Científicos de la Universidad de Rochester muestran cómo los asteroides podrían ser futuros hábitats espaciales viables utilizando principios de física e ingeniería.

El año pasado, Jeff Bezos se lanzó al espacio, mientras que Elon Musk financió vuelos espaciales para una tripulación que no era astronauta. Colaboraciones espaciales entre entidades gubernamentales y privadas, incluida la de Musk espaciox y la de Bezos origen azul, son cada vez más comunes. Sin embargo, con el surgimiento reciente del llamado movimiento «Nuevo espacio», las compañías aeroespaciales están trabajando para desarrollar un acceso al espacio de bajo costo para todos, no solo para los multimillonarios.

Pero para un futuro más allá de la Tierra, los humanos necesitarán lugares para albergar hogares, edificios y otras estructuras para que millones de personas vivan y trabajen.

Hasta ahora, las ciudades espaciales solo existen en la ciencia ficción. Pero, ¿son las ciudades espaciales factibles en la realidad? Y si es así, ¿cómo?

Según una nueva investigación de científicos de la Universidad de Rochester, nuestro futuro puede estar en los asteroides.

En lo que consideran un artículo «extremadamente teórico», los investigadores describen un plan para crear grandes ciudades en asteroides. Publicado en la revista Fronteras en astronomía y ciencia espacialLos científicos incluyen a Adam Frank, profesor de física y astronomía Helen F. y Fred H. Gowen, y Peter Miklavčič, candidato a doctorado en ingeniería mecánica y primer autor del artículo.

“Nuestra revista vive en la frontera de la ciencia y la ciencia ficción”, dice Frank. «Estamos tomando una idea de ciencia ficción que ha sido muy popular recientemente, en programas de televisión como el de Amazon. El grado– y ofrece una nueva forma de usar un asteroide para construir una ciudad en el espacio.

Representación artística de un par de cilindros de O’Neill. Un cilindro de O’Neill (también llamado colonia de O’Neill) es un concepto de asentamiento espacial propuesto por el físico estadounidense Gerard K. O’Neill en su libro de 1976 The High Frontier: Human Colonies in Space. Crédito: Rick Guidice/NASA

Una metrópolis espacial giratoria

en 1972[{» attribute=»»>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.

“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.”

Reference: “Habitat Bennu: Design Concepts for Spinning Habitats Constructed From Rubble Pile Near-Earth Asteroids” by Peter M. Miklavčič, John Siu, Esteban Wright, Alex Debrecht, Hesam Askari, Alice C. Quillen and Adam Frank, 3 January 2022, Frontiers in Astronomy and Space Sciences.
DOI: 10.3389/fspas.2021.645363