After some grandiose plans and a few small-scale experiments in the 1950s and 1960s, work on nuclear-propelled rockets stalled in the United States and elsewhere. Now, Sean O’Keefe (Administrator of the National Aeronautics and Space Administration) and veteran space expert Robert Zubrin (President of the Mars Society) call for a thoroughly rejuvenated program of nuclear space propulsion. In the November issue of IEEE Spectrum, they argue nuclear power is essential if significant human and robotic missions are to be mounted to Mars and beyond.