Concordia is real engineering applied at city scale. Each system below is built from physics you can check, and each page shows the work.
How the pages work
Every page opens with the idea in everyday terms: a bucket swung overhead, a bicycle wheel, a barrel hoop. Then it shows how Concordia applies the idea, with numbers, and what it feels like to live with. A Go deeper block holds the equations and a worked example using Concordia's own figures. Real-world claims carry a source at the bottom of the page.
Nothing needs math to follow. The deeper blocks are there for students and engineers who want to check the arithmetic.
The thirteen pages
- Artificial gravity: how spin makes weight, and why it fades toward the axis.
- Counter-rotation and momentum: why the rotors spin in opposite pairs.
- Structure and pressure: the vessel, the megaframe and the end walls.
- Radiation and debris: the shield stack, storm shelters and the watch for rocks.
- Air, water and food: the loops that keep a city alive.
- Light and sky: an artificial sky and its day lengths.
- Power and heat: solar platforms, HVDC and radiators.
- Moving around: metro, ascenders, spin transfer and the spine express.
- Flying in a spinning world: fly a glider in a rotor, drop a ball and stand still in space.
- Materials: regolith, asteroid volatiles and the stores.
- Mining the Moon and asteroids: what still comes from Earth, the bag haulers, and lunar rock at scale.
- Getting there: L5, the launcher and the 15 day Earth transfer.
- Safety: what changed since the 1970s, and why no single failure reaches everyone.
Use the engineering overlays
Each page links to the place where its idea can be seen. Open the simulation in Engineer mode and pick an overlay: gravity, rotational frame, pressure, shielding, thermal, electrical, transportation, material flow, structural, momentum, defence or satellites. Callouts label the view with the numbers from these pages, and the panel links back to the page that explains them. The guide lists the controls.
Open in the simulation: Start with the gravity overlay Open in the simulation: Momentum overlay
In this section
Artificial gravity
Concordia makes gravity by turning. Each city rotor is a cylinder 5 km wide that spins once every 100 seconds, and the floor is the inside of its outer wall.
Counter-rotation and momentum
A spinning city is a giant gyroscope, and a gyroscope fights every push that tries to tilt it. Concordia spins its four city rotors in opposite pairs, so the total spin is zero.
Structure and pressure
A rotor is a pressure vessel 5 km across and 2.5 km long. It holds in a full atmosphere while spinning under the weight of a city.
Radiation and debris
Space is full of fast particles and drifting rocks. Concordia answers with mass: a thick layered shell of regolith and water, shelters for solar storms, and a layered watch for...
Air, water and food
Concordia breathes air at Earth sea-level pressure, drinks water it has used many times and eats food grown in the upper city. The loops are almost closed.
Light and the artificial sky
Concordia has no big windows. The sky is a ceiling of light panels hung 450 m above the ground, and it is bright enough that the street below sits in daylight.
Power and heat
Concordia gets its power from the Sun, through solar platforms kilometres behind the station, and sheds all of it as heat through radiators.
Moving around a spinning world
In Concordia you walk, ride the metro, take a lift to the axis and cross to other rotors by train. Each trip feels a different piece of the spin.
Flying in a spinning world
The air in a rotor turns with the floor, so a wing works there, and it shows what spin gravity really is.
Materials from the Moon and asteroids
Concordia is made almost entirely of the Moon and of asteroids. The Moon supplies oxygen, metals, glass and bulk stone.
Mining the Moon and asteroids
Concordia buys almost nothing heavy from Earth. Its first metal came from small asteroids, bagged whole and hauled to L5.
Getting there from L5
Concordia floats in the Earth-Moon L5 region, 384,400 km from Earth.
Safety: what changed since the 1970s
Gerard O'Neill and NASA's 1975 summer study showed that a city in space could be built.