Building cities on the Moon
A first-principles pass: what the Moon does to you, how you'd build anyway, what roads and utilities look like, and where the cities should go. The site choices and highway numbers below come from the LOLA terrain analysis on the map page.
Short version. Water and sunlight decide where the first city goes: the south pole, on a sunlit ridge beside permanently shadowed craters holding ice.
Radiation and the vacuum decide what it looks like: pressurised vessels buried under metres of regolith, or sealed lava tubes. Dust and low gravity shape the roads:
they are paved mainly to keep dust down, and their geometry limited by how little grip 1/6 g gives a vehicle. Power and communications run along the same corridors as the roads.
1 · The limitations
| Constraint | Number | What it forces |
|---|---|---|
| Vacuum | 0 kPa outside vs ~57–101 kPa inside | The main structural load is internal pressure, not gravity. A 1 atm habitat pushes up at ~10 t/m². Regolith weighs only ~2.4 kPa per metre of depth (1.5 t/m³ × 1.62 m/s²), so it takes ~40 m of cover to balance 1 atm. Buildings are anchored, tension-dominated pressure vessels, held down rather than held up. |
| Radiation | ≈1.4 mSv/day at the surface (Chang'e-4 LND) ≈ 0.5 Sv/yr | About 10× the yearly limit for radiation workers on Earth. People live under ≥2–3 m of regolith or inside lava tubes, with a deeper storm shelter for solar particle events. Surface work is time-budgeted. |
| Day/night cycle | 29.5-day day; ~354 h nights away from the poles | Solar power needs two weeks of storage. A 1 MW town would need ~354 MWh, about 1,800 t of batteries at 200 Wh/kg. So: polar ridges with near-constant sun, or nuclear fission. |
| Temperature | +120 °C day / −170 °C night (equator); ~40 K in polar cold traps | Materials, seals and pavements cycle by about 300 K each month. Underground is stable at ~−20 °C, another reason to bury. |
| Gravity | 1.62 m/s² (1/6 g) | Light structures, easy lifting and launch. But traction and braking are 1/6 of Earth's, and long-term health effects on adults and children are unknown. This is the biggest open question for a city rather than an outpost. |
| Dust | sharp, glassy, electrostatically charged | Apollo suits and seals degraded within ~3 days. Everything needs dust locks. Rocket plumes sandblast ejecta at up to ~km/s: Apollo 12 pitted Surveyor 3 from ~160 m away. Landing pads go kilometres from habitats, paved and bermed. |
| Micrometeoroids | constant, up to tens of km/s | Regolith cover handles this as well. Exposed radiators and solar panels slowly degrade. |
| Moonquakes | shallow quakes up to ~M5; ring for 10+ minutes | Dry rock barely damps vibration. Design for long-duration shaking, with flexible joints in pipes and roads. |
| Horizon | 2.4 km for eye height, 18.6 km for a 100 m tower | The small radius (1737 km) limits line-of-sight radio. Surface networks need towers on crater rims, or fibre along the highways. |
| Water | LCROSS: ~5.6 ± 2.9 wt% water at Cabeus | Water exists only as ice in permanently shadowed craters at the poles, or as traces elsewhere. It means drinking water, oxygen and rocket propellant, which makes it the strategic resource. |
| Earth link | 1.3 s one-way; far side never sees Earth | Near-side sites have direct links. The far side and much of the polar terrain need relays: see the Constellation page. |
2 · How we would build
Phase 0 – Robots first
Prospect the ice (ground truth on the grade and depth of cold-trap deposits). Sinter landing pads. Put up power towers on the sunlit ridges. Lay the first cable/fibre corridor. No humans are needed for any of this, and all of it de-risks the rest.
Phase 1 – Outpost
Landed pressure modules, buried by robotic bulldozers under 2–3 m of regolith. One or two fission units (NASA's Fission Surface Power class, ~40 kWe each) plus vertical solar arrays that track a Sun circling the horizon.
Phase 2 – Live off the land (ISRU)
Regolith is ~40–45% oxygen by mass. Molten-regolith electrolysis yields O₂ plus Fe/Si/Al/Ti metal. Ice gives water, which gives LOX/LH₂ propellant. Sintered and 3D-printed regolith, cast basalt, basalt fibre and glass replace imported structure.
Phase 3 – City
Large volumes: sealed lava tubes (skylights 50–100 m wide hint at tubes hundreds of metres across) or cut-and-cover vaults. Inflatable membranes under regolith, closed-loop life support, LED agriculture. Mass drivers export oxygen and metals to orbit.
Design rule: pressure goes in membranes, shielding goes on top, structure goes in tension. A sealed lava tube does all three for free. That is why lava-tube pits rank highly on the map.
3 · Highways
What a lunar road is for
- Dust control, more than load-bearing. Wheels on loose regolith throw dust that coats radiators, solar panels and optics. Paving mainly keeps dust down; loads are light at 1/6 g.
