. Scientific Frontline: Cities on asteroids? It could work—in theory

Thursday, December 8, 2022

Cities on asteroids? It could work—in theory

In what they deem a “wildly theoretical” paper, Rochester researchers imagine covering an asteroid in a flexible, mesh bag made of ultralight and high-strength carbon nanofibers as the key to creating human cities in space.
Illustration Credit: University of Rochester | Michael Osadciw

Rochester scientists use physics and engineering principles to show how asteroids could be future viable space habitats.

This past year, Jeff Bezos launched himself into space, while Elon Musk funded a space flight for a non-astronaut crew. Space collaborations between government and private entities, including Musk’s SpaceX and Bezos’s Blue Origin have become increasingly common. But with the recent emergence of the so-called “New Space” movement, aerospace companies are working to develop low-cost access to space for everyone, not only billionaires.

For a future beyond Earth, however, humans need places to accommodate homes, buildings, and other structures for millions of people to live and work.

Right now, space cities exist only in science fiction. But are space cities feasible in reality? And, if so, how?

According to new research from University of Rochester scientists, our future may lie in asteroids.

In what they deem a “wildly theoretical” paper published in the journal Frontiers in Astronomy and Space Sciences, the researchers, including Adam Frank, the Helen F. and Fred H. Gowen Professor of Physics and Astronomy, and Peter Miklavčič, a PhD candidate in mechanical engineering and the paper’s first author, outline a plan for creating large cities on asteroids.

“Our paper lives on the edge of science and science fiction,” Frank says. “We’re taking a science fiction idea that has been very popular recently—in TV shows like Amazon’s The Expanse—and offering a new path for using an asteroid to build a city in space.”

A spinning space metropolis

In 1972 NASA commissioned physicist Gerard O’Neill to design a space habitat that could feasibly allow humans to live in space. O’Neill and his colleagues worked out a plan for “O’Neill cylinders,” spinning space metropolises consisting of two cylinders rotating in opposite directions, with a rod connecting the cylinders at each end. The cylinders would rotate fast enough to provide artificial gravity on their inner surface but slow enough that people living in them would not experience motion sickness.

Since then, TV shows and movies including Star Trek and books such as Orson Scott Card’s 1985 novel Ender’s Game have depicted O’Neill cylinder-like habitats populated with human beings. Both Bezos and Musk have referenced O’Neill cylinders in their visions for future space habitats.

However, while O’Neill cylinders offer a solution to space’s lack of gravity, getting the necessary building supplies from Earth to space to create the O’Neill cylinders would be difficult and cost prohibitive.

A pandemic project

During the COVID-19 pandemic and lockdown, Miklavčič, Frank, and several Rochester students and colleagues—John Siu ’20; Esteban Wright ’22 (PhD); Alex Debrecht ’21 (PhD); Hesam Askari, an assistant professor of mechanical engineering; and Alice Quillen, a professor of physics and astronomy—considered this conundrum of creating cost-effective O’Neill cylinders.

“All those flying mountains whirling around the sun might provide a faster, cheaper, and more effective path to space cities.”

“This project started as just a way for physicists and engineers to blow off steam, set aside worldly stresses for a while, and imagine something crazy,” Miklavčič says.

They soon discovered, however, that they might be onto something: could asteroids be used to create O’Neill cylinders?

A fast, cheap, and effective path

Asteroids are rocky bodies orbiting the sun, leftover from the formation of the solar system approximately 4.6 billion years ago. Scientists estimate there are about 1,000 asteroids larger than one mile across traveling in our solar system.

“All those flying mountains whirling around the sun might provide a faster, cheaper, and more effective path to space cities,” Frank says.

Besides their abundance in the solar system, asteroids have many other advantages for human habitation, including their rock layers, which provide a natural shield against deadly cosmic radiation from the sun.

But asteroids have several major drawbacks, the researchers found: the rock that comprises asteroids is not strong enough to handle getting even one-third of Earth’s gravity from spinning. Once an asteroid was set into rotation, it would merely fracture and break. Moreover, most asteroids are not even solid rock but “rubble piles”—clusters of loose boulders, stones, and sand held together by the weak mutual gravity of space. If the researchers wanted to make space habitats out of these asteroids, they’d have to figure out how to work with rubble piles.

Managing rubble

Miklavčič’s research focuses on granular systems—systems composed of many tiny particles, such as sand or grain. In particular, he studies how these systems respond in environments with low or no gravity; for instance, how space rovers might impact and disperse granular surfaces of planets when they touch down.

“My typical research and this project are on two ends of a spectrum,” Miklavčič says. “I’m normally interested in the grain-level response of granular media, whereas this project was more of a big picture exercise managing rubble as a large system.”

Miklavčič and his colleagues conducted calculations of forces, materials, and strategies for constructing rotating asteroid settlements and came up with an idea for containing the rubble that would inevitably result from forming an O’Neill cylinder out of an asteroid.

Containing an asteroid

Their solution? A very big, very flexible bag.

The researchers imagine covering an asteroid in a flexible, mesh bag made of ultralight and high-strength carbon nanofibers—tubes made of carbon, each just a few atoms in diameter. The bag would envelope and support the entire spinning mass of the asteroid’s rubble and the habitat within, while also supporting its own weight as it spins.

“A cylindrical containment bag constructed from carbon nanotubes would be extremely light relative to the mass of the asteroid rubble and the habitat, yet strong enough to hold everything together,” Miklavčič says. “Even better, carbon nanotubes are being developed today, with much interest in scaling up their production for use in larger-scale applications.”

The process could theoretically go something like this:

  • The asteroid would be spun to create artificial gravity. This process would inevitably cause the asteroid to break apart.
  • The bits of the asteroid rubble would fling outward, expanding the carbon nanofiber bag enveloping the asteroid.
  • When the bag reached its maximum extent, the carbon nanofibers would snap taut, catching the expanding rubble.
  • As the rubble settled against the bag, it would produce a layer thick enough to shield against radiation for anyone living inside. The spin of the cylinder would induce artificial gravity on the inner surface.
  • “Based on our calculations, a 300-meter-diameter asteroid just a few football fields across could be expanded into a cylindrical space habitat with about 22 square miles of living area,” Frank says. “That’s roughly the size of Manhattan.”

Just theoretical—for now

Living inside asteroids is still the fancy of science fiction, but Frank and Miklavčič say the physics and mechanics are there to make science fiction a reality.

“Obviously, no one will be building asteroid cities anytime soon, but the technologies required to accomplish this kind of engineering don’t break any laws of physics,” Frank says.

Everything the researchers imagine in their study—from the motors needed to spin up the asteroid, to the carbon-nanofiber bag—are technologies people are currently either using or developing.

“The idea of asteroid cities might seem too distant until you realize that in 1900 no one had ever flown in an airplane, yet right this minute thousands of people are sitting comfortably in chairs as they hurdle at hundreds of miles an hour, miles above the ground,” Frank says. “Space cities might seem like a fantasy now, but history shows that a century or so of technological progress can make impossible things possible.”

Source/Credit: University of Rochester | Lindsey Valich


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