A long while back, when I worked for a company trying to branch into the "industrial gas" business - that is, condensing constituent gases from the free atmosphere and bottling the results - I learned that all sources of helium on the planet are underground, and associated with natural gas or oil wells. How it got there to begin with is a mystery to me, since helium is inert and (like the equally exotic heavy metals) almost entirely a product of stellar evolution. I imagine: helium entrained as clathrates in primordial planetesimals, most of which escaped to space aeons ago, but some of which was trapped beneath relatively impervious rock strata.

Point is - helium is a finite, non-renewable resource. Even if fusion ever comes online, the amounts of helium generated will be negligible. In the long run, as energy-demanding as water hydrolysis is, H2 is still the better idea as fuel and (it would seem) as a source of bouyancy, too.

Powdered aluminum and iron oxide??? What *were* they thinking?

E'