3.5-ton satellite falling back to Earth

Artist's depiction of the Extreme Ultraviolet Explorer

By Richard Stenger
CNN Sci-Tech

(CNN) -- A retired satellite with no onboard steering system should re-enter Earth's atmosphere within hours and leave a trail of debris in its wake, NASA cautioned Wednesday.

The defunct space telescope will tumble into the atmosphere Wednesday at about 11 p.m. ET, NASA scientists predicted.

Most of the doomed satellite will burn up in the atmosphere, but a handful of metal chunks could survive, ranging from four pounds to 100 pounds (1.8 kg to 45 kg), NASA space flight engineers said.

Fragments of the 3.5-ton orbiter could scatter along a trail extending up to 625 miles (1,000 km) long, somewhere in the middle latitudes on either side of the equator, according to NASA.

Predictions of when and where the Extreme Ultraviolet Explorer (EUVE) will drop from orbit remain sketchy because it will fall in an uncontrolled manner. As of Wednesday evening, EUVE was about 100 miles (160 km) above Earth, but is losing about 15.5 miles (25 km) of altitude each day.

VIDEO Where EUVE might fall and what it looks like in space  (MPEG / 1M) Courtesy: Analytical Graphics, Inc   DANGER ZONE Target area extends along either side of Equator.     Mission at a glance Satellite: Extreme Ultraviolet Energy Explorer Weight: 7,000 pounds (3,200 kilograms) Lifetime: Launched in 1992 from Cape Canaveral, EUVE conducted observations until 2000 Instruments: Three scanning telescopes and a deep sky survey spectrometer Highlights: Offered new insights into comets, white dwarfs and the atmospheres of stars

It is expected to begin breaking up when it descends to within 50 miles (80 km), take four or five final 90-minute laps around Earth and then re-enter the atmosphere.

The re-entry window extends along the middle latitudes, from as far north as Orlando, Florida, and as far south as Brisbane, Australia.

The danger area covers parts of Florida, South and Central America, the Caribbean, much of Africa, South Asia and Indonesia. Major cities in the red zone include Miami, Florida; Mexico City, Mexico; and Bangkok, Thailand.

Trying to peg the bulls-eye on the planet has frustrated NASA. The space agency suggested early Wednesday that EUVE chunks would fall in the South Pacific. Hours later, it speculated that they would land east of South America.

"Based on the latest … predictions and the predicted debris field it is believed the heavier objects will fall harmlessly into the Atlantic Ocean," reported the Web site of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The U.S. Space Command in Colorado Springs, Colorado, which tracks almost 9,000 objects in orbit, declined to conjecture on where it would land.

"Quite frankly, they're predictions and there are so many variables we can't control," said Maj. Barry Venable, U.S. Space Command spokesman.

Launched in 1992, EUVE was the first space observatory dedicated to studying extreme ultraviolet light. The $215 million satellite lasted much longer than its intended three years, studying celestial objects first for NASA and later the University of California, Berkeley, until it ceased operations one year ago.

In contrast to EUVE's uncontrolled descent, NASA in 2000 safely guided the Compton Gamma Ray Observatory into the ocean because the 17-ton craft had an onboard steering system.

Likewise, in 2001, Russian ground controllers relied on similar means to coax the 135-ton Mir space station, the heaviest object in Earth orbit besides the moon, into its watery grave without a hitch.

The most massive NASA spacecraft to re-enter the atmosphere in an uncontrolled descent was the 78-ton Skylab space station, which in 1979 scattered debris in the Indian Ocean and an isolated stretch of Western Australia.

Orbital debris has never been known to have injured a human, but legend has it a chunk of Skylab brought an untimely end to an Australian cow.