Space Elevator within 15 years?

Great Debates
21

The point is that you don’t have to re-build your launch hardware from scratch with each launch. The fuel is only a fraction of the cost of a conventional rocket - most of the expense is in building the rocket itself, which gets thrown away with each launch. Even the Space Shuttle needs extrnsive refurbishing after each launch. Once your tether is built, your only cost for launching payloads is in energy.

Also, you should in theory be able to capture the energy from the enpty carriers coming back down the tether somehow.

22

I haven’t read the article yet, but I’ve read a lot of SF about Space Elevators. Plus I gotta coupla physics degrees.

Once you get the canister full of nuclear waste to the top of your space elevator you’re still in Earth’s gravity well. If you let it go it will continue to sit in the vicinity of your elevator’s “top floor”. You have to push it to get it to go somewhere, and, unless you push really hard, it’s going to stay pretty close to a geosynch orbit. Even if you push harder, it’s going to end up in a 1 AU orbit around the sun, probably not terribly far from the earth. Where were you planning on putting all this stuff? I know space is big, but isopotentials are small, and things can still run into each other.

23

I remember reading an article a decade or so ago in Discover or Scientific American or some such (great cite, huh?), about space shuttle costs and maintenance. While space shuttle technology may have advanced since then, we’re still using the same shuttles, so I figure the situation’s still basically the same.

The article said each shuttle trip cost close to a billion dollars. I remember phrases like “Phyrric reusability” and such. So the limited degree of space travel we presently have, costs a bundle.

So even a pretty expensive alternative could well be cheaper.

But I’m kinda wondering about the orbital stresses on the cable. The part at geosynchronous altitude is going to want to stay right over the anchor. But everything closer in is going to want to pick up speed. I presume the length of cable above geosynchronous altitude is there to put a countervailing, slowing force on the space station at geosynch altitude, so that the lower part of the cable can’t pull it along faster than it would otherwise go.

But that ground anchor had better be extremely well-anchored, it seems to me. I’m thinking that tidal forces are puny relative to what we’re messing with, here - and we can’t exactly master tides. That cable is forever going to be trying to rip loose from its ground mooring, and to rip loose from itself. I’m assuming they’ve got theoretical answers to those problems, but the article didn’t address them.

And there’s a lot of difference between having theoretical solutions to problems, and having workable engineering solutions. I’m hoping I live long enough to see something this amazing, but I’m figuring it’ll take well over any 15-20 years.

[sub]Smartass throwaway line: “I’ll believe in nanotech when I see it!” [/sub]

24

I’m not an engineer, but it seems to me that this idea will require the development of new technologies. For example, let’s see one of these “climbers” that can weave carbon nano-tubes together, and is powered by energy conducted by laser light. Let’s see these people build a ten foot nano-tube cable, using climbers and lasers.

I’m skeptical that they have the technology to do even that.

And the thing is, it is often difficult to predict how long it will take to develop new technologies. So it seems to me that 10-15 years and $5billion is kinda pie-in-the-sky (har har).

Engineers, feel free to correct me!

25

A reply to my earlier question . . .

I’ve done a little digging around, and it doesn’t seem that the art of nanotube weaving has improved all that much since I left the field. Some of the ones I’ve found for sale (not my old lab, but hey) are still in the 5-20 micron length range. 20 microns is better than what I used to make, but it’s a far cry from tens of thousands of miles. I just don’t think the technology is here right now to construct the thing.

26

So 60,000+ cable starts falling to the Earth: Results?

In KSR’s “Mars” trilogy the station at the end of the cable is severed from the cable in a terrorist (or loyalist - depending on which side you come in on) action.

So assume that the station doesn’t come down, but for some reason the cable breaks at the top and cable comes plunging down. The circumference of the Earth is about 24,000 miles. That means the cable could wrap around the earth as many as 2 1/2 times!!! This would cause some serious damage making the WTC attack look minor. How could we protect against such an occurance?

What is an ideal location for this? Where is the part of the globe that has the shortest distance to space? Or is it the same no matter where you stand on the globe?

As far as production, this claims they can make 15 kilograms per hour annual output 120 tons. Is that more than you remember, Mighty Maximino?

DaLovin’ Dj

27

Everybody seems to be working on the assumption that the empty elevators would need to descend the cable; why wouldn’t they design them for safe re-entry and just unclip them at the top?

I’d love it if somebody could do the conservation of momentum calcs; as far as I remember, the sideways forces on the tether work out to be quite unbelievably large.

28

Much, much more. We were selling quantities in the gram range for over $1000; our annual output was probably 300 grams. Still, it’s not just the mass but also the length. Your mass of nanotubes would be either a black powder (or a suspension) that is worse than asbestos if you inhale it. I don’t know of any way of un-powdering them at this time, which would seem to be a critical step in this project! Seriously, if anyone’s succeeded in making a macroscale nanotube, I really want to hear about it.

29

In large-scale engineering projects, the devil is always in the details. In theory, you can build a 5,000 ft building, or a 15 mile wide bridge. We even have the materials today to do it, and proven engineering methods to rely on. Even so, the Gibralter bridge is projected to cost $20 billion.

Something like a space tether requires a tremendous amount of basic research, plus a lot of engineering and fabrication research, before you can even start. For example, the tether is going to build up one hell of an electric charge cutting through the Earth’s magnetic field. The shuttle did a tether experiment a couple of years ago. Air trapped in the tether material bubbled out and cause a 3500 volt plasma which burned up the tether.

What happens to the nanotubes over time? Does the high electric charge coupled with extreme temperature changes and such do anything to them?

This is the worl’d biggest lightning rod. How does decades of constant lightning strikes effect it? How does ONE lightning strike effect it?

