Image: UARS breakup
AGI
An artist's conception shows NASA's Upper Atmosphere Research Satellite breaking up and burning up during atmospheric re-entry.
msnbc.com staff and news service reports
updated 9/24/2011 4:18:48 AM ET 2011-09-24T08:18:48

After days of worldwide suspense, NASA declared Saturday that its six-ton Upper Atmosphere Research Satellite came apart during a fiery fall over the Pacific Ocean.

The space agency said the decommissioned spacecraft fell back to Earth between 11:23 p.m. ET Friday and 1:09 a.m. ET Saturday. NASA spokesman Bob Jacobs said the Joint Space Operations Center, headquartered at California's Vandenberg Air Force Base, reported that the satellite entered the atmosphere over the Pacific.

"Precise time and locale aren't yet known," he added in a Twitter update.

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Hours after the satellite's demise, it was still occasionally hard to separate the truth from the fakery. There were multiple reports of fireballs and bright debris being sighted over Canada, but one of those reports turned out to be a "War of the Worlds" prank — which led Jacobs to complain on Twitter about "a lot of hoax data and false info going viral."

Determining the precise time and place of impact was difficult because of the uncertainties surrounding the satellite's altitude toward the end.

Any surviving wreckage was expected to be sparsely distributed across a 500-mile-long (800-kilometer-long) ellipse. "The risk to public safety was very remote," NASA said in a statement.

Delayed demise
The projected time of re-entry was pushed later and later during the satellite's final hours. "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.

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 (160-kilometer) orbit.

"In the last 24 hours, something has happened to the spacecraft," said NASA orbital debris scientist Mark Matney.

Uncontrolled re-entry
The Upper Atmosphere Research Satellite, or UARS, was 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 that was a controlled dive into the Pacific.

NASA expected about two dozen pieces of the UARS satellite — representing 1,200 pounds of heavy metal — to survive re-entry. The biggest surviving chunk should have been around 300 pounds (150 kilograms).

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 that 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. If someone finds a piece of it, NASA has the right to ask for its return. There are no toxic chemicals on board, but sharp edges could be dangerous, so the space agency warned the public to keep hands off and call the authorities.

Minimizing space junk
The $740 million UARS was launched in 1991 from the 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.

This report includes information from The Associated Press and msnbc.com.

© 2013 msnbc.com

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
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  5. Accidental art

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  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
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    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
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    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
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    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
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    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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