Chapter 5

⚡ Lunar Resource Utilization (ISRU)

The Importance of ISRU

In-Situ Resource Utilization (ISRU) means "using resources on site." Because it is impossible to bring everything from Earth, the Moon's resources must be used to the fullest extent possible.

1. Water Ice Mining

The Importance of Water

Water is the most important resource at a lunar base. Uses:

• Drinking water: 2-3 liters per person per day, within a total budget of about 10 liters (§6.2.1)
• Oxygen production: Breathable oxygen generated by water electrolysis
• Hydrogen fuel: Used as rocket propellant
• Radiation shielding: Water tanks used as walls
• Agriculture: Essential for growing plants

Mining Methods

1. Surface Excavation

• Collect regolith in permanently shadowed regions (PSRs)
• Depth: 0.5-2 m (§7.1.1)
• Equipment: drills, excavators, bucket wheels

2. Thermal Extraction

• Heat the collected regolith in a sealed vessel
• Temperature: 100-200°C (§7.1.1)
• The ice vaporizes and is separated as water vapor
• Water is recovered with a condenser

3. Microwave Extraction

• Heat subsurface ice directly with microwaves
• Water vapor rises to the surface and is captured
• Potential advantages: no excavation, lower handling mass (still experimental)

Water Purification

Mined water is of low purity and must be purified:

1. Filtration: Removes dust and solids
2. Distillation: Boiling to separate pure water
3. Electrolysis: Split into oxygen and hydrogen, or stored as is

2. Oxygen Production

Method 1: Water Electrolysis

Passing electricity through water (H₂O) splits it into oxygen (O₂) and hydrogen (H₂):

• Reaction: 2H₂O → 2H₂ + O₂
• Yield: 0.89 kg of oxygen from 1 kg of water (§7.2)
• Energy: About 5 kWh per kg of oxygen at the thermodynamic minimum; practical systems need more (the standard requires >90% efficiency, §6.1.2)
• By-product: Hydrogen is used as rocket propellant

Method 2: Oxygen Extraction from Regolith

About 45% of regolith by mass is oxygen, bound in SiO₂, FeO, Al₂O₃, and other oxides; the standard assumes a practical yield of about 40% by mass (§7.2). Methods for extracting it:

Molten Regolith Electrolysis

• Melt regolith at about 1600°C (§7.2)
• Separate oxygen gas and metals by electrolysis
• By-products: iron, silicon, aluminum, and others

Hydrogen Reduction

• React regolith with hydrogen gas at 900-1000°C (§7.2); this recovers only the oxygen in iron oxides, so yields are much lower than with molten regolith electrolysis
• FeO + H₂ → Fe + H₂O
• The resulting water is electrolyzed to regenerate oxygen

3. Helium-3 Mining

The Value of Helium-3

Helium-3 is often proposed as a future fusion fuel, which has made it the most discussed, and most speculative, lunar resource.

Distribution

• Adsorbed in surface regolith on the Moon
• Concentration: on the order of 10 parts per billion by mass (roughly 0.01 g per tonne of regolith)
• Higher concentrations in titanium-rich mare regolith

Mining Methods

1. Collect surface regolith in bulk (millions of tonnes)
2. Heat above 700°C to release gases
3. Separate helium-3 from the released gases
4. Liquefy and store by cryogenic cooling

Feasibility

Helium-3 mining becomes economically viable only once fusion power is commercialized. For now, it is a concept for future investment.

4. Metal Smelting

Metal Constituents of Regolith

The values below are approximate averages; composition differs strongly between mare and highland regolith (for example, iron and titanium are much higher in mare soils, aluminum in highland soils).

Element	Approx. content (wt%)	Uses
Oxygen	45	Breathing, oxidizer
Silicon	21	Solar cells, glass
Aluminum	10	Structural material, wiring
Calcium	8	Cement
Iron	6	Structural material, tools
Titanium	0.5	High-strength alloys

Smelting Processes

Iron Extraction

• Concentrate iron oxide (FeO) with magnets
• Hydrogen reduction: FeO + H₂ → Fe + H₂O
• Melting and casting

Aluminum Extraction

• Separated from Al₂O₃ by electrolysis
• Requires high temperature (1000°C) and high power

Silicon Extraction

• SiO₂ + 2C → Si + 2CO (carbon reduction; carbon is scarce on the Moon, so the reductant must be recycled or imported)
• Used in solar cell manufacturing

5. Construction Material Production

Regolith Concrete

• Regolith + sulfur binder → concrete (§7.3)
• Compressive strength: must meet the 20 MPa minimum of §5.3.1 for structural use
• Uses: roads, landing pads, shielding walls

Glass Manufacturing

• Produce glass by melting regolith at about 1400°C (§7.3)
• Uses: windows, optical fibers, insulation

Ceramics

• High-strength ceramics by sintering regolith
• Uses: heat-resistant components, insulators

6. ISRU Facility Configuration

Module Configuration

Power figures are illustrative planning values, not requirements of the standard.

Module	Function	Power (kW)
Mining module	Regolith/ice collection	10-20
Extraction module	Heating, evaporation, condensation	20-50
Electrolysis module	Water splitting, oxygen production	30-60
Storage module	Liquid oxygen/hydrogen storage	5-10
Smelting module	Metal extraction and refining	50-100

7. Phased ISRU Plan

Phase 1: Pilot ISRU (2026-2028)

• Small-scale water extraction experiments
• Validation of oxygen production
• Regolith 3D printing tests

Phase 2: Commercial ISRU (2028-2035)

• Water production: 10 tonnes/month by 2035 (§7.1.1)
• Oxygen production from water and regolith
• Production of construction materials

Phase 3: Full Self-Sufficiency (2035+)

• Self-sufficiency in water and oxygen; 90%+ local food production from 2040 (§6.3.3)
• Rocket propellant production (Moon-Earth round trips)
• Metal smelting and manufacturing
• Helium-3 extraction, only if fusion power makes it viable

Conclusion

ISRU is the key technology that makes a lunar base sustainable. Dependence on Earth will be high at first, but over time self-reliance will steadily increase until the base ultimately becomes largely self-sufficient, in line with the standard's 90%+ recycling target (§14.2). The next chapter covers life support systems.