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What about space debris? If we build such a large stucture up to the geostationary orbit, won't it be exposed and how can it be protected? The top station can't

by Kenji 13y ago

What about space debris? If we build such a large stucture up to the geostationary orbit, won't it be exposed and how can it be protected? The top station can't dodge - or can it?

sentientmachine 13y ago
Self healing cables. You could use three parallel cables separated from each other by struts, with sufficient margin of safety that severing just one or two strands still allows the surviving strand to hold the elevator's entire weight while repairs are performed. When a meteorite hits a strand, or two, robots going up and down the cable will immediately repair the break. What about lightning though? When a cloud contains an imbalance of electrons, won't the lightning strike much rather travel through the cable and weaken the material so it breaks?
- mrfusion 13y ago
  If anything it would work like a lightening rod and discharge the currently gradually so it never builds up in the first place.
  - mmphosis 13y ago
    And, could that current in the tether be used as a source of energy? And, would stopping lightning cause other problems for Earth?
    - Tuna-Fish 13y ago
      > And, could that current in the tether be used as a source of energy? Yes, but the actual continuous power delivered by it would be surprisingly low, making it pointless. > And, would stopping lightning cause other problems for Earth? No, as the effect would be very localized.
- VLM 13y ago
  "What about lightning though?" We have commercial experience (well, at least in Russia) making communications towers a mile or so tall. Making one five miles tall would not be a huge stretch of the imagination, and those are fairly tolerant of all kinds of ridiculous abuse. Simply attach the elevator at the top of the tower instead of ground level and you've eliminate pretty much any man-portable non nuke attack potential and most mechanized vehicle attacks (or accidents). Ditto the elevator material. We can't afford for weight reasons to make the entire thing "airliner proof" but we can afford to make the bottom 10 miles or so "small cessna proof". So make the bottom couple miles quadruple redundant steel battleship anchor chain or whatever. 99% of it will still have to be light as a feather, but nothing can hit it, so thats OK.
  - LoganCale 13y ago
    What tower has been built a mile tall? According to Wikipedia, the tallest radio tower ever was the Warsaw radio mast at 646.38 meters.
    - VLM 13y ago
      You are correct. I had the peculiar idea that Ostankino was 1800 meters tall (well over a mile) its actually 1800 feet. Which is still pretty tall. There are other towers taller than Ostankino now. This comes up a lot at a telecom company, "You think climbing a 100M tower is a PITA, there's one in Russia thats.. etc etc"
Udo 13y ago
It would be at risk, yes, and probably more so than most space vehicles. Gladly our space junk hasn't yet reached the point where surprise cascades happen so we can track debris well in advance. But we'll be needing real countermeasures, active spacecraft that can clean up our orbits. One interesting aspect of the space elevator remains its failure modes though. Cable failure, for any reason, is going to be a problem. We'll need a safety concept both for the ground as well as the payload if humans are going up there. I hope this isn't going to be one of these things where everybody ends up agreeing that it's not feasible to save lives in the event of catastrophic failures.
- BugBrother 13y ago
  From what I've read of carbon tube based cables, most of the length would burn up in the atmosphere before reaching the ground. Edit: VLM does have a point in that a falling cable might be a problem on Mars. The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway. :-) More advanced rotating elevators in a moon orbit, maybe. But it might be hard because of the moon mascons (the moon is lumpy internally with different density, which results in gravitational anomalies).
  - gliese1337 13y ago
    The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway. Actually, it does: http://en.wikipedia.org/wiki/Lunar_space_elevator http://en.wikipedia.org/wiki/Lunar_space_elevator You're just fairly restricted in where you can put it- you can only put one near the sub-Earth and anti-Earth points, such that the cable passes through the L1 or L2 Lagrange points, rather than anywhere along the equator. The cable would have to much, much longer than for a space elevator on Earth, but the Moon's lower gravity actually makes the engineering challenges Not As Bad- i.e., we could build a lunar space elevator with current materials.
    - BugBrother 13y ago
      OK ok, but it is economical insanity. On the moon, an electric rail launcher with 5-10G only needs to be a few km long. (Iirc, 1G acceleration of four minutes is the launch velocity of the moon? ~ 2.4 km/s.) Edit: This assumes local materials for the electric launcher. If everything is skipped from Earth, it might be different. But, consider -- if you need to launch so much stuff from the moon, you must already have the infrastructure to build things there.
farginay 13y ago
I've always wondered about the aggregate effect of wind pressure across the length of the cable. It seems like it could be significant.
- bronson 13y ago
  The cable is 62,000 miles long. The atmosphere goes up maybe 100 miles (0.16%) of it, and meaningful wind only goes up about ten miles (0.016%). The pressure doesn't even register. That said, I've got to imagine that bottom .1% of the cable will be made differently to counteract all the water and oxygen around it.
  - joshdulac 13y ago
    But you can't rule out the possibility of a storm crossing the cable.
    - bronson 13y ago
      Compared to the rest of the tension and abuse on the cable? I think you pretty much can. Lightning might be interesting but wind is no big deal.
- smoyer 13y ago
  I wonder about the rotational speed changes of the payload mass more than the wind. The counterweight will tend to speed up and slow down as the mass of the payload is accelerated and decelerated (during climbs and descents respectively), but I keep hearing that the counterweight is just a mass.
  - darkmighty 13y ago
    If you think the counterweight will move down when you thrust a mass up, you have a misconception. The tether will be consistently under tension, so unless the acceleration mA is sufficient to surpass MV^2/R, that won't happen.
- 31reasons 13y ago
kahirsch 13y ago
Every lower orbit will eventually intersect with the cable, so the cable would actually have to dodge most existing satellites. I've read estimates that it would only need to dodge something on average once or twice a year, but I don't know if that number is correct.

