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Space Elevators Are Possible

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Re: Space Elevators Are Possible

#41

Post by S4M »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

How about making the elevator start in the North pole (or South pole) and go vertically from there. That way, we can be sure that it will never meet the trajectory of a satellite?

Of course, it would prove harder to build it in those cold regions.

Re: Space Elevators Are Possible

#42

Post by phest »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

In theory, could elevators replace satellites? If so perhaps an initial batch of elevators could also be used to clean up the space junk (including the now obsolete satellites).

Re: Space Elevators Are Possible

#43

Post by mehwoot »

badsock wrote: post #18
mehwoot wrote: post #8

What happens if something hits the cable and it breaks? Does the whole thing drift off into space?

Your question's been well answered by ars, but often the next question is: how dangerous would it be to people on earth if it broke? The answer is not at all. As lutorm points out the cable would be vanishingly thin - there would be a lot of gentle drifting and no firey death from above.

I'm not thinking of the danger, more the immense cost if it drifts off.

Re: Space Elevators Are Possible

#44

Post by InclinedPlane »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

It's not as big a problem as it seems. Space is big, even tethers are small, the amount of time between a collision occurring would normally be quite long. Satellites can have their orbits adjusted just enough every once in a while to avoid the tether.

The value of the tether would be so high that it would be worth the cost of keeping every satellite diverted around it.

Re: Space Elevators Are Possible

#45

Post by Tuna-Fish »

grecy wrote: post #31
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

Would a satellite/tether collision damage the tether, or just destroy the satellite? If it just destroys the satellite, I'm kind of tempted to say "who cares", because by then we will have other solutions, or satellites out past the counterweight, or we can easily launch more now that we have the fancy elevator, or whatever... but then we'd have the problem of an unimaginable amount of space junk orbiting the earth.

Everything in low earth orbit has 30MJ/kg worth of kinetic energy. TNT has 4.6MJ/kg worth of chemical energy. A rule of thumb: when the kinetic energy of things goes above the chemical energy of high explosives, you can assume that nothing survives.

Re: Space Elevators Are Possible

#46

Post by shoyer »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

"given enough time every satellite will hit the tether"

Let's do a back of the envelope calculation: https://www.google.com/search?q=(pi%20*%20(radius%20of%20the...

If a satellite in low-earth orbit has a cross-section of 10 meters, then the timescale for hitting the space elevator is about 300 years.

Given that there are about 3600 satellites in orbit (http://en.wikipedia.org/wiki/Satellite), a satellite would crash into the space elevator about once a month.

Re: Space Elevators Are Possible

#47

Post by manicdee »

atgm wrote: post #22
ars wrote: post #10

Earlier quoted context omitted.

Depends where it hits. On the tether there is a "zero" point. Below that point things fall toward the Earth, above that point things "fall" away from the Earth. So it depends on where it broke and how much weight there is above vs below that point. (To keep the tether in the air they put lots of weight above the point, which falls away from the Earth and pulls the tether taught.) If I were making one of these I'd mak…

> If I were making one of these I'd make several tethers, spaced such that a single object can not break more than one at once. What I'd worry about is security, honestly. What if some nation decides that the space elevator existing isn't in the best interest of their national security, or some paramilitary group wants to make a point? Bombing the base station would hurt the elevator. But of course, we should expect…

And indeed the scenario of "terrorists sever the tether from its geostationary anchor" was part of the story in Red Mars.

https://en.wikipedia.org/wiki/Mars_trilogy

Re: Space Elevators Are Possible

#48

Post by jccooper »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

We already monitor very small debris (anything 1cm or larger), and move things out of the way if needed. The ISS moves about 6 times a year, mostly to maintain a very large margin.

Orbits are quite predictable, and moving the tether around isn't all that bad--after all, it makes getting fuel to LEO altitudes cheap. Also, I would expect active sats to avoid the tether, and the presence of a tether will make removal of dead sats both desirable and much easier.

One would also expect the tether to be multi stranded (which is not so hard once you already have one). You would want at least two, up and down. If erosion or collision in LEO looks problematic, you could run even more stands in that area. It's only a few hundred miles.

My main concern is the lack of a good market to justify investing in a tether. It's only a good deal if there are enough trips to amortize the cost. Hopefully we'll see rockets become cheap enough to help develop larger uses in space that will justify something like a tether.

Re: Space Elevators Are Possible

#49

Post by kamaal »

At the risk of appearing stupid, I just have few simple questions

1. What exactly holds the counter weight in position?

2. Such a long rope, which the article says is around 62000 miles, won't it function more like rubber band than function like a rope? Due to mere stretching/elastic effect?

3. I'm sure traveling 62000 miles is nothing like fuel efficient especially when you travel in the direction of highest friction(Up). So how do you store the fuel and of what weight that would be? Will such a vehicle be even practical?

Re: Space Elevators Are Possible

#50

Post by tantalor »

spiritplumber wrote: post #39
beloch wrote: post #30

Earlier quoted context omitted.

http://en.wikipedia.org/wiki/Project_Babylon Iraq (with a Canadian scientist) almost made an artillery piece capable of putting material into orbit. Obviously, international sanctions gummed up the project a tad and it was basically over when the scientist was assassinated. Still, it was within the realm of possibility. Only recently have rail-guns started to usurp chemically propelled artillery in some roles, so it'…

Into space, or into orbit? The two are vastly different in terms of energy required.

https://en.wikipedia.org/wiki/Quicklaunch was trying. Looks defunct now.
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