[meteorite-list] UARS Fiery Return Now Expected Overnight Tonight

[Ron Baalke]

http://www.spaceflightnow.com/news/n1109/23uars/

Satellite's fiery return now expected overnight tonight
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE"
& USED WITH PERMISSION
September 23, 2011

NASA's decommissioned Upper Atmosphere Research Satellite, out of gas
and out of control, is not descending toward re-entry as rapidly as
expected, officials say, likely delaying the satellite's kamikaze plunge
to Earth by a few hours to late Friday or early Saturday. Experts expect
more than two dozen chunks of debris to survive re-entry and hit the
ground in a 500-mile-long footprint somewhere along the satellite's
orbital track.

But given the bus-size 6.3-ton's satellite's trajectory and the vast
areas of ocean and sparsely populated areas UARS passes over, experts
say it is unlikely any falling debris will result in injuries or
significant property damage. Additional radar tracking is required to
pinpoint when -- and where -- the satellite will make its final descent.

"As of 10:30 a.m. EDT on Sept. 23, 2011, the orbit of UARS was 100 miles
by 105 miles (160 km by 170 km)," NASA said in a brief update. "Re-entry
is expected late Friday, Sept. 23, or early Saturday, Sept. 24, Eastern
Daylight Time. Solar activity is no longer the major factor in the
satellite's rate of descent. The satellite's orientation or
configuration apparently has changed, and that is now slowing its descent.

"There is a low probability any debris that survives re-entry will land
in the United States, but the possibility cannot be discounted because
of this changing rate of descent. It is still too early to predict the
time and location of re-entry with any certainty, but predictions will
become more refined in the next 12 to 18 hours."

A subsequent update from U.S. Strategic Command, which operates a global
radar network used to monitor more than 20,000 objects in low-Earth
orbit, predicted the satellite would re-enter sometime around 11:34 p.m.
EDT Friday as the spacecraft flies over the southern Indian Ocean. But
the prediction was uncertain by several hours and at orbital velocities
of 5 miles per second, just 10-minutes of uncertainty translates into
3,000 miles of uncertainty in position.

The centerpiece of a $750 million mission, the Upper Atmosphere Research
satellite was launched from the shuttle Discovery in September 1991. The
solar-powered satellite studied a wide variety of atmospheric phenomena,
including the depletion of Earth's ozone layer 15 to 30 miles up.

The long-lived satellite was decommissioned in 2005 and one side of its
orbit was lowered using the last of its fuel to hasten re-entry and
minimize the chances of orbital collisions that could produce even more
orbital debris. No more fuel is available for maneuvering and the
satellite's re-entry will be "uncontrolled."

Nick Johnson, chief scientist with NASA's Orbital Debris Program at the
Johnson Space Center in Houston, told reporters last week he expects
most of the satellite to burn up as it slams into the dense lower
atmosphere at more than 17,000 mph. But computer software used to
analyze possible re-entry outcomes predicts 26 pieces of debris will
survive to impact the surface in a 500-mile-long down-range footprint.

"We looked at those 26 pieces and how big they are and we've looked at
the fact they can hit anywhere in the world between 57 north and 57
south and we looked at what the population density of the world is," he
said. "Numerically, it comes out to a chance of 1-in-3,200 that one
person anywhere in the world might be struck by a piece of debris. Those
are obviously very, very low odds that anybody's going to be impacted by
this debris."

For comparison, some 42.5 tons of wreckage from the shuttle Columbia hit
the ground in a footprint stretching from central Texas to Louisiana
when the orbiter broke apart during re-entry in 2003. No one on the
ground was injured and no significant property damage was reported.