Falling German Satellite Poses 1-in-2,000 Risk of Striking Someone This Month (SPACE.com)

A big German satellite near the end of life is expected to plunge back to Earth this month, just weeks after a NASA satellite fell from orbit, and where this latest piece of space junk will hit is a mystery.

The 2.4-ton spacecraft, Germany's Roentgen Satellite (ROSAT), is expected to fall Oct.  22 or 23.

The satellite will break up into fragments, some of which will disintegrate due to intense re-entry heat. But studies predict that about 1.6 tons of satellite leftovers could reach the Earth’s surface. That's nearly half ROSAT's entire mass.

There is a 1-in-2,000 chance that debris from the satellite could hit someone on Earth, though the likelihood of an injury is extremely remote, German space officials say. For German citizens, the risk of being struck is much lower, about 1 in 700,000.

All areas under the orbit of ROSAT, which extends to 53 degrees northern and southern latitude, could be in the strike zone of the satellite's re-entry.

The bulk of the debris is likely to hit near the ground/ocean track of the satellite. However, isolated fragments could descend to Earth in a 50-mile (80-kilometer) swath along that track. [Photos: Germany's ROSAT Satellite Falling to Earth] 

The satellite will be the second large spacecraft to make a pre-announced fall from space in as many months. On Sept. 24, NASA's 20-year-old Upper Atmosphere Research Satellite (UARS) crashed into the Pacific Ocean in a widely publicized death plunge.

The ROSAT project was a collaborative venture among Germany, the United States, and the United Kingdom. It was developed, built and launched on behalf of and under the leadership of the Deutsches Zentrum für Luft- und Raumfahrt (DLR), Germany's space agency.

The uncontrollable ROSAT

ROSAT was placed into Earth orbit on June 1, 1990. The highly successful astronomy mission ended after nearly nine years, with commands sent on Feb. 12, 1999, to shut the spacecraft down. 

The spacecraft does not have its own propulsion system, so it could not  be maneuvered into a controlled re-entry at the end of its mission.

Moreover, the satellite is zipping through space in deaf and silent mode. That is, ROSAT is no longer able to communicate with DLR’s control center in Oberpfaffenhofen, nor is it possible to establish contact with the spacecraft.

Still, the DLR says the probability of ROSAT coming down over an inhabited area is extremely low. [6 Biggest Uncontrolled Spacecraft Falls From Space]

Re-entry prediction practice

Even in its death throes, ROSAT is expected to be a useful servant, albeit in a way unintended at launch.

According to Heiner Klinkrad, head of the European Space Operations Center's Space Debris Office in Darmstadt, Germany, the ROSAT tumble from space will be useful in sharpening re-entry prediction tools.

"ROSAT will be an official re-entry test campaign," Klinkrad told SPACE.com.

Klinkrad serves as secretary of the Inter-Agency Space Debris Coordination Committee, an international governmental forum for the worldwide coordination of activities related to the issues of human-made and natural debris in space.

The IADC has performed re-entry prediction test campaigns since 1998. Data-sharing has led to more-accurate re-entry predictions.

Targets used for IADC re-entry initiatives have included the UARS spacecraft, several Russian Cosmos satellites, various upper stages, and even the fall of a huge ammonia coolant tank that was purposely tossed off the International Space Station by spacewalking astronauts in July 2007. The ammonia tank burned up over the South Pacific in November 2008.

Heavy metal (really)

ROSAT's nose-dive may result in as many as 30 individual pieces striking the surface of the Earth. About 1.6 tons of the satellite could survive re-entry, according to DLR description.

The heaviest component to reach Earth could be the satellite’s X-ray optical system — with its mirrors and a mechanical support structure made of carbon-fiber reinforced composite  —  or at least a part of it, DLR officials said.

Fragments striking the surface of Earth could be traveling at speeds of up to roughly 280 mph (450 kph).

As ROSAT's demise approaches, German scientists will be evaluating data provided by the U.S. Space Surveillance Network. In addition, the Tracking and Imaging Radar, the large radar facility at the Fraunhofer Institute for High-Frequency Physics and Radar Techniques in Wachtberg near Bonn, will be monitoring the descent to further improve calculations of its trajectory.

Experts will be analyzing data to predict the moment of re-entry. All of this information will be collected and evaluated in the European Satellite Operations Center in Darmstadt, then forwarded to the DLR.

