ROSAT — Down, but Missing

Defunct German Satellite Hits Earth in Fiery Death Dive

Denise Chow, SPACE.com Staff Writer
Date: 23 October 2011 Time: 03:45 AM ET
ROSAT satellite

 

This still from an animation by Analytical Graphics, Inc., depicts the re-entry of Germany’s defunct ROSAT satellite in October 2011.
CREDIT: Analytical Graphics, Inc.

This story was updated at 11:18 p.m. ET.

An old German satellite plunged to Earth today (Oct. 22) after languishing in a dead orbit for more than a decade, but officials do not yet know where it fell.

The 2.7-ton Roentgen Satellite, or ROSAT, slammed into Earth’s atmosphere sometime between 9:45 p.m. EDT (0145 GMT Sunday) and 10:15 p.m. EDT (0215 GMT Sunday), according to officials at the German Aerospace Center.

“There is currently no confirmation if pieces of debris have reached Earth’s surface,” German aerospace officials said in a statement.

While the 21-year-old satellite broke apart as it re-entered Earth’s atmosphere, German aerospace officials estimated that up to 30 pieces totaling 1.9 tons (1.7 metric tons), consisting mostly of the observatory’s heat-resistant mirrors and ceramic parts, could survive the fiery trip and reach the surface of the planet.

Based on ROSAT’s orbital path, these fragments could be scattered along a swath of the planet about 50 miles (80 kilometers) wide, German aerospace officials have said.

The satellite, which weighs 5,348 pounds (2,426 kilograms), was launched into orbit in June 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. [Photos of Doomed ROSAT Satellite]

In 1998, the ROSAT’s star tracker failed and its X-ray sensors pointed directly at the sun. This caused irreparable damage to the satellite, and it was officially decommissioned in February 1999.

to read more, go to:    http://www.livescience.com/16680-falling-german-satellite-rosat-death-dive.html

Incoming — ROSAT

Satellite picture: The ROSAT satellite.

An artist’s impression of ROSAT in orbit.

Illustration courtesy DLR

Traci Watson

for National Geographic News

Published October 19, 2011

If you see a large glowing object plummeting from the sky late Saturday or early Sunday, duck.

defunct European satellite called ROSAT is headed straight for Earth this weekend—and chances are even higher that a piece of space debris could hit someone than the odds placed on a NASA satellite that fell from orbit last month.

The German Aerospace Center, which led the development and construction of ROSAT, estimates that the chance of anyone being harmed by debris from the satellite is 1 in 2,000. For NASA’s UARS, the injury risk was roughly a third lower, at 1 in 3,200.

ROSAT is currently estimated to make an uncontrolled reentry during the early morning hours on Sunday, Greenwich Mean Time, said Heiner Klinkrad, head of the European Space Agency’s space debris office.

But Klinkrad cautions that the satellite could enter Earth’s atmosphere up to 24 hours earlier or later than the estimated time.

That’s because shifts in radiation from the sun aren’t 100-percent predictable. If solar radiation increases, there’s more heating and expansion of the atmosphere, which would increase drag on the spacecraft and cause it to hurtle downward sooner than expected.

Don’t Touch the Space Junk

Unfortunately, neither Klinkrad nor anyone else can say exactly where on Earth ROSAT is headed.

Debris could come down anywhere between 53 degrees north latitude and 53 degrees south latitude, an area that includes most of Earth’s land mass, the German Aerospace Center’s Roland Gräve said via email.

That could be a worry, because the satellite’s 1.5-ton mirror is likely to survive the superheated trip through the atmosphere all the way to the ground, where it could make a major dent in whatever it strikes.

By contrast, the biggest piece of NASA’s UARS spacecraft thought to hit the planet was a 300-pound (150-kilogram) chunk of the craft’s frame.

In the end, the remnants of UARS splashed down into an isolated stretch of the Pacific Ocean, disturbing no one except perhaps a few fish. (See “NASA Satellite Debris Likely Fell in Ocean, May Never Be Found.”)

Despite the higher odds, ROSAT is also unlikely to hurt anyone, scientists say, given the planet’s large stretches of ocean and thinly populated areas.

