Nasa is developing ways to use nuclear power to send spacecraft to their destinations. Nuclear propulsion could greatly reduce the journey time to Mars, perhaps cutting a voyage of more than six months to three or four months.

The idea of nuclear propulsion in space goes back to the cold war. But Nasa has been pursuing it more aggressively since Jared Isaacman took over as the agency’s chief in December 2025. Isaacman is a well-known advocate of the technology and says it can “truly unlock humankind’s ability to explore among the stars”.

In March 2026, the agency even announced an uncrewed, nuclear-powered mission to the red planet, targeted for late 2028.

Every spacecraft begins its journey fighting Earth’s gravity by burning chemical fuel. Rockets mix fuel with an oxidiser, ignite them, and force the expanding gas through a nozzle. According to Isaac Newton’s third law, when gas pushes downward, the rocket gets an equal push upward.

Chemical propulsion is powerful, reliable, and quite simply the only practical way to leave Earth’s gravity. But it comes with a severe limitation. Rockets must carry both their fuel and, in most cases, the oxidiser needed to burn it.

That means much of a rocket’s mass at launch is propellant, not payload. The longer and more ambitious the journey, the more propellant is needed, and the heavier the rocket becomes.

Mars is far enough away that a long journey time, the threat to astronauts from cosmic radiation, the mass required to carry life-support systems and constraints on the return journey all pose serious problems for planning a mission.

This is why engineers keep looking for........

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