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On-orbit Satellite Collision
nprev
post Feb 16 2009, 02:46 AM
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Hmm. The speed of the object is fairly slow, which is consistent for a debris re-entry, but it could still be a natural meteor. Either way, if I was in central/eastern Texas right now I'd start lookin' for chunks! smile.gif


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Guest_PhilCo126_*
post Feb 16 2009, 07:29 AM
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Another weblink with the video footage:
http://www.news8austin.com/content/top_sto...asp?ArID=232081
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Exploitcorporati...
post Feb 17 2009, 03:44 AM
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I've been following this story with astonishment and dismay. Such infinitesimal odds, and so much potential for harm! Just a few weeks ago I was watching WALL-E with my son and explaining why I thought it was funny when they ploughed through the mass of satellites when leaving Earth. Doesn't seem so funny now. I stumbled across this lovely image while working on another project today, and it seems appropriate.

Attached Image


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mcaplinger
post Feb 23 2009, 02:48 PM
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http://www.thespacereview.com/article/1314/1 is a very good summary of this event.


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stevesliva
post Feb 23 2009, 04:42 PM
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QUOTE (mcaplinger @ Feb 23 2009, 10:48 AM) *
http://www.thespacereview.com/article/1314/1 is a very good summary of this event.


QUOTE
In this vein, I think it can be argued that the US military committed a sin of omission in the case of the Iridium-Cosmos collision. The US military maintains the best and most complete satellite catalog in the world and had the data to provide collision warning to Iridium. But as was discussed earlier in this article, the US military only looks at a limited list of satellites for collisions. It also appears that at some point they stopped providing collision warning for the Iridium constellation.

Given the complexities of the conjunction assessment process, it is understandable that the US military does not have the resources or capability to screen all of the estimated 900 payloads in Earth orbit. But both the US military and Iridium knew that there were many close approaches with the Iridium constellation and that eventually one could collide. Perhaps both thought that if they stopped looking at the problem it would go away.


My bold. Ha. Given that supercomputers and salaries are an order of magnitude cheaper than satellites, perhaps that will change. (Although the Iridium constellation is odd in that is was essentially gotten for free after bankruptcy.) The conclusions in the article are a little more nuanced. Good article!
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helvick
post Feb 23 2009, 06:12 PM
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Nice post on the collision by Diandra over at CocktailPArtyPhysics.

She mentions two things that I hadn't come across before - firstly that the predicted closest approach of the two satellites prior to the impact had been around 600m and secondly that the increased atmospheric drag caused by the recent Sunspot minimum is a prime suspect in explaining why the predicted orbits were sufficiently incorrect to turn that 600m into 0.

600m would still seem like far too close for comfort to me but does anyone know what the normal error in such things would have been expected to be?
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Tom Womack
post Feb 24 2009, 01:39 PM
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QUOTE (helvick @ Feb 23 2009, 06:12 PM) *
Nice post on the collision by Diandra over at CocktailPArtyPhysics.

She mentions two things that I hadn't come across before - firstly that the predicted closest approach of the two satellites prior to the impact had been around 600m and secondly that the increased atmospheric drag caused by the recent Sunspot minimum is a prime suspect in explaining why the predicted orbits were sufficiently incorrect to turn that 600m into 0.

600m would still seem like far too close for comfort to me but does anyone know what the normal error in such things would have been expected to be?


http://celestrak.com/SOCRATES/top10maxprob.asp almost always shows at least one expected pass at 0.1km or less, with an estimated probability of collision more than one in a thousand; since we don't see a collision every few years, I suspect their model is not perfect.

From a 500km circular orbit, a change in velocity by 1 centimetre per second changes the radius of the orbit by 18 metres, so you have to know the velocity very accurately indeed.
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