the first strand of cable fully extended with a small counterweight, just enough to hold itself and a small payload. From there it's trivial, to add more cable you carry it up the initial cable, and to add more counterweight you have the cable-laying climbers go all the way to the end and become part of the counterweight, and/or send separate climbers to carry up the counterweight.
_The Fountains of Paradise_, by Clarke. A good read, too!
You don't get it. I don't blame you because it is not trivial.
When the tether is in place but no payloads move up or down, the top of the tether is directly overhead of the base station, so there is no net force on the top. But when a payload moves upwards, it will create a coriolis force which pulls the tether slightly backwards relative to the rotation of the earth.
Thus the force of the part of the tether below the payload has a component in the direction of the orbital motion of the payload, and the tether accelerates the payload and thus conserves angular momentum.
There is no need for thrust at the top of the tether. That is why space elevators are so attractive.
Private property is the central institution of a free society (David Friedman)
I wish I had modpoints. Rotovators are indeed much more practical than space elevators. They do not require exotic new materials such as carbon nanotubes. They can be built with cheap materials like spectra or zylon fiber. They are also much shorter (100km instead of 36000km) and more flexible.
This system could double the payload capacity of launchers to geosynchronous transfer orbit or pick up small payloads from suborbital trajectories.
This could be built today. Rotovators are also a very good addition to suborbital space transports such as SpaceShipOne.
Private property is the central institution of a free society (David Friedman)
A tether that is not in contact with the ground would indeed need propulsion.
:-)
But in all designs I know there is a contact between tether and ground. Since the tether is bent slightly backwards by the coriolis force of the upward-moving climber, there is a force component at the anchor point that is parallel to the motion of the attachment point, so angular momentum is transferred.
Since the payload moves very slowly and is much lighter than the tether, the tether at the attachment point is almost vertical, but not completely vertical.
And I am not getting energy out of nothing. There are two invariants that must be conserved: energy and angular momentum. Energy is supplied from the outside (from a ground-based laser), and angular momentum is supplied from the earth via the attachment point.
This is simple newtonian mechanics, so I am 100% sure that it works that way. You want to bet over a box of beer? I suggest Henry Spencer of sci.space.policy as an authority to decide who is right
Private property is the central institution of a free society (David Friedman)
We have passed the peak of oil production
Speaking as someone who works in the oil and gas industry, I can say without hesitation that this is untrue. Peak oil has been looming for the last 10 years at least, yet it keeps being pushed ahead by improvements in recovery technology. This trend does not show any sign of slowing, at the moment. Remember, an average oil reservoir still has 85% of its original oil still there. Recovery factors these days have grown from 10-15% to 20-25% and rising. Yes, it is more costly to get more than 10-15% out of an oil reservoir, and prices will continue to go up as the cost of production goes up. But peak production? Only if people stop buying gasoline due to the prices. Good luck on that.
Random and weird software I've written.
Remember that satellites in LEO make 16 revolutions per day (once every 89 minutes) and cross the equator twice on each (ascending and descending). Multiply that by nearly 10,000 objects big enough to track (~5cm) and many more they can't see. NASA has a good description of the problem that explains the physics and gives examples of high velocity impacts.
This is not a trivial problem.
Since it would be around the equator wind wouldn't be much of a problem. Remember the oceans in that area is famous for doldrums which is a sign of how much wind is around the equator.
DarkMantle I been bored, so I started a blog.
I guess that by "really weird book" you mean The Fountains of Paradise by Arthur C Clarke?
Indeed, we are a long way from making 40,000-km-long carbon nanotubes. One serious question is how practical it is to depend on something like this being built.
But it's only been a few years since the first carbon nanotubes were created. The first were only nanometers long. Then others reported making some that were micrometers long. And a couple of months ago, there was the first report of millimeter-long nanotubes.
This is rather rapid progress, around 9 orders of magnitude in about a decade. And the folks at Duke not only reached a 2-mm length, but they did it by continuously growing the tubes. And they can generate cross-connections between the tubes. Others are now experimenting with continuously-grown nanotubes. With funding to support the flock of researchers, it wouldn't be at all surprising to read about indefinitely-long nanotubes (or sheets of them with periodic cross-connections) within a year or two.
Then, instead of the first construction being done by sending up a huge spool of nanotubes and unwinding it in orbit, we'll read of them sending up a nanotube-manufacturing machine, which will extrude the tubes a few at a time and lower them to Earth.
A bigger problem, mentioned by Clark in Fountains of Paradise, is the cloud of space junk left over from thousands of earlier launches. The real expense will be the equipment to track every little particle passing through the Earth's neighborhood. To keep the elevator safe, we'll have to spot even tiny objects far enough in advance to send a wiggle down the rope just in time to move it aside when an object passes.
But, of course, this observing equipment will have huge scientific value itself, as it builds up a huge database of every little object in the solar system.
And the intermediate uses are developing. There are already sensors and drug-deliver devices being built that use nanotubes of various lengths. This is helping to get funding to the nanotube researchers.
Those who do study history are doomed to stand helplessly by while everyone else repeats it.
"Unaddressed are...the way it would wrap around the equator when it tries to lift any significant mass (most of orbital launch acceleration is horizontal, not vertical)." The climber would drift westward, and the net bend in the ribbon would impart a horizontal eastward acceleration. (The angular momentum gained by the climber comes from the earth. ) You can think of the elevator as the world's largest stringed instrument. A climber falling off in mid-climb would pluck it.
Check out the "Challenges" page of the NIAC paper here.
It covers things like lightning, meteors, wind and other factors.
Nothing.
It's a ribbon. It's literally nearly equal to the weight of an equal width of Saran Wrap.
How much unrolled saran wrap do you have to drop on someone before it hurts them?
How many buildings will be devastated by having something that flimsy dropped on them?
The devastating space elevator fall is bad science fiction. If it breaks, stuff above will stay in orbit, and stuff below the break will fall harmlessly.
However, if you take the train, you go from downtown london to downtown paris. If you're on one of the French high-speed trains, the trip is only about an hour longer than it is by air. Factor in the fact that you can clear customs on the train rather than on the ground after you land, as well as the hour+ drives/cab rides to and from heathrow and charles de gaulle airports, and the train is actually faster for buisiness commuters by at least an hour. Now, there's not many people whose time is worth 149 - 64 = 80 GBP/hour, but they do exist.
There's other reasons, mostly regarding how train travel is generally more pleasant than air travel, and then theres the fact that you can bring your car across to calais from britain, but I found the revelation that the train can be faster door-to-door to be particularly insightful.
The main thing this is good for is for propulsion. A rotating tether can pickup and toss payloads but it looses some momentum unless there is other traffic going the other way. But with an electrodynamic tether pushing on the Earth's magnetic field you can get momentum without using rocket fuel. This is way cool.