Energy Budgets for Extraction
Every ISRU process converts raw lunar material into something useful — oxygen, water, metals, propellant. Each conversion has an energy cost measured in kilowatt-hours per kilogram of output. These costs determine whether a given ISRU operation is viable at a given location with a given power source.
Most published ISRU roadmaps state extraction rates without stating the energy required to achieve them. We fill that gap.
Benchmark Data
| Process | Feedstock | Output | Energy Cost (kWh/kg) | Source |
|---|---|---|---|---|
| Hydrogen Reduction | Ilmenite-rich regolith | O₂ | ~24.3 | Sargeant et al. 2025 (PNAS) |
| Molten Regolith Electrolysis | Bulk regolith | O₂ + metals | 18–35 | NASA GRC estimates |
| Water Ice Sublimation + Electrolysis | Polar ice deposits | O₂ + H₂ | ~11.3 | Derived from thermodynamic models |
| Carbothermal Reduction | Regolith + methane | O₂ + CO | ~50 | NASA 2024 experimental (20g O₂/kWh thermal) |
These are physics-constrained energy budgets — not projections of future efficiency improvements. The range within each method reflects variation in feedstock composition, reactor design, and thermal management assumptions.
What This Means
A sustained lunar base producing 1,000 tonnes of oxygen per year via hydrogen reduction needs approximately 24.3 GWh annually — equivalent to a 3 MW solar array running at 100% capacity factor. No lunar solar array achieves 100% capacity factor.
Water-ice-based extraction halves the energy cost per kilogram but introduces a different constraint: no one has confirmed the concentration, form, or accessibility of polar water deposits at production-relevant scales.
Current Work
We are building a standardized comparison framework that normalizes energy costs across methods, accounting for:
- Thermal management overhead — maintaining reactor temperatures in lunar vacuum adds 15–30% to baseline energy costs
- Beneficiation energy — sorting feedstock to increase ilmenite concentration (for hydrogen reduction) requires mechanical energy input
- Storage and liquefaction — converting gaseous oxygen to storable LOX adds ~2 kWh/kg
The goal is a reference table that any ISRU mission planner can use to estimate total energy requirements for a given extraction rate, method, and location.