> Until we crack compact, high yield fusion, I doubt we will make much progress in realizing our space-faring dreams.
What about regular, fission nuclear power?
What about regular, fission nuclear power?
Projections that there's enough uranium for 200 years[1] are based on levels of present utilization: around 3.7% of global energy use[2]. Bump that to 100% and we'd run through all available reserves in less than a decade (7.4 years, if you're counting).
Solar energy (including solar mediated via plants, wind, or water), hydrogen fusion, possibly geothermal energy, or with really long odds: hydrocarbon prospecting from another body (say, maybe Titan) are the only energy sources which could last a considerable human population for the possible maximum lifetime of the species.
Yes, a small Mars outpost could be powered off of nuclear power for a considerable period, but that would take away from available nuclear fuel supplies on Earth.
The likelihood of managing usable sustainable fusion under terrestrial or other contained circumstances are fairly unlikely IMO.
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Notes:
1. http://www.scientificamerican.com/article/how-long-will-glob...
Rob Lister gives global annual energy consumption as 140 TWh.
The true number is 211,782 TWh, for 2011, from IEA (expressed as 18,210 Mtoe -- million tons of oil equivalent)
http://www.iea.org/Sankey/index.html
That's 1512x higher than Lister's value. Dividing his 64,000 year supply by 1512, we get 42 years supply of thorium.
I see a problem.
It might not be 64ky, but >1ky seems to be very realistic.
Edit: See also the Wikipedia section on it: http://en.wikipedia.org/wiki/Thorium#Reserve_estimates
I'm not claiming otherwise.
Liquid thorium reactors are another option. There's no thorium in seawater, but on land there's several times as much thorium as U238, and it's all the same, useful isotope. China has an aggressive R&D program hoping to get a prototype reactor ready in a decade.
But personally I think it's likely that we will achieve sustainable fusion in the fairly near future.
...which says that EROI is 22 assuming a conventional reactor. Ie., we'd get 22 times as much energy out as we spent on extraction. With a fast reactor the ratio would be a hundred times better, since we could use all that uranium instead of 0.7% of it.
http://www-formal.stanford.edu/jmc/progress/cohen.html
Of course in the context of the current discussion we should also consider the possibility of getting uranium from various other spots in the solar system: http://nextbigfuture.com/2009/08/how-much-uranium-is-in-sola...