Space missions rely on power systems that can operate out of sunlight and without maintenance. Solar panels struggle in deep space, where light weakens with distance.
This limitation has led agencies to rely on nuclear energy sources for decades. These systems, known as radioisotope power systems, quietly support missions operating across the solar system.Spacecraft such as Voyager 1 and the Perseverance rover continue to operate using this technology. This concept is not new, but developments around alternative isotopes are attracting renewed interest. Work led by NASA in collaboration with the University of Leicester signals a shift in how long future missions may operate.
A nuclear battery that can last for centuries is no longer just a theory.
Space Nuclear Batteries Plutonium-238: The primary fuel used in space nuclear batteries
For decades, plutonium-238 has been the primary fuel used in space nuclear batteries. As reported, its half-life is about 88 years, which means that its energy production slowly decreases over time. Expeditions run 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 energy systems.
Spacecraft like Curiosity continue to operate using plutonium-based systems. Continuous isotope decomposition provides enough heat to maintain on-board instruments, communications systems and electronics for long periods.Production has resumed after a period of limited production, supported by coordinated efforts across national laboratories. The supply process remains carefully managed due to the complexity of material handling and production.
Americium-241 and extended half-life
Attention is now turning to americium-241 as a potential alternative. It has a half-life of about 433 years, much longer than plutonium-238. This property means that the isotope retains usable energy over a much longer period. It does not necessarily produce more energy at a given moment, but it decays at a slower rate.Research in which Los Alamos National Laboratory is involved focuses on improving production methods and evaluating safety and performance.
Early-stage studies suggest it may be suitable for long-duration missions that require extended power availability. According to NASA reports, americium-241 is still being tested. It has not replaced plutonium in operational spacecraft. The evaluation process includes material stability, heat production efficiency, and long-term reliability under space conditions.
How do nuclear batteries generate energy?
Radioisotope power systems, commonly called RPS, use the natural decay of radioisotopes.
As the radioactive isotopes decay, heat is produced. This heat is then harnessed to produce electricity through specialized means. This process is continuous, which means no recharging, and does not depend on the sun. It can work in the dark, in the cold, or in extreme conditions.Within a radioisotope energy system, the radioisotope is in a solid ceramic state. This reduces risks while maintaining the stability of the radioisotopes.
The heat produced is then transferred to a converter, which then uses the heat to produce electricity. The electricity produced is constant, not pulsating. They are small, reliable and long-lasting power supplies, well suited for tasks where reliability is paramount rather than the amount of power produced.
Free-piston Stirling converters in space nuclear batteries
The heat generated by radioactive decay must be converted into useful electrical energy. Conversion is done using Stirling free piston converters. Free piston stirrers have moving parts that float in the system. The moving parts are moved by temperature differences, and the movement is converted into electricity. The system is designed to be less corrosive, and the components float in the system, making it suitable for long-term use in microgravity.Free-piston stirred converters were tested, and results showed that the system could operate for long periods without maintenance. According to reports, the system can operate continuously for more than a decade.
