Closing the Isru Loop: Clinostat-Based Modeling of Long-Duration Molten Oxide Electrolysis

Oxide electrolysis represents a critical technology for in-situ resource utilization in space, enabling the production of vital oxygen and metals from extraterrestrial minerals. In reduced-gravity environments, oxygen bubbles accumulate on the anode surface, creating an electrically insulating layer that increases cell resistance, compromising efficiency and increasing power consumption—critical limitations for space operations. Understanding long-duration electrolysis behavior in low gravity remains challenging, as current experimental platforms only provide brief microgravity periods: 20-25 seconds during parabolic flights or up to 12 minutes on sounding rockets. These timeframes are insufficient for cell resistance to reach steady state, preventing the development of comprehensive bubble dynamics models for extended operations. This work introduces a novel approach using a two-axis clinostat (random positioning machine, RPM) to simulate reduced-gravity electrolysis for extended periods of minutes to hours, providing cost-effective access to comprehensive data required for robust model development. We present a custom-designed RPM motion algorithm and investigate electrolysis behavior in potassium hydroxide solutions with glycerol-modified viscosities ranging from 1 cP (water-like) to over 100 cP (comparable to molten minerals). Notably, the expected correlation between reduced gravity and increased cell resistance was observed consistently only in the highest viscosity solution (173 cP). Lower-viscosity electrolytes showed minimal gravity effects, likely due to inertial forces dislodging bubbles during RPM directional changes. These results suggest two critical engineering priorities for future ground-based simulations: (1) optimizing acceleration/deceleration profiles to minimize artificial bubble detachment during RPM directional changes, and (2) increasing RPM angular velocity to achieve effective viscosity scaling for aqueous electrolytes (1-10 cP range). Implementing these operational adjustments could extend clinostat simulation capabilities to relevant fluids while improving oxygen bubble behavior fidelity – essential steps toward designing reliable electrolysis systems for lunar/Martian oxygen production and metal refining. Figure 1