WASHINGTON -- The wreckage of a failed 1996 space project was expected to tumble back into the earth's atmosphere beginning Sunday, but very little of the 535-kilogram element was expected to survive reentry, according to NASA space officials quoted by Reuters.

In Greenbelt, Maryland, a NASA official Saturday dismissed speculation that the falling space junk was connected to multiple reports of fire balls and unusual light phenomena in five cities in southern Germany Saturday evening, German police said.

Residents in Munich, Augsburg, Passau, Rosenheim and Weilheim reported the sightings to police.

The NASA official said the remains of the Hete satellite, launched in a joint U.S.-Argentina project to collect information about gamma radiation, could start reentering the atmosphere as early as 0400 GMT Sunday, or anytime in the following two days.

NASA expected that only four batteries, with a total weight of 15 kilograms, would reach the earth's surface. The rest was expected to be burnt up in reentry.

After the successful 1996 launch of the Hete satellite with a Pegasus rocket, the satellite failed to separate from the third stage of the rocket and has orbited uncontrolled in space since then.