Meteoroid impacts may explain some satellite mysteries
— -- With one of NASA's defunct satellites crashing down to Earth this weekend, forgetting our more commonplace visitors from space, meteors, might be easy.
But bear in mind that roughly 100 tons of space dust and rubble, or meteoroids, rain down on Earth every day. And that before the space agency's Upper Atmosphere Research Satellite (UARS) was allowed to take a final plunge to keep it from cluttering space, something smacked into the spacecraft four years ago, hard enough to dislodge four pieces from its frame.
"We create space junk, so we're obligated to get rid of it. But we're a little bit oblivious to meteoroids," says aerospace engineer Sigrid Close of Stanford University. "And we can't go out and kill the comets that cause meteoroids."
Meteor showers look pretty in the nighttime sky, caused by space rocks as big as 30 feet across streaking across the heavens. But Close and colleagues have diagnosed a previously unsuspected way that even the humblest bit of space dust — as small as four-thousandths of an inch across — may end up zapping satellite electronics. These bits of comets and asteroids routinely swoop down on Earth at speeds ranging from 24,600 to 160,000 miles-per-hour, much faster than the orbital zip of most satellites.
For fans of categorizing stuff, I should probably mention that meteoroids are what space rocks are called when they are flying through space, meteors are what they are called when they are burning through the sky, and meteorites are what they are called after they land. Any meteoroid much bigger than 30 feet across is generally dubbed by astronomers as an asteroid, or else a comet.
"Most of the time we think of a bullet hole left behind in the spacecraft (from meteoroids)," Close says, and impacts do abrade satellite surfaces and make holes. "But these things are traveling so fast that they leave a little cloud behind when they hit," she adds. "We're trying to figure out what that can do."
Some evidence that meteoroid strikes cause bad things to happen comes from the August Perseids meteor shower. The Perseids seem to have discombobulated the European Space Agency's Olympus satellite in 1993 and may have done the same to Landsat V in 2009. Two Japanese satellites, ADEOS II and the ALOS spacecraft, have lost power amid other meteor showers. And the Jason-I satellite was knocked 11 inches sideways by something in 2002 that boosted the current in its solar power cells for its next three orbits.
As Close and colleagues reported in a Journal of Geophysical Research study last year, spacecraft designers have suspected since 1963 that high-speed meteoroid impacts with spacecraft created little clouds of electrified gas, or "plasma." Exactly how this screws up satellites isn't clear, but the team proposed a mechanism in the paper, a so-called electromagnetic pulse, a sudden oversized outburst of electrical activity.
In doomsday thrillers, nuclear bombs create hefty electromagnetic pulses that overload the nation's power grid. In the study, and in experiments presented this summer by Close's student, Nicolas Lee, at an American Institute of Aeronautics and Astronautics meeting in Honolulu, the engineers looked at whether meteoroids would generate small electromagnetic pulses on satellites they hit.
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