6% is about the best we can do with a closed cycle. Extra-terrestrial sources could push those numbers even lower by running up to a pure D-He3 reaction.
Yep. I think 6% is pretty good...it's enough so you don't need a heat cycle to extract electricity, and dealing with the neutron damage is easier than going to Uranus. But working fusion reactors probably also means working fusion rockets, and if we find ourselves going to Uranus anyway, all the better.
If we get really good at fusion we could also use boron fusion. It uses the most common isotope of boron, which is plentiful on Earth, plus regular hydrogen, and the main reaction is aneutronic. There'd be some minor side reactions but it'd be under 1% of energy as neutron radiation, probably better than you'd get with deuterium in the mix.
If we get really good at fusion we could also use boron fusion. It uses the most common isotope of boron, which is plentiful on Earth, plus regular hydrogen, and the main reaction is aneutronic. There'd be some minor side reactions but it'd be under 1% of energy as neutron radiation, probably better than you'd get with deuterium in the mix.