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Still More on Space Elevators
parseexception writes "The NYTimes is reporting
Not Science Fiction: An Elevator to Space. Not a whole lot of technical detail but good read. It is interesting to see alternatives to current space technologies being explored."
Not Science Fiction: An Elevator to Space
meh.
Clarke's Fountains of Paradise is a wonderful book. It presents the basic physical problems of a space elevator and some ways to solve them (and it has a great plot too).
Right now, as Clarke envisioned, carbon nanotubes are the only engineering material that could be used to make this elevator. The basic technological question is whether we will ever be able to make cheap and long nanotubes. Despite the enthusiasm for a space elevator in the NYT article, we really have no idea how to do that. And any cost estimates like "$6 billion" are very immature without that kind of detail.
This is the best thing for the success of the project. All it really needs is publicity. The Space Elevator is a solution to so many problems with current space technology that it should be operating right now.
The good publicity drumming up the imaginations of people in this country can only get this thing built faster. The technology needed for the ribbon is almost perfected. In 5-10 years or so (maybe after all this terrorism and war bs has ended) this thing might really get off the ground and the more people who know about it and want it to happen the better success the project will have.
--"The perfect example of the man of action is the suicide." - William Carlos Williams
Once we have a number of people going into space, and it builds a travel industry around it, suddenly we will see lots of innovations like the space elevator, etc. become not only practical but quite cheap. If only the government used computers, computers would cost a fortune, but since there is such competition, we have computers that sell for $300 or less now. If that same concept is applied to space travel, there WILL be competition, and there WILL be new better, cheaper ways to get up there, which may or may not involve the space elevator.
My theory has always been that once we have a hotel on the moon, due to it's gravity, people will not have as much of a hard time adapting to it for their vacation, more hotels will open up in competition. Initially, a lot of money would be spent setting up, but the costs of everything would continue to go down. Before we knew it, we would have faster propulsion technologies, better gravity-like technology, and we would be off to Mars for our next resort, resulting in even better competition for innovation.
space elevator
Hasn't the confectionery industry already done this? I hope these NASA folks know to watch out for Vermicious Knids.
I've put in a request... hopefully our headlines will be added as a slashbox here soon.
Not one thing.
the most mysterious thing you'll see today
"If the elevator gets stuck, do not become alarmed. There is little danger of the elevator running out of air. Then again...."
I have thought of this beffor. It's intresting though what made me thank of it is in the anime Armitage: Dule Matrix they use, one and the finaly fight takes place there. hmmm. I wonder if the scientist who came up with this idea saw Armitage too?
In addition to the other MAJOR engineering challenges that this project would require, how will the satellite at the other end of the elevator stay in place? I understand that if it has the proper mass and is at the proper altitude it will orbit directly above the base station - but what happens when you deliver a 13-ton payload there? Won't all that additional weight cause the satellite to swing forward?
every stain tells a story
to be the first to stand in that elevator...and press all the buttons so that the next guy will have to stop at every port before the 60,000 mile trip is over. hehehe cb
Remember, licking doorknobs is illegal on other planets.
So how does escape velocity play into this? If we can leave the earth without reaching an escape velocity then (on a very theoretical level) could we ride a space elevator out of the event horizon of a black hole? I realize there's a million other reasons why we couldn't get near a black hole, hawking radiation, strong gravity would rip us apart, etc. But you could also apply this argument to other things, like going into Jupiters' upper atmosphere which has bucko gravity. I was taught escape velocity was unavoidable to get out of a gravity hole.
-Steve
$7.95/mo, 200 GB disk, 2TBxfer, MySQL, PHP, RoR.
Actually I would suggest some liquid movement tanks high and low on the counterweight to maintain the balance without actually having to shorten the cable/distance to the balance point. Or you could have some type of elevator/freight system moving large plugs/masses of rock up and down to do the job. Better yet, both, having a dual system (or even ternary) would make sense considering the importance of balancing the system...*GRIN* I would do a great deal of work making it as foolproof as possible cause goodness knows we keep making the fools.
Actually, no...
Think about this for a second.
Picture an object in a circular orbit. Gravity is F = GMm/r^2, and the centripetal force required to keep it in that orbit is F = mv^2/r. So, so long as v^2 = GM/r, everything's happy.
