[meteorite-list] NASA Space Junk to Hit This Week

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http://www.washingtonpost.com/national/health-science/nasa-satellite-expected-to-hit-earth-this-week/2011/09/18/gIQARnpVdK_story.html?hpid=z3

NASA satellite expected to hit Earth this week:

By Joel Achenbach,
The sky is not falling. A 12,500-pound NASA satellite the size of a school 
bus is, however.

It's the Upper Atmosphere Research Satellite, or UARS - YOU-arz - and it's 
currently tumbling in orbit and succumbing to Earth's gravity. It will crash 
to the surface Friday.

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Graphic



A NASA satellite is expected to re-enter Earth's atmosphere later this week.

Gallery


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Or maybe Thursday. Or Saturday.

Out-of-control crashing satellites don't lend themselves to exact estimates 
even for the precision-minded folks at NASA. The uncertainty about the 
 "when" makes the "where" all the trickier, because a small change in the 
timing of the reentry translates into thousands of miles of difference in 
the crash site.

As of the moment, NASA says the 35-foot-long satellite will crash somewhere 
between 57 degrees north latitude and 57 degrees south latitude - a 
projected crash zone that covers most of the planet, and particularly the 
inhabited parts. In this hemisphere, that includes everyone living between 
northern Newfoundland and the frigid ocean beyond the last point of land in 
South America.

Polar bears and Antarctic scientists are safe.

It's the biggest piece of NASA space junk to fall to Earth in more than 30 
years. It should create a light show. The satellite will partially burn up 
during reentry and, by NASA's calculation, break into about 100 pieces, 
creating fireballs that should be visible even in daytime.

An estimated 26 of those pieces will survive the re-entry burn and will 
spray themselves in a linear debris field 500 miles long. The largest chunk 
should weigh about 300 pounds.

As the Friday-ish crash gets closer, NASA will refine its estimate of timing 
and location, but the fudge factor will remain high.

"There are too many variations on solar activity which affect the 
atmosphere, the drag on the vehicle," said Nicholas Johnson, chief scientist 
for orbital debris at NASA. He said that when NASA estimates that the 
satellite is two hours away from hitting Earth, there will still be a margin 
of error of 25 minutes.

"That equates to plus or minus 5,000 miles. That's a lot of real estate," he 
said.

The good news is that UARS will probably splatter into the open ocean, 
because Earth is a water planet. And humans, for all their sprawl, occupy a 
very limited portion of its surface.

NASA did a calculation of the odds that someone would be struck by UARS 
debris. It's very unlikely: about a 1-in-3,200 chance that one person 
somewhere in the world would be hit. That's not the odds for any specific 
person (say, a reader of this story), but for the entire human population, 
which is about 7 billion.

Used fuel tanks and rocket bodies fall to Earth frequently, Johnson said, 
"and in over 50 years of these things coming back around the world, no one 
has ever been hurt. There has never been any significant property damage."

The satellite was launched on the space shuttle Discovery in 1991 and spent 
14 years studying the atmosphere as part of an effort to understand, among 
other things, the human influence on climate change. It measured chemicals 
that damage the ozone layer, aerosols from Mount Pinatubo and changes in 
solar radiation that affect the upper atmosphere. But NASA decided in 2005 
that UARS's work had become redundant to that performed by other satellites, 
and it received its scientific pink slip.

Left alone, it would have orbited for an additional 25 years or so as a 
large piece of space junk in the increasingly crowded region known as Low 
Earth Orbit, but NASA was able to alter the satellite's orbit to bring it to 
the surface sooner. In 2007, a small meteor hit UARS in orbit and knocked 
off four pieces but didn't change its motion significantly.

The granddaddy of crashing NASA satellites was Skylab, which was 15 times 
the size of UARS and rained charred chunks on the Indian Ocean and western 
Australia in 1979.



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Graphic



A NASA satellite is expected to re-enter Earth's atmosphere later this week.

Gallery


?A look at the work of private space companies that will attempt to fill the 
hole left by the end of NASA's shuttle program.

More on this Story

  a.. NASA satellite expected to hit earth
  b.. NASA launches twin spacecraft to the moon
  c.. Astronomers announce discovery of 50 new planets
  d.. Diamond planet discovered by astronomers
View all Items in this Story

  a.. Supernova is brightest in decades
  b.. Orion space shuttle begins to take shape
  c.. Innovator of the Week: NASA vs. China
  d.. Read more news and ideas on Innovations
  e.. Read more on Health, Environment and Science
About 22,000 distinct man-made objects, many of them no bigger than a 
softball, are currently being tracked in orbit by the U.S. military. Because 
space is not truly empty, but rather is a very thin soup of particles, 
objects in Low Earth Orbit lose speed over time and eventually fall to 
Earth.

Most of the small objects burn up completely as they plunge into the upper 
atmosphere. But if they survive that initial immolation, they will slow down 
and cool as they reach thicker layers of the atmosphere. They'll hit the 
ground at subsonic speed.

In 1995 NASA developed a "design for demise" guideline in which new 
satellites of a certain size are capable of being de-orbited in a controlled 
manner and dropped into the vast landing zone of the South Pacific. That 
rule applies to the international space station, which under current policy 
will remain aloft until 2020 but could remain operable at least until 2028 
under NASA's projections.

Eventually the space station has to come down. NASA plans to attach a 
spacecraft that will slow the station in a precise manner that permits a 
Pacific splashdown.

Even then, it's not an exact science. The space station is 80 times the size 
of UARS and its breaking apart will create a debris field nearly 4,000 miles 
long.

"Rest assured that we have it totally in control," said Jeff Arend, NASA's 
program integration manager for the space station.

When UARS fragments hit the surface, people should be cautious about 
handling them. There's nothing toxic in the mix, but somebody could get cut 
on the metal, Johnson said. And, for the record, the debris belongs to the 
U.S. government.

Some years ago, a man in Texas tried to use the crashed cone of a rocket for 
a hot tub in his back yard. NASA dissuaded him, Johnson said, with the 
assistance of the Justice Department.


-------------------------
Phil Whitmer