In Situ Resource Utilization in Support of Manned Space Exploration

The first major thrust of this research developed a sizing model for a Molten Regolith Electrolysis (MRE) reactor that produces oxygen and metals from lunar regolith. This reactor model predicts performance characteristics, such as the reactor mass and volume, energy/power requirements, regolith throughput requirements, and oxygen production capabilities. Design characteristics, such as reactor diameter, height, and electrode separation, are also predicted. The MRE reactor model was leveraged to better understand the appropriate method for scaling up MRE reactor designs from small demonstration-level experiments to higher production levels required to support space missions. The model also showed that an MRE reactor (with a non-optimized design) can produce on the order of 10 (kg of oxygen per year) per kg of reactor mass and spends around 4 W of power to produce a kg of oxygen per year. The second major thrust of this research integrated the MRE reactor model with several others into an In-Situ Resource Utilization (ISRU) system model. The ISRU system model includes models for a reactor, oxygen separator, regolith excavator, oxygen liquefaction and storage, and power system. The ISRU system model allows engineers to evaluate the system-level effects certain design variables for each subsystem, such as the reactor operating temperature, the excavation mobility type (tracks vs. wheels), the type of power system (solar arrays vs. nuclear), etc. A graphical interface allows users to link together existing Excel-based models to conduct system-level optimizations and tradespace explorations. The optimization of the ISRU system model revealed a number of things. First, it showed how the optimal system design scaled up with production level. Higher operating temperatures and batch times appeared optimal for higher production levels. Also, the constraint that the average electrode separation be no less than 2cm was a major driver of resistive heating in the reactor and radiative heat loss. Comparing the production performance to total system mass (including a power system), it was found that an optimized MRE-based ISRU system can produce up to 9 (kg of oxygen per year) per kg system mass. This number, when combined with previous space mission architecture work from MIT, indicates that lunar ISRU may prove useful in supporting a Mars exploration campaign. Also, comparing the optimized system design between Highlands and Mare regolith revealed that an MRE-based ISRU system is relatively feedstock insensitive, opening up a range of feasible mission scenarios at various locations on the moon. This research dramatically reduced the uncertainty in the design and scaling of an MRE reactor and the associated ISRU system.