“We accept risks in everyday life that are many orders of magnitude higher than the risks we incur from reentering space objects,” ESA’s Klinkrad said.

If bits of the satellite do land in a populated area, “they will be extremely hot,” added the German Aerospace Center’s Gräve. “This is why we recommend not touching any satellite parts” that do make it to the ground.

And any ROSAT debris, no matter where it’s found, belongs to the German government, he said.

ROSAT Worthy of a Wake

ROSAT—short for Roentgen Satellite—launched in 1990 on a Delta II rocket to measure the x-rays emitted by objects such as neutron stars, dense stellar cores left behind by some supernovae.

The mission was supposed to last only 18 months, but the satellite kept chugging for eight years. Scientists finally shut it down in 1999 after its last functional scientific instrument accidentally pointed too close to the sun, blinding the sensors.

When ROSAT was on the drawing board in the 1980s, spacecraft designers didn’t plan for the end of their vehicles’ lives. So ROSAT was built without a propulsion system that would’ve allowed for a carefully choreographed demise.

“The attitude 20 years ago was still very much, Eh, space is big, and things that reenter probably won’t hit anyone, so we won’t worry about it,” said Jonathan McDowell, a Harvard-Smithsonian Center for Astrophysics scientist who relied on data from ROSAT.

As far as McDowell can remember, nothing as big as the ROSAT mirror has smashed into the Earth’s surface since the reentry of the Soviet space station Salyut-7 in 1991.

 

to read more, go to:    http://news.nationalgeographic.com/news/2011/10/111019-satellite-fall-earth-rosat-space-debris-nasa-science/?source=hp_dl1_news_satellite201120

More on ROSAT Re-Entry Dates & Conditions

SATELLITE RE-ENTRY: The ROSAT X-ray observatory, launched in 1990 by NASA and managed for years by the German Aerospace Center (DLR), will return to Earth within the next two weeks. Current best estimates place the re-entry between Oct. 22nd and 24th over an unknown part of Earth. Although ROSAT is smaller and less massive than UARS, which grabbed headlines when it re-entered on Sept. 24th, more of ROSAT could reach the planet’s surface. This is because the observatory is made of heat-tolerant materials. According to a DLR study, as many as 30 individual pieces could survive the fires of re-entry. The largest single fragment would likely be the telescope’s mirror, which is very heat resistant and may weigh as much as 1.7 tons.

ROSAT is coming, but it’s not here yet. On Oct. 13th, Marco Langbroek photographed the observatory still in orbit over Leiden, the Netherlands:


Photo details: 5 second exposure, Canon EOS 450D, ISO 400

“I observed ROSAT this evening in deep twilight,” says Langbroek. “It was bright, magnitude +1, and an easy naked-eye object zipping across the sky where the first stars just had become visible.”

Update: Scott Tilley of Roberts Creek, British Columbia, made a video of ROSATon Oct. 15th: “It did get pretty bright, at least 1st magnitude, as it passed overhead after sunset.”

ROSAT will become even brighter in the nights ahead as it descends toward Earth. Local flyby times may be found on the web or on your smartphone.

Also, check the German ROSAT re-entry page for updates.

The role of space weather: Solar activity has strongly affected ROSAT’s decay. Only a few months ago, experts expected the satellite to re-enter in December. However, they did not anticipate the recent increase in sunspot count. Extreme ultraviolet radiation from sunspots has heated and “puffed up” Earth’s atmosphere, accelerating the rate of orbital decay. The massive observatory now has a date with its home planet in October.

from:    spaceweather.com

German Satellite is Due to Hit October 22/23

Falling German Satellite Poses 1-in-2,000 Risk of Striking Someone This Month

by Leonard David, SPACE.com’s Space Insider Columnist
Date: 12 October 2011 Time: 07:41 AM ET
Artist's impression of the ROSAT satellite in space
Artist’s impression of the ROSAT satellite in space
CREDIT: German Aerospace Center

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.

ROSAT undergoing tests in the space simulation chamber
The ROSAT satellite undergoing tests in the space simulation chamber at Dornier.
CREDIT: Dornier (now Astrium Friedrichshafen).

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.

to read more, go to:    http://www.space.com/13261-german-satellite-falling-earth-rosat-risk.html