Thorium has been around for a while and we have a good supply ,what I like is the ability to clean up nuclear waste,No storage is needed. the wildest rocket I read about was the Orion Project.Steve, thanks for posting that....very interesting...and NOT stupid. I would be curious about Hafnium power cycles, also; This was in some of the science rags a few years ago for a nuclear powered Hawk A/C that could stay aloft for weeks or even months......the Hafnium wasn't radiactive, but would generate heat by being hit with X-rays...turn it off, and it's basically safe. But Thorium sounds very interesting; Every country has some and yet it can't be used for weapons. I just checked and Hienlien used Thorium as the fuel in the book, "Rocket Ship Galileo" back in 1947.