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Errant satellite maps the sky.

ASTRONOMY

Errant satellite maps the sky

The most accurate map of the heavens is being made by the errant Hipparcos satellite, which was launched in 1989.

Although the European Space Agency's $375 million satellite is in a highly irregular orbit, it still is expected to meet its goals of mapping the positions of up to 120,000 stars to an accuracy of 0.002 arc-sec.

The best star map from Earth observations gives the position of only a couple thousand stars and an accuracy at best of 0.02 arc-sec. Hipparcos will provide a whole sky survey.

Hipparcos became trapped in a highly irregular orbit when a rocket motor failed after it was brought up 300 mi from Earth by an Ariane rocket. Hipparcos's orbit stretches from 300 to 22,500 mi (480 to 36,200 km) from Earth.

The satellite dips into Earth's radiation belt every five hours. It originally was estimated that Hipparcos would last only six months, instead of its designed lifetime of 2.5 years.

ESA officials had feared that charged particles in the belt would destroy the satellite's solar panels, rendering it useless. A drastic voltage decrease initially was observed, says Floor van Leeuwen, a project manager at the Royal Greenwich Observatory, Cambridge, England.

But a reassessment of the panels' condition indicates that the plucky satellite could operate up to four more years, giving astronomers enough time to map 120,000 stars. Van Leeuwen says that while the project will be stretched out to accommodate working with Hipparcos's irregular orbit, team members are upbeat about attaining all of their goals.

"A year ago, we were all gloomy," says van Leeuwen. "Now, we are working as if nothing at all happened."

PHOTO : Hipparcos might be in an irregular orbit, but it still is expected to provide the most accurate star map ever, say European scientists working on the project.

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Title Annotation:R&D News of Science and Technology; Astronomy
Publication:R & D
Article Type:column
Date:Dec 1, 1990
Words:313
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