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

by mehwoot 13y ago

ars 13y ago
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 make several tethers, spaced such that a single object can not break more than one at once. Then tie the tethers together periodically. This object is about max: https://en.wikipedia.org/wiki/Tunguska_event https://en.wikipedia.org/wiki/Tunguska_event so I'd make the multiple tethers at least 200m apart. That's pretty far apart, so I'd invest in better detection technology to reduce the size maximum undetected object. (Although that raises the question of what to do if you do find a big one and it's headed right toward you.)
- atgm 13y ago
  > 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 that to be secured. That still leaves the entire length of cable running up and down the elevator -- that's a huge volume of space to secure against anything explosive or fragmentary.
  - manicdee 13y ago
    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 https://en.wikipedia.org/wiki/Mars_trilogy
lutorm 13y ago
I didn't see it mentioned in this article, but the cable is actually very small. I read this older NASA study that said that for a carbon nanotube tether, an optimal cable would be a thin tape something like an inch across. That has pretty small cross section for being hit by a meteoroid.
- andrewflnr 13y ago
  On the other hand, a satellite a couple meters across has plenty of cross section with which to find the cable. Even if we take all those down (not in our lifetime), there is a lot of little stuff in orbit, and it would only take one.
badsock 13y ago
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.
- mehwoot 13y ago
  I'm not thinking of the danger, more the immense cost if it drifts off.

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

by mehwoot 13y ago

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

ars 13y ago

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 make several tethers, spaced such that a single object can not break more than one at once. Then tie the tethers together periodically. This object is about max: https://en.wikipedia.org/wiki/Tunguska_event https://en.wikipedia.org/wiki/Tunguska_event so I'd make the multiple tethers at least 200m apart. That's pretty far apart, so I'd invest in better detection technology to reduce the size maximum undetected object. (Although that raises the question of what to do if you do find a big one and it's headed right toward you.)

atgm 13y ago
> 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 that to be secured. That still leaves the entire length of cable running up and down the elevator -- that's a huge volume of space to secure against anything explosive or fragmentary.
- manicdee 13y ago
  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 https://en.wikipedia.org/wiki/Mars_trilogy

lutorm 13y ago

I didn't see it mentioned in this article, but the cable is actually very small. I read this older NASA study that said that for a carbon nanotube tether, an optimal cable would be a thin tape something like an inch across. That has pretty small cross section for being hit by a meteoroid.

andrewflnr 13y ago
On the other hand, a satellite a couple meters across has plenty of cross section with which to find the cable. Even if we take all those down (not in our lifetime), there is a lot of little stuff in orbit, and it would only take one.

badsock 13y ago

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.

mehwoot 13y ago
I'm not thinking of the danger, more the immense cost if it drifts off.