RE: starship-design: Staged Fusion Power

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

Hello Lee,

You requested:
>You seem to have chosen a reaction that is rather poor in terms of energy
>produced for this comparison. Perhaps you would like to illustrate the same
>relationship using something like He3 and Li6?

BTW. I just discovered to have made a typo in my last letter, which luckely
did not continue in the calculations.

I originally wrote:
( I)   1 (2H) + 2 (3He) -> 1 (4He) + 1 (1H) +  18.4 MeV

But instead of 2 helium cores one needs only 1.

Here the correct version:
( I)   1 (2H) + 1 (3He) -> 1 (4He) + 1 (1H) +  18.4 MeV

------

Here's an example as closely to your choice:

- I've switched to the apparently more conventional notation.
- I don't know what the result of fusing He3 and Li6 will be.
  The simplest result would be B9 which is highly unstable (doesn't
  appear in my table), H1 + Be8 isn't ideal either because Be8 is
  also very unstable.
  So let me modify your which into He4 + Li6 -> B10

(III)  1 (He4) + 1 (Li6) -> 1 (B10) + 4.5 MeV

The initial weight is 4+6=10, so one can do reaction (III) 54/10=5.4 times
before one has used the same weight as reaction (II)

Doing reaction (III) 5.4 times will yield: 5.4*4.5MeV=24.3MeV

In this case fusing all the way to Iron would have given a 401.4/24.3=16.5
times higher yield.

So you may conclude that multi-stage fusion may be worth the effort. I can
even think of a multitude of reactions that have much lower yields per unit
of weight and which thus would show to be over 100 times worse than fusing
all the way to Iron.

But this approach is not very useful. We are trying to optimize "ease" and
"yield per unit weight". He4+Li6 is harder to fuse than H2+He3 AND has a
lower yield per unit of weight, thus two reasons for it being a bad choice.
My H2+He3 was one of the best choices according to the mentioned criteria.
I think there is no point in trying to find a worst case scenario.
If you feel this is not correct, don't hesitate to comment.

Timothy