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Will humans one day be able to live elsewhere than on Earth? Can we envisage the construction of spatial cities, and if so, how? In a theoretical article, published in Frontiers in Astronomy and Space Sciencesresearchers at the University of Rochester are exploring the possibility that small near-Earth asteroids could one day be used as supports for human habitats.
Much of the attention focused on colonizing the solar system is focused on Mars. Planets and large moons indeed offer the advantage of having gravitational fields in situ more important and the possibility of building underground colonies to provide protection against radiation, explain the authors of the study. Another possibility, they say, is near-Earth asteroids, which follow elliptical orbits through the inner solar system.
These asteroids could in theory harbor underground colonies, shielding humans from solar and cosmic radiation. There remains the problem of gravity, which must be strong enough to preserve human health. Near-Earth gravity could be induced by a rapidly rotating asteroid that has been hollowed out, but the ability of these bodies to withstand the material stresses caused by the rotation is unclear. A team from the University of Rochester offers a solution to the problem.
A carbon nanofiber wrap to contain debris
In a pioneering study on the subject, published in 2019, astrophysicist Thomas Maindl and his colleagues at the University of Vienna explored the possibility that a solid asteroid could be converted into a habitat if it were hollowed out and its rotation increased so that the acceleration centrifugal approaches 38% of Earth’s gravity (which is equivalent to the gravity of Mars). They concluded that small asteroids, a few hundred meters in radius, could serve as a rotating habitat without exceeding the material elastic limit of the rock.
This work is inspired by O’Neill’s cylinders — a theoretical space habitat project proposed by American physicist Gerard K. O’Neill in the 1970s: two counter-rotating cylinders, connected at each end, which would rotate enough quickly to provide artificial gravity on their inner surface.
But Peter Miklavčič and his colleagues point out that the “small” asteroids considered in Maindl’s study are generally not solid bodies, but rather “piles of rubble”, loose conglomerates of material, composed of particles of very variable size. (grain of sand to rock), which are held together by mutual gravitational attraction. This idea has also been supported by recent images of the Itokawa, Bennu and Ryugu asteroids.
The “digging” technique is therefore not viable for asteroids of this type, which would break down under the effect of rapid rotation. As for larger asteroids, the strength required exceeds the yield strength of solid rock material. They are also much less numerous in the solar system: there are more than 10,000 near-Earth asteroids (or NEA for Near Earth Asteroids) with a diameter greater than 100 meters, but only about 900 with a diameter greater than one kilometer — which supports the use of small asteroids for the design of new habitats.
In this new study, the researchers therefore propose not only to hollow out the asteroid, but consider the addition of an outer, flexible containment structure, made of ultra-light and very resistant carbon nanofibers, intended to contain the rubble.
Existing or developing technologies
” A cylindrical containment bag constructed from carbon nanotubes would be extremely light compared to the mass of the asteroid and habitat rubble, but strong enough to hold everything together. », explains Miklavčič.
To convert an asteroid into a hollow cylindrical shell, they therefore propose a two-step process. During the first stage, the rotation of the asteroid would be gradually increased in a controlled manner from a certain initial value to the desired rotation rate. The resulting centrifugal forces would inevitably cause the asteroid to break apart. The challenge of this step is to identify the appropriate mechanism to induce rotation. The researchers here envisage the use of “debris cannons”, powered by solar energy, which would eject mass tangentially to the surface of the asteroid.
In the second stage, the rubble would be captured in the outer carbon nanofiber bag, which would initially be in a compressed state enveloping the asteroid and which could expand until it reached the desired cylindrical geometry. ” The result is a hollow, shielded volume that can be rotated up to a significant fraction of Earth’s gravity due to the additional force provided by the support structure. “, they summarize. As the rubble settles against the bag, it will form a layer thick enough to shield anyone living inside from radiation.
” According to our calculations, an asteroid 300 meters in diameter could be transformed into a cylindrical space habitat with a living area of approximately 35 square kilometers. It’s about the size of Manhattan “says Adam Frank, co-author of the study.
While the concept of a space city is still science fiction, the study’s authors claim that the technologies required do not break any laws of physics and are technologies in common use or under development. ” Space cities may seem fanciful today, but history shows that a century or so of technological advancement can make things possible once impossible. “, concludes the physicist.
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Researchers show how asteroids could become future space habitats
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