Saturday, 24 September 2011

Falling satellite slows down, Earth strike delayed

CAPE CANAVERAL, Fla. (AP) — A 6-ton NASA satellite on a collision course with Earth clung to space Friday, apparently flipping position in its ever-lower orbit and stalling its death plunge.
The old research spacecraft was targeted to crash through the atmosphere sometime Friday night or early Saturday, putting the U.S. back in the potential crosshairs, although most of the satellite should burn up during re-entry.
"It just doesn't want to come down," said Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics.
McDowell said the satellite's delayed demise demonstrates how unreliable predictions can be. That said, "the best guess is that it will still splash in the ocean, just because there's more ocean out there."
Until Friday, increased solar activity was causing the atmosphere to expand and the 35-foot, bus-size satellite to free fall more quickly. But late Friday morning, NASA said the sun was no longer the major factor in the rate of descent and that the satellite's position, shape or both had changed by the time it slipped down to a 100-mile orbit.
"In the last 24 hours, something has happened to the spacecraft," said NASA orbital debris scientist Mark Matney.
NASA cautioned there was now a slim chance any surviving debris would land in the United States. Earlier this week, the space agency said North America would be in the clear.
"It is still too early to predict the time and location of re-entry with any certainty," NASA said in a statement.
The Aerospace Corp., which tracks space debris, estimates the strike will happen sometime between about 9 p.m. and 3 a.m. EDT, which would make a huge difference in where the debris falls. Those late-night, early morning passes show the satellite flying over parts of the United States.
Any surviving wreckage is expected to be limited to a 500-mile swath.
The Upper Atmosphere Research Satellite, or UARS, will be the biggest NASA spacecraft to crash back to Earth, uncontrolled, since the post-Apollo 75-ton Skylab space station and the more than 10-ton Pegasus 2 satellite, both in 1979.
Russia's 135-ton Mir space station slammed through the atmosphere in 2001, but it was a controlled dive into the Pacific.
Some 26 pieces of the UARS satellite — representing 1,200 pounds of heavy metal — are expected to rain down somewhere. The biggest surviving chunk should be no more than 300 pounds.

Earthlings can take comfort in the fact that no one has ever been hurt by falling space junk — to anyone's knowledge — and there has been no serious property damage. NASA put the chances that somebody somewhere on Earth would get hurt at 1-in-3,200. But any one person's odds of being struck were estimated at 1-in-22 trillion, given there are 7 billion people on the planet.
"Keep in mind that we have bits of debris re-entering the atmosphere every single day," Matney said in brief remarks broadcast on NASA TV.
In any case, finders definitely aren't keepers.
Any surviving wreckage belongs to NASA, and it is against the law to keep or sell even the smallest piece. There are no toxic chemicals on board, but sharp edges could be dangerous, so the space agency is warning the public to keep hands off and call police.
The $740 million UARS was launched in 1991 from space shuttle Discovery to study the atmosphere and the ozone layer. At the time, the rules weren't as firm for safe satellite disposal; now a spacecraft must be built to burn up upon re-entry or have a motor to propel it into a much higher, long-term orbit.
NASA shut UARS down in 2005 after lowering its orbit to hurry its end. A potential satellite-retrieval mission was ruled out following the 2003 shuttle Columbia disaster, and NASA did not want the satellite hanging around orbit posing a debris hazard.
Space junk is a growing problem in low-Earth orbit. More than 20,000 pieces of debris, at least 4 inches in diameter, are being tracked on a daily basis. These objects pose a serious threat to the International Space Station.
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Online:
Satellite updates: www.nasa.gov/uars
Aerospace Corp: http://reentrynews.aero.org/1991063b.html

NASA's Upper Atmosphere Research Satellite, or UARS, is expected to re-enter Earth's atmosphere late Sept. 23 or early Sept. 24 Eastern Daylight Time, almost six years after the end of a productive scientific life. Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere.

The risk to public safety or property is extremely small, and safety is NASA's top priority. Since the beginning of the Space Age in the late-1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. Nor is there a record of significant property damage resulting from a satellite re-entry.

It is still too early to say exactly when UARS will re-enter and what geographic area may be affected, but NASA is watching the satellite closely and will keep you informed. Visit this page for updates on the satellite's orbital track and predicted re-entry date.

› Re-Entry and Risk Assessment (498 KB PDF)
› Frequently Asked Questions: Orbital Debris

The updates posted here come from the Joint Space Operations Center of U.S. Strategic Command at Vandenberg Air Force Base, Calif., which works around the clock detecting, identifying and tracking all man-made objects in Earth orbit, including space junk.

The actual time of re-entry is difficult to predict because it depends on solar flux and the spacecraft's orientation as its orbit decays. As re-entry draws closer, predictions on the date will become more reliable.

Because the satellite's orbit is inclined 57 degrees to the equator, any surviving components of UARS will land within a zone between 57 degrees north latitude and 57 degrees south latitude. It is impossible to pinpoint just where in that zone the debris will land, but NASA estimates the debris footprint will be about 500 miles long.

If you find something you think may be a piece of UARS, do not touch it. Contact a local law enforcement official for assistance.