Re: starship-design: Staged Fusion Power

[Timothy van der Linden <Shealiak@XS4ALL.nl>]

Hi Nels,

Multistaged fusion all the way up to iron should be theoretically possible,
but the yield isn't spectacular more than a well chosen single stage:

Take:
( I)   1 (2H) + 2 (3He) -> 1 (4He) + 1 (1H) +  18.4 MeV
(II)  24 (2H) + 2 (3H)  -> 1 (54)Fe         + 401.4 MeV

24 (2H) means 24 atoms of Hydrogen, where the Hydrogen has atomic mass 2.

Reaction (I) is the most efficient single fusion reaction.
Reaction (II) is the short-circuit of the multi stage fusion.

The input mass of reaction (I) is 1*2 + 2*3 = 5
The input mass of reaction (II) is 24*2 + 2*3 = 54

So we can repeat reaction (I) 54/5=10.8 times before we've used the same
amount of mass as needed for reaction (II).

Doing reaction (I) 10.8 times will yield: 10.8*18.4=198.7 MeV

So fusing all the way to Iron has a yield (401.4/198.7)=2 times better than
fusing merely to light elements.

So, all the trouble (eg. higher fusion temperature, unwanted fusion
ractions) for a two times higher yield, is likely not worth it.

Timothy