by Kenji 13y ago

What about space debris? If we build such a large stucture up to the geostationary orbit, won't it be exposed and how can it be protected? The top station can't dodge - or can it?

sentientmachine 13y ago

Self healing cables. You could use three parallel cables separated from each other by struts, with sufficient margin of safety that severing just one or two strands still allows the surviving strand to hold the elevator's entire weight while repairs are performed. When a meteorite hits a strand, or two, robots going up and down the cable will immediately repair the break. What about lightning though? When a cloud contains an imbalance of electrons, won't the lightning strike much rather travel through the cable and weaken the material so it breaks?

mrfusion 13y ago
If anything it would work like a lightening rod and discharge the currently gradually so it never builds up in the first place.
- mmphosis 13y ago
  And, could that current in the tether be used as a source of energy? And, would stopping lightning cause other problems for Earth?
  - Tuna-Fish 13y ago
    > And, could that current in the tether be used as a source of energy? Yes, but the actual continuous power delivered by it would be surprisingly low, making it pointless. > And, would stopping lightning cause other problems for Earth? No, as the effect would be very localized.
VLM 13y ago
"What about lightning though?" We have commercial experience (well, at least in Russia) making communications towers a mile or so tall. Making one five miles tall would not be a huge stretch of the imagination, and those are fairly tolerant of all kinds of ridiculous abuse. Simply attach the elevator at the top of the tower instead of ground level and you've eliminate pretty much any man-portable non nuke attack potential and most mechanized vehicle attacks (or accidents). Ditto the elevator material. We can't afford for weight reasons to make the entire thing "airliner proof" but we can afford to make the bottom 10 miles or so "small cessna proof". So make the bottom couple miles quadruple redundant steel battleship anchor chain or whatever. 99% of it will still have to be light as a feather, but nothing can hit it, so thats OK.
- LoganCale 13y ago
  What tower has been built a mile tall? According to Wikipedia, the tallest radio tower ever was the Warsaw radio mast at 646.38 meters.
  - VLM 13y ago
    You are correct. I had the peculiar idea that Ostankino was 1800 meters tall (well over a mile) its actually 1800 feet. Which is still pretty tall. There are other towers taller than Ostankino now. This comes up a lot at a telecom company, "You think climbing a 100M tower is a PITA, there's one in Russia thats.. etc etc"

Udo 13y ago

It would be at risk, yes, and probably more so than most space vehicles. Gladly our space junk hasn't yet reached the point where surprise cascades happen so we can track debris well in advance. But we'll be needing real countermeasures, active spacecraft that can clean up our orbits. One interesting aspect of the space elevator remains its failure modes though. Cable failure, for any reason, is going to be a problem. We'll need a safety concept both for the ground as well as the payload if humans are going up there. I hope this isn't going to be one of these things where everybody ends up agreeing that it's not feasible to save lives in the event of catastrophic failures.

BugBrother 13y ago
From what I've read of carbon tube based cables, most of the length would burn up in the atmosphere before reaching the ground. Edit: VLM does have a point in that a falling cable might be a problem on Mars. The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway. :-) More advanced rotating elevators in a moon orbit, maybe. But it might be hard because of the moon mascons (the moon is lumpy internally with different density, which results in gravitational anomalies).
- gliese1337 13y ago
  The moon doesn't have enough rotation for a fixed skyhook (space elevator) anyway. Actually, it does: http://en.wikipedia.org/wiki/Lunar_space_elevator http://en.wikipedia.org/wiki/Lunar_space_elevator You're just fairly restricted in where you can put it- you can only put one near the sub-Earth and anti-Earth points, such that the cable passes through the L1 or L2 Lagrange points, rather than anywhere along the equator. The cable would have to much, much longer than for a space elevator on Earth, but the Moon's lower gravity actually makes the engineering challenges Not As Bad- i.e., we could build a lunar space elevator with current materials.
  - BugBrother 13y ago
    OK ok, but it is economical insanity. On the moon, an electric rail launcher with 5-10G only needs to be a few km long. (Iirc, 1G acceleration of four minutes is the launch velocity of the moon? ~ 2.4 km/s.) Edit: This assumes local materials for the electric launcher. If everything is skipped from Earth, it might be different. But, consider -- if you need to launch so much stuff from the moon, you must already have the infrastructure to build things there.

farginay 13y ago

I've always wondered about the aggregate effect of wind pressure across the length of the cable. It seems like it could be significant.

bronson 13y ago
The cable is 62,000 miles long. The atmosphere goes up maybe 100 miles (0.16%) of it, and meaningful wind only goes up about ten miles (0.016%). The pressure doesn't even register. That said, I've got to imagine that bottom .1% of the cable will be made differently to counteract all the water and oxygen around it.
- joshdulac 13y ago
  But you can't rule out the possibility of a storm crossing the cable.
  - bronson 13y ago
    Compared to the rest of the tension and abuse on the cable? I think you pretty much can. Lightning might be interesting but wind is no big deal.
smoyer 13y ago
I wonder about the rotational speed changes of the payload mass more than the wind. The counterweight will tend to speed up and slow down as the mass of the payload is accelerated and decelerated (during climbs and descents respectively), but I keep hearing that the counterweight is just a mass.
- darkmighty 13y ago
  If you think the counterweight will move down when you thrust a mass up, you have a misconception. The tether will be consistently under tension, so unless the acceleration mA is sufficient to surpass MV^2/R, that won't happen.
31reasons 13y ago

kahirsch 13y ago

Every lower orbit will eventually intersect with the cable, so the cable would actually have to dodge most existing satellites. I've read estimates that it would only need to dodge something on average once or twice a year, but I don't know if that number is correct.