NASA's decommissioned 6.3-ton
Upper Atmosphere Research Satellite, out of gas and out of control after two decades in space, plunged back into the atmosphere early Saturday, heating up, breaking apart, and presumably showering chunks of debris along a 500-mile-long Pacific Ocean impact zone.
Maybe.
U.S. Strategic Command radar tracking indicated re-entry would occur around 12:16 a.m. EDT (
GMT-4) Saturday as the satellite was descending across the Pacific Ocean on a southwest-to-northeast trajectory approaching Canada's west coast. If re-entry occurred on or before the predicted time, any wreckage that survived atmospheric heating almost certainly fell into the Pacific Ocean.
NASA's derelict Upper Atmosphere Research Satellite fell to Earth Saturday, presumably into the Pacific Ocean west of Canada. But it's not yet a sure thing.
"Because we don't know where the re-entry point actually was, we don't know where the debris field might be," said
Nicholas Johnson, chief orbital debris scientist at NASA's
Johnson Space Center.
"If the re-entry point was at the (predicted time) of 04:16 GMT, then all that debris wound up in the Pacific Ocean. If the re-entry point occurred earlier than that, practically the entire pass before 04:16...is over water. So the only way debris could have probably reached land would be if the re-entry occurred after 04:16."
Johnson said amateur satellite watchers in the U.S. northwest and the Canadian southwest were "looking to observe UARS as it came over. Every one of those attempts came up negative. That would suggest that the re-entry did, in fact, occur before it reached the North American coast, which, again, would mean most of this debris fell into the Pacific."
But it's not yet certain and it's equally possible a delayed re-entry resulted in debris falling somewhere in northern Canada or elsewhere along the trajectory.
"We may never know," Johnson told reporters in an afternoon teleconference.
The centerpiece of a $750 million mission, the Upper Atmosphere Research satellite was launched from the shuttle Discovery at 12:23 a.m. EDT (GMT-4) on Sept. 15, 1991. The solar-powered satellite studied a wide variety of atmospheric phenomena, including the depletion of
Earth's ozone layer 15 to 30 miles up.
The long-lived satellite was decommissioned in 2005, and one side of its orbit was lowered using the last of its fuel to hasten re-entry and minimize the chances of orbital collisions that could produce even more orbital debris. No more fuel was available for maneuvering and the satellite's re-entry was "uncontrolled."
As with all satellites in
low-Earth orbit, UARS was a victim of atmospheric drag, the slow but steady reduction in velocity, and thus altitude, caused by flying through the tenuous extreme upper atmosphere at some five miles per second.
UARS' final trajectory as it neared the discernible atmosphere proved difficult to predict. The descent slowed somewhat Friday, presumably because the spacecraft's orientation changed. As the day wore on, the predicted impact time slipped from Friday afternoon to early Saturday.
Johnson said falling satellites typically begin breaking up at an altitude of around 50 miles. In the case of UARS, computer analysis indicated about 26 pieces of debris would survive to reach the surface, spread out along a 500-mile-long down-range footprint. Johnson said the heel of the footprint, the area where the lightest debris might fall, is typically 300 miles or so beyond the breakup point.
But so far, "we've got no reports of anyone seeing anything that we believe are credible," Johnson said.
Johnson told reporters last week he expected most of the satellite to burn up as it slammed into the dense lower atmosphere at more than 17,000 mph. But computer software used to analyze possible re-entry outcomes predicted 26 pieces of debris would survive to impact the surface, the largest weighing some 330 pounds. Impact velocities were expected to range from 30 mph to 240 mph.
"We looked at those 26 pieces and how big they are, and we've looked at the fact they can hit anywhere in the world between 57 north and 57 south, and we looked at what the population density of the world is," he said. "Numerically, it comes out to a chance of 1 in 3,200 that one person anywhere in the world might be struck by a piece of debris. Those are obviously very, very low odds that anybody's going to be impacted by this debris."
For comparison, some 42.5 tons of wreckage from the shuttle Columbia hit the ground in a footprint stretching from central Texas to Louisiana when the orbiter broke apart during re-entry in 2003. No one on the ground was injured and no significant property damage was reported.
Lifeless satellite falls back to Earth
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Junk left from colliding satellites floats through space in this computer-generated image. NASA confirmed that two communication satellites from the United States and Russia collided 800 kilometers above northern Siberia on Sept 10. [Provided to China Daily] |
NASA assures public that there is little chance of getting hit by debrisWASHINGTON - Fragments from an old 6-ton NASA satellite hurtled toward Earth on Friday, while the exact site of the crash-landing remained a mystery into the final hours.
The US space agency has stressed that the risk is "extremely small" that any of the 26 chunks that are expected to survive the fiery re-entry into
Earth's atmosphere will hit one of the planet's seven billion people a one in 3,200 chance.
"Re-entry is possible sometime during the afternoon or early evening of Sept 23,
Eastern Daylight Time," NASA said on its website on Thursday night.
That would be early morning Saturday
Beijing time.
"It is still too early to predict the time and location of re-entry with any more certainty, but predictions will become more refined in the next 24 hours."
The influence of solar flares and the tumbling motion of the satellite make narrowing down the landing a particularly difficult task, experts said as the Internet lit up with rumors of where and when it would fall.
