On Tue, Oct 31, 2017 at 10:07:01PM -0400, Kurt Feltenberger (via tml list) wrote:
> Could there be additives, essentially catalysts, that would make a
> "premium" fuel (say it reduces fuel consumption by x% in normal
> drives, but some performance drives - racing pinnace for example,
> require it).

There are a great many possible fusion fuels, and the common
assumption of just "hydrogen" (presumably p-p fusion) is very far from
the easiest.  Perhaps other fuels give better performance, at the cost
of being more expensive in any of a number of ways.  Fuel cost itself
is unlikely to be a meaningful factor even in multi-gigawatt
spacecraft applications, but there are other aspects that may cost
more.

Most other fusion reactions are more likely to produce neutrons, which
are annoying to shield and can cause materials that absorb them to
become radioactive.  This leads to the idea of additives that
deliberately promote some of those side-reactions for extra reaction
rates -- or microscopic traces of contaminants that do so in a less
controlled manner.

- Tim