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Excellent point. So far no satellite has been taken out by a collision. There is a lot of room up there. And while close may count in horseshoes, it doesn't in space collisions. You either have a direct hit or you have nothing.MeteorWayne":2awlaw1g said:Yeah, except that closer "conjunctions" have resulted in no impact. So the question becomes do you want to spend your fuel (propellant) on impacts that most likely might not happen, or do you want to spend your propelant on impacts that most likely won't happen. Oops, they are the same thing!
If you want your satellite to last as long as possible (a desirable goal), then you can't waste your propellant dodgeing every possible imapct.
Life in space is tough, and fraught with risk,
Here's a question. How often do you think there are "high probability" conjunctions ?job1207":3pmgsihq said:I am not saying that the satellites should be moved for every threat. That is absurd as your assertion that I am saying that. i am not.
If Dr. Strosser were grading your logic, you would not pass the course.
High prob - confirm - do something. That makes sense, esp for a satellite about to be taken out of service.
I note that as of today I've yet to read about another satellite collision so I'll assume that means it (the collision predicted a few posts up) didn't happen. This illustrates the problem nicely. We have predictions from "noisy" data of a potential collision. It happens frequently enough that moving a satellite whenever such a prediction was made would quickly use up all the fuel. Yet the consequences of allowing a few more collisions to occur is going to be baaad !MeteorWayne":2z6lsou6 said:If you watch the SOCRATES list daily, you will see they are quite common.
As for why one disappeared, further refinements of the orbits of the objects (or time expired)
You are correct in that there was indeed one, just one but relatively recent, quite accidental collision. Pretty much a fluke. And the projections for the encounter were apparently for a miss: http://tmfassociates.com/blog/2009/02/1 ... collision/job1207":3q9oafp1 said:huh?
First of all we just had an Iridium hit. Where were you? Secondly, these set of satellites are due for replacement. Thirdly, the likelihood of a hit is predicted at 1.00.
Now, on these occasions, a hit has not always occurred, that is true, but moving this satellite should be routine.
I am truly shocked by the comments so far.
Here is the data. Not the probability of a hit is 1.000, with three zeros, not two or one.
11869 COSMOS 1190 3.953 1.000E+00 0.000 0.006 14.492
25468 IRIDIUM 81 4.038 2009 Apr 07 08:50:46.491 2009 Apr 07 08:50:46.836 2009 Apr 07 08:50:47.181
As you know I have seriously proposed de-orbiting the Iridium system in another thread (missing). ...but the thread seems to now be one of many of silylene's that unfortunately disappeared during the de-Pluckification of the forums. Iridium is not all that useful (and we all know that, despite supportive statements that people had posted), and the likelyhood of another Iridium collision in the upcoming years remains high, and in fact much higher than before, as thousands of debris were injected into the Iridium altitude window by the prior collision. I do believe that the risk of an escalating runaway of collisions is high, and this risk and the dangers it will pose to all future space travel and satellites far exceeds the minor benefits of keeping Iridium in orbit. I also recall that several of you agreed with me (in the prior (missing) thread) on this subject that there is a high likelyhood that we will get into a runaway escalation of collisions in the next few decades unless we de-orbit.MeteorWayne":24rvsubo said:Well you've really hit the nail on the head of the satellite there. At the current level of accuracy, moving for every possible collision would quickly exhaust all the fuel, so you might as well deorbit every satellite in orbit now before the fuel runs out. Of course, that's not realistic.
I don't know how much better the precision could be in orbital object tracking without spending multi millions of dollars for multiple locations of radars. Then it comes down to, of course, who will pay for it?
I don't know the answer.
Do you think we could get a sensible answer to a question regarding covariance of random variables from any person or group who thinks that quoting a probability as 1.000 is meaningful ?drwayne":2zap3jve said:I wonder what the covariance was on the states during the period of time when the probability of
collision was nominally so high?
To be fair to the poster, he was quoting what the SOCRATES people call "maximum probability". I've not bothered to read how this parameter is derived but I think the explanation can be found here.DrRocket":dlaedu9g said:Do you think we could get a sensible answer to a question regarding covariance of random variables from any person or group who thinks that quoting a probability as 1.000 is meaningful ?drwayne":dlaedu9g said:I wonder what the covariance was on the states during the period of time when the probability of
collision was nominally so high?
There are couple of issues here.Mee_n_Mac":c6vm9t2u said:To be fair to the poster, he was quoting what the SOCRATES people call "maximum probability". I've not bothered to read how this parameter is derived but I think the explanation can be found here.
Perhaps when I have time I'll read the above and figure out how something which supposedly has (had) a probability of 1.0 doesn't (didn't) happen.