Friday, October 21, 2011

UPDATE: 10-23-2011 1:24PM GMT...ROSAT. What Are The Odds You Are Going To Get Hit? Coming Down To Earth (Maybe At A Place Near You).

UPDATE: 10-23-2011 1:42PM GMT


THE DECAY OF ROSAT: The doomed ROSAT X-ray space telescope continues to descend toward Earth. Multiple experts agree that re-entry should occur on Oct. 23rd, with most favoring the early hours of the day. Decay time uncertainties exceed 8 hours, so it is still impossible to say exactly where ROSAT will disintegrate.
Sky watchers say ROSAT is bright and easy to see, but photographers are having a hard time catching it. Dewey Vanderhoff tracked it over Cody, Wyoming, on Oct. 18th: "It was easily the fastest-moving satellite I have ever seen, being in such a low orbit and accelerating towards its doom. I barely got off a 'shotgun' 2-second exposure as ROSAT raced between Pegasus and Pisces (image)."
On Oct. 16th, astrophotographer Thierry Legault trained his 14-inch telescope on the observatory, and this is what he saw:
A video of the flyby may be found on Legault's web site. "The satellite looks very steady," he says, "there was no sign of tumbling or flares. Visually, ROSAT was crossing the sky so fast! I hope that it will give a nice fireworks over my place when it re-enters."
Until then, sky watchers should be alert for a fast-moving light in the night sky. To catch ROSAT, check Spaceweather's Satellite Tracker for local flyby times. You can also turn your smartphone into a field-tested ROSAT tracker.
UPDATE--ROSAT FLARES! Last night, multiple observers in California reported seeing a bright flash of light from ROSAT. "In addition to the satellite screaming thru the sky because of it's low altitude, it also displayed a short brilliant flare," says Derek Breit of Morgan Hill, CA. He caught the event in this 14 MB video:

Video credit: BREIT IDEAS Obs. Morgan Hill
"I must have seen the same flare Derek captured on the 0226Z ROSAT pass over Northern California," adds Kent Yeglin. "ROSAT was 3.2 seconds earlier than expected. The magnitude was around 0 with a short-duration flare to perhaps magnitude -6 to -8, comparable to brightest Iridiums. Flare peak was very short duration -- under a second -- more of a flash."

Doomed German Satellite to Fall to Earth This Weekend

Date: 21 October 2011 Time: 12:25 PM ET

Artist's impression of the ROSAT satellite in space
Artist's impression of the ROSAT satellite in space.
CREDIT: German Aerospace Center 

A defunct German satellite is expected to fall to Earth this weekend, with experts predicting that up to 30 big pieces of the junked spacecraft could hit the planet. But exactly when and where the satellite will fall remains a mystery.

The 2.7-ton Roentgen Satellite, or ROSAT, will likely plummet to Earth on Saturday or Sunday (Oct. 22 or 23), according to the latest update from the German Aerospace Center.

"Currently, the re-entry date can only be calculated to within plus/minus one day," agency officials said in a statement. "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."

Air & Space - SCITECH

What Are the Odds You'll Get Struck by the Falling ROSAT Satellite?

Published October 20, 2011
| TechMediaNetwork
ROSAT satellite seen in space false color
Another huge piece of space debris, a 2.6-ton, defunct German telescope called the Roentgen Satellite (ROSAT), will crash back to Earth Saturday or Sunday (Oct. 22 or 23), and the chances it will hit someone are even greater this time around.
The odds are 1-in-2,000 that a chunk of ROSAT will strike a person. For the UARS satellite that fell into the southern Pacific Ocean in September, the odds were 1-in-3,200. According to Heiner Klinkrad, head of the European Space Agency's Orbital Debris Office, ROSAT poses a higher risk than UARS because more of its mass is expected to survive atmospheric re-entry and reach Earth's surface.

"The fact that the ROSAT re-entry risk estimate is higher than for UARS lies in the surviving mass, which, percentage-wise, is considerably higher for ROSAT than for UARS, and hence, the net mass reaching ground is higher for ROSAT than for UARS," Klinkrad told Life's Little Mysteries, a sister site to "This is due to the ROSAT internal mirror assembly that is very resistant to [heat] during re-entry."

Typically, when a satellite crashes to Earth, only 20 to 40 percent of its mass survives; the rest burns up from heat generated by friction between the satellite and particles in the atmosphere, Klinkrad said. Because ROSAT's mirrors -- which collected X-rays and extreme ultraviolet light emitted by celestial objects -- resist heat, they reduce the percentage of the spacecraft that will burn up, and over half of the spacecraft's mass, about 1.7 tons of it, is expected to reach the surface. 

According to scientists in NASA's orbital debris office at Johnson Space Center in Houston, calculating the risk of space debris hitting someone requires first working out how much debris makes landfall. Analysts then make a grid of how the human population is distributed around the globe. Oceans, deserts and the North and South poles are largely devoid of people, for example, whereas coastlines are brimming with them. In short, the analysts must figure out which patches of Earth have people standing on them.

Throwing in a few more minor details, such as the latitudes over which satellites spend most of their time orbiting - ROSAT will most likely fall between 53 degrees north and 53 degrees south latitudes - the scientists calculate how likely it is that a piece of space junk will strike the ground where a person happens to be. This time around, the odds are 1-in-2,000, and there's a one-in-several-trillion chance that not only will a person get hit, but that person will be you.
ROSAT satellite
Two dead satellites have crashed to Earth in as many months, after years of gradually getting dragged down to lower and lower orbits. More will re-enter the atmosphere in the future. With this in mind, you may be interested to know the overall risk of getting struck in a given year, or in your lifetime.

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1 comment:

Rahul said...

Nothing can harm earth. There is a impregnable ionosphere above earths atmosphere. Anything that passes through it will get pulverized.