As alluded to in a previous post, I spent some time listening to Steven Howe yesterday on the Space Show's mp3 archived file.
Based upon what I've learned about the Thorium fuel cycle, I'd say U233 fuel rods for nuclear thermal is just too impractical.
But maybe that is not a show stopper. You can still use the Thorium fuel cycle off world. Perhaps not for interplanetary missions. Perhaps. For that, you need the good old fashioned Uranium fuel cycle and U235. This can be imported or exported from Earth depending upon your point of view.
However, the idea of using the Thorium fuel cycle for interplanetary missions doesn't die easily for me. It would really be a big deal if you could make that work. But how?
The problem, as I understand it now, is the impurities in the U233- which is U232, and it is very radioactive. You really can't get around that very easily, or at all.
Or can you?
Now, what if you just pay the mass penalty and deal with that radioactivity with lots and lots of shielding? You'd still have problems, but the shielding would take care of the gamma rays ( I think). The problem then becomes the mass penalty, but in a shallow gravity well, such as with the moon or Mars, perhaps this can be handled. One additional point- you don't want to use the nuclear rocket to take off or land. It would be parked at EML2 in the Earth Moon system, or at Phobos or Deimos in Mars orbit. Conventional rockets, maybe even U235 rockets, would get you off the surface. Once in orbit, the U233 fueled nuclear rocket would take over. Of course, this would be on a different vehicle.
The idea is to minimize the amount of mass that has to be lifted off the Earth. Secondly, to use a concentrated source of power for thrust for your rockets. This will further minimize the amount of mass needed, and reduce the mass penalty.
Overall, you'd like a system that requires a minimum of launches from Earth, with most of the mass for propulsion and life support being provided off world. The Earth would supply complex manufactured goods, rare materials not found off world, plus people.
Howe's tungsten fuel rods may make nuclear thermal more acceptable as a means of getting to orbit. But that is a whole new ballgame. But isn't that the whole point?
