The microstructure and mechanical properties of microwave-heated lunar simulants at different input powers under vacuum

To achieve a sustainable human presence on the Moon, it is critical to develop technologies utilising the local resources (a.k.a. in-situ resource utilisation or ISRU) for construction and resource extraction. In this study, we investigate the viability of microwave heating of two lunar soil simulants (JSC-1A and OPRH3N) under vacuum conditions, to simulate a lunar surface environment compared to previous studies performed at atmospheric pressure. All simulants are thermally treated in a bespoke 2.45 GHz microwave apparatus using three input powers: 1000 W, 600 W and 250 W. The microstructures and mechanical properties of the microwaved samples are analysed to identify their potential applications. Our key findings are: (i) higher input powers generate materials in shorter fabrication times with higher mechanical strengths and higher yields despite the same total energy input; (ii) the microstructures of the microwaved samples under vacuum are very different from those under atmospheric conditions due to the widespread vesicles/bubbles; and (iii) different heating rates caused by different input powers can be utilised for specific ISRU purposes: higher input powers for extra-terrestrial construction and lower input powers for resource extraction. Findings from this study have significant implications for developing a microwave-heating payload for lunar ISRU demonstration missions.