Extreme solar activity that blasted Earth last weekend sent a Japanese satellite out of control, threatening to prematurely end the orbiting X-ray telescopes study of black holes, dark matter and evolution of the universe.

Japans Institute of Space and Astronautical Science (ISAS) made no mention of the problem Friday on its internet website. But a Thursday July 20 message from Japanese official Fumiaki Nagase was posted on a NASA website for U.S. astronomers who use the satellite.

Nagese said the Advanced Satellite for Cosmology and Astrophysics (ASCA) went into a hibernation-like "safe hold" between 3:04 p.m. Eastern Daylight Time (19:04 GMT) July 15 and 7:43 a.m. EDT (11:43 GMT) July 16.

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That period began little more than four hours after the start of a geomagnetic storm that reached extreme levels and was the worst since 1989. A major solar flare on July 14 and a related mass ejection of electrified gas from the sun triggered the geomagnetic storm and an associated proton radiation storm.

Nagese called ASCAs situation "critical" and blamed high solar activity for expanding Earths atmosphere to increase atmospheric drag on ASCA, which has an orbital low point of only 273 miles (440 kilometers). The increased drag applied a torque that sent the satellite into a spin.

"We lost completely the control of ASCA attitude, and ASCA is under the most strict power-save mode, including power-down of all scientific instruments," he said.

Once in safe hold, the satellites solar panels "unfortunately rather departed from the direction towards the sun," allowing power to run down to critical levels about 2:10 p.m. EDT (18:10 GMT) July 16, he added.

Regular observations have been impossible since July 15, and ISAS engineers and scientists "have been working on recovery operations to return ASCA from this emergent state," Nagase said.

ASCA, formerly named Astro D, was launched February 20, 1993, on a Japanese M 3-S launch vehicle. The United States provided part of the science payload.

"The main objectives for the ASCA mission include the search for black holes, evolution of the universe and the distribution of dark matter," the Japanese space agency said.

The satellite was supposed to work for only five years, and astronomers had hoped to continue observations until it reentered Earths atmosphere next year.

ASCA is less sensitive than other X-ray telescopes, such as the Chandra observatory, but the sensitive telescopes cannot make observations lasting for two or three weeks, as ASCA commonly did.