Processes and Materials for Space Exploration and Colonization

Nowadays, Earth-based space exploration is extraordinarily challenging and still expensive, but significant efforts are being made to develop new space launchers according to the most cutting edge technologies. Indeed, more affordable and cost-efficient techniques are needed to guarantee both better performances and lower costs. In this regard, material research in the field of Ultra High Temperature Ceramics (UHTCs) is expected to contribute to the increase in performances of refractory parts that play an important role in rocket launchers and space vehicles. In this thesis work, new materials based on transition metal diborides are being synthesized, sintered and characterized according to innovative technologies, and their performance are being assessed in terms of mechanical properties and oxidation resistance. Research is focused on multicomponent transition metal borides (TMBs), from binary to quinary compositions. Mathematical modelling of the two key production techniques, called Self Propagating High-temperature Synthesis (SHS) and Spark Plasma Sintering (SPS), is also considered to give a valuable contribution for making the production of such materials more efficient. Another crucial problem addressed in this Thesis, that highly affects the proposed space colonization of Mars, is that all payload mass shipped from Earth must escape the gravity field of our planet, and lifting propellant is a significant contributor to space exploration costs. The paradigm of In Situ Resource Utilization (ISRU) is a long-time established concept to minimize such costs. In this regard, instead of bringing the required materials from Earth, it is worth to study how to maximize the use of in-situ available resources such as regolith, Mars soil, for several applications. To this aim, regolith simulants are processed and tested in this Thesis to obtain useful products for possibly sustaining human presence on the red planet. This Thesis is organized as follows. The general aspects of processes and materials for space exploration and colonization will be provided in the Introduction (Chapter 1). Information on UHTCs material synthesis and consolidation techniques, and a description of Mars regolith simulants available to the scientific community are also given in this Chapter. The most important methods employed for the UHTCs processing (synthesis and consolidation) will be reported in Chapter 2, along with the precursors used for their synthesis. Subsequently, the regolith simulants employed in this thesis as well as with the consolidation technologies adopted for their densification will be described. The different studies involving UHTCs are reported in Chapter 3. In particular, the synthesis, sintering and characterization of multicomponent TMBs, are considered in Sections 3.1-3.3. The optimization of the SHS process is addressed in Section 3.4, while modelling activity regarding the densification mechanism of individual diborides by SPS is investigated in Section 3.5. Chapter 4 is focused on ISRU technologies aimed to obtain bulk materials from Martian regolith for solar energy harvesting (Section 4.1), construction materials with high mechanical properties (Section 4.3) and complex parts via additive manufacturing (Section 4.3). Finally, some concluding remarks on the investigated materials and processes are provided in Chapter 5.