From the ABC 7 Weather team

Falling ROSAT satellite to make reentry between Oct. 21 - 25

October 17, 2011 - 02:18 PM
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The German-built ROSAT satellite and its 1.7-ton telescope is expected to plunge haphazardly back to earth as early as this week.

A German satellite, ROSAT, carrying a 7.1-ton telescope will soon fall to earth, possibly as early as Friday. (German Aerospace Center)

UPDATE 2:30 P.M.: The giant satellite is now expected to reenter the earth's atmosphere around 8 a.m. EDT on Oct. 23, reports Spaceweather: "Uncertainties exceed 10 hours, which makes it impossible to say exactly where ROSAT will re-enter."

ORIGINAL: Achtung: A satellite strapped to a 1.7-ton telescope will soon be descending in a flaming heap back to earth, possibly as soon as Friday. Because this out-of-control spacecraft, known as the Roentgen Satellite or ROSAT, was built with the finest German engineering, the "very heat resistant" optical device is expected to crash to the ground relatively unscathed.

The ROSAT satellite was launched by NASA in 1990 and managed by the Germans until its fuel ran out and its mission ended in the late '90s. People who bought killer-satellite insurance after the UARS reentry in late September might be feeling smug right now. But although the hunk of expensive junk could make an impromptu landing pad out of basically any major city, the chances of a telescope-on-noggin impact are still abysmally low. Consider that 71 percent of the earth's surface is ocean, and that 369 satellites made uncontrolled reentries in 2010 without any known harm (although this woman was hit by part of a Delta II rocket in the '90s, if you're the type who can't stop fretting about things).

The window of the ROSAT reentry, which the German Aerospace Center puts at Oct. 21 to 25 (though the dates could change slightly), should not be a time for finger-biting but for reflection about the probe's accomplishments. Namely, ROSAT gave the universe a thorough X-ray scan shortly after its launch in 1990. This "all-sky" observation recorded 80,000 things out in the black that are spewing out Roentgens, a finding that among other things helped scientists understand the nature of nearby stars and supernovae. The satellite even caught the moon and comets emitting X-rays!

NASA praised the vehicle's discoveries in 2001:

Using these data, for the first time, astronomers could see in full the large X-ray structures in the Milky Way Galaxy, and in other galaxies; could get a nearly complete measurement of bright X-ray sources, including stars in all stages of evolution, and neutron stars and black holes too; could see the shape and brightness of the "diffuse X-ray background", the high energy emission which seems to surround us... and could use the shape of the X-ray emission to trace the hidden material making up most of the known Universe.

In other words, it was much cooler than what you'll see at the dentist's office. The visual results of ROSAT's penetrating scan are wonderful to behold:

rosat falling satellite x-ray all-sky

The "all-sky" map of X-ray sources in the nearby universe. Large version. (ROSAT / DLR)

So why the uncertainly about the satellite's reentry? The sun's recent, mercurial outbursts have been heating and cooling the atmosphere, altering the drag that ROSAT experiences while traveling over the planet. Here's the latest from the German space agency's ROSAT page, a good source to check if you want to keep up with this device's death plunge:

Currently, the re-entry date can only be calculated to within plus/minus three days. This time slot of uncertainty will be reduced as the date of re-entry approaches. However, even one day before re-entry, the estimate will only be accurate to within plus/minus five hours. All areas under the orbit of ROSAT, which extends to 53 degrees northern and southern latitude could be affected by its re-entry.

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