How to collect and store solar energy on the Moon

An Italian research team (CNR INO, INAF Arcetri Astrophysical Observatory and the University of Cagliari) is working to make space exploration and (human and robotic) colonization on planetary bodies such as the Moon, Mars and asteroids ever more feasible. Utopia? No, if it will be possible to travel while keeping the equipment light on spacecraft and using the resources available in situ to survive in environments currently not favourable to human life.

In a recent paper published in the international scientific journal Acta Astronautica (https://www.sciencedirect.com/science/article/pii/S0094576522004817), the researchers describe the results of a study carried out on the dust that covers the surface of the Moon: the regolith. The experiment showed how to modify its properties to obtain a solid ceramic for collecting and storing solar energy.

Using a regolith simulant, the researchers applied a technology called Spark Plasma Sintering to obtain a ceramic capable of absorbing solar radiation to produce and store heat, which could then be transformed into other forms of energy as necessary (e.g. electricity). By changing the sintering conditions, they obtained ceramics with different properties, optimized for different uses.

The researchers discovered that the sintering process, i.e. baking the powder in a mould at a high temperature, actually modifies the optical properties of the regolith, increasing its ability to absorb solar energy and heat emittance. The characterization of these optical properties was possible thanks to high-tech spectroscopic instrumentation in the laboratories of the team.

There is still a long way to go in the “In Situ Resource Utilization” (IRSU) research field: this study shows that Italian research can provide concrete answers to the technological needs required by future space colonization.

The National Institute of Optics of the National Research Council carried out the complete characterization of the optical properties of the ceramics and the original powder. The “Laboratory of Intelligent Materials and Solar Energy” has been active since 2012 (https://www.ino.cnr.it/?page_id=16178&lang=it&p=a6). Its cutting-edge spectroscopic instrumentation allows the characterization of materials in an extremely wide range of wavelengths, from ultraviolet to far infrared. The fact that this spectral range is seamlessly accessible makes this laboratory unique, and active both in terms of cutting-edge scientific research and in scientific and technological support to the business world. The responsible for the laboratory, Elisa Sani, answers some questions about the research she carried out with colleagues from the INAF Astrophysical Observatory of Arcetri and the University of Cagliari.

How did the idea of ​​using regolith to collect energy on the Moon come about?

After all, it is a simple idea: the regolith is the first material encountered on the lunar surface, abundant and widespread. From the scientific literature, we were aware that “fired” regolith in ceramic form has a different thermal conductivity than the original powder. We got the curiosity to go and look at what happens to the optical properties: until now no one had thought of using these ceramics as a means of absorbing solar energy. The CNR-INO research group has been working for over ten years on innovative ceramics for new-generation thermodynamic solar absorbers. Therefore, strengthened by this baggage of “terrestrial” experience, we have tried to extend the application to an environment that is completely different from Earth. It must also be said that the regolith ceramic is very different from the extremely engineered ceramics with which we have worked so far, since it is a heterogeneous material, whose composition cannot be simply modified, and therefore much more “rigid”. It was a good challenge.

What was the result of this study that gave you the most satisfaction?

Undoubtedly, the discovery of the changes in the properties of the regolith depending on the parameters of the sintering! This means that we have a way to obviate, or at least mitigate, the stiffness I mentioned above. Moreover, it allows obtaining ceramics optimized for two different uses (collection/storage of solar energy) from the same starting powder.

What was the role of CNR-INO?

We were the light specialists. We have studied the response of materials to the different types of radiation with which the material interacts in different uses: the radiation that comes from the Sun and the thermal radiation emitted by themselves at the various temperatures to which they are subjected.

More information

CNR – National Institute of Optics
Elisa Sani, email: elisa.sani@ino.cnr.it

More details on the results are described in the interview by Rossella Spiga with Aldo Dell’Oro (INAF-Osservatorio Astrofisico di Arcetri) and in the article by Ivo Cabiddu available at the University of Cagliari website.