Project Bifrost:Rockets of the Future?

Project Bifrost is an ambitious study examining emerging space technologies that could lay the foundation for future interstellar flights and investigates the utility of fission for future space missions.....
The rockets that sent men to the moon were powered by chemical combustion, which in its most powerful form ignites hydrogen with oxygen. The space shuttle main engine, essentially the state of the art for rocket propulsion, uses the same chemicals.
No doubt, these rockets do their job well for what we ask of them. Send astronauts to the International Space Station? No problem. Send astronauts to the Moon? Sure. But, suppose we wanted to dream a little bit bigger, and actually explore the rest of the solar system and beyond. How far can these chemical rockets send us?
Not very far. It turns out, through the quirky laws of Newtonian mechanics, that the exhaust velocity of a rocket is one of the most important parameters in determining how far it can send a payload. Chemical rockets have fundamental energy limits which give them a maximum exhaust velocity that is too low for most piloted missions with destinations further than the moon.
Continued on Discovery News