A Systematic Investigation to Obtain Physical Assets on the Moon through Self-propagating High-temperature Reactions

Abstract

Future space missions on the Moon, Mars and near Earth asteroids, etc., are expected to be strongly facilitated and time extended by the possibility of “In-Situ Fabrication and Repair” (ISFR) the required equipments and infrastructures. In addition, the combination of the latter approach with the “In-Situ Resources Utilization” (ISRU) paradigm contributes to overcome drawbacks related to the transportation of the needed material from the Earth. In this regard, various technologies have been recently proposed with the aim of developing suitable structures to be placed on the Moon surface for the protection against cosmic rays, solar wind, meteoroids, etc. Specifically, the possibility of exploiting combustion synthesistype reactions using Lunar resources for the fabrication of ceramic-based products was considered. Along these lines, by taking advantage of the fact that Lunar soil contains up to 20 wt.% of ilmenite (FeTiO3), the highly exothermic thermite reduction of the latter oxide with Al is systematically investigated in this work. A self-propagating (SHS) behavior is displayed only above a certain Al/FeTiO3 molar ratio (0.9). In addition, as the amount of Al in the mixture is increased, the reactive process proceeds faster and the combustion temperature becomes higher, due to the increased system exothermicity. Correspondingly, the maximum amount of Lunar regolith to be possibly reacted with additional FeTiO3 and Al is identified. The obtained products (a mixture of Al-, Ti-, Mg-, and Ca-oxides, and metallic phases) exhibit satisfactory compressive strength properties (≥ 25.8 MPa) that make them promising as construction materials. Parabolic flight experiments evidenced that SHS process dynamics and product characteristics are barely affected by gravity. The obtained findings allow us to conclude that the optimal conditions identified during terrestrial experiments are still valid for in-situ applications in Lunar environment.