Self-Sufficient Production of Lunar Regolith Gravels on the Moon by Ultrarapid Microwave Sintering

A sintered lunar regolith is expected to be used to construct buildings, roads, and landing pads for spacecrafts on the Moon. Here, we demonstrate that focused microwave heating is effective for the rapid solidification of the lunar regolith simulant to obtain regolith gravel without any microwave susceptor. The conventional multimode microwave oven cannot heat lunar regolith simulants and requires microwave susceptors such as silicon carbide (SiC) and thermal insulators because of its low dielectric loss. We achieved rapid microwave heating of a lunar regolith simulant without using a susceptor or thermal insulator by forming an intense microwave electric field using a cavity resonator and a semiconductor microwave oscillator. Focused microwaves at 2.45 GHz produced the gravel-shaped and solidified lunar regolith at 300 °C lower temperature than a conventional electrical furnace, where more than 1050 °C temperature was required to sinter the lunar regolith simulant. In addition, we produced larger gravel of the lunar regolith simulant using 915 MHz. The intense electric field generated by the single-mode resonator promoted the solidification of the lunar regolith simulant without any additional substances. This process enables the local production of structured lunar regoliths on the Moon without the transport of any materials from the Earth.