The US Department of Defense and NASA were busy tracking the debris and keeping all federal disaster agencies informed, a NASA spokeswoman said.
The Federal Aviation Administration issued a notice on Thursday to pilots and flight crews of the potential hazard and urged them to "report any observed falling space debris to the appropriate (air traffic control) facility and include position, altitude, time and direction of debris observed," CNN said.
The satellite was launched in 1991 and was designed to provide data for better understanding Earth's upper atmosphere and the effects of natural and human interactions on the atmosphere. The satellite was deactivated in 2005 as it ran out of fuel and was left orbiting Earth.
Orbital debris experts say
space junk of this size from broken-down satellites and spent rockets tends to fall back to Earth about once a year, though this is the biggest NASA satellite to fall in three decades.
NASA's Skylab crashed into western Australia in 1979.
The surviving chunks of the tour-bus sized satellite will include titanium fuel tanks, beryllium housing and stainless steel batteries and wheel rims. The parts may weigh as little as one kg or as much as 158 kg, NASA said.
Orbital debris scientists say the pieces will fall somewhere between 57 north latitude and 57 south latitude, which covers most of the populated world.
The debris field is expected to span 800 square kilometers.
Pang Zhihao, a researcher from the Chinese Research
Institute of Space Technology, told Xinhua that the crash could have been avoided had the satellite been put into a higher orbit, or manipulated to drop in the South Pacific when it had abundant fuel.
Pang said most spacecraft will incinerate upon re-entering Earth's atmosphere, and the debris will mostly likely fall into the ocean or hit an uninhabited area.
NASA has also said that in 50 years of space exploration no one has ever been confirmed injured by falling space junk.
The craft contains no fuel and so is not expected to explode on impact.
"No consideration ever was given to shooting it down," NASA spokeswoman Beth Dickey said.
NASA has warned anyone who comes across what they believe may be debris not to touch it but to contact authorities for assistance.
Space law professor Frans von der Dunk from the University of Nebraska-Lincoln's College of Law told AFP that the United States will likely have to pay damages to any country where the debris falls.
"The damage to be compensated is essentially without limit," von der Dunk said, referring to the 1972
Liability Convention to which the United States is one of 80 signatories.
"Damage here concerns 'loss of life, personal injury or other impairment of health; or loss of or damage to property of States or of persons, natural or juridical, or property of international intergovernmental organizations,'" he said, reading from the agreement.
However, the issue could get thornier if the debris causes damage in a country that is not part of the convention.
"The number of countries so far theoretically at risk is rather large, so there may be an issue if damage would be caused to a state not being party to the Liability Convention," he said.
AFP-XinhuaHuge Tumbling Satellite Could Fall to Earth Over US Tonight or Saturday, NASA Says
by Tariq Malik, SPACE.com Managing Editor
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The Upper Atmosphere Research Satellite is in the grasp of the remote manipulator system end effector above the payload bay of the Earth-orbiting Discovery during STS-48 pre-deployment checkout procedures.
CREDIT: NASA Johnson Space Center
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This story was updated at 2:04 p.m. ETA huge, dead satellite tumbling to Earth is falling slower than expected, and may now plummet down somewhere over the United States tonight or early Saturday, despite forecasts that it would miss North America entirely, NASA officials now say.
The 6 1/2-ton
Upper Atmosphere Research Satellite (UARS) was expected to fall to Earth sometime this afternoon (Sept. 23), but changes in the school bus-size satellite's motion may push it to early Saturday, according to NASA's latest observations of the spacecraft.
"The satellite's orientation or configuration apparently has changed, and that is now slowing its descent," NASA officials wrote in a morning status update today. "There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent." [
Complete coverage of NASA's falling satellite]
NASA expects about 26 large pieces of the UARS spacecraft to survive re-entry through Earth's atmosphere and reach the planet's surface. The biggest piece should weigh about 300 pounds. The spacecraft is the largest NASA satellite to fall from space uncontrolled since 1979. [
6 Biggest Spacecraft to Fall Uncontrolled From Space]
NASA officials have said the the chances that a piece of UARS debris hits and injures one of the nearly 7 billion people on the planet are about 1 in 3,200. However, the personal
odds of you being struck by UARS satellite debris are actually about 1 in several trillion, NASA officials have said.
As of 10:30 a.m. EDT (1430 GMT) today, the UARS satellite was flying in an orbit of about 100 miles by 105 miles (160 kilometers by 170 km), and dropping. NASA launched the UARS satellite in 1991 to study Earth's ozone layer and upper atmosphere. The satellite was decommissioned in 2005.
"Re-entry is expected late Friday, Sept. 23, or early Saturday, Sept. 24, Eastern Daylight Time," NASA officials wrote. "Solar activity is no longer the major factor in the satellite's rate of descent."
The sun has had an extremely active week, one that has included several solar flares. High solar activity can cause the
Earth's atmosphere to heat and expand, which can increase drag on a low-flying satellite like UARS, making it fall faster.
Get a snapshot view of NASA's Upper Atmosphere Research Satellite (UARS), which will fall to Earth in 2011, in this SPACE.com infographic.
CREDIT: Karl Tate, SPACE.com Contributor
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