Meteor storm may scour satellites Leonids: Spacecraft in Earth orbit face possible hazard when planet passes through cosmic barrage of dust, rocks.

October 13, 1998|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Stargazers can't wait for it. Professional astronomers are flying to the Far East for a better look. But satellite operators are biting their nails.

They're all gearing up for this year's annual Leonid meteor shower Nov. 17, and it could be one to remember.

This year's Leonids could produce their most intense and beautiful barrage in 32 years -- hundreds or even thousands of meteors per hour over Eastern Asia and the Western Pacific as Earth plows through the trail of Comet Tempel-Tuttle. There might even be some delightful leftovers for the rest of us.

But in space, hundreds of scientific, military and communications satellites will come under fire from high-speed particles and pebbles ejected by the comet.

The threat is rated as small but important, and satellite operators are not brushing it off. Too much depends on their satellites.

The failure of PanAmSat's Galaxy IV satellite in May was traced to a faulty relay switch, not a meteor. But it interrupted radio and TV broadcasts, pager service and commercial data streams -- some for days --and millions of people were affected.

Like a sailor in a stinging gale, the Hubble Space Telescope will turn its back to the storm. The maneuver will minimize the telescope's profile and protect its vulnerable mirror.

"The back end has a little thicker construction," said project scientist Larry Petro, of the Space Telescope Science Institute in Baltimore. "Even if we were to get pinged by a meteoroid, it would be a little more resistant. We want to minimize the chance that anything might happen."

NASA scheduled the space shuttle Discovery, carrying Sen. John Glenn, to be safely back on Earth Nov. 7, well before the Leonid "storm." Planners also put off until Dec. 3 the launch of the shuttle Endeavour.

"Space flight is dangerous," said Walter Marker, senior NASA scientist with the Leonid Project in Houston. "You do what you can to minimize the risk."

At the Goddard Space Flight Center in Greenbelt, scientists and engineers responsible for a fleet of scientific satellites will turn solar panels "edge-on" to the meteors. Vulnerable instruments will be turned away, and electrical systems will be powered down.

"It would take billions of dollars and years to replace them, which is definitely not in NASA's plans. So it's very important that we do everything that reasonably can be done to protect them," said Bill Worrall, Goddard's manager for 11 satellites.

The Leonid meteor shower occurs every November as the Earth passes through the path that Tempel-Tuttle follows in its 33-year orbit around the sun. The Leonids were so named because the meteors appear to radiate from the stars of the constellation Leo.

Normally, Leonid observers spot 10 to 15 meteors an hour -- up from 1 or 2 an hour on an ordinary night.

But every 32 or 33 years, after Tempel-Tuttle crosses Earth's path, the planet encounters an especially dense swarm of debris in the comet's wake. The shower becomes a storm.

The biggest Leonid storms in recent history occurred in 1799, 1833 and 1966. In 1966, observers in the central and western states counted thousands of meteors in a 20-minute period. The actual "star-fall" may have been nearly 150,000 an hour.

Leonid storms have also fizzled, as they did in 1933.

Tempel-Tuttle passed this way again in January. The Earth will plow through its trail Nov. 17, and again next year on Nov. 18.

The storm's peak is expected during daylight hours in the United States. People in East Asia and the Western Pacific, where it will be night, will likely have the best view. But U.S. observers may see extra meteors before dawn and after dark on the 17th.

At an international Leonid conference in April, scientists forecast the 1998 Leonid storm would be less intense than in 1966. Rates of 200 to 5,000 meteors an hour are expected.

Most Leonid meteors are tiny grains of rock and dust released as the comet's gritty ices are vaporized by solar heating. They become visible as "shooting stars" when they burn up in Earth's atmosphere. A few may be big enough to produce fireballs with luminous trails, but they pose no danger on the ground.

Scientists equipped with radar, telescopes and low-light video systems will fan out to study them for clues to the composition of comets. Meteor counts also provide data for the assembly of TC three-dimensional maps of a comet's trail that may help predict the intensity of future showers.

Satellites in orbit, however, face real hazards.

"It's the velocity that kills you," said NASA spokesman Phil West. The Leonids are nearly four times speedier than typical meteors. They will encounter the Earth at more than 155,000 miles per hour -- more than 200 times the speed of sound.

At that speed, a grain of sand packs the punch of a .22 caliber bullet. The Giotto spacecraft, en route to Halley's Comet in 1986, was struck and sent spinning, temporarily losing radio contact with Earth.

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