Space missions depend on power systems that can function far away from sunlight and without maintenance. Solar panels struggle in deep space, where light weakens with distance. That limitation has pushed agencies to rely on nuclear-based energy sources for decades. These systems, known as radioisotope power systems, have quietly supported missions operating across the Solar System.Spacecraft like Voyager 1 and the Perseverance rover continue to function using this technology. The concept is not new, but developments around alternative isotopes are drawing renewed attention. Work led by NASA in collaboration with the University of Leicester suggests a shift in how long future missions might operate. A nuclear battery that could last centuries is no longer just theoretical.
Plutonium-238 space nuclear batteries: Primary fuel used in space nuclear batteries
For decades, plutonium-238 has been the primary fuel used in space nuclear batteries. As reported, it has a half-life of around 88 years, meaning its energy output decreases slowly over time. Missions operated by Oak Ridge National Laboratory and Idaho National Laboratory have relied on this isotope for production and supply. It remains the backbone of current deep-space power systems.Spacecraft such as the Curiosity rover continue to function using plutonium-based systems. The steady decay of the isotope provides enough heat to sustain instruments, communication systems, and onboard electronics over long durations.Production restarted after a period of limited output, supported by coordinated efforts across national laboratories. Supply remains carefully managed due to the complexity of handling and producing the material.
Americium-241 and its extended half-life
Attention is now turning toward americium-241 as a possible alternative. Its half-life is around 433 years, which is significantly longer than plutonium-238. This property means the isotope retains usable energy over a much longer period. It does not necessarily produce more power at a given moment, but it decays at a slower rate.Research involving Los Alamos National Laboratory is focused on improving production methods and evaluating safety and performance. Early-stage studies suggest it could be suitable for long-duration missions where extended power availability is required. According to the NASA reports, Americium-241 is still under testing. It has not replaced plutonium in operational spacecraft. The evaluation process includes material stability, heat output efficiency, and long-term reliability under space conditions.
How nuclear batteries generate energy
Radioisotope power systems, commonly called RPS, use the natural degradation of radioisotopes. As the radioisotope degrades, heat is produced. This heat is then harnessed to produce electricity through specialised means. This process is continuous, meaning no recharging is done, nor is it dependent on the sun. It can function in the dark, in the cold, or in extreme conditions.Inside the radioisotope power system, the radioisotope is in a solid ceramic state. This minimises the dangers while keeping the radioisotope stable. The heat produced is then transferred to a converter, which then uses the heat to produce electricity. The electricity produced is constant, not pulsating. These are small, reliable, and long-lasting power sources, best suited for missions where reliability is paramount rather than the amount of power produced.
Free-piston Stirling converters in space nuclear batteries
The heat produced by the radioactive decay must be converted into useful electrical energy. The conversion is done using free piston stirling converters. The free piston stirling converters have moving parts that float in the system. The moving parts are driven by the temperature differences, and the motion is converted into electricity. The system is designed to have less wear and tear, and the components float in the system, making it suitable for long-term use in microgravity.The free piston stirling converters have been tested, and the results show that the system can function for long periods without maintenance. According to the reports, the system can function continuously for over a decade.
