O’Neill Cylinders: Future Colonies


Despite the fact that most manned missions into space today revolve around the International Space Station (ISS) and efforts to colonize outer space have become drastically reduced since the success of the Apollo program, experts have theorized ways for humans to exist among the stars for years. One design, like the Stanford-Torus ring habitats, involves large mega-structures and is designed to support thousands of individuals. That design is called the O’Neill Cylinder.

An O’Neill Cylinder, shown being directed at the Sun

Gerard O’Neill was an exceptionally talented and intelligent individual, with three careers as a writer and teacher, an entrepreneur, and an experimental physicist. He served as a radar technician in the U.S. Navy as well as later working as a physics professor at Princeton University until his retirement in 1985, when he became an advocate for the private sector on the National Commission on Space. He died on April 27th, 1992 after a long struggle with leukemia. One of his more notable traits was that O’Neill would craft an invention based on his ideas (whether it was about physics or space craft) in his own workshop to determine if it was feasible. Interestingly, every single one of his ideas failed for political or financial reasons rather than technical.

In terms of space, O’Neill founded the Space Studies Institute which sought to explore ideas for space exploration and colonization without the hindrances of politics or bureaucracies, things which had troubled him throughout his career. Then in 1976, O’Neill published his first book entitled The High Frontier: Human Colonies in Space which discussed how humans might survive in space by living in large artificial habitats. One such idea was the aptly-named O’Neill Cylinder, although the idea had been printed earlier in a 1974 article of Physics Today called The Colonization of Space. In the article, O’Neill stated four main points that he had come to after studying factors in space exploration such as economics, meteoroid damage, and materials sources:

A pair of O’Neill Cylinders

1.) We can colonize space, and do so without robbing or harming anyone and without polluting anything.

2.) If work is begun soon, nearly all our industrial activity could be moved away from Earth’s fragile biosphere within less than a century from now.

3.) The technical imperatives of this kind of migration of people and industry into space are likely to encourage self-sufficiency, small-scale governmental units, cultural diversity and a high degree of independence.

4.) The ultimate size limit for the human race on the newly available frontier is at least 20,000 times its present value.

It is important to note that even though many of the arguments O’Neill made in the article and in his book about it being possible to colonize space at the time using existing technology were correct, there was the issue of political backing or popular support. Regardless, the ideas presented for the O’Neill Cylinder concept were very interesting.

An artist’s impression of a Lunar Mass Driver

An O’Neill Cylinder, also known as an “Island Three” (being the third in a series of islands or colonies devised by O’Neill) was essentially an extremely large cylinder that would rotate at a speed of one revolution every 114 seconds in order to simulate Earth gravity, while colonists would live on the inside of the cylinder. An important aspect of the design is that there are actually two cylinders which counter-rotate around each other which keeps them aimed towards the Sun in order to collect solar energy. The materials to construct the O’Neill Cylinder would be provided by the Moon and asteroids which could be fired into location by Mass Drivers, another concept devised by Gerard O’Neill (of which a successful prototype was the first accomplishment by the Space Studies Institute). A mass driver was seen as the method of choice because of its ability to use electromagnetism to fire payloads into space, which (if fired from the Moon or an asteroid) would be easier due to the lack of gravity, while also being much more economical than rockets.

However, unlike the Stanford-Torus design in which the occupants would live on the outside half of the structure, the occupants of an O’Neill Cylinder would live on three walls, or “valleys,” stretching from each end of the cylinder, while the other three walls would actually be mirrors. These mirrors would reflect light into the three valleys, and could open and close in order to reproduce the concept of day and night despite being in space. The valleys would contain not just the towns where occupants would live, but also lakes and forests as the vegetation would be necessary for converting carbon dioxide into oxygen, much like on Earth.

The interior of an O’Neill Cylinder, showing the three valleys and mirrors

O’Neill Cylinders would have a radius of 3.2km and a length of 32km (or 20 miles long and 4 miles in diameter) allowing for a population ranging from the hundreds of thousands to millions, while the area inside for people to live on would be roughly 500 square miles of land. To power the colony, a massive parabolic collector at one end of the structure would focus solar energy towards steam generators. Interestingly, the O’Neil Cylinder would be theoretically large enough to have its own weather patterns, which could even be made to change on purpose in order to coincide with the seasons on Earth or according to a vote held by the colonists.

Like many of Gerard O’Neill’s designs, the O’Neill Cylinder was concocted at a time during the late 70’s when popular interest in space exploration was at an all-time high and his students’ enthusiasm at Princeton inspired him and NASA to consider long-term investments in colonizing space. Unfortunately, despite such designs being seemingly technically sound, are simply too far ahead of their time and have only found use in multiple science fiction series. However, there’s certainly no reason to believe that the O’Neill Cylinders won’t be used one day to help humanity spread into space.