6 ms·

The cost to do so would be so prohibitively high that it would never be worth doing. Whatever gains you got from "cheaply processing" it here would be completel

by mabbo 8y ago

The cost to do so would be so prohibitively high that it would never be worth doing. Whatever gains you got from "cheaply processing" it here would be completely eclipsed by the cost of bringing it back. The simple rule of space is that changing the velocity of anything is the most expensive thing. Getting an asteroid from whatever orbit around the sun it's currently in and bringing it to earth would cost far more than it would to instead bring an entire mineral processing plant to the asteroid, and just sending back the bits worth a lot of money.

DmenshunlAnlsis 8y ago
Alternative: crash the asteroids into the moon, have robots recover the valuable minerals. Use a rail gun system to fire it back to Earth, processed, while enjoying the low gravity of the moon.
- celticninja 8y ago
  And firing chunks of metal at the earth doesn't seem problematic to you?
  - DmenshunlAnlsis 8y ago
    You can fire it relatively slowly because of the low gravity of the moon, and take plenty of time bleeding v. Ideally there would be a space elevator and capture system to bring them back, but other methods work. You’re not just firing “at” Earth. Even if you were, Earth is mostly covered by oceans, and landing them there would be acceptable.
    - ben_w 8y ago
      The low gravity of the moon isn’t the problem, it’s the high gravity of the earth: it will hit hard even if you had a lunar space elevator and gave it the minimum possible delta-v to reach Earth from that Lagrange point. The other problem is that even if you intend to use it safely, you have just built a massive gun which is too far away to shoot back at and which has the capability to target specific locations on this planet.
      - resu_nimda 8y ago
        "The Moon is a Harsh Mistress" by Robert Heinlein involves some of that. But how difficult would it be to intercept the payload safely outside the atmosphere? Seems it would be easier than intercepting an ICBM.
        ben_w 8y ago
        I get the impression it would be harder, because ICBM launches are really obvious (to current equipment) and you can at least make a good guess about their ballistic path, while anything of that size launched from the moon would be invisible until it had almost hit you. While it is often said that stealth is impossible in space, that tends to assume the appropriate tech has actually been manufactured rather than sitting in a lab somewhere waiting for a purchase order. Radar, even lidar, is going to have awful signal-to-noise ratios and almost all of the return signal will be stuff that bounced off the moon rather than any projectile. Even the lunar retroreflector turns 10^17 photons out into one photon back, according to Wikipedia, and that’s about as far from stealth as you can get. Edit: I suppose one could reasonably argue that any industrialisation of Luna would, as a result of my own argument, make governments choose to put loads of effort into appropriate defence technology. On the other hand, I’m told trench warfare was more accident than deliberate planning in WW1, so perhaps governments would be as myopic as ever even with a massive space gun on the moon.
        piannucci 8y ago
        Once it gets within a few tens of megameters, pulsed radar systems could easily distinguish an incoming projectile thanks to the 2.4 second round-trip-time to the moon. Metallic objects have ideal visibility. If you are concerned about solar thermal radio emissions bouncing off the moon and reducing SNR, that could be an issue -- a phase-of-the-moon bug in the system, if you will. But based on what I’ve overheard from friends working on 21-cm radar teaching telescopes, I doubt the luminosity of the continuous background is high enough to pose a big problem, assuming you have a decently large antenna. I’m more concerned that there’s nothing much you can do to redirect such an object in the few hours it takes to fall on your head. By that time it will have reached 4km/s.
- mabbo 8y ago
  That's like saying "It's too far to travel from France to my house, so instead we're going to travel from France to my neighbour's house, who is slightly further east". The moon is, astronomically speaking, as near to Earth as you can get. The problem is that everything else, including asteroids, are many thousands of times further away.

by mabbo 8y ago

DmenshunlAnlsis 8y ago

Alternative: crash the asteroids into the moon, have robots recover the valuable minerals. Use a rail gun system to fire it back to Earth, processed, while enjoying the low gravity of the moon.

celticninja 8y ago
And firing chunks of metal at the earth doesn't seem problematic to you?
- DmenshunlAnlsis 8y ago
  You can fire it relatively slowly because of the low gravity of the moon, and take plenty of time bleeding v. Ideally there would be a space elevator and capture system to bring them back, but other methods work. You’re not just firing “at” Earth. Even if you were, Earth is mostly covered by oceans, and landing them there would be acceptable.
  - ben_w 8y ago
    The low gravity of the moon isn’t the problem, it’s the high gravity of the earth: it will hit hard even if you had a lunar space elevator and gave it the minimum possible delta-v to reach Earth from that Lagrange point. The other problem is that even if you intend to use it safely, you have just built a massive gun which is too far away to shoot back at and which has the capability to target specific locations on this planet.
    - resu_nimda 8y ago
      "The Moon is a Harsh Mistress" by Robert Heinlein involves some of that. But how difficult would it be to intercept the payload safely outside the atmosphere? Seems it would be easier than intercepting an ICBM.
      - ben_w 8y ago
        I get the impression it would be harder, because ICBM launches are really obvious (to current equipment) and you can at least make a good guess about their ballistic path, while anything of that size launched from the moon would be invisible until it had almost hit you. While it is often said that stealth is impossible in space, that tends to assume the appropriate tech has actually been manufactured rather than sitting in a lab somewhere waiting for a purchase order. Radar, even lidar, is going to have awful signal-to-noise ratios and almost all of the return signal will be stuff that bounced off the moon rather than any projectile. Even the lunar retroreflector turns 10^17 photons out into one photon back, according to Wikipedia, and that’s about as far from stealth as you can get. Edit: I suppose one could reasonably argue that any industrialisation of Luna would, as a result of my own argument, make governments choose to put loads of effort into appropriate defence technology. On the other hand, I’m told trench warfare was more accident than deliberate planning in WW1, so perhaps governments would be as myopic as ever even with a massive space gun on the moon.
        piannucci 8y ago
        Once it gets within a few tens of megameters, pulsed radar systems could easily distinguish an incoming projectile thanks to the 2.4 second round-trip-time to the moon. Metallic objects have ideal visibility. If you are concerned about solar thermal radio emissions bouncing off the moon and reducing SNR, that could be an issue -- a phase-of-the-moon bug in the system, if you will. But based on what I’ve overheard from friends working on 21-cm radar teaching telescopes, I doubt the luminosity of the continuous background is high enough to pose a big problem, assuming you have a decently large antenna. I’m more concerned that there’s nothing much you can do to redirect such an object in the few hours it takes to fall on your head. By that time it will have reached 4km/s.
mabbo 8y ago
That's like saying "It's too far to travel from France to my house, so instead we're going to travel from France to my neighbour's house, who is slightly further east". The moon is, astronomically speaking, as near to Earth as you can get. The problem is that everything else, including asteroids, are many thousands of times further away.