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NASA Could Replace the ISS With a Space Station Design Straight Out of Sci-Fi

The O’Neill Cylinder has been a pop culture fixture for three decades, but its origins go back even further.

Lais Borges/Inverse; Warner Bros.; Getty
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Every year, humankind comes up with new dreams of establishing permanent outposts in space, whether on the Moon or even Mars. Elon Musk’s lofty proposal to establish a self-sustaining “Mars city” by 2050 is probably the most well-known example. But other organizations like the Space Settlement Institute are firmly committed to making space settlement a reality in our lifetime.

Yet, the closest humans have come to colonizing space is the International Space Station, where astronauts have temporarily lived and worked together since November 2, 2000. But four years before the launch of the ISS, one sci-fi show imagined an even bolder way to live in space.

Originally released 30 years ago in January 1994, Babylon 5 took place on a 5-mile-long, self-sufficient space station that served as both a diplomatic way station for celestial travelers, and as a home to thousands of personnel that live there. The space station’s design loosely takes inspiration from the real-life O’Neill Cylinder, which physicist Gerard K. O’Neill proposed in a 1974 Physics Today article. More recently, Jeff Bezos’ space company, Blue Origin, proposed its own concept for a futuristic space station based on O’Neill’s design. But how realistic is any of this, really? According to Paul Byrne, the NASA PDS Geosciences Node director and an associate professor of planetary sciences at Washington University in St. Louis, the answer is: not very.

“For the foreseeable future, O'Neill cylinders aren't a realistic prospect for humanity whatsoever,” Byrne tells Inverse.

On the 30th anniversary of Babylon 5, Inverse explores the scientific origins of its titular space station and what’s holding us back from building one today.

What is an O’Neill Cylinder?

An artist's depiction of O’Neill’s space station design.

Public Domain

While movies and shows like 2001: A Space Odyssey, Star Trek, and Star Wars were envisioning what fictional models of space travel might look like, physicists like O’Neill were busy coming up with real-world models for space colonization.

O’Neill imagined a utopian space community filled with forests and lakes replicating the environment of Earth, which, in his own words, could be achieved within the next century “without robbing or harming anyone and without polluting anything.”

Establishing a permanent, self-sustaining settlement of humans in space requires a few basic things:

  1. Continuous energy supply.
  2. The ability to simulate gravity.
  3. The means to grow food.

The O’Neill Cylinder is a space station prototype that theoretically delivers all three. Here’s how it works (in theory):

A pair of rotating cylinders up to 4 miles in diameter and 16 miles in length houses the human population living in space. The centrifugal rotating force of the cylinders simulates gravity for its human occupants similar to the way a fast-spinning merry-go-round exerts a gravitational force, pulling you away from the center of the ride.

The view from inside an O’Neill cylinder.

Public Domain

But the most essential detail in O’Neill’s proposal is that the dual cylinders must rotate in opposite directions to enable the space station to continuously point toward the Sun — the source of energy for this human settlement. This setup differs from the space station seen in 2001: A Space Odyssey, which relies on a single rotating space station.

“The problem is that if you just have one cylinder or one big wheel, like in 2001: A Space Odyssey, it will always try to maintain its axis in a fixed orientation. So it would be very difficult to keep it pointed toward the sun,” Timothy Gay, the Willa Cather professor of physics at the University of Nebraska, tells Inverse.

According to Gay, these counter-rotating cylinders in O’Neill’s work by eliminating “angular momentum,” which is the property of any rotating object.

Angular momentum means you have to apply a lot of force to keep something pointing in a certain direction — like towards the Sun. You’d likely need to use some rocket to keep the space station on track, which makes fueling the space station with solar energy less feasible.

But the rotating cylinders in O’Neill’s method cancel out angular momentum, meaning you can point the space station toward the Sun with much less effort — and a lot less energy. Bingo: you have renewable solar energy and the prospect of a surviving human colony.

Babylon 5 and the O’Neill Cylinder

The Babylon 5 space station takes its inspiration from O’Neill’s design.

Warner Bros.

Unlike the O’Neill Cylinder, the space station in Babylon 5 bypasses the whole issue of solar energy by drawing its power from fusion reactors. But since humans just achieved their first nuclear fusion breakthrough last year, we’re probably a far cry from using the technology to reliably power Earth — let alone a colony among the stars. (For what it’s worth, Babylon 5 takes place between the years 2257 and 2262. So maybe it’s not so unrealistic in that sense.)

Gay notes that the design of the Babylon 5 differs from artists’ renderings of the O’Neill Cylinder. O’Neill’s version features two cylinders that rotate on parallel axes — like hot dogs broiling side-by-side on a roller in your local gas station shop or 7-Eleven. But the Babylon 5’s cylinders rotate about the same line or axis.

In any case: both designs would theoretically work to sustain a human colony.

“The point is that those are both viable ideas because you still have zero angular momentum,” Gay says.

Byrne also says the conditions in the habitat of a space station like the O’Neill Cylinder would be similar to Earth in terms of having a day-night cycle and environmental similarities, reducing the likelihood of cabin fever.

Will the O’Neill Cylinder Become the Next ISS?

NASA has plans to replace the ISS, but with what?


Physicists are clear on one thing: the O’Neill Cylinder checks out — at least, theoretically. But whether the O’Neill Cylinder could plausibly become the next ISS is another question altogether.

“There's no physics problem with any of it,” Gay says. “I think there's a big engineering problem with it.”

Byrne agrees. He says the problem with the cylinders in O’Neill’s concept is that their size is “so far beyond our current technological capabilities” that they likely won’t be practical for centuries or even thousands of years.

For comparison, the ISS is roughly 420 tons, while a space station the size of the O’Neill Cylinder would probably be in the range of millions of tons. Building something of that size requires an enormous amount of resources, and it wouldn’t be cost-effective to bring those materials from Earth in a rocket. You’d have to mine them from the Moon or, more likely, a metal-rich asteroid.

Researchers at the University of Rochester have come up with a scientific proposal to get around these engineering challenges. Their plan: cover an asteroid with a giant flexible bag made of carbon nanofibers to create an O’Neill Cylinder.

Asteroids would be a cheap source of resources for a space station, but the problem is that asteroids aren’t tough enough to handle anything like Earth’s gravity without crumbling, since they essentially consist of piles of rubble. To get around this issue, you need something like a giant bag to hold the asteroid’s rubble together while you spin it around to simulate gravity. However, that’s probably easier said than done.

“The long and short of it is that we don't have a single replacement platform ready to take over from the ISS,” Byrne says. He believes only a few thousand people will be living “off-world” by the end of the century.

So until science catches up with science fiction, we’ll just have to settle for the fictional space settlement in Babylon 5 to fuel our imagination.

Correction 1/28/24: This story was updated with the accurate date that humans first boarded the ISS. We regret the error. Thanks, Dan!

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