Defunct UARS is the largest NASA satellite to make uncontrolled fall back to earth in years; dangers of orbital space debris...

The junk in low Earth orbit: space pollution and rising hazard from debris

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NASA: 'We May Never Know' Whereabouts of Satellite Debris
NASA scientists are still not sure exactly where pieces of a huge, defunct satellite landed after re-entering Earth's atmosphere this morning, but early evidence suggests that the debris landed somewhere in the Pacific Ocean, which could complicate recovery efforts.

During a Saturday afternoon conference call with reporters, Nicholas Johnson, chief orbital debris scientist for NASA, acknowledged that "we may never know" the whereabouts of the Upper Atmosphere Research Satellite (UARS).

Data from the Department of Defense's Joint Space Operations Center (JSOC) indicate that UARS fell to the Earth sometime between 11:23pm Eastern Friday night and 1:09am Saturday morning. At that point, the satellite passed over Canada, the African continent, and the Pacific, Atlantic, and Indian Oceans. The mid-point of that path, and likely point of entry, according to those calculations, is off the West Coast of the U.S., as indicated by the green circle on a map published by NASA.

Every year, the Inter-Agency Space Debris Coordination Committee (IADC), a group made up of 12 space agencies from around the world, conduct a re-entry exercise, and UARS was this year's target. "We're now waiting to see if we can verify that," Johnson said. "If it came down over one of the oceans, of course, that's going to be problematic."

How did NASA know that UARS was back? To find out if a satellite is no longer in orbit, you send out sensors. If you don't get a response back, that's a good indication that it has re-entered the Earth's atmosphere, Johnson said. Typically, scientists will try sending out these sensors at least three times just to make sure the data is accurate. That can take between two and three hours, which is why NASA did not immediately know if UARS had successful re-entered the atmosphere.

The debris recovery process, meanwhile, will rely mainly on eyewitness accounts. "Most of the time, we do rely heavily on people on the ground," Johnson said. "UARS, whether it came in during local day or night, would've been clearly visible, so if we continue to have a lack of reports, particularly in Canada or Africa - that would typically give further credence to the fact that it's probably over the water."

The UARS satellite was launched in 1991 by the Space Shuttle Discovery. At launch, it was 35-feet long, 15 feet in diameter, and weighed 13,000 pounds. It was used to measure ozone and chemical compounds found in the ozone layer, which affect ozone chemistry and processes, as well as winds and temperatures in the stratosphere and the energy input from the Sun. "Together, these help define the role of the upper atmosphere in climate and climate variability," according to NASA.

UARS was officially decommissioned on December 14, 2005 and has since been hanging out in space. While pieces of satellites typically burn up upon re-entry into the Earth's atmosphere, other pieces survive the process and crash land on Earth. Early on, NASA said the chances of UARS pieces hitting someone here on Earth were remote, but really, officials had no idea where UARS would hit, so all eyes have been on the sky.

A recent NASA-sponsored report from the National Research Council found that the space agency needs a better plan for dealing with this space junk, or orbital debris, before it gets out of hand and damages valuable spacecraft.

According to NASA, most orbital debris is within 1,250 miles of the Earth's surface; the greatest concentrations of debris is found between 500 and 530 miles. Most of this debris circles the Earth at speeds between 4-5 miles per second.

Dead NASA Satellite Falling From Space, But When & Where? [VIDEOS]
The spacecraft, called the Upper Atmosphere Research Satellite, is about the size of a school bus and is expected to re-enter Earth's atmosphere sometime between late September and early October, NASA officials said. The nearly 12,500-pound (5,668-kilogram) satellite will fall over a stretch of land more than 500 miles (804 kilometers) long somewhere between northern Canada and southern South America.

Even two hours before re-entry, the military will only be able to pinpoint the area of impact to within about 6,000 miles (10,000 kilometers). 26 large pieces of the UARS satellite are expected to survive the re-entry and reach the Earth's surface. Altogether, about 1,170 pounds (532 kg) of material from the UARS satellite are expected to reach Earth. The largest piece of debris could weigh nearly 300 pounds (150 kg).

The $750 million UARS satellite is the largest NASA satellite to make an uncontrolled fall back to Earth in years, agency officials said. It is about 35 feet (10.7 meters) long and 15 feet (4.5 m) wide.

The danger of space debris
In late June, six astronauts living on board the International Space Station (ISS), which orbits some 200 miles above the earth’s surface, received notice that a piece of space debris travelling 29,000 miles per hour would pass dangerously nearby. NASA officials calculated that the probability of the ISS being hit at around one in 360. (One in 10,000 is NASA’s nominal threshold for which it will authorize a "collision avoidance maneuver"”)

Normally, the ISS receives ample notice so that it can maneuver out of the pathway of potential space debris. However, with less than fifteen hours’ warning, the astronauts were forced to relocate to Soyuz space capsules for only the second time in the ISS’s thirteen-year history.

While the debris missed the space station by 1,100 feet, orbital space debris is a growing threat to civil, military, and commercial satellites in space.

Presently, there are some 22,000 items over ten centimeters across, or roughly the size of a softball, which can be regularly tracked with existing resources and technology. These include the upper stages of launch vehicles, disabled spacecraft, dead batteries, solid rocket motor waste, and refuse from human missions. In addition, there are approximately 300,000 other fragments of space junk measuring between one and ten centimeters, and over 135,000,000 less than one centimeter, which could potentially damage operational spacecraft.

