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As Meteors Approach, Steps Taken to Protect Orbiting UNH Sensor
DURHAM, N.H. -- The upcoming Leonid meteor shower may be an entertaining light show for sky-watchers, but it will be a definite hazard to orbiting sensors, including a University of New Hampshire instrument.

Eberhard Moebius of the UNH Institute for the Study of Earth, Oceans and Space, says even tiny dust particles, not considered dangerous to most satellites, could irreparably damage the UNH-developed Solar Energetic Particle Ionic Charge Analyzer (SEPICA) now orbiting between the Earth and Sun aboard NASA's Advanced Composition Explorer, or ACE.

That's why he and other scientists are planning to tilt ACE to move the detectors out of harm's way, or so they hope. Its axis now pointing toward the sun, ACE will be turned 20 degrees by technicians at NASA's Goddard Space Flight Center one day before the Nov. 17 Leonid meteor shower.

(The Leonid storm this year peaks at 2:43 p.m. on Nov. 17, so the United States will miss the highlight, although remnants might make interesting viewing after midnight).

SEPICA examines the composition of accelerated particles from solar flares and is designed to measure the temperature at their origin. It uses a detector similar to a Geiger counter, in which gas is trapped within very thin window-like apertures. For these thin windows, even the smallest dust grains trailing Comet 55P/Tempel/Tuttle are like bullets.

"As one of my colleagues said, for the ACE satellite, it takes the one rock with our name on it," says Moebius with a wan smile. But it's not large chunks of meteoroid that have Moebius and colleagues concerned. The smaller, more numerous particles, even dust, pose a greater hazard, since "the smaller in size you go, the more you have," Moebius points out.

In addition, ACE will be closer than any other spacecraft to the Leonid meteor stream, a dubious honor, Moebius points out.

The Leonid meteor shower is seen every November, but it rises to storm conditions every 33 years. It is caused by the countless fragments and particles trailing the Comet 55P/Tempel/Tuttle as it comes close to the Earth this year.

Yes, they put on a spectacular light show, even Moebius admits. Back in 1966, some sky-watchers counted more than 100,000 meteors an hour.

SEPICA "could take a few thousand hits if we don't do anything," Moebius explains. A project team met in mid-October and decided to tilt the axis. "And, with that, we'll ride out the storm."

Plans also call for technicians to shut down SEPICA's high voltage because a stray impact could cause electric charges. "So, there may be a major solar flare happening at that time, and we'll miss it," says Moebius, who saw some of his work destroyed in the 1996 explosion of the CLUSTER mission. "But I think we are willing to pay that price."

He adds that SEPICA has already uncovered significant information concerning the source of solar flare particles and Moebius hopes to continue to receive data, especially since solar flare activity is expected to increase in upcoming months.

By Carmelle Druchniak
UNH News Bureau