There’s a good chance that crewed missions to Mars will be nuclear-powered: NASA and the U.S. Defense Advanced Research Projects Agency (DARPA) are partnering to develop and demonstrate advanced nuclear thermal propulsion.

As part of DARPA's Demonstration Rocket for Agile Cislunar Operations (DRACO) program launched in 2021, the agencies will engineer an efficient and energy-dense propulsion system based on nuclear reactor technology. Powered by a nuclear thermal engine to heat a propellant to extremely high temperatures to generate thrust, a rocket could have over three times the efficiency of a conventional chemical-fueled one, which would reduce transit times and increase payload potential. For a crewed Mars mission, this would mean less radiation exposure, fewer detrimental effects from weightlessness, and reduced need for supplies or overly robust flight systems.

[See also: NASA to test nuclear fuel for space missions]

DARPA will develop the nuclear reactor and engine for an experimental DRACO spacecraft, which the agency and NASA hope to fly in an in-space demonstration as early as 2027.