Aerospace Daily and Defense Report
09/25/2007
By Frank Morring, Jr./Aerospace Daily & Defense Report
HYDERABAD, India - A growing awareness of the threat to Earth posed by even relatively small asteroids and comet chunks suggests a potential career path for budding engineers.
William Ailor, an engineer who directs the Center for Orbital and Reentry Debris Studies at The Aerospace Corp., told the International Astronautical Congress here Sept. 24 that the possibility of another event the size of the one that leveled a Siberian forest in 1908 with an airburst estimated as the equivalent of 10-15 megatons of high explosive is about one in 10 in any given century.
That blast, which flattened more than 2,000 square kilometers and killed at least two people, is believed to have been caused by an asteroid measuring about 50 meters (160 feet) in diameter. Had it happened near Manhattan instead of the isolated Tunguska River, it would have been an unprecedented disaster with societal results that can only be crudely extrapolated from the aftermath of the 2001 terror attack there.
The chance of an actual civilization-threatening impact - caused by an asteroid a kilometer across - is about one in 1,000 over a century, while an extinction-level event like the one that wiped out the dinosaurs has a one-in-a-million chance of happening over a century, he said.
Awareness of the danger has gone up dramatically since Congress ordered NASA to begin cataloguing near-Earth objects - with orbits that take them within 1.3 astronomical units of the sun - measuring 1 kilometer in diameter or more. Apophis, a known 300-meter (1,000-foot) object that will be visible from the ground when it passes about 30,000 kilometers from Earth on April 13, 2029, would have about 850 explosive megatons if it were to hit, something that remains a possibility when it returns in 2036 (DAILY, June 13, 2005).
Comets are even harder to detect with enough lead time to attempt some sort of deflection mission, since they can approach from any direction with high relative velocity. Sometimes they aren't seen until they have passed the Earth in their elliptical orbits around the sun.
NASA's goal is to identify 90 percent of the 1-kilometer near-Earth objects by the end of next year, and there is an unfunded plan to catalogue objects down to 140 meters (460 feet) by 2020. Tracking an object after it is spotted with enough accuracy and lead time to justify and accomplish a multibillion international attempt to deflect it is very tricky, and the methods for doing so are uncertain at best.
"If you're a young person and you're just getting into the space field, it is not unlikely that you might get involved in actually doing some serious planning for a deflection mission," Ailor said. "This is not something that is many generations off. It's something that we really should be preparing for."
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