The Nov. 17 Leonids meteor storm will present an elevated, though not serious, threat to spacecraft in the vicinity of the Earth for about half a day, according to NASA and Department of Defense experts, who have been studying the potential risk.
The annual Leonids are expected to have an intensity not seen in more than three decades, but will not reach the levels of the 1966 meteor storm. Even so, the event could provide a spectacular "light show" for some parts of the world, particularly East Asia and the western Pacific region.
The Leonid meteors originate from the debris released from the Comet Tempel-Tuttle, which completes an orbit around the Sun every 33 years, leaving a trail of debris such as dust and other tiny particles in its path. Each November the Earth crosses this debris trail and the result is the Leonids meteor storm -- "shooting stars" streaking through Earth's upper atmosphere, sometimes at rates of dozens per hour.
When this passage occurs within a few years of the comet's closest approach to the Sun, called perihelion, conditions for encountering larger-than-normal numbers of meteors - a meteor storm -- may exist. Comet Tempel-Tuttle passed perihelion early in 1998, setting the stage for a probable meteor storm in 1998 and perhaps again in 1999, as jointly reported by NASA's Johnson Space Center Orbital Debris Program Office in Houston and the Air Force Deputy Chief of Staff for Air and Space Operations.
Leonids travel at about 45 miles per second compared to about 12 miles per second for typical meteors. This means the risk of physical or electrical damage to near-Earth spacecraft will be greater than normal.
As a precaution, the Space Shuttle will not be in orbit during the Leonids storm, and the launch of the first element of the International Space Station will not take place until after the storm subsides. The Hubble Space Telescope will turn so that the opening to its mirrors and instruments is pointed away from the approaching meteors during the storm.
Other measures being taken by U.S. government satellite operators to reduce spacecraft risk from the Leonids include minimizing the spacecraft cross-section (including solar arrays) to the meteors; reorienting sensitive spacecraft surfaces away from the direction of the Leonids; powering down non-critical systems; developing contingency and recovery plans to counter the likely effects of electrical discharge; minimizing communications to the spacecraft during the threat period; and augmenting crews at spacecraft operations centers during the period of intense Leonids activity.
NASA and the Air Force will conduct studies of the 1998 Leonid storm and will use these data in forecasting the potential 1999 storm.
Additional information on the expected Leonids meteor storm can be found on the worldwide web at:
Simple software to calculate the probability of impacts by Leonid meteors on spacecraft in Earth orbit can be found on the worldwide web at:
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