The notion of an asteroid headed for Earth is typically seen as a bad omen. On the flip side, some scientists and entrepreneurs increasingly see this scenario as a potential opportunity. Deliberately redirecting asteroids to our planet’s vicinity could enable us to study them up close, or even mine them.
Given that these objects are packed with valuable resources, building a collection of them nearby could spark major advances in spaceflight, to say nothing of the scientific research that might result from easy access to these extraterrestrial bodies.
A recent paper published in Acta Astronautica suggests that asteroids could be captured in Earth’s orbit with aerobraking, a maneuver that uses atmospheric drag to decelerate and position objects in stable trajectories around a planet. Aerobraking has helped place interplanetary spacecraft in orbit around Mars and Venus, and to slow down spacecraft returning to Earth.
Led by Minghu Tan, a PhD student at the University of Glasgow, the paper immediately addresses the most obvious concern with this scenario: What if there’s some mistake in the redirect process and an asteroid accidentally impacts Earth? It’s bad enough that the dinosaurs were oblivious to their doomsday space rock, but it would be especially embarrassing if we humans smack ourselves in the face with one.
Tan and his co-authors suggest mitigating this risk by selecting asteroids under 30 meters in diameter for aerobraking, as they’d burn up in the atmosphere if the maneuver failed. Tan also told me, in an email, that a redirected asteroid might collide with spacecraft in orbit around Earth. That’s why “accurate guidance and control strategies would be required,” he said.
Assuming that such guidance measures would be in place, the paper maps out two possible strategies for capturing small asteroids with low-energy aerobraking techniques. In each case, Tan and his co-authors envision a rendezvous, far from Earth, in which a spacecraft applies enough force to put an asteroid on a path to graze our planet’s atmosphere, initiating the capture.
The spacecraft could stay coupled with the asteroid on its journey, in case mid-flight course corrections were needed. The team identified the asteroid 2005 VL1 as a particularly good potential target for such a mission, because it has the ideal size and speed to be redirected, and it theoretically would not lose as much mass during aerobraking as other candidate asteroids, making it an economical choice.
Other concepts for asteroid redirect missions have tried to assuage the possibility of accidental impacts by choosing targets that are farther from Earth. Directing an asteroid into orbit around the Moon, a strategy NASA has considered, seems less existentially perilous than aerobraking them in Earth’s atmosphere, but both scenarios have advantages and drawbacks.
Ultimately, the rewards of asteroid capture missions will have to outweigh current risks before these futuristic concepts come to fruition—but it never hurts to get all the math worked out in the meantime.
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