you'll find a very pro-fusion series of documents that make extraordinary performance predictions. These should all be taken with a grain of salt. [...]
Curious what Tom Ligon, who wrote those slides, has to say.
With all due respect for Tom, he didn't even begin to look at the limits of the materials any supposed fusion rocket would use, or he would never have drawn slides with Isp's>5k. IIRC, the only reason we can propose to build craft with 5k Isp's, is because nuclear lightbulbs at 25,000*C produce almost all their EM at the UV range and we can make quartz that is better than 99% transparent to UV. Thus we suppose we can contain the reaction and heat our propellant to produce this amazing 5k Isp. Now if someone has a scheme for doing something similar to produce 1.2 million Isp, or even 6k Isp, I'm all ears.
As far as rockets are concerned, here's what seems to me to be top shelf:
GIT, you are not thinking right. A fusion rocket engine would not be any more limited by material technology than a fusion reactor would. Look at the proposal for a FRC- based fusion rocket engine as John Slough describes it in one of his papers! This man does actually understand something about nuclear propulsion and plasma rocket engines through his work on the ELF- thruster (which already exists as a prototype) and he understands FRC type fusion reactors through his reactor research. So he really does know what he is talking about.
Anyway, an FRC reactor based fusion rocket engine would not work like a NERVA fission rocket engine. Instead it would directly expell the hot plasma that is the result of the nuclear fusion. The plasma never touches the walls of the reactor or a fusion reactor would never be possible (because it would be destroyed)!
The fusion engine proposed by Slough would also not be all that big. It would easily fit into the first stage of a current rocket. You still need the fuel of course and the capacitors, though I am not sure aber the latter, because you might just need them to start the vehicle while it is still on the ground and then rely on the energy created by the reactor.