from spaceflightnow.com
Two satellites collide in orbit
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: February 11, 2009
In an unprecedented space collision, a commercial Iridium communications
satellite and a presumably defunct Russian Cosmos satellite ran into
each other Tuesday above northern Siberia, creating a cloud of wreckage,
officials said today.
The international space station does not appear to be threatened by the
debris, they said, but it's not yet clear whether it poses a risk to any
other military or civilian satellites.
"They collided at an altitude of 790 kilometers (491 miles) over
northern Siberia Tuesday about noon Washington time," said Nicholas
Johnson, NASA's chief scientist for orbital debris at the Johnson Space
Center in Houston. "The U.S. space surveillance network detected a large
number of debris from both objects."
One source said nearly 300 fragments were being tracked, but Johnson
said it was not yet clear how much debris was generated.
"It's going to take a while," he said. "It's very, very difficult to
discriminate all those objects when they're really close together. And
so, over the next couple of days, we'll have a much better
understanding. But it's at a minimum, I think we're talking many, many
dozens, if not hundreds."
Asked which satellite was at fault, Johnson said "they ran into each
other. Nothing has the right of way up there. We don't have an air
traffic controller in space. There is no universal way of knowing what's
coming in your direction."
Iridium Satellite LLC operates a constellation of some 66 satellites,
along with orbital spares, to support satellite telephone operations
around the world. The spacecraft, which weigh about 1,485 pounds when
fully fueled, are in orbits tilted 86.4 degrees to the equator at an
altitude of about 485 miles. Ninety-five Iridium satellites were
launched between 1997 and 2002 and several have failed over the years.
Representatives of Iridium did not immediately return calls for
additional details.
Johnson said the collision Tuesday was unprecedented.
"Nothing to this extent (has happened before)," he said. "We've had
three other accidental collisions between what we call catalog objects,
but they were all much smaller than this and always a moderate sized
objects and a very small object. And these are two relatively big
objects. So this is a first, unfortunately."
As for the threat posed by the debris, Johnson said NASA carried out an
immediate analysis to determine whether the space station faced any
increased risk. The station, carrying three crew members, circles the
globe at an altitude of about 220 miles in an orbit tilted 51.6 degrees
to the equator.
"There are two issues: the immediate threat and a longer-term threat,"
he said. "It turns out, when you have a collision like this the debris
is thrown very energetically both to higher orbits and to lower orbits.
So there are actually debris from this event which we believe are going
through the space station's altitude already. Most of it is not, most of
it is still clustered up where the event took place. But a small number
are going through station's altitude.
"Yesterday, we did an assessment of what the risk might be to station
and we found it's going to be very, very small. As time goes on, those
debris will (come down) some over months, most over years and decades
and as the big ones come down they'll be tracked, we'll see them and the
worst-case scenario, we'll just dodge them if we have to. It's the small
things you can't see are the ones that can do you harm."
Asked if other satellites might be at risk, Johnson said "technically,
yes. What we're doing now is trying to quantify that risk. That's a work
in progress. It's only been 24 hours. We put first things first, which
is station and preparing for the next shuttle mission."
Most, if not all, of the debris is expected to eventually burn up in
Earth's atmosphere.
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