Apr. 13, 1998 CHAMPAIGN, Ill. - The spectacular plunge of Comet Shoemaker-Levy 9 into Jupiter in July 1994 and recent concern about the projected "near miss" of Asteroid 1997 XF11 with Earth in October 2028 brought renewed awareness that collision events do occur within our solar system and the next one could involve our planet. In fact, such a collision may be long overdue, and steps should be taken to alleviate the risk, a University of Illinois researcher says.
"If faced with this kind of danger, we would want to send a spacecraft to intercept the object as far from Earth as possible," said Bruce Conway, a professor of aeronautical and astronautical engineering. "This would allow whatever mitigation strategy we use to have the longest time to act."
There are two practical problems that must be solved, however, Conway said. "The first is simply getting a sizable payload to the object in the shortest amount of time, and the second is deciding what to do when we get it there."
In a paper published in the September-October (1997) issue of the Journal of Guidance, Control, and Dynamics, Conway described the optimal low-thrust interception of a potential collider. The proposed mission scenario would combine the speed of conventional chemical rockets with the increased payload capability of continuous-thrust electric propulsion. Having arrived at the destination, however, what should be done to prevent the impending collision?
"For years, we assumed that the best mitigation strategy was to blow up the object with a nuclear warhead," Conway said. "But that may not be such a good idea. If we blow it up, instead of having just one large mass hurtling toward the Earth, we could end up with a multitude of smaller -- but equally lethal -- objects coming at us. A better alternative would be to deflect the object."
One possible mechanism to accomplish this would involve detonating a nuclear warhead above the asteroid surface, Conway said. "That would create a crater, and a large portion of the jet of vaporized material would shoot off in one direction -- like a rocket -- and push the object in the opposite direction."
But which direction should the object be pushed to ensure that it will miss the Earth? And would it make more sense to speed the object up or slow it down?
Conway's latest research has focused on answering these questions. He developed an analytical method that, given the orbital parameters of the object and the interval between interception and close approach, determines the proper direction in which to push the object to maximize the deflection in the required time.
Such calculations may never be needed, but they're nice to have just in case.
"While the probability of a large asteroid or comet colliding with the Earth is low, the potential for destruction is immense," Conway said. "It's probably not something we should lose sleep over; but, on the other hand, it would be really silly not to do anything."
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