Lunar regolith is ~40–45% oxygen by mass, locked up in metal-oxide minerals like ilmenite (FeTiO₃) and silicates. Molten oxide electrolysis melts the regolith at roughly 1600°C — with concentrated sunlight or electric heating — then drives a current through the melt. The current breaks the oxide bonds directly: pure O₂ gas bubbles out at one electrode while a molten metal alloy (iron, silicon, titanium) sinks and pools at the bottom as a useful byproduct for construction feedstock.
2 MxOy (molten) --current--> 2x M (liquid) + y O2 (gas)
O2 collected [kg] -> days of air = O2_kg / (0.84 kg * crew)
- Heating power — raises chamber temperature toward the melting point. Below ~1300°C the regolith stays solid dust; between 1300–1600°C it softens and partially melts; above 1600°C it is fully molten.
- Electrolysis current — only splits oxide bonds once the melt is conductive, i.e. once the regolith is molten. Current on cold, solid dust does essentially nothing.
- Cost comparison — the reactor's electricity is cheap once the hardware is on-site; launching an equivalent kilogram of oxygen from Earth costs on the order of a million dollars, dwarfing the reactor's running cost almost immediately.