Nov 16, 1998

NASA spacecraft take cover from the Leonids

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Updated: June 18th, 2018


But the Hubble Space Telescope won't stop observing....
November 16, 1998: When the Leonid meteor shower erupts tomorrow, sky-watchers on Earth have little to fear. Leonid meteoriods, cast-off debris from comet Tempel-Tuttle, are smaller than a grain of sand and much less dense. They are so insubstantial that they disintegrate almost immediately when they hit Earth's atmosphere. The result is a shooting star.

Right: The Advanced Composition Explorer (ACE), a sun-studying satellite shown here in the laboratory, is now in orbit between the Sun and Earth at the L-1 point (a point in space where the gravitational pulls of Earth and the sun are balanced). Since the center of the Leonid stream is closer to the L-1 orbit than to Earth, ACE will see an even more intense storm than Earth-orbiting satellites.

Earth-orbiting satellites might have more to worry about. Tiny meteoroids can poke holes in solar panels, pit surfaces, and short out electronics. The hazard from the Leonids is greater than the danger from most meteor showers for two reasons. The debris stream from comet Tempel-Tuttle is particularly dense, and the Leonid meteoroids travel at very high velocities, nearly 45 miles per second compared to 12 miles per second for average meteoroids. Nevertheless, NASA and Department of Defense experts do not classify the risk to most satellites as serious. With proper precautions, such as pointing vulnerable systems away from the incoming meteoroids, most damage can be avoided.


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The spacecraft closest to the predicted position of the Leonids meteor stream is NASA's Advanced Composition Explorer (ACE), a sun-studying satellite managed from the Goddard Space Flight Center (GSFC). GSFC technicians plan to tilt ACE by 20 degrees and power down sensitive instruments to avoid electrical discharges if a meteoroid should hit. Goddard controllers will take similar steps to protect 22 other GSFC-managed spacecraft including SOHO and the Hubble Space Telescope. Short circuits are one of the greatest dangers to satellites. Meteoroids that hit spacecraft can disintegrate, creating a cloud of electrically charged plasma. Under the right conditions, this plasma cloud can set off a chain reaction causing a massive short circuit. The loss of the European Space Agency's Olympus communications satellite in 1993 was attributed to a strike from a Perseid meteoroid, and the resulting plasma discharge that zapped the spacecraft's delicate electronics.
Hubble weathers the storm
Like many other spacecraft, he Hubble Space Telescope (HST) will point away from the Leonids to avoid damage, but it won't stop observing. For a 10-hour period around the peak of the storm the telescope will be oriented with its aft bulkhead facing into the direction of the meteoroid stream. Hubble's solar panels will lay flat, or parallel to the meteoroid flow.

Hubble will be aimed at a quasar, the bright core of an active galaxy, approximately 10 billion light-years away. The object of study is not the quasar itself but the surrounding galaxies, protogalaxies and primordial hydrogen clouds between us and the quasar.



A 900 micron impact crater found on the HST WF/PC camera radiator in 1994. more info..

Hubble will also be used, indirectly, to study the meteor stream. Each time a meteoroid hits, the telescope will wobble slightly. Scientists plan to record the series of bumps and wiggles as the HST stares at the quasar to learn about the distribution of meteoroid masses and velocities.

The HST has had an encounter with the Leonids once before. This image shows a 900 micron impact crater in the radiator of Hubble's Wide Field and Planetary Camera. It was discovered in 1994 after a Leonid meteor shower in 1993. The camera was not damaged by the impact.

Watch Your Favorite Satellite Weather the Storm

Experts are predicting that the Leonid meteor storm will be most intense at 1900 UT November 17th over eastern Asia. That's the part of Earth that will face into the meteor stream as we pass through the the orbital plane of comet Tempel-Tuttle. Thanks to NASA Liftoff you can monitor your favorite satellites during the storm using a Java applet called JTrack.

Right: A screen shot from JTrack 3D showing the Earth facing into the Leonid meteor stream.

If instead of surfing the web you happen to be outside watching the Leonids on November 17th, NASA would like to hear from you.


meteor flash!
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Author: Tony Phillips
Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Responsible NASA official: John M. Horack