Leonard David has been reporting on the space industry for more than five decades. He is a winner of this year's National Space Club Press Award and a past editor-in-chief of the National Space Society's Ad Astra and Space World magazines. He has written for SPACE.com since 1999.

View the original article here

Falling Satellite Poses Little Risk to Public, NASA Says (SPACE.com)

An outdated NASA satellite, which has been adrift in orbit for six years, is falling back to Earth, and some of its debris is expected to reach the ground in the next few weeks. But despite the chance that bits of debris could land in North or South America, the space agency is assuring the public that there is no reason to be alarmed.

"Satellites re-entering is actually very commonplace," Nick Johnson, chief scientist of the Orbital Debris Program at NASA's Johnson Space Center in Houston, said at a news briefing today (Sept. 9). "Last year, for example, we averaged over one object per day falling back uncontrolled into the atmosphere." [Photos: Space Debris & Cleanup Concepts]

NASA's Upper Atmosphere Research Satellite (UARS), a school bus-size spacecraft, will re-enter Earth's atmosphere sometime in late September or early October, agency officials said. Debris from the satellite could fall over a swath of land stretching more than 500 miles (804 kilometers) anywhere between northern Canada and southern South America.

Narrowing down the area of impact will not be possible until much closer to when the pieces will hit, said Air Force Maj. Michael  Duncan, deputy chief of the U.S. Strategic Command's space situational awareness division.

Johnson stressed that these incidents are not so rare. In 2010 alone, some 400 pieces of space debris were cataloged by the U.S. Space Surveillance Network, he said.

On average, one moderate-size object, which could be an old, intact spacecraft or rocket body, falls to Earth every week. The majority of the debris disintegrates upon re-entry into Earth's atmosphere, but some of the vehicle components do reach the surface, Johnson said. These pieces of space junk typically fall over broad ocean areas or desolate regions like the Australian outback or the Canadian tundra.

Regarding larger objects such as the nearly 12,500-pound (5,668 kilograms) UARS, the U.S. Space Surveillance Network typically sees one of these re-entering the atmosphere per year.

The spacecraft is about 35 feet (10.7 meters) long and 15 feet (4.5 m) wide. And while agency officials said UARS is the largest NASA satellite to make an uncontrolled fall back to Earth in years, Johnson clarified that re-entry events of this size are "certainly not unknown or unprecedented." [Related: Space Junk FAQ: Falling Space Debris Explained]

"Last year there were 75 metric tons of spacecraft and rocket bodies falling back to Earth in an uncontrolled manner," Johnson explained. "In perspective, UARS is less than 6 metric tons, so it's a very small percentage of the annual re-entry of satellites into Earth's atmosphere."

Even when pieces of defunct satellites and rocket bodies do reach the ground, the chances of them posing a risk to people and their property is very remote, NASA said.

NASA officials estimate that there is a 1-in-3,200 chance that a person somewhere on Earth will be hit by UARS debris, and the odds of the dead satellite re-entering over a densely populated area is very small. [Video: The Expanding Danger of Space Debris]

NASA and the U.S. Space Surveillance Network has closely studied the satellite to determine the potential risks during its re-entry. Current projections show that 26 large pieces, totaling approximately 1,170 pounds (532 kg), will survive the trip through Earth's atmosphere.

Still, the chances of the UARS satellite causing any real harm is very small, officials said.

"Throughout the entire 54 years of the Space Age there has been no report of anyone being injured or impacted by any re-entering debris," Johnson said.

You can follow SPACE.com staff writer Denise Chow on Twitter @denisechow. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

View the original article here

Dead NASA Satellite Falling From Space, But When & Where? (SPACE.com)

This story was updated at 2:05 p.m. EDT.

An out-of-control NASA satellite that is dead in space will plunge back to Earth in the next few weeks, but exactly when and where the spacecraft will fall are still a mystery, space agency and military officials said today.

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.

But NASA and U.S. military officials tracking the defunct UARS satellite won't have a better idea of where the spacecraft will fall until around two hours before it happens. [Photos: Space Debris & Cleanup Concepts]

"We continue to say late September is the best estimate that we can give right now," Air Force Maj. Michael  Duncan, deputy chief of the U.S. Strategic Command's space situational awareness division, told reporters today (Sept. 9).  " There are so many factors that will affect it between now and that point in time — the atmosphere changes on a daily basis —  that it's impossible to say how that's going to impact this re-entry."

