Human space travel to the planets beyond the moon will require transporting tremendous mass over long periods of time – and that requires power. Using conventional propulsion systems, most of that mass will be fuel, while needing to carry half the fuel to the destination for the return trip. So using that fuel as efficiently as possible is important. Electric propulsion (using plasmas to propel spacecraft) is one solution, but you still need power. In this video, Dr. Kurt Polzin of NASA Marshall Space Flight Center describes concepts for using power generated by a nuclear reactor to propel spacecraft. This power is used to generate electricity for plasma propulsion or to directly heat the fuel. Dr. Polzin describes proposed designs for nuclear powered spacecraft and the challenges of safely deploying these systems.