Now, let's suppose that something grabs onto the elevator, say, something that's 10K pounds (pounds, because pounds is a force, and that simplifies things). So, now, the force that's pulling on the object is an F > mv^2/r. But it's still *moving* with v^2 = GM/r, so it can't simply be "pulled downwards" - instead, it starts to *lean forward*. All you've done is increased the centripetal acceleration, which means all you're going to do is bend the velocity vector such that it *starts* to head towards you. If it were a satellite, you'd be putting it into a lower elliptical orbit that still keeps that point-of-increased-a_c as its perigee. Since its an elevator, it starts "falling down" - leaning forward.
OK, now send the object up the elevator. As it goes up, it's now *torquing* the elevator (because the radial vector - perpendicular to the velocity vector - is no longer in the same direction as the force vector, so there's a torque), trying to make it lean forward.
Once the mass gets beyond geosynchronous orbit, it's now shifted the center-of-mass of the elevator above GEO, and it's now trying to make the elevator lean *backward*.
See a pattern? Sending a load up the elevator will induce an oscillation in the ribbon. It won't make it slowly fall, unless you send loads constantly to less-than-GEO and let them go, and don't bother trying to actively damp the oscillations at the base.
Yah, you could just actively damp the oscillations. The elevator starts leaning one way, you pull the elevator the other way. The two oscillations cancel each other out. No balancing act needed.
(Yes, you can keep a satellite in the "wrong orbit" - imagine if the satellite was too close to the Earth, such that it tried to fall. Now imagine constantly blowing on the underside of the satellite, such that the sum of your force and the force of gravity equals the necessary centripetal force. Poof. Satellite in an orbit again. That's what active damping would do).
...*GRIN* So you should be able to make the trip in 6'ish hours. That
6 hours? No way. 2 weeks, nominally.
The whole reason a space elevator wins over a rocket is because you can avoid air resistance by going slow. In 6 hours, you might as well be using a rocket. You're talking about 60,000 km, so roughly 10,000 km an *hour*.
There's another problem with a 6 hour trip, too - the speed of sound in the elevator produces about a 7 hour natural vibration. A 6 hour trip means that you're actually travelling supersonically up the elevator (supersonic with respect to the cable).
Anyway, with a 2 week trip, you can easily see that even a very gentle push (I think it's in the "few newtons" range) can counteract the slight lean of the elevator.
Once you're outside the atmosphere there are no outstanding reasons for not moving faster. That is why I mentioned magnetic drive/coupling instead of any physical connection. And of course carbon nanotubes can be configured to carry power, it should also be relatively simple to configure part of the elevator as a track for a magnetic linear accelerator. No inefficient rocket power required (although to be honest I'm not sure what the efficiency of a linear accelerator is).
:)
Damage to the ribbon is a good reason. However, avoiding the Van Allen belts is a better reason to move quicker once you're a bit farther up, so point. However, counterpoint is that you don't torque the ribbon as heavily once you're up at a higher point, as you're shifting the center of mass less.
However, the best reason for not moving faster is, of course, because you don't really have the power. It's silly to carry the power with you (reduction of launch mass), so you beam it up from the ground. I've a feeling that this will *stay* the main method for scaling a space elevator for a long time to come, simply because it's the easiest, and the most launch-mass efficient.
Also, the nanotube power carry thing is a bit of a red herring. There are two problems:
1) The elevator won't use continuous nanotubes - it'll be using composite nanotube fiber, which, of course, cannot carry power, as it's just glue with a bunch of really weird things called 'nanotubes' inside it, and the glue probably won't conduct.
2) Even if they end up using continuous nanotubes (maybe multiwall nanotubes, as it appears you may want to fuse them), nanotubes conduct power along their axis, and a continuous string of nanotubes would have no way of conducting power off-axis. Plus, when you're talking a length of 60,000 miles, the nanotubes would have to superconduct (which they don't - they do weird things with electrons, but it doesn't look like true superconductivity) - even the best conductor known to Man would appear to be a gigantic resistor when it's 60,000 miles long.
Last but not least, I do want to thank you for an interesting discussion. I find real thinking to be a rare pleasure these days and I do enjoy it.
Whew! I normally call lack of thinking death. Interesting discussion is the only reason to wake up in the morning.