- A utility corridor. Every highway carries an HVDC power cable (vehicles and outposts recharge from the grid, not batteries that die in the night), fibre, and later water/O₂ pipelines. The road is the spine of the infrastructure.
Why 1/6 g changes road geometry
- Crests launch vehicles. A vehicle leaves the ground over a crest when v²/r > g. On a 100 m-radius crest that happens at 12.7 m/s (46 km/h) on the Moon, vs 113 km/h on Earth. Vertical curves must be very gentle: grading is mostly about smoothing, not flattening.
- Corners and braking. Maximum cornering speed is √(μ·g·r), 2.45× lower than on Earth for the same curve. Braking distances are 6× longer. Expect banked curves, wide radii and speed limits set by grip, not engines.
- Grades. The routing penalises slope steeply: under ~10° is easy, 15–25° needs switchbacks or cut-and-fill, and over ~28° (approaching regolith's ~30–35° angle of repose) is treated as impassable. The 80 m polar DEM shows crater walls into the ice traps are often too steep. Cable cars or funiculars beat switchbacks there. Example: the best road from Shackleton's sunlit rim down to its ice-filled floor still hits ~31° slopes on its steepest 5%, too steep for a road.
How to pave
- Microwave/laser sintering in place. Lunar regolith contains nanophase iron that couples well to microwaves. ESA's PAVER study laser-melted regolith simulant into interlocking tiles. Interlocking pavers tolerate the ±150 K thermal cycle better than a continuous slab.
- Graded + compacted + binder for low-traffic spurs. Regolith is fluffy at the top few cm but very dense below ~30 cm, so compaction works.
- Long-haul: rail or maglev. With no air drag, a vacuum maglev between the pole and the near-side maria is far more energy-efficient than trucks once traffic justifies it. The routes on the map are the alignments it would follow.
Route results from the terrain analysis
Least-cost routes (cost = distance × slope penalty). Global corridors use 7.5 km cells: good for alignment, optimistic on slope. Polar roads use 400 m cells from the 80 m DEM.
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4 · Other infrastructure
| System | Approach |
|---|---|
| Power | Sunlit polar ridges (~85% sunlight at ground level in our analysis; towers tens of metres tall get more, since shadows come from distant terrain). Fission for night-side cities. An HVDC grid along the highways links ridges with complementary sunlight, so the network as a whole is almost never dark. Regenerative fuel cells using local water for storage. |
| Water & air | Ice mining in the permanently shadowed craters: excavate, then heat to sublimate and capture. Electrolysis for O₂ and H₂. Oxygen also comes from regolith anywhere. Closed-loop recycling targets >95%. |
| Spaceports | Sintered pads with ejecta berms, several km from habitats. Propellant depots at the poles. Mass driver on flat near-side mare for exports (lunar escape velocity is 2.38 km/s, about 1/5 of Earth's). |
| Communications | Fibre along highways, towers on rims, and a relay constellation for the far side and polar terrain (see Constellation). The far-side radio-quiet zone should stay quiet. |
| Thermal | Radiators plus the permanently shadowed craters themselves (~40 K) as natural cryogenic sinks for superconducting lines, propellant storage and infrared telescopes. |
| Protection | Regolith overburden, storm shelters, dust airlocks with suitports, and a solar-flare warning network. |
5 · Where the cities go
| Criterion | Why it matters | Best places |
|---|---|---|
| Water | Life support + propellant | Permanently shadowed craters at both poles |
| Continuous power | No 2-week night | Polar ridges and crater rims (Shackleton, de Gerlache, Peary) |
| Shielding | Radiation, thermal, micrometeoroids | Lava tubes: Marius Hills, Mare Tranquillitatis, Mare Ingenii pits |
| Earth contact | Comms, psychology, teleoperation | Near side; polar massifs like Malapert |
| Flat ground | Pads, solar fields, mass drivers | Maria (Imbrium, Procellarum) |
| Resources | Metals, oxygen, He-3, thorium | Ti-rich Tranquillitatis, KREEP-rich Procellarum, Aristarchus pyroclastics |
| Radio silence | Unique science asset | Far-side centre (Daedalus): an outpost, not a city |
The chosen network
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Polar sites (sunlit ridges, Earth-link hub, ice mines) were picked automatically from the analysis: sunlight × slope <12° × permanently shadowed ice within ~20 km, peaks ≥12 km apart. Mid-latitude sites are hand-picked from known lava-tube pits, resource deposits and flat maria.
Caveats
- Sunlight figures come from horizon ray-tracing on a 400 m grid with 72 azimuths. Published high-res studies find the best points reach ~90%+ at tower height. Treat our numbers as ground-level and slightly conservative.
- Global slopes are computed at ~474 m spacing, so metre-scale boulders and small craters are invisible. Real routing needs LRO NAC-derived DEMs (≈2–5 m) along each corridor.
- Polar site names are the nearest named crater or massif from a small built-in gazetteer, so a few may be loose. The coordinates are what count.
- Health effects of 1/6 g over years, and on child development, are unknown. They might cap a "city" at a rotating workforce until data exists.