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), Duncan said.

There is a 1-in-3,200 chance that a person somewhere on Earth could be hit by falling satellite debris, but the odds of the UARS spacecraft re-entering over a populated area are extremely remote, NASA officials said.

"So those are actually very, very low odds that anyone is going to be struck by a piece of debris," said Nick Johnson, the chief scientist of NASA's Orbital Debris Program at the agency's Johnson Space Center in Houston.

Johnson said 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).

"Throughout the entire 54 years of the Space Age there has been no report of anyone being injured or impacted by any re-entering debris," Johnson said.

Dead satellite in space

The $750 million UARS satellite has been dead in orbit since 2005, when it was decommissioned after a 14-year Earth-observation mission.

The spacecraft 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.

Johnson said that, on average, a spacecraft as large as UARS falls back to Earth about once a year. In 2010, a total of 400 pieces of satellites or spent rockets fell back to Earth, though most pieces either burned up during re-entry, fell into the ocean or fell over unpopulated areas, he added.

"Satellites re-entering is actually very commonplace," Johnson said.

NASA is encouraging any member of the public who finds a piece of the UARS satellite to not touch the object and notify local law enforcement authorities. The satellite's remains are still owned by the United States government and cannot be sold to space memorabilia hunters NASA officials said.

NASA launched the UARS satellite in 1991 aboard the space shuttle Discovery on a mission to study Earth's upper atmosphere. In particular, the spacecraft examined Earth's ozone layer to help scientists better understand ozone layer depletion. The satellite was also able to track atmospheric effects from the Mt. Pinatubo volcano eruption in the Philippines at the time, said Paul Hertz, chief scientist for NASA's science missions.

Hertz said that the UARS satellite was shut down because the observations it was collecting were being performed by newer, better satellites.

In 2005, NASA commanded the spacecraft to use all of its remaining propellant to move into a lower orbit, one that would send it on a funeral dive back through Earth's atmosphere in about five or six years, Johnson said.

"The current orbit is about 245 kilometers by 275 kilometers," he added. "And obviously decreasing every day."

Eyes on the sky

NASA and the military's space tracking division are keeping a close watch on the UARS satellite for any changes in its descent over the next few weeks.

The space agency is posting weekly updates on the falling spacecraft on a special UARS mission website. The updates are coming from the Joint Space Operations Center at the U.S. Strategic Command at Vandenberg Air Force Base, Calif., which is tracking the satellite.

"The reason for the updates on NASA's part is to keep you and the public informed," said NASA spokeswoman Beth Dickey. "We know we will get a lot of questions about it, so we want to be up front about it."

Space debris is one of the most challenging hurdles facing space agencies and satellite operators today. According to NASA, there are about 22,000 pieces of space junk larger than 4 inches (10 cm) currently being tracked by the U.S. Space Surveillance Network. Only 1,000 of those objects are actually working spacecraft, the agency states.

Last week, a report by the National Research Council found that the amount of space junk around Earth has reached a tipping point in which, even if no new debris were added, objects would continue to create more debris through collisions. That report states that the need to limit or clean up space debris is more important than ever.

Skywatchers on alert

Keeping a skywatching eye on the comings and goings of UARS as it nears re-entry is a global network of satellite surveillance amateurs.

According to satellite sleuth Harro Zimmer of Berlin, Germany, his current analysis — based on couple of different methods — shows a possible decay window between Sept. 29 and Oct. 5.

"The last word will be coming from the solar activity over the next two weeks," Zimmer told SPACE.com.

Zimmer also advised that Belgian observer, Bram Dorreman, has reported that UARS looks to be slowly rotating with a period of 17 seconds. Its magnitude changes from 1.2 to 3.5 on the scale astronomers use to measure the brightness of objects in space. On that scale, the brighter an object is, the lower the number of its magnitude.

Johnson said that if the UARS satellite does re-enter over a populated region, it should be a magnificent sight to skywatchers on the ground. But even that is a long shot.

"This would be quite a nice show. It is a relatively large vehicle, it would be visible in daylight, Johnson said. "Odds are it's going to happen over an ocean, unlikely to be seen unless it's, you know, an airliner. We've had reports like that before. "

SPACE.com's Space Insider Columnist Leonard David contributed to this report from Colorado.You can follow SPACE.com Managing Editor Tariq Malik on Twitter @tariqjmalik. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

View the original article here