The PULSAR research consortium, led by the Belgian engineering company Tractebel, has unveiled a design for a radioisotope generator based on plutonium-238 for lunar expeditions.
Tractebel said that with existing nuclear battery technologies, “significant amounts of nuclear fuel and large radioisotope thermoelectric generators are required to power missions, increasing the weight of the launch vehicle…the project aims to significantly improve the efficiency of the radioisotope power system through an advanced Stirling engine.”
PULSAR also aims to develop the technology and capabilities for plutonium-238 production in Europe.
Currently, Europe does not produce plutonium-238 or radioisotope power systems, and “as space has become a strategic and economic priority for Europe”, its dependence on other countries “is a matter of serious concern”.
Completed in late 2024, the project produced significant results, including a conceptual design of a radioisotope power system adapted for use on the Moon, a feasibility study for the production of plutonium-238 in Europe, and a market analysis of radioisotope systems on Earth.
The PULSAR radioisotope power system is designed to power a lunar rover or lunar lander. It is equipped with two Stirling engines powered by a centrally located plutonium-238 heat source and is biosecured for safe transport and handling. The modular design provides resilience to engine failure with an expected thermoelectric conversion efficiency of 20%.
Tractebel reported that its experts conducted extensive engineering studies, including structural integrity verification, radiation dose assessment, thermal analysis, and mechanical assembly design. The team developed a 3D mechanical and thermal model to simulate lunar conditions, providing a basis for future design iterations and a higher level of technical readiness. It is noted that this work lays the foundation for Europe’s participation in the future Argonaut lunar lander mission.
The space industry has mainly relied on photovoltaic power systems, a technology originally developed for space but which has found many applications on Earth.
However, these systems have serious limitations for missions to places such as the outer solar system.
The available solar energy decreases with the square of the distance from the Sun. For example, the density of solar energy on Saturn is a hundred times less than on Earth. There is also the problem of two-week lunar nights.
Radioisotope power sources based on Pu-238 have been used in space missions since the early 1960s. Some space missions, such as the Soviet Lunokhod 1 and Lunokhod 2, used polonium-210 as a heat source in the equipment heating system.
Radioisotope thermoelectric generators and radioisotope heaters can provide continuous power and heat during long deep space missions. Plutonium-238 is produced by irradiating neptunium-237 separated from research reactor fuel or special targets in research reactors. Plutonium-238 has a half-life of 88 years, making it possible to produce powerful and long-lasting power sources.
