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Chandra Prepares for the Leonid Meteor Shower

November 15, 2001 ::

Illustration of the Chandra X-ray Observatory

While skywatchers eagerly anticipate this weekend's Leonid meteor shower, members of the Chandra X-ray Center team will be busy in their own right. However, instead of gazing into the night sky for "shooting stars," they will be monitoring and maneuvering Chandra to protect NASA's premier X-ray facility from harm's way.

Roger Brissenden, Manager of the CXC

"The chances of Chandra getting hit by one of the meteors in this shower is really very low," said Roger Brissenden, manager of Chandra's Operation Control Center (OCC) which is responsible for operating and communicating with the satellite. "Regardless, we will still take every precaution to make sure that Chandra is safe." Despite what their name suggests, "shooting stars" are not stars at all, but, in fact, they are meteors. Meteors are produced when bits of cometary or asteroidal debris in space, usually between the size of a sand grain and a pebble, enter the Earth's atmosphere and burn up, creating a brief, usually white, streak of light.

This schematic shows Chandra's orbit in relation to the Earth and the Sun. The light green portion indicates when the Chandra spacecraft will be in the predicted path of the meteors. [Click to enlarge]

Chandra's orbit in comparison to the predicted path of the 2001 meteor shower & the location of previous Leonids. [Click to enlarge]

Labeled sketch of Chandra [Click for details]

So what causes a meteor shower? Although some meteor showers surprise scientists when the Earth passes through previously undetected space debris, the best known annual meteor showers occur on approximately the same date every year, when the Earth's orbit takes it through an area of space filled with rocks and dust. The Leonid meteor shower -- so-called because the meteors appear to come from the direction of the constellation Leo -- is due to a trail of debris left by Comet Tempel-Tuttle on its 33-year orbit of the Sun. When the Earth passes through this stream of rocks, dust grains, and gas every November, observers on Earth can be treated to a wonderful show.

Because the stream from Tempel-Tuttle hits the Earth almost head-on, the Leonids are among the fastest meteors around -- entering the Earth's atmosphere at 44 miles per second. Every so often, the Earth passes through an especially dense clump of dust from Tempel-Tuttle, and a truly spectacular meteor storm occurs, such as the Leonid storm in 1966 that produced 150,000 meteors per hour. Just such an intense show has been predicted by several models to occur this year.

This potential increase in the number of meteors has pushed the Chandra team to be extra cautious during this year's Leonid shower. Since Chandra must travel through this debris field, controllers at the OCC will take several steps to ensure that Chandra avoids these bits of rock and dust.

"We have done many things to safeguard Chandra against this year's Leonid meteor shower," said Dan Shropshire who leads Chandra's Flight Operations Engineering Team. "Chandra will be pointed in the exact opposite direction as the incoming meteors, for example. We have made sure that the solar arrays are angled to protect the sensitive back of the arrays and minimize the surface area presented to the meteor direction."

During the Leonid meteor shower, researchers at the Marshall Space Flight Center in Huntsville, Alabama will use special cameras to scan the skies and report meteor activity around the clock Nov. 17 and 18. From six key points on the globe, they will record and transmit their observations to Marshall's Leonid Environment Operations Center, a data clearinghouse that will provide meteor updates in near real-time through http://www.SpaceWeather.com -- a Web site sponsored by science@nasa.gov.

At the OCC, Shropshire and his colleagues in Cambridge, Mass., will be prepared to send additional commands via the Deep Space Network if necessary. The spacecraft will not go into its official "safe" mode, where instruments are locked in and powered down, but certain critical instruments will be moved to a more protected area of the spacecraft.

This plot shows one prediction of the Leonid meteor shower's intensity versus time. This model predicts the Leonids will peak around 20:00 Universal Time on Nov. 18. [Click to enlarge]

Still, despite all of the possible hazards, Chandra officials don't anticipate any problems to occur with the spacecraft. "We've gone through a number of other meteor showers before with Chandra and we've done all our homework for this event," said Brissenden. "Still, I think we'll all breathe a little sigh of relief when this weekend is over."

Where's Chandra now? See a representation of the current position of Chandra in relation to the surface of the Earth.

Read Part II: Planning Pays Off - Chandra Sails Through the Leonids Unharmed

2001 Leonid briefing charts courtesy of Dan Shropshire, Head, Chandra FOT Engineering

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