The dynamics of the impact also affect the kinetic energy transfer. Remember, you don't just "lose" energy, it's translated into other forms of energy, other vectors, etc.
If the two bodies hit pretty much directly, then much of the "lost" orbital energy would be used up in melting, shattering and vaporizing the structures of the bodies. If the collision path would have only a half or a quarter of one of the bodies intersecting the other, less kinetic energy is used up in vaporization and the resulting debris' orbits are altered less than in a direct impact. If only a very small physical interaction occurs (i.e., if an antenna on one vehicle snags an antenna on the other vehicle), the two bodies will still break up (especially if the "just barely" contact comes at 11 km/sec!), but they'll break up due to the extreme rotational rates imparted by the "brush-by". This last scenario changes the orbits of the resulting debris the least.
I don't know if our "security assets" are able to image satellites at 800km range well enough to characterize the resulting debris from the Cosmos-Iridium collision, but the extent of debris and its orbital characteristics (as tracked by radar) ought to give us some idea as to how direct a hit they endured.
-the other Doug
Full Version: On-orbit Satellite Collision
As noted by kwan3217, there is already a very nice service to look at collision probabilities: http://celestrak.com/SOCRATES
If you look at today's top 10, the highest probability is 2.785E-03 (1 in 359). This is certainly a lot higher than I would have expected. I wonder if Iridium was using this service, and if so how, and if they were concerned at all before the collision.
If you look at today's top 10, the highest probability is 2.785E-03 (1 in 359). This is certainly a lot higher than I would have expected. I wonder if Iridium was using this service, and if so how, and if they were concerned at all before the collision.
Via NSF.com - a couple of simulations showing debris evolution: http://www.agi.com/corporate/mediaCenter/n...iridium-cosmos/
QUOTE (mcaplinger @ Feb 14 2009, 12:41 AM) 
As noted by kwan3217, there is already a very nice service to look at collision probabilities: http://celestrak.com/SOCRATES
That is indeed a extremely interesting service, and I'm equally amazed at the results, didn't know also there were regularly so many encounters at such close ranges!
If the Iridium collision didn't even make it into the top 10 I'm not surprised that no prior avoidance action was undertaken, as has been mentioned already if you start maneuvering for each of these close encounters you will run out of fuel quite soon, and indeed it causes problems with your commercial service as satellites will be drifting out of their slots, etc, etc.
Still, now the question opens, if the Iridium collision did not make it into the top 10, then how accurate where/are the details of the orbits? Did either of the satellites recently manoeuvre ( I know the Cosmos satellite was dead, but it could have been losing fuel or some pressurized gas, causing a slight propulsion), how accurate is the tracking really and how often are those parameters updated?
At such speeds and with almost 90 degree intersection, you need only a very, very, minor tracking error and the situation completely changes...
It will be interesting to see how (or if) regulatory bodies will respond. (For that matter, what regulatory body would have jurisdiction? The US government could make laws requiring the US companies to take precautions, but they have no authority over non-US companies, or the space agencies of other nations. It seems unlikely that the UN will respond, but you never know...)
Well, the right answer IMHO would be at this point to add it to the duties of the International Civil Aviation Organization (ICAO); they're sort of like an international version of the FAA. Any sort of regulation's gotta be multinational, obviously.
From SpaceWeather:
"LISTEN UP: The US Air Force Space Surveillance Radar is monitoring the skies above Texas for echoes from satellite fragments. Try listening on Saturday, Feb. 14th between 10:45 and 10:55 am CST (1645 - 1655 UT). That's when Iridium 33 would have passed over the radar intact had it not been shattered."
On the spaceweather site 'Try listening' is an active link (I think).
"LISTEN UP: The US Air Force Space Surveillance Radar is monitoring the skies above Texas for echoes from satellite fragments. Try listening on Saturday, Feb. 14th between 10:45 and 10:55 am CST (1645 - 1655 UT). That's when Iridium 33 would have passed over the radar intact had it not been shattered."
On the spaceweather site 'Try listening' is an active link (I think).
QUOTE (Vultur @ Feb 14 2009, 03:47 AM)
It will be interesting to see how (or if) regulatory bodies will respond. ...... It seems unlikely that the UN will respond, but you never know...)
Well we might not have to wait too long……in July 08 the UN General Assembly recommendation that the Scientific and Technical Subcommittee of the Committee on the Peaceful Uses of Outer Space should consider space debris as an agenda item at it next session. The next session (the 46th) started on 9th Feb 09 in Vienna and according to the agenda (published in Dec 08) it’s due to discuss space debris this Monday/Tuesday (16 -17 Feb 09). What timing…no guesses as to what they will be talking about! It will probably be a closed session but the daily report might be interesting.
The GA also ”.. noted with appreciation that some States were already implementing space debris mitigation measures on a voluntary basis, through national mechanisms and consistent with the Inter-Agency Space Debris Coordination Committee Guidelines and the Space Debris Mitigation Guidelines …..(and) invited other Member States to implement, through relevant national mechanisms, the Space Debris Mitigation Guidelines.” Space Debris Mitigation Guidelines cover both Prevention of on-orbit collisions and Post-mission disposal.
I'm surprised this happened in my lifetime! The future is now...
Does anyone know if de-orbit tethers have been / will be added to any existing/future payloads?
I wonder how many more collisions like this there can be before the debris situation becomes unmanageable....
Does anyone know if de-orbit tethers have been / will be added to any existing/future payloads?
I wonder how many more collisions like this there can be before the debris situation becomes unmanageable....
CNN reporting that a fireball was imaged and sonic booms were heard over Texas: http://www.cnn.com/2009/US/02/15/texas.sky.debris/index.html
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! 
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.
Click to view attachment
Click to view attachment
http://www.thespacereview.com/article/1314/1 is a very good summary of this event.
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.
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!
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?
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?
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?
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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