6 ms·

I want to see an analysis of the different failure modes (catastrophic failure, hit by a satellite) and the consequences of the failure. I believe this idea is

I want to see an analysis of the different failure modes (catastrophic failure, hit by a satellite) and the consequences of the failure. I believe this idea is just incompatible with reality.

corodra 7y ago
Let's ignore the physical catastrophe of a cable at 380,000+ km long dislodging and becoming either locked in earth orbit or crashing into earth. Let's ignore that. What if the cable attached to the moon and then locking the other end to earth orbit alters the month's orbit? There was some stuff I read that the moon doesn't neccesarily orbit the earth. It's the earth and moon orbit each other. Essentially our orbit is significantly affected by our moon compared to other planets and their moons. We have a ton of wildlife that depends on the current orbit pattern. Wouldn't this cable greatly alter said orbit? Plus, 380,000km worth of material? Along with they just hand wave that all failure will happen on the moon side and never affect earth... um okay? Because of testing? This seems more like a joke paper in all honesty. Kind of like the paper based on Silicon valley where they dev an algorithm to find out how long it would take to give an audience handjobs. d2f ratio
- saagarjha 7y ago
  > Wouldn't this cable greatly alter said orbit? Only if it's extremely massive.
  - corodra 7y ago
    So a cable at 300,000km at, oh, I dont know, an average of 1 meter wide, is not massive? I think scrapping together enough material on earth to build this will be the first problem. 2.36 x10^8m for rough cylinder volume. Steel weight would be 1,864,400,000,000 kg. Yes itd be a hybrid material. So, half of that? Maybe a quarter? That's not an insignificant amount of material at a 1m diameter cable. We haven't even gotten to labor costs and energy required. I get astronomically, its insignificant. But I doubt it's going to have no effect.
    - pavel_lishin 7y ago
      The moon weighs 70,000,000,000,000,000,000,000 kg. That's 37,545,591,074 times your projected weight of the cable.
      - Rychard 7y ago
        Is it valid to say this is the "weight" of the moon? I would have assumed such measurements would deal exclusively with the moon's mass. Are the two terms used interchangeably in this context? (honest question, I really have no idea)
        pavel_lishin 7y ago
        I'm using them interchangeably here, but you're right, it was sloppy - I should have said mass. (They're only equivalent on Earth, and even there a given mass's weight changes based on where you are!)
    - liability 7y ago
      > So a cable at 300,000km at, oh, I dont know, an average of 1 meter wide, is not massive Massive to a man, not a moon...
    - mlindner 7y ago
      No it would actually have no effect... Again your numbers are vastly out of scale.
    - eutropia 7y ago
      "Let’s say such a line was made of a cable witha0=10−7m2: its total mass would then be around 40,000 kg. This is about twice the mass of the original lunar lander,and would make transporting and constructing such a cable completely plausible" -- From the linked paper.
- wbl 7y ago
  A cable in geosynchronous orbit isn't a problem. Of course the problem is it won't stay there: the dynamics are likely to be interesting. Now let's do some basic arithmetic. Moon is about 10^22 kg. Saying it will move as a result is like worrying that a semi will stop because of a fly.
  - marcosdumay 7y ago