How does this thing interact with the upper atmosphere? What about the effect of storms or extremely high winds on the cars going up and down?

What happens if a car malfunctions on its way up? If it jams on the cable, how do you get it down? What if the electrical system fails? How do you test these vehicles when you don’t have a prototype tether to test them on?

How do you protect against terrorists? This will be the biggest target in the world.

What about satellites and space junk in orbit? This thing is a sitting duck.

I would love to see a space elevator. But I think the time frame and cost projection is nuts. Hell, just the X-38 crew return vehicle program was going to cost over a billion dollars, and was in development for years before being cancelled.

In my opinion, if all the materials were available today, and a method for weaving the nanotubes were known, we’d still be decades away from being able to build something like this.

30

More questions.

  • What is the basic tensile strength of a carbon nanotube thread? What calculations are these folks using to calculate the strength of a cable made of such things? Ideal, or practical?

  • What is the lateral coefficent of friction of a carbon nanotube? Anyone who has put too much olive oil in a pot of boiling spaghetti knows what happens when strands don’t bond well laterally. Is a bonding agent included in the weight calculations?

  • How does one ensure that a nanotube strand is unbroken and not merely conjoined somewhere along the way? What is the cost of making absolutely certain, if one needs to be that certain?

I’ll say this. If the materials scientists say they can do it someday, they may very well be right. The Apollo project was kicked off with designs that presumed better materials would be created by the time it came to build the rocket, and we were correct in assuming so.

Nevertheless, with the mention of Clarke, his elevator, and his Gibraltar bridge all in the same article, along with the swiftly approaching first of April, I cannot help but be a little skeptical. I’ll gladly be proven wrong.

31

dalovindj:

The shortest distances to space are right over our geographic poles - the centrifugal force, incidentally what’s keeping our theoretical cable up, pulls the atmosphere outwards towards the euqators.

Carry on, chaps.

32

The more I think about it, the more I wonder if the real concern here is safety. A big, stationary tower 40,000 km high is a sitting duck. A plane or three ramming it would do vast damage, especially if it’s half completed. How would you protect it?

And then there are natural problems, like meteors and lower orbit space debris. You’d have to proof it against something moving 7 or more km/sec, which may prove difficult. I’d like to see a long-term duration study.

NASA has occassional meeting for advanced ideas. If one is ever in my neck of the woods, I think I’ll drop by. I’m interested in this topic very much.

33

I don’t suppose there’s any way to use that charge as part of your power source?

34

Other than being able to hawk a monster loogy off the top, well no, it’d hafta be somewhere down lower where there’s gravity, this sounds like a hell-bent endeavor that doesn’t even seem efficient considering the amount of material required. The writer may have been somebody trying to scare up a market for the carbon nanotubes, which is not to say that it shouldn’t be considered theoretically. I’d prefer that it be tested in a less populated area, like the moon, the problem being, in order to get to the moon, you gotta have the space elevator - Catch 22!

35

I was more thinking of moving the radioactive waste into an asteroidal waste-dump, located in an almost assuredly safe orbit, well away from Earth. :slight_smile:

36

Please excuse me asking another dumb question, but could you plot a trajectory that ends up in the sun, or is this not possible?

And before people berate me for asking this, I did try searching GQ, google, et al.

37

The alternatives seem to be[list=a][li]Leave the radioactive waste where it is–Worldwide.[*]Consolidate the nuclear waste in several spots, such as the Yucca Mt. proposal here in the U.S.[/list=a]Either of these alternatives have huge costs; I reference you, for example, to last Sunday’s 60 Minutes report.[/li]
While I agree that there is some slight chance that a man-made nuclear waste-dump asteroid might suffer a bump by a fellow asteroid or comet, if it were to be located well away from Earth, the chance of radioactive contamination on Earth itself from such a collision would be miniscule.

Consolidation of the radioactive waste in a few spots here on Earth, or just leaving the waste to rot where it is now, both have a high chance of substantial radioactive leakage into our environment. :frowning:

38

Dude! That’d take as much energy as dropping it into the sun! Moving from orbit to orbit comes a cost… Reaction mass, if nothing else. Easier and far cheaper to manage it on earth. Hell, it came from earth in the first place, it’s not like we’re making the earth any more radiactive than it was to begin… We’re just rearranging what radioactive matter is already here.

39

Your suggestion would be the most obvious and easiest thing to do.

I admit to being overly cautious about others’ feelings. Does the Sun have feelings? I don’t know the answer to that question; but neither does anyone else now alive on Earth. Only a few hundred years ago, we all felt that animals had no feelings and that mistreatment of an animal was OK. Only a couple of years ago, M.D.'s believed that babies had no real feelings; today such thoughts are in a process of rapid and huge change toward the belief that babies do have feelings and are fully aware of their immediate environment. The Sun? The Earth? The Amazon Rain Forest? Feelings?

Better to err on the side of caution and think about an artificial asteroid rather than ship radioactive waste into the Sun without any idea of the consequences.

40

Actually, there are ways to move things into other orbits using tethers. You just put a tether in space and spin it. Objects match with the center of it, then move out to the point at which their velocity matches what they need, and then let go at the right moment. This causes the tether to slow down, of course (nothing’s free) but you’re trading rotational energy for linear motion, and that’s a good tradeoff. If you’ve got capsules coming the other way, they can match with the part of the tether going the same speed they are, grab it, then climb down to the center. The tether then speeds up again, and you have a way to move things to another orbit and back for free.

That said, I think that anyone who thinks that flying nuclear waste off of the earth is a good idea doesn’t understand safety engineering. The risk you incur just by moving the stuff to the elevator and up into orbit outweighs the risk of leaving it in a place like Yucca mountain.