Well, here's an interesting bit of information to ponder: a "new" proposal for a fusion thruster by a NASA physicist presented at this years IEEE Symposium:
Now, for those who've read my Nazi International and the sections concerning Nazi scientist Dr. Ronald Richter, this should sound vaguely familiar. Note first the use of boron to boost reactions, precisely as Dr. Richter outlined to his American inquisitors. He also outlined a process of using electrical shock and the induction of shockwaves in a magnetically rotated plasma to induce the fusion, and all this, he proposed, was also utilizable in a propulsion system.
Well, this is similar, in some respects anyway, to the NASA proposal, the only difference being the materials - with the exception of boron - being used, and in the use of a laser, replacing Richter's clumsier electrical arc-induced shocks. What gives me pause is that Richter outlined his proposals to the USAF in secret briefings almost 60 years ago. Yet, in this article, we're told something very significant at the end:
"Unfortunately, as great as this all sounds, it doesn’t mean we’ll have spacecraft utilizing such technology any time soon; even if it pans out as Chapman suggests, he says it would still likely be a decade before anything tangible could be produced, and that’s if a concerted effort were made over that time frame by scientists all over the world to figure out how to make it all work as proposed."
Well, that's precisely the point: with enough money, manpower, and time, one could perhaps bring such propulsion methods to bear....
....or perhaps, they already have been.