NASA is building the first nuclear reactor-powered interplanetary spacecraft. How will it work?

More than half a century after America's only space-based nuclear reactor lasted just over a month in orbit, NASA administrator Jared Isaacman announced plans to launch the first nuclear-powered interplanetary spacecraft to Mars by late 2028. The Space Reactor-1 Freedom will use nuclear electric propulsion, plugging a 20-kilowatt uranium reactor into repurposed hardware from the canceled Gateway lunar station project.

The spacecraft resembles "a colossal fletched arrow" with massive cooling fins to vent the reactor's intense heat into space. Nuclear propulsion offers orders of magnitude more efficiency than chemical rockets, solving a crucial problem for Mars missions by dramatically reducing travel time and astronauts' exposure to deadly cosmic radiation.

"You get more bang per kilogram," says Simon Middleburgh from Bangor University's Nuclear Futures Institute, who called the announcement smile-inducing after decades of canceled nuclear propulsion programs. The aggressive timeline appears driven partly by competition with China and Russia, who plan their own lunar nuclear reactor by 2035.

The reactor will activate two days after launch for safety reasons, with Mars arrival expected about a year later.