Performance improvement of radioisotope thermoelectric generators (RTGs) by design optimization

Lunar exploration requires a continuous supply of electrical power, independent of solar irradiation availability. This can be provided by Radioisotope Thermoelectric Generators (RTG) which have been successfully deployed in various deep-space missions, proving their reliability and longevity. Design and operation of an RTG is a complex multi-disciplinary challenge, as they consist of a multitude of functionally interlinked components. To optimize the system, we developed a thermoelectric network model to rapidly simulate RTG operation. Using an iterative process, our network model calculates the heat flow and the temperature difference across each RTG component and from this evaluates the electrical power generated by the thermoelectric modules. We used the 241Am-based RTG design with Bi2Te3-based thermoelectric modules, developed by the European Space Agency, as baseline and coupled our network model to a genetic algorithm to identify an RTG design with maximum specific power while maintaining safe operating temperature limits. The optimized RTG design reaches a specific power of 1.38 W/kg at a power output of 13.9 Wel assuming environmental temperatures typical for the lunar surface, a considerable increase over earlier results of 1 W/kg and 10 Wel. Validation of our tool with a finite element analysis model revealed excellent agreement, with a power output difference of 1.1% and a three order of magnitude reduction in computational time. Our methodology thus allows for fast but accurate optimization of RTGs, an understanding of the interplay between the different parameters, and the adaptation of RTGs to different environments, accelerating their advancement for future deployment.