    If you hang a cable from your home ceiling with a little weight at the free end, what position do you expect the cable to stay? Why do you not expect it to stay down if you hang it on the Moon? The cable in not in geosynchronous orbit, it's in geosynchronous altitude. If it is cut, it will fall into Earth.
    - ben_w 7y ago
      Just to check, are you asking about a tiny cable on the surface of the Moon, or a 1-light-second-long cable where both ends are “the bottom” in local gravity even though they’re on opposite ends of the straight cable?
      - marcosdumay 7y ago
        Oh, thanks, I see the problem now. I imagine it would be nailed down at the Moon, even though it 's going "up" on that end too, the Earth end will very likely weight much more than the Moon and pull the entire cable. But the fact that it must be much fatter near the Moon does indeed complicate things.
- pavel_lishin 7y ago
  > they just hand wave that all failure will happen on the moon side and never affect earth... um okay? Because of testing? They don't handwave it, they calculate it. It's significantly less handwavy than your back-of-napkin objections.
  - wbhart 7y ago
    Can you point to the specific section of the paper where this is calculated. I admittedly only skim read, but I did go through the whole thing, and I'm convinced I missed this kind of analysis somewhere.
- yongjik 7y ago
  Your intuition is out of proportion, because astronomical objects are big. Really big. A spider riding on the left side mirror of a 18-wheeler has a better chance of drastically changing its course.
- mlindner 7y ago
  > What if the cable attached to the moon and then locking the other end to earth orbit alters the month's orbit? Sorry that's functionally just not possible. More so the moon is already moving away from the Earth at a couple centimeters per year. You're not even going to slow that down.
brianhorakh 7y ago
Ask Russell @ xkcd
dredmorbius 7y ago
I've suspected for a few years now that any long linear space structure will be prone to very high electrical potential deltas, particularly as it moves through different radiation and magnetic fields. How the structure behaves will depend on its own conductivity, with conductive structures creating sizeable currents, and insulating ones, massive charge differentials.
- Atheros 7y ago
  So free electricity?
  - dredmorbius 7y ago
    Maybe, but more likely a bit of a problem. Huge charges across long distances mean very large currents. That tends to create difficulties, such as massive heating. Whether or not this will be the case I don't know, though experiments with simple long tethers (several km to 10s or 100s of km) should be relatively easy to test: try them in some empty space and instrument for charges and magnetic fields. Might produce an interesting de-orbiting spectacle as well.
    - carapace 7y ago
      https://www-istp.gsfc.nasa.gov/Education/wtether.html https://www-istp.gsfc.nasa.gov/Education/wtether.html "The Space Tether Experiment" > The space tether experiment, a joint venture of the US and Italy, called for a scientific payload--a large, spherical satellite--to be deployed from the US space shuttle at the end of a conducting cable (tether) 20 km (12.5 miles) long. The idea was to let the shuttle drag the tether across the Earth's magnetic field, producing one part of a dynamo circuit. The experiment failed, for a fascinating reason...
      - dredmorbius 7y ago
        Thanks! I was vaguely aware that the experiment had been tried. I'd either forgotten or never known the specific reasons for the failure. Though it rather closely matches the scenario I'd suggested above.
m463 7y ago
I was wondering the same thing - does it burn up in the atmosphere, or destroy all life on the planet?

