Two satellites collide in orbit

From: Greg Williams (
Date: Wed Feb 11 2009 - 21:59:32 UTC

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    Two satellites collide in orbit
    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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