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The future.
What is a MetroCircus? A City on the Moon?

by Gregory Nemitz
A Variant of an O’Neill Space City Proposed for
Inhabiting the Moon or Asteroids

Photo, Courtesy of NASA
Proposed location of Eros' Capital City, "Gagarin" MetroCircus on Asteroid 433, Eros.

Images, Courtesy of Artemis Society International.
Twin 3-Ring MetroCircus


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The MetroCircus
Also known as a "Nemitz Ring-City", or "doughnut train" is an improvement on the O’Neill space city concept first developed by Gerard K. O’Neill. The MetroCircus design offers incremental growth and development of space city systems, allowing a learning curve towards building full-fledged O’Neill space cities.

A MetroCircus is a moving train on a circular track. It has no front or back, it’s a seamless circle, or a circular track full of cars. The train may use wheels on the track or be a mag-lev system. The MetroCircus is inside a 1 kilometer diameter circular trench or tunnel in an asteroid or small planet, like Eros or Ceres. A train track is placed on the outer wall of the trench or tunnel. The MetroCircus runs on the track, producing simulated gravity by centripetal force. 

One main advantage of this design is that the moving structure does not include the radiation shielding mass. This enables far less massive structures and enables the early development of large-scale habitable structures with simulated gravity on the Moon or asteroids.

The construction method can vary, from multiple cars to a welded construction for a completely solid circle. The hull could be up to several inches thick and made of nickel-iron or aluminium. One kilometer in diameter is large enough to reduce or eliminate debilitating coriolis effects. A one-kilometer MetroCircus would run at about 150 kph to simulate 0.40 gravity.

To get on and off the moving city, another track runs alongside. A ‘commuter bus’ accelerates to match speed with the city, then workers and materials are transferred. thanks the Artemis Society International,, a non-profit research foundation, Gregory Bennett, and Mike Delaney for providing supporting technical analysis and MetroCircus images.