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Date: 1997-07-06 13:15:11 EDT
Author: Unknown

It sounds like a "Star Trek" scenario. A space dust "hurricane" envelops a spacecraft. Electrically charged gas called plasma disrupts electronic systems, disorienting the craft.

For scientists concerned about the fate of the billion worth of satellites orbiting Earth, this isn't science fiction. It's a vision of what might actually happen.

The Leonid meteor storms are returning after a 33-year absence. Blizzards of these meteor particles will arrive with increasing intensity every November. As seen from Earth, they will appear to come from a direction that lies in the constellation Leo, hence the name Leonid. Scientists don't yet know how much of a hazard the storms will be. But they could disrupt some satellite operations.

During a meeting of the American Geophysical Union in Baltimore last month, Peter Brown, a meteor physicist from Canada's University of Western Ontario at London, warned that "this is not just a theoretical possibility." He noted that the European Olympus communications satellite apparently encountered a stray plasma- generating particle in 1993. Olympus spun out of control. Engineers used so much fuel to regain control that they had to retire the satellite.

Meteor storms are a rare, industrial-strength version of the more benign annual meteor showers that entertain sky watchers with "shooting stars." In these showers, meteors flash overhead at rates of a few hundred or less per hour. In the forthcoming Leonid storms, those rates could shoot up a thousandfold.

The Leonids are dust particles thrown off by the periodic comet Tempel-Tuttle. The comet follows a 33-year-path that loops out as far as the orbit of Uranus. It was spotted on its current return course March 10. It will make its closest approach to the Sun next Feb. 22. Earth will pass through the comet's dust tail each November for the next several years.

Slamming into a satellite at speeds several hundred times that of a high powered rifle bullet, tiny meteor particles would vaporize into spacecraft-threatening plasma, according to Dr. Brown. He notes that the likelihood of this happening to any given satellite is low even during what he characterized as an intense "space-dust hurricane."

He adds, however, that given the number of satellites now in orbit, the likelihood of this happening to some member of the satellite fleet during a storm is relatively high.

Brown pointed out that the potential of a meteor storm to cause disruption within the satellite fleet is something safety engineers haven't investigated. Moreover, the lack of relevant data from previous Leonid visitations is a handicap. It's a situation where scientists "don't know if the Leonids will be a problem," Brown said. "But, there is a need to investigate this."

He explained that, given advance knowledge of what to expect, "there are a number of things" satellite operators could do to mitigate the Leonid hazard. These include developing strategies for maneuvering threatened satellites so as to minimize the surface exposed to the incoming dust. Operators could also plan to turn off certain satellite equipment to avoid electrical damage at critical times.

Scientists also don't know what danger, if any, Leonid storms might present to astronauts building the international space station. Boston University meteor physicist Michael Mendillo says that Nov. 17 and 18 of 1998 and '99 "might not be a wise time to put astronauts into space." He adds: "We don't know. But it's something to think about."

Mr. Mendillo urged people to "look up on Nov. 17 and 18." That's when the Leonids should be most active. The most intense storm won't occur until November 1998. But this year's display should be a fairly good show, weather permitting.

Exactly what people may see is something of a scientific puzzle. Michael Kelly, a Cornell University meteor investigator, noted that there is "some evidence that there is a dust blanket around the earth." If meteor particles interact with that blanket, there could be long-lived light shows.

Also, Dr. Kelley said he thinks the meteors might form something akin to aircraft contrails. But meteor observer Peter Jenniskens from the NASA/Ames Research Center in Mountain View, Calif., explained that experience with such storms is so rare, "even scientists ... don't know what they will see and what to expect."