Analysis of an In-Situ Material Production Concept for Potential Thermal Applications in a Lunar Mission

Kurzfassung

In-Situ Resource Utilization (ISRU) has long been suggested as a possible path to reduce the cost of missions to the Moon and Mars. Extracting oxygen from lunar regolith has been established as the most promising ISRU process. Oxygen could be used for life support and in-situ propellant production. However, oxygen is not the only resource that can be extracted from lunar soils. Lunar regolith also contains abundant metals and metalloids that could be processed to build space infrastructure and enable a sustainable human presence on the Moon. Before ISRU processes are considered as a feasible alternative to transporting all material resources from Earth, the mass and performance of the required systems must be rigorously investigated. To this end, a lunar surface reference mission is defined at the South Pole as a case study. The Moonbase is composed of an Environmental Control and Life Support Systems (ECLSS) for six crew members and an ISRU facility. The ISRU facility must produce 15 t/y of O2 and enough metallic byproducts to manufacture a radiator that rejects the heat generated by the Moonbase. Analytical sizing models are developed for the entire ISRU process chain, including the individual production stages: excavation, beneficiation, oxygen extraction, metal processing, and manufacturing. Focus is given to the oxygen extraction and metal processing. The oxygen extraction stage analyzes hydrogen reduction, molten regolith electrolysis (MRE), and molten salt electrolysis (MSE). The metal processing stage investigates carbonylation, melt-refining, and vacuum distillation. The models return their mass, volume, power, and cooling requirements based on previously published works, analytical calculations, data extrapolated from experimental research, and analogies drawn between terrestrial and space components. Besides oxygen, five refined metallic byproducts are characterized in terms of their mechanical and thermal properties: carbonyl and melt-refined irons, ferrosilicon alloys, highlands metallic mixtures, and distilled aluminum. Thermo-fluid dynamic simulations return the mass per unit of heat rejected for different radiator materials, designs, and positions. A multi-criteria analysis (MCA) evaluates eight production concepts. The MCA comprises an Equivalent System Mass (ESM) analysis and a qualitative evaluation of the ISRU process chain versatility. The versatility criteria evaluate the advantages and disadvantages of the production concepts that cannot be quantitatively included in an ESM analysis. The most suitable concept consists of an MRE reactor that produces 15 tons of oxygen and 6.7 tons of ferrosilicon alloys per year. 800 t/y of highlands regolith are excavated and beneficiated to reach a concentration of 20 wt.% of FeO-rich minerals. Fe-Si alloys are extruded to produce wire feedstock. Wire-based additive manufacturing techniques manufacture a radiator that rejects 34.2 kW of heat. The entire ISRU process chain requires 1100 kg and 2.8 m3, consuming 61 kW of electric power and rejecting 1.4 kW of heat. The MRE electrodes (237 kg/y) must be regularly brought from Earth.