I want to see an analysis of the different failure modes (catastrophic failure, hit by a satellite) and the consequences of the failure. I believe this idea is just incompatible with reality.

corodra 7y ago

Let's ignore the physical catastrophe of a cable at 380,000+ km long dislodging and becoming either locked in earth orbit or crashing into earth. Let's ignore that. What if the cable attached to the moon and then locking the other end to earth orbit alters the month's orbit? There was some stuff I read that the moon doesn't neccesarily orbit the earth. It's the earth and moon orbit each other. Essentially our orbit is significantly affected by our moon compared to other planets and their moons. We have a ton of wildlife that depends on the current orbit pattern. Wouldn't this cable greatly alter said orbit? Plus, 380,000km worth of material? Along with they just hand wave that all failure will happen on the moon side and never affect earth... um okay? Because of testing? This seems more like a joke paper in all honesty. Kind of like the paper based on Silicon valley where they dev an algorithm to find out how long it would take to give an audience handjobs. d2f ratio

saagarjha 7y ago
> Wouldn't this cable greatly alter said orbit? Only if it's extremely massive.
- corodra 7y ago
  So a cable at 300,000km at, oh, I dont know, an average of 1 meter wide, is not massive? I think scrapping together enough material on earth to build this will be the first problem. 2.36 x10^8m for rough cylinder volume. Steel weight would be 1,864,400,000,000 kg. Yes itd be a hybrid material. So, half of that? Maybe a quarter? That's not an insignificant amount of material at a 1m diameter cable. We haven't even gotten to labor costs and energy required. I get astronomically, its insignificant. But I doubt it's going to have no effect.
  - pavel_lishin 7y ago
    The moon weighs 70,000,000,000,000,000,000,000 kg. That's 37,545,591,074 times your projected weight of the cable.
    - Rychard 7y ago
      Is it valid to say this is the "weight" of the moon? I would have assumed such measurements would deal exclusively with the moon's mass. Are the two terms used interchangeably in this context? (honest question, I really have no idea)
      - pavel_lishin 7y ago
        I'm using them interchangeably here, but you're right, it was sloppy - I should have said mass. (They're only equivalent on Earth, and even there a given mass's weight changes based on where you are!)
  - liability 7y ago
    > So a cable at 300,000km at, oh, I dont know, an average of 1 meter wide, is not massive Massive to a man, not a moon...
  - mlindner 7y ago
    No it would actually have no effect... Again your numbers are vastly out of scale.
  - eutropia 7y ago
    "Let’s say such a line was made of a cable witha0=10−7m2: its total mass would then be around 40,000 kg. This is about twice the mass of the original lunar lander,and would make transporting and constructing such a cable completely plausible" -- From the linked paper.
wbl 7y ago
A cable in geosynchronous orbit isn't a problem. Of course the problem is it won't stay there: the dynamics are likely to be interesting. Now let's do some basic arithmetic. Moon is about 10^22 kg. Saying it will move as a result is like worrying that a semi will stop because of a fly.
- marcosdumay 7y ago
  If you hang a cable from your home ceiling with a little weight at the free end, what position do you expect the cable to stay? Why do you not expect it to stay down if you hang it on the Moon? The cable in not in geosynchronous orbit, it's in geosynchronous altitude. If it is cut, it will fall into Earth.
  - ben_w 7y ago
    Just to check, are you asking about a tiny cable on the surface of the Moon, or a 1-light-second-long cable where both ends are “the bottom” in local gravity even though they’re on opposite ends of the straight cable?
    - marcosdumay 7y ago
      Oh, thanks, I see the problem now. I imagine it would be nailed down at the Moon, even though it 's going "up" on that end too, the Earth end will very likely weight much more than the Moon and pull the entire cable. But the fact that it must be much fatter near the Moon does indeed complicate things.
pavel_lishin 7y ago
> they just hand wave that all failure will happen on the moon side and never affect earth... um okay? Because of testing? They don't handwave it, they calculate it. It's significantly less handwavy than your back-of-napkin objections.
- wbhart 7y ago
  Can you point to the specific section of the paper where this is calculated. I admittedly only skim read, but I did go through the whole thing, and I'm convinced I missed this kind of analysis somewhere.
yongjik 7y ago
Your intuition is out of proportion, because astronomical objects are big. Really big. A spider riding on the left side mirror of a 18-wheeler has a better chance of drastically changing its course.
mlindner 7y ago
> What if the cable attached to the moon and then locking the other end to earth orbit alters the month's orbit? Sorry that's functionally just not possible. More so the moon is already moving away from the Earth at a couple centimeters per year. You're not even going to slow that down.

brianhorakh 7y ago

Ask Russell @ xkcd

dredmorbius 7y ago

I've suspected for a few years now that any long linear space structure will be prone to very high electrical potential deltas, particularly as it moves through different radiation and magnetic fields. How the structure behaves will depend on its own conductivity, with conductive structures creating sizeable currents, and insulating ones, massive charge differentials.

Atheros 7y ago
So free electricity?
- dredmorbius 7y ago
  Maybe, but more likely a bit of a problem. Huge charges across long distances mean very large currents. That tends to create difficulties, such as massive heating. Whether or not this will be the case I don't know, though experiments with simple long tethers (several km to 10s or 100s of km) should be relatively easy to test: try them in some empty space and instrument for charges and magnetic fields. Might produce an interesting de-orbiting spectacle as well.
  - carapace 7y ago
    https://www-istp.gsfc.nasa.gov/Education/wtether.html https://www-istp.gsfc.nasa.gov/Education/wtether.html "The Space Tether Experiment" > The space tether experiment, a joint venture of the US and Italy, called for a scientific payload--a large, spherical satellite--to be deployed from the US space shuttle at the end of a conducting cable (tether) 20 km (12.5 miles) long. The idea was to let the shuttle drag the tether across the Earth's magnetic field, producing one part of a dynamo circuit. The experiment failed, for a fascinating reason...
    - dredmorbius 7y ago
      Thanks! I was vaguely aware that the experiment had been tried. I'd either forgotten or never known the specific reasons for the failure. Though it rather closely matches the scenario I'd suggested above.

m463 7y ago

I was wondering the same thing - does it burn up in the atmosphere, or destroy all life on the planet?