4 ms·

there is no wind on the moon.

by nakedrobot2 4y ago

JumpCrisscross 4y ago
> there is no wind on the moon There is near a Moon base, which is presumably where you’d need power.
- ben_w 4y ago
  "Near" is a relative term; 10 km is a rounding error for resistive losses even in a mediocre cable at unspectacular voltages, even 1000 km isn't much loss for an HVDC cable, and it's economically reasonable to loop the moon with a 600Ω conductor if SpaceX's Starship price estimate works out.
  - JumpCrisscross 4y ago
    I was going to rebut with distance and maintenance, but it's a hell of a lot easier to go 10km over than 10km up. (I think?) > it's economically reasonable to loop the moon with a 600Ω conductor Could you generate nontrivial power from the Moon's motion through the Earth's magnetic field?
    - WJW 4y ago
      My gut feeling says that it is not impossible but you would probably need many loops around the moon to generate a sufficient coil, making the whole thing cost prohibitive. You could probably dot some solar farms around the equator of the moon and loop them all up with a big cable for a fraction of the price.
    - ben_w 4y ago
      > Could you generate nontrivial power from the Moon's motion through the Earth's magnetic field? Not sure, but my gut feeling says no: the Moon is a very long way from the Earth relative to the Earth's size, therefore the magnetic field is likely to be fairly uniform around the Moon and so that can't extract much work. That said, one fun idea I've had is to just assume that the Dark Energy expansion of the universe is pushing the Moon away very slowly; 73 (km/s)/Mpc * distance to the moon ≈ 9.5e-10 m/s, which is pretty close to the actual current Moon-Earth recession speed. Plugging that into the formula for far-field gravitational potential energy given the mass of Earth and the Moon, that's about 170 GW at the present time. (But don't go trying to crowd-fund a Dark Energy field reactor on my say-so: At my [rather limited] level of understanding, it looks like physicists haven't yet reached any sort of consensus as to whether or not Dark Energy might work like that).
      - JumpCrisscross 4y ago
        I'll shoot you the DEFCoin white paper.
  - LarryMullins 4y ago
    Laying ten thousand kilometers of cable to loop around the moon sounds like a huge undertaking, even if you've got a rocket that can bring the cable there. What would the cable layer look like? A huge robotic rover? Could you get all 10,000 km onto one spool, or deliver new spools to it?
    - ben_w 4y ago
      I doubt this is a good guess, given I'm neither a civil engineer nor a space engineer, but my guess would be it would look like a machine for laying a railway. It's a Starship-scale project: something like 100 launches, which is only feasible because Starship is targeting such low launch costs. I don't know (see previous disclaimer) but I wouldn't be surprised if (assuming circumlunar power is even the chosen solution) this is done by sending up an aluminium factory instead and processing regolith.
LarryMullins 4y ago
There's still a bit of dust falling on the moon, kicked up by meteorite impacts and perhaps electrostatic effects. Probably not enough dust to cause issues though.

there is no wind on the moon.

JumpCrisscross 4y ago

> there is no wind on the moon There is near a Moon base, which is presumably where you’d need power.

ben_w 4y ago
"Near" is a relative term; 10 km is a rounding error for resistive losses even in a mediocre cable at unspectacular voltages, even 1000 km isn't much loss for an HVDC cable, and it's economically reasonable to loop the moon with a 600Ω conductor if SpaceX's Starship price estimate works out.
- JumpCrisscross 4y ago
  I was going to rebut with distance and maintenance, but it's a hell of a lot easier to go 10km over than 10km up. (I think?) > it's economically reasonable to loop the moon with a 600Ω conductor Could you generate nontrivial power from the Moon's motion through the Earth's magnetic field?
  - WJW 4y ago
    My gut feeling says that it is not impossible but you would probably need many loops around the moon to generate a sufficient coil, making the whole thing cost prohibitive. You could probably dot some solar farms around the equator of the moon and loop them all up with a big cable for a fraction of the price.
  - ben_w 4y ago
    > Could you generate nontrivial power from the Moon's motion through the Earth's magnetic field? Not sure, but my gut feeling says no: the Moon is a very long way from the Earth relative to the Earth's size, therefore the magnetic field is likely to be fairly uniform around the Moon and so that can't extract much work. That said, one fun idea I've had is to just assume that the Dark Energy expansion of the universe is pushing the Moon away very slowly; 73 (km/s)/Mpc * distance to the moon ≈ 9.5e-10 m/s, which is pretty close to the actual current Moon-Earth recession speed. Plugging that into the formula for far-field gravitational potential energy given the mass of Earth and the Moon, that's about 170 GW at the present time. (But don't go trying to crowd-fund a Dark Energy field reactor on my say-so: At my [rather limited] level of understanding, it looks like physicists haven't yet reached any sort of consensus as to whether or not Dark Energy might work like that).
    - JumpCrisscross 4y ago
      I'll shoot you the DEFCoin white paper.
- LarryMullins 4y ago
  Laying ten thousand kilometers of cable to loop around the moon sounds like a huge undertaking, even if you've got a rocket that can bring the cable there. What would the cable layer look like? A huge robotic rover? Could you get all 10,000 km onto one spool, or deliver new spools to it?
  - ben_w 4y ago
    I doubt this is a good guess, given I'm neither a civil engineer nor a space engineer, but my guess would be it would look like a machine for laying a railway. It's a Starship-scale project: something like 100 launches, which is only feasible because Starship is targeting such low launch costs. I don't know (see previous disclaimer) but I wouldn't be surprised if (assuming circumlunar power is even the chosen solution) this is done by sending up an aluminium factory instead and processing regolith.

LarryMullins 4y ago

There's still a bit of dust falling on the moon, kicked up by meteorite impacts and perhaps electrostatic effects. Probably not enough dust to cause issues though.