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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糖心传媒檚 SpaceX and Bezos糖心传媒檚 Blue Origin have become increasingly common. But with the recent emergence of the so-called 糖心传媒淣ew Space糖心传媒� 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 scientists, our future may lie in asteroids.

In what they deem a 糖心传媒渨ildly theoretical糖心传媒� published in the journal Frontiers in Astronomy and Space Sciences, the researchers, including , the Helen F. and Fred H. Gowen Professor of Physics and Astronomy, and Peter Miklav膷i膷, a PhD candidate in mechanical engineering and the paper糖心传媒檚 first author, outline a plan for creating large cities on asteroids.

糖心传媒淥ur paper lives on the edge of science and science fiction,糖心传媒� Frank says. 糖心传媒淲e糖心传媒檙e taking a science fiction idea that has been very popular recently糖心传媒攊n TV shows like Amazon糖心传媒檚 The Expanse糖心传媒攁nd offering a new path for using an asteroid to build a city in space.糖心传媒�

A spinning space metropolis

In 1972 NASA commissioned physicist Gerard O糖心传媒橬eill to design a space habitat that could feasibly allow humans to live in space. O糖心传媒橬eill and his colleagues worked out a plan for 糖心传媒淥糖心传媒橬eill cylinders,糖心传媒� 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糖心传媒檚 1985 novel Ender糖心传媒檚 Game have depicted O糖心传媒橬eill cylinder-like habitats populated with human beings. Both Bezos and Musk have referenced O糖心传媒橬eill cylinders in their visions for future space habitats.

However, while O糖心传媒橬eill cylinders offer a solution to space糖心传媒檚 lack of gravity, getting the necessary building supplies from Earth to space to create the O糖心传媒橬eill cylinders would be difficult and cost prohibitive.

A pandemic project

During the COVID-19 pandemic and lockdown, Miklav膷i膷, Frank, and several Rochester students and colleagues糖心传媒擩ohn Siu 糖心传媒�20; Esteban Wright 糖心传媒�22 (PhD); Alex Debrecht 糖心传媒�21 (PhD); , an assistant professor of mechanical engineering; and , a professor of physics and astronomy糖心传媒攃onsidered this conundrum of creating cost-effective O糖心传媒橬eill cylinders.

糖心传媒淭his 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,糖心传媒� Miklav膷i膷 says.

They soon discovered, however, that they might be onto something: could asteroids be used to create O糖心传媒橬eill 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.

糖心传媒淎ll those flying mountains whirling around the sun might provide a faster, cheaper, and more effective path to space cities,糖心传媒� 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糖心传媒檚 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 糖心传媒渞ubble piles糖心传媒澨切拇�媒攃lusters 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糖心传媒檇 have to figure out how to work with rubble piles.

Managing rubble

Miklav膷i膷糖心传媒檚 research focuses on granular systems糖心传媒攕ystems 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.

糖心传媒淢y typical research and this project are on two ends of a spectrum,糖心传媒� Miklav膷i膷 says. 糖心传媒淚糖心传媒檓 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.糖心传媒�

Miklav膷i膷 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糖心传媒橬eill 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糖心传媒攖ubes made of carbon, each just a few atoms in diameter. The bag would envelope and support the entire spinning mass of the asteroid糖心传媒檚 rubble and the habitat within, while also supporting its own weight as it spins.

糖心传媒淎 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,糖心传媒� Miklav膷i膷 says. 糖心传媒淓ven better, carbon nanotubes are being developed today, with much interest in scaling up their production for use in larger-scale applications.糖心传媒�

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.

糖心传媒淏ased 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,糖心传媒� Frank says. 糖心传媒淭hat糖心传媒檚 roughly the size of Manhattan.糖心传媒�

Just theoretical糖心传媒攆or now

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

糖心传媒淥bviously, no one will be building asteroid cities anytime soon, but the technologies required to accomplish this kind of engineering don糖心传媒檛 break any laws of physics,糖心传媒� Frank says.

Everything the researchers imagine in their study糖心传媒攆rom the motors needed to spin up the asteroid, to the carbon-nanofiber bag糖心传媒攁re technologies people are currently either using or developing.

糖心传媒淭he 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,糖心传媒� Frank says. 糖心传媒淪pace cities might seem like a fantasy now, but history shows that a century or so of technological progress can make impossible things possible.糖心传媒�

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