Would He3 make fusion easier? :- Can a fusion rocket launch from Moon?

[Al_]

TL;DR Summary

Is He3 on the Moon? Does it help fusion? Can a He3 fusion rocket work? Would the Moon be a good place to launch?

Heard talk about He3 on the Moon and launching a fusion rocket. Is this all just a mashup of Sci-fi ideas?

 

[phyzguy]

There is this idea that you often see that He3 makes fusion energy much more attractive, because the D-He3 reaction generates only charged particles and no neutrons, and therefore generates no radioactivity. This is false, because a D-He3 plasma would also generate D-D reactions, which do generate neutrons, as well as generate T, which fuses with D to generate even more neutrons. Also, the D-He3 reaction has a smaller cross-section than the D-T reaction, meaning that D-He3 fusion is harder to intiate than D-T fusion, which we have not yet managed to make practical despite decades of trying. In addition, mining lunar rocks for their tiny fraction of He3 would be a huge undertaking. So the idea that we will go to the moon, pick up some He3 which is lying around, and fusion will then be this wonderful energy source that will save the world and allow us to build fusion rockets is just what you said, "a mashup of Sci-Fi ideas".

 

[mfb]

D-T is by far the easiest reaction. It's unclear if fusion using He-3 can be net positive at all, and even if it can it's much harder than D-T fusion. And that's for power plants. For a rocket you would make it mass-efficient as additional requirement.

He-3 + He-3 -> He-4 + 2 p + 13 MeV is a possible aneutronic fusion reaction.

 

[swampwiz]

There is this idea that you often see that He3 makes fusion energy much more attractive, because the D-He3 reaction generates only charged particles and no neutrons, and therefore generates no radioactivity. This is false, because a D-He3 plasma would also generate D-D reactions, which do generate neutrons, as well as generate T, which fuses with D to generate even more neutrons. Also, the D-He3 reaction has a smaller cross-section than the D-T reaction, meaning that D-He3 fusion is harder to intiate than D-T fusion, which we have not yet managed to make practical despite decades of trying. In addition, mining lunar rocks for their tiny fraction of He3 would be a huge undertaking. So the idea that we will go to the moon, pick up some He3 which is lying around, and fusion will then be this wonderful energy source that will save the world and allow us to build fusion rockets is just what you said, "a mashup of Sci-Fi ideas".

I find the idea that somehow a factory could be sent to on the Moon or Mars, and come up with finished rocket propellant to be preposterous, at least for a long, long, LONG time. I guess the folks at NASA need to have something to dream about without spending the enormous amount of cash to actually do something.