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SKY & TELESCOPE'S NEWS BULLETIN - JULY 21, 2000
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JAPANESE X-RAY SATELLITE IN TROUBLE

Last week's spectacular solar storms claimed an unexpected victim, as Japanese space officials now report that their workhorse X-ray observatory is spinning out of control as it circles the Earth. Named ASCA (Advanced Satellite for Cosmology and Astrophysics), the satellite lost attitude control and put itself into a state of electronic hybernation sometime on July 15th or 16th. According to mission spokesperson Fumiaki Nagese (Institute of Space and Astronautical Science), the satellite's troubles began when the intense solar bombardment heated Earth's upper atmosphere and caused it to balloon into space. ASCA's orbit has a perigee (low point) of 440 kilometers, and the increased aerodynamic drag twisted the spacecraft and briefly overwhelmed its ability to maintain a stable orientation. Once the uncontrolled spin began, ASCA's solar-cell panels could not supply enough power to maintain operation, and an automatic emergency shutdown soon followed. Right now, the onboard batteries are cold and dead, so Japanese controllers are concentrating their efforts on getting the batteries warm enough to recharge them.

Nicholas White, who head the ASCA guest-investigator program at NASA's Goddard Space Flight Center, says the situation is critical. "The satellite was to reenter next year," he explains, "so in this tail end of the mission we've been making long-duration observations of special targets." Other X-ray missions like the Chandra observatory and Europe's XMM-Newton have more sensitive detectors, but they are unable to study a cosmic source for days or weeks at a time. "We had hoped to get 6 to 9 more months of observations," White explains, but the intense solar activity will dramatically shorten that timeline -- assuming the spacecraft can be restored to operation.

The fourth in a series of highly successful Japanese X-ray observatories, ASCA has already exceeded its planned 5-year lifetime. Launched on February 20, 1993, the cylindrical spacecraft is 4.7 meters long and weighs 420 kilograms. Its X-ray telescopes have studied supernova remnants, neutron stars, active galactic nuclei, and other high-energy phenomena. Japanese astrophysicists had hoped to loft its successor, Astro E, earlier this year. But on February 10th the solid-fuel Mu V launch rocket veered off course, causing the satellite to plunge into the atmosphere before it ever reached orbit.

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