A NASA study has found that a spacecraft's gravity may be enough to deflect the orbit of Earth-threatening asteroids.
Image: Asteroid 951 Gaspra. Credit: NASA
The research by NASA's Jet Propulsion Laboratory showed that, though such "gravity tractors" had only a weak gravitational pull, it may be enough to deflect an asteroid threatening the Earth if the technique was applied when the object was at least one orbit away from collision.
The New Scientist, quoting the NASA report, said such a technique could be effective in deflecting a hypothetical asteroid measuring up to 140 metres, a size large enough to cause regional devastation should it hit the Earth -- and certainly large-scale loss of life should it strike a heavily-populated area.
"Prior to this study, the gravity tractor deflection technique had been proven in only a conceptual way," outlined Clark Chapman of the Southwest Research Institute in Boulder, Colorado, who was not involved in the study.
"Although there were few, if any, substantive criticisms of these concepts, some of us had the feeling that the ideas were viewed as quaint but not-ready-for-prime-time," he said. "The JPL study gives it the solid engineering underpinnings that we never really doubted, but now are there for anyone to see."
The intricacies of asteroid deflection depend on a number of factors, including how early the "gravity tractors" are used, and the type of orbit the asteroid is going to follow in the interval, explained Rusty Schweickart, a former Apollo astronaut and chairman of the B612 Foundation, which provided funding for the study.
According to Schweickart, asteroids sometimes pass through a narrow keyhole in space before returning to hit the planet. If an asteroid can be deflected from this keyhole, sometimes only a few hundred metres across, it may not return on a collision course.
"The gravity tractor is a wimp, but it's a precise wimp," Schweickart said. "It can make very small, precise changes in orbit, and that's what you need to avoid a keyhole."
The JPL is working on trial simulations it believes would be effective if a large asteroid were discovered to be Earth-bound.
The scientists envisage a two-pronged approach: first they would attempt to crash-land a spacecraft on the asteroid, which would alter its orbit albeit in an unpredictable manner; while a second spacecraft, the "gravity tractor" would be sent to hover 150 metres away from the asteroid's surface, gently working on changing the asteroid's velocity and direction over a prolonged period of time.
A preliminary report on the simulation was presented by JPL's Don Yeomans at the recent Asteroids, Comets and Meteors meeting in Baltimore, Maryland.
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