Nuclear-powered spaceships

NASA is developing Space Reactor-1 Freedom (SR-1), the first nuclear-reactor-powered spacecraft designed for interplanetary travel. Scheduled for an uncrewed mission to Mars by the end of 2028, with arrival planned for 2029, SR-1 aims to make spaceflight more efficient and faster. This could reduce travel time and lower astronauts' exposure to harmful cosmic radiation during long journeys. The project has been met with optimism by experts like Simon Middleburgh, co-director of the Nuclear Futures Institute at Bangor University in Wales, who described the announcement as inspiring.

While nuclear reactors in space may sound futuristic, the concept is not new. The Soviet Union launched dozens of nuclear reactors into orbit, primarily to power spy satellites. Despite this, progress in developing nuclear-powered space propulsion has been slow in the United States. Over the past 75 years, several programs, including DRACO—a collaboration between NASA and the Department of Defense—have been initiated and later canceled. DRACO ended in 2025 due to high costs, lack of cost competitiveness with conventional rockets, and challenges in safely conducting ground tests. These issues highlight the technical and financial hurdles of nuclear propulsion.

SR-1 will use a technology called nuclear electric propulsion. This system relies on a nuclear reactor fueled by uranium atoms, which split in a process called nuclear fission, releasing heat and neutrons. The heat is converted into electricity, which then ionizes a gas (typically xenon or krypton). The ionized gas is accelerated and expelled through magnetic fields, creating thrust. This method produces low thrust but is highly efficient, allowing the spacecraft to operate for extended periods. The reactor for SR-1 will generate at least 20 kilowatts of power, though this is significantly less than Earth-based nuclear plants, which typically produce around 1 gigawatt (1,000,000 kilowatts).

The SR-1 spacecraft is designed to resemble a large arrow, with the power-and-propulsion system at the rear and the uranium-filled nuclear reactor at the front. The reactor will have a capacity of at least 20 kilowatts. To manage heat, the craft features large fins that radiate excess heat into space, similar to how a car's radiator works. Safety is a critical concern, as the reactor must withstand the intense vibrations and forces of a rocket launch. For this reason, the reactor will only be activated about two days after launch, once the spacecraft is far from Earth. Uranium itself is relatively stable, but the byproducts of the fission reaction can be hazardous.

Developing and testing SR-1 presents significant challenges, including ensuring the reactor can survive launch and operate safely in space. The Idaho National Laboratory is building SR-1's reactor and is reportedly on track for a late-2028 launch. Key components are being procured, and integration of the power and propulsion system is advancing. The mission to Mars is expected to take about one year if successful. The timeline is considered aggressive by experts like Lindsey Holmes, vice president of advanced projects at Analytical Mechanics Associates, who suggests that geopolitical factors, such as China's and Russia's plans to place nuclear reactors on the moon by the mid-2030s, may be driving NASA's urgency.