WASHINGTON — Chunks of a 7,000-pound satellite designed by Berkeley astronomers and launched a decade ago to study the heavens will plunge to Earth Wednesday night or before dawn Thursday, NASA flight controllers said Tuesday.

It is highly unlikely that any pieces will fall in a populated area, engineers said. Most of the spacecraft is expected to break apart and burn up as it re-enters the upper atmosphere about 50 miles above Earth's surface.

But as many as nine pieces of debris from the spacecraft, each of stainless steel or titanium and weighing from 4 to 100 pounds, may survive passage through the dense atmosphere and reach the ground, flight controllers said.

Late Tuesday, the satellite was reported to be falling at a rate of about 15 miles a day from its final orbits 125 miles high. It was expected to end its last four or five orbits sometime between 8 Wednesday night and 5 a.m. Thursday, space agency officials said.

The satellite's orbits have been carrying it around the globe on a path as far north as Orlando, Fla., and as far south as Brisbane, Australia, with much of it over the Atlantic and Pacific oceans.

"The probability of the few surviving pieces falling into a populated area and hurting someone is very small," said Ronald E. Mahmot, project manager for space science missions at the Goddard Space Flight Center in Greenbelt, Md. "It is more likely that the small pieces will fall into the ocean or harmlessly to the ground."

Named the Extreme Ultraviolet Explorer, the spacecraft was launched in 1992 with a life expectancy of only three or four years. But it continued transmitting data to Earth-bound astronomers until Jan. 31, 2001.

It carried four instruments with which it surveyed the galaxy for objects radiating their energy at the unexplored far end of the ultraviolet spectrum. The astronomers had expected to detect several dozen such sources, but they ultimately collected images of more than 1,000 — including at least three dozen lying in spiral galaxies far beyond the Milky Way.Led by C. Stuart Bowyer and Roger Malina, the UC Berkeley team designed a unique payload of telescopes and spectrometers aboard the satellite, which during its lifetime in orbit detected a variety of unsuspected phenomena.

Among them were violent outbursts of radiation from dwarf stars, gigantic flares exploding from cool stars, emanations of energy from distant spiral galaxies and — much closer to Earth — the day glow of the planet Venus.

In a major discovery, the Explorer also detected unsuspected clouds of relatively cool gas extending across the cosmos for millions of light-years, permeating entire clusters of distant galaxies — a find that added a major puzzle to the mystery of the so-called missing mass of the universe.

Before the Explorer was launched, astronomers had long believed the interstellar dust and gas filling all galaxies would prove impenetrable to instruments operating at extreme ultraviolet wavelengths. Bowyer and his Berkeley team disagreed and spent more than 15 years researching and designing their satellite's instruments. The Explorer spacecraft proved them right.