Re: Fusion rocket engines - the gist
You want the highest possible exhaust velocity. What you should therefore throw out of tail of rocket is as far as you can manage is the gammas & fast neutrons from the fusion. For everything else I think fusion buys you much less than you might think: exhaust velocity depends on temperature you can raise reaction mass to, and limit of that is what you can contain in the engine. Suspect strongly that existing chemical rockets are already limited by this: you can have fuels which already burn too hot and so cannot be used even though they would get you high specific impulse. Using part of fuel itself to cool engine is clever idea (also old one) but since this must be cooler it reduces specific impulse.
Fusion rocket is not magic bullet unless you eject fusion products directly in other words. In that case it is not only magic bullet but extremely effective weapon (is famous quote about this).
Also ... if you can build a fusion rocket you have sustained, strongly exothermic, fusion. And if you have that you are then not building a fusion rocket you are using your device to heat water, make steam, and drive turbines.
So these people neither have one nor are close to having one. What are they doing, in fact, other than extracting money from investors?
Biting the hand that feeds IT
