Harvesting solar power in space and sending it back to Earth • Hacker News Board

Re: Harvesting solar power in space and sending it back to Earth

#81

Post by jacques_chester » Sat, Aug 31, 2013, 1:29 PM UTC

justincormack wrote: post #80

jacques_chester wrote: post #60

Earlier quoted context omitted.

Absolutely, but in the meantime solar panels have improved enormously also. The third part of the equation is launch costs, which haven't really fallen at all.

Launch prices basically are energy costs, plus a markup, so they are never going to make this work unless you could make the whole thing extremely light...

O'Neill's plan was to bootstrap manufacturing in situ, starting with robotic mining of moon dust or rock. The ore would be sent to L5 by linear launchers and then smelted into simple metals to make reflective surfaces.

Re: Harvesting solar power in space and sending it back to Earth

#82

Post by schiffern » Sat, Aug 31, 2013, 11:21 PM UTC

dredmorbius wrote: post #76

schiffern wrote: post #71

Earlier quoted context omitted.

All energy is actually nuclear energy. (Of course Earth-based nuclear power doesn't have the entire mantle of the sun as radiation shielding. So there's that…)

No, some is gravitational: tidal, arguably hydroelectric, though that's a combination of solar (feeding the water cycle) and gravitational (capturing gravitational potential of lifted water). Geothermal is in part latent residual heat of formation, which is arguably either kinetic or gravitational energy again. Some is _also_ the result of radioactive decay, though I don't have the precise breakdown. I suppose there…

True, tidal isn't nuclear. Basically everything else is.

>Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.

Neither do I, but here's my logic: if there were no nuclear power in the center of Earth, Lord Kelvin tells us it would solidify in only ~40 million years[1]. The Earth being 100 times older, the amount of residual heat left today must be insignificant.

Stellar magnetic fields come from the convective mantle, which is nuclear powered. Not sure about planetary magnetic fields, but the above analysis suggests nuclear as well. Collapsed stars will be heated by gravitational potential, but we don't see a lot of those 'round these parts.

[1] https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kel...

Re: Harvesting solar power in space and sending it back to Earth

#83

Post by dredmorbius » Sun, Sep 01, 2013, 8:41 PM UTC

schiffern wrote: post #82

dredmorbius wrote: post #76

Earlier quoted context omitted.

No, some is gravitational: tidal, arguably hydroelectric, though that's a combination of solar (feeding the water cycle) and gravitational (capturing gravitational potential of lifted water). Geothermal is in part latent residual heat of formation, which is arguably either kinetic or gravitational energy again. Some is _also_ the result of radioactive decay, though I don't have the precise breakdown. I suppose there…

True, tidal isn't nuclear. Basically everything else is. >Some is _also_ the result of radioactive decay, though I don't have the precise breakdown. Neither do I, but here's my logic: if there were no nuclear power in the center of Earth, Lord Kelvin tells us it would solidify in only ~40 million years[1]. The Earth being 100 times older, the amount of residual heat left today must be insignificant. Stellar magnetic…

My point wasn't that the vast, vast majority of energy available to humans on Earth isn't ultimately nuclear in origin. Just that there are energy potentials in the Universe which aren't nuclear in origin. If you trace back the formation of the Solar System itself, as a generation 3-4 system, even the gravitational potential represented in it originates from nuclear reactions.

The Big Bang (background microwave radiation) and Dark Energy would also come to mind as non-nuclear energy systems.

Not of much practical use to us on Earth, however.