Though it took forty years to produce the first 10,000 pieces of softball-sized space debris, it required less than a decade for the next 12,000. This recent increase was due in part to two worrying incidents, which, according to NASA, combined to increase the number of total space objects by over 60 percent. In January 2007, the Chinese military destroyed a defunct polar-orbiting weather satellite with a mobile ballistic missile, and in February 2009 an active Iridium communication satellite and a defunct Russian satellite, which had been predicted to pass each other 1,900 feet apart, unexpectedly collided.

The ability to detect, track, characterize, and predict objects in space and space-related events is known as space situational awareness (SSA). The U.S. Strategic Command’s Joint Space Operations Center (JSpOC) provides this function for the Pentagon by monitoring space debris (over ten centimeters) with a worldwide network of twenty-nine ground-based radars and optical sensors.

In addition to supporting U.S. military and intelligence agencies, JSpOC provides e-mail notifications to commercial space operators when their satellites are at risk from space debris. JSpOC provides twenty to thirty close-approach notifications per day, which last year resulted in satellite owners maneuvering 126 times to avoid collision with other satellites or debris. According to U.S. officials, the United States even notifies the Chinese government when their satellites are threatened by space debris created by the 2007 anti-satellite test. Despite JSpOC’s best efforts, however, these same officials acknowledge that no country has the resources, technical expertise, or geography to meet the growing demands for SSA.

The space debris problem is a classic global governance dilemma: though eleven states can launch satellites, and over sixty countries or government consortia own or operate the approximately 1,100 active satellites, no one country or group of countries has the sovereign authority or responsibility for regulating space. Under Article II of the 1967 Outer Space Treaty: "Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty"”

The solution to reducing the amount of new space debris, mitigating the threat it poses to satellites and spacecraft, and eventually removing on-orbit debris from space, will require enhanced international cooperation. Last summer, the Obama administration released its National Space Policy, which featured the objective of preserving the space environment via "the continued development and adoption of international and industry standards and policies to minimize debris," and "fostering the development of space collision warning measures"” Unfortunately, progress toward constructing international agreed upon rules of the road for the responsible uses of space have been slow going.

*Update Oct 23, 2011*

Dead satellite tumbles to Earth - but where? Up to 30 fragments weighing a total of 1.87 tons could have hit the planet, experts believe

Scientists were trying to establish how and where a defunct research satellite returned to the Earth Sunday, after warning that some parts might survive re-entry and crash at up to 280 mph.

There was no immediate solid evidence to determine above which continent or country the ROSAT scientific research satellite entered the atmosphere, said Andreas Schuetz, spokesman for the German Aerospace Center.

Most parts of the minivan-sized German satellite were expected to burn up, but up to 30 fragments weighing a total of 1.87 tons could have hit the planet.

Citing officials, Space.com reported that ROSAT slammed into Earth's atmosphere sometime between 9:45 p.m. and 10:15 p.m. ET on Saturday. Scientists were no longer able to communicate with the dead satellite and it must have traveled about 12,500 miles in the final 30 minutes before entering the atmosphere, Schuetz said.

Schuetz said it could take days to determine exactly where pieces of the satellite had fallen, but that the agency had not received any reports that it had hit any populated areas. "We have no such information," he said Sunday.

Based on ROSAT's orbital path, these fragments could be scattered along a swath of the planet about 50 miles wide, German aerospace officials have said.

Scientists said hours before the re-entry into the atmosphere that the satellite was not expected to hit over Europe, Africa or Australia. According to a precalculated path it could have been above Asia, possibly China, at the time of its re-entry, but Schuetz said he could not confirm that.

The 2.69-ton scientific ROSAT satellite was launched in 1990 to study X-ray radiation from stars, comets, supernovas, nebulas and black holes, among other things. The satellite was originally designed for an 18-month mission, but it far outlived its projected lifespan.

Heat-resistant mirror
It retired in 1999 after performing the first all-sky survey of X-ray sources with an imaging telescope.

The largest single fragment of ROSAT that could hit into the earth is the telescope's heat-resistant mirror.

During its mission, the satellite orbited about 370 miles above the Earth's surface, but since its decommissioning it has lost altitude, circling at a distance of only 205 miles above ground in June for example, the agency said.

Even in the last days, the satellite still circled the planet every 90 minutes, making it hard to predict where on Earth it would eventually come down.

Mission controllers initially estimated that ROSAT could fall to Earth in November, but increased solar activity caused the satellite's orbit to decay faster than originally expected. As the sun's activity ramps up, it heats up and expands the atmosphere, which creates more drag on satellites in orbit.

'Catch them'
ROSAT's fall from space shone a spotlight on the growing problem of debris in space. "One option is we want to be able to catch uncontrolled satellites in the future," Jan Woerner, head of the executive board of the German Aerospace Center, told Space.com. "We're working on such a mission to catch them, depending on their state, and have a controlled re-entry or send them to a graveyard, in order to prevent this situation in the future."

A dead NASA satellite fell into the southern Pacific Ocean last month, causing no damage, despite fears it would hit a populated area and cause damage or kill people. Experts believe about two dozen metal pieces from the bus-sized satellite fell over a 500-mile span.

The German space agency puts the odds of somebody somewhere on Earth being hurt by its satellite at one in 2,000 — a slightly higher level of risk than was calculated for the NASA satellite. But any one individual's odds of being struck are one in 14 trillion, given there are 7 billion people on the planet.

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Images courtesy of NASA Marshall Space Flight Center and European Space Agency