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I've been wondering if tritium could be used as an alternative power source for the nuclear batteries used on space missions. Of course tritium has to be "manu

by curtis 12y ago

I've been wondering if tritium could be used as an alternative power source for the nuclear batteries used on space missions. Of course tritium has to be "manufactured" just like plutonium-238, but on the other hand it can be made from lithium using a fusion reactor [1]. But wait, you're thinking, fusion reactors based on current technology consume more energy than they can produce. That's true, but also irrelevant if your business model is producing tritium rather than energy. This is because the going rate for tritium (according to Wikipedia) is something like $30,000 per gram [2]. I'm not sure what the licensing requirements are on fusion reactors, but I think they're a lot less onerous than licensing a new fission reactor. I don't think there's any licensing requirement at all for a small fusion reactor like a Farnsworth fusor. Disclaimer: This is just idle speculation because I haven't done the math. [1] http://en.wikipedia.org/wiki/Fusion_power#Power_Production http://en.wikipedia.org/wiki/Fusion_power#Power_Production [2] http://en.wikipedia.org/wiki/Tritium#Self-powered_lighting http://en.wikipedia.org/wiki/Tritium#Self-powered_lighting

daeken 12y ago
Nuclear 'batteries' are radioisotope thermoelectric generators (RTGs). They require a pretty substantial amount of heat to produce electricity. I don't know about temperatures, but tritium produces a decay energy of 0.018590 MeV, versus plutonium-238's 5.593 MeV. Assuming you can scale it up directly, the 4.8kg of plutonium-238 in Curiosity would be equivalent to 1444kg of tritium. It's just way, way less energy dense. Edit: This explanation is way, way off. See response from 'throwaway_yy2Di
- throwaway_yy2Di 12y ago
  There's two other differences you'd need to account for: * One Pu-238 nucleus weighs 238 amu; a triton only weighs 3 amu * Tritium decays 7 times faster -- a 12.32 year half-life, vs. 87.7 years for Pu-238 Put together, the specific power (watts/kg) of pure tritium is about twice as high. That's chemically just hydrogen gas, which I'd guess isn't practical. The solids with the highest hydrogen density, like polyethylene ([C2H4]n), would be less power-dense, but not by much. But I think there's some slack here. The ESA is designing their future RTGs to use Americium-241, which is drastically worse (in terms of these figures), yet still usable.
  - daeken 12y ago
    Ah hah -- great points, thanks! Edited my original post to note that my analysis was woefully incomplete.
tarre 12y ago
Maybe the biggest drawback for tritium is the decay energy of 0.02 MeV compared to 5 MeV of Pu238. On longer missions also half-life may create problems (12 years / 70 years). E: I'm very slow with my phone...
- curtis 12y ago
  That's a good point. Of course if you can produce tritium cheap enough it might be feasible to just start each mission with a grossly over-powered nuclear battery.

by curtis 12y ago

daeken 12y ago

Nuclear 'batteries' are radioisotope thermoelectric generators (RTGs). They require a pretty substantial amount of heat to produce electricity. I don't know about temperatures, but tritium produces a decay energy of 0.018590 MeV, versus plutonium-238's 5.593 MeV. Assuming you can scale it up directly, the 4.8kg of plutonium-238 in Curiosity would be equivalent to 1444kg of tritium. It's just way, way less energy dense. Edit: This explanation is way, way off. See response from 'throwaway_yy2Di

throwaway_yy2Di 12y ago
There's two other differences you'd need to account for: * One Pu-238 nucleus weighs 238 amu; a triton only weighs 3 amu * Tritium decays 7 times faster -- a 12.32 year half-life, vs. 87.7 years for Pu-238 Put together, the specific power (watts/kg) of pure tritium is about twice as high. That's chemically just hydrogen gas, which I'd guess isn't practical. The solids with the highest hydrogen density, like polyethylene ([C2H4]n), would be less power-dense, but not by much. But I think there's some slack here. The ESA is designing their future RTGs to use Americium-241, which is drastically worse (in terms of these figures), yet still usable.
- daeken 12y ago
  Ah hah -- great points, thanks! Edited my original post to note that my analysis was woefully incomplete.

tarre 12y ago

Maybe the biggest drawback for tritium is the decay energy of 0.02 MeV compared to 5 MeV of Pu238. On longer missions also half-life may create problems (12 years / 70 years). E: I'm very slow with my phone...

curtis 12y ago
That's a good point. Of course if you can produce tritium cheap enough it might be feasible to just start each mission with a grossly over-powered nuclear battery.