MORE AND MORE SPACE DEBRIS COLLISIONS OCCURING.

[MeteorWayne]

The first Iridium 33 debris has started showing up on the SOCRATES page:

http://celestrak.com/SOCRATES/top10minrange.asp

 

[cyclonebuster]

We need a few solar powered ABLs in orbit to zap this stuff and deorbit it.


Experts: Get Ready for More Close Calls in Orbit

WASHINGTON — The near-hit of space junk Thursday was a warning shot fired across the bow of the international space station , experts said. There's likely more to come in the future.

With less than an hour's notice, the three astronauts were told they'd have to seek shelter in a Russian capsule parked at the space station in case a speeding piece of space junk hit Thursday.

If it hit and they were in the main part of the station, they'd have only 10 minutes of safety, Mission Control told them. A hole in the space station could mean loss of air, loss of pressure and eventual loss of life.

http://www.foxnews.com/story/0,2933,509130,00.html

 

[cyclonebuster]

Space Shuttle, Space Station Dodge More Space Junk

CAPE CANAVERAL, Fla. — Confronted with orbiting junk again, NASA ordered the astronauts aboard the linked space station and shuttle Discovery to move out of the way of a piece of debris Sunday.

Discovery's pilots fired their ship's thrusters to reorient the docked spacecraft to avoid a small piece from a 10-year-old Chinese rocket body that was due to pass uncomfortably close during Monday's planned spacewalk.

Mission Control said keeping the spacecraft in this position for about three hours — with Discovery's belly facing forward — would result in a slow, natural drag of about a foot per second, enough to get the complex out of the way of the 4-inch piece of junk.

http://www.foxnews.com/story/0,2933,510056,00.html

 

[MeteorWayne]

And your point is? In consideration of the all capital letter thread title, and since there are more than 3 current discussions, I'm inclined to close this one.

 

[cyclonebuster]

What for I started this subject years ago when the first ones collided?

 

[MeteorWayne]

Actually, this thread with the ALL CAPITAL LETTER TITLE was started about 5 weeks ago, not years ago....

 

[job1207]

http://celestrak.com/cgi-bin/searchSOCRATES.pl

If you check, there is ANOTHER IRIDIUM HIT predicted for April 7th!!!!!

Really. The sky is falling.

Cosmos 1190 and Iridium 81 at 08:50 Rel velocity is 14.492 km/sec. That is predicting a pretty much head on collision at orbital speeds!!!

Someone call Iridium. Seriously.

 

[MeteorWayne]

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 dodging every possible impact.

Life in space is tough, and fraught with risk...

 

[DrRocket]

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,

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.

The limiting factor in the life of most satellites is the fuel for stationkeeping. You are quite correct in recommending that it not be wasted playing dodgeball when the chances of a collision, even when a body is predicted to pass near by, is very small. A satellite is a pretty small target in the grand scheme of the available volume for orbiting bodies.

 

[job1207]

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

 

[MeteorWayne]

Again, you don't get the point. The impact probabilities were lower for the actual Iridium/Kosmos impact. If the operators spent the propellant on every low probability impact, there would be no fuel left to keep it in orbit. So you might as well deorbit everything. That's just not realistic. Sorry, but pragmatism is a valid point of view.

 

[job1207]

You are not answering the ? and acting in a superior manner. u are implying that you should never move a satellite. That is absurd.

This is predicted to be a HIGH PROBABILITY of impact. NOT LOW.

So what do you do for the high probability impacts????

First, I would recompute
Second if confirmed I would move the Iridium.
The increase in space debris is more of a concern then a satellite which is at the end of it's useful life.

 

[MeteorWayne]

I can't beat it into your head. If the satellites were moved for every potential impact, they would use all ther propellant and would not be able to stay in their orbit. Might as well deorbit them ASAP, and have no useful satellites in orbit anywhere.

That would have serious impacts on our lives....no cellphones, no GPS, no beepers, no well, almost anything....

 

[job1207]

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.

 

[MeteorWayne]

Again, the Iridium 33/Kosmos collision was a low risk interception. If the tracks were shifted for every such "close" conjunction, there would be no propellant left for normal stationkeeping. So you might as well deorbit everything out there.

 

[Mee_n_Mac]

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.

Here's a question. How often do you think there are "high probability" conjunctions ?

EDIT : I note that a collision between Cosmos 1190 and Iridium 81 no longer makes the top 10 on SOCRATES page. So what happened ?

 

[MeteorWayne]

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)

 

[Mee_n_Mac]

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)

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 !

Seems to me the world needs some really high precision tracking radars / sensors to reduce the error bars on the track(s) so a better estimation of collision probability can be made. Then we can talk about how we address the clean-up issue.

 

[MeteorWayne]

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.

 

[DrRocket]

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

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/

Anyone who quotes probabilities as "1.000, with threee zeroes, not two or one" clearly does not understand probability theory at all. It is pretty clear that the actual probability, significant figures asside, can be NO LARGER than 1, probabilities are rather like that. Now, if one has any potential for error, any at all, the predicted probability must be something less than 1, and since 0.999999999999......... =1. when one quotes probabilities approaching 1 one simply needs to tell the audience just how many "9s there are. If the quote is 1.000 then it would seem that someone is simply playing games and hoping that the audience is unschooled in mathematics, or just isn't too bright. Which is your case ?

The remainder of what I and MeteroWayne have tried to tell you is not changed by your little tantrum. It simply is not rational or reasonable for satellites to start playing dodgeball because of imagined collisions. To do so would simply put undersirable and artifical limitation on the lifetimes of valuable satellites with no benefit in alsmost all cases. If any steps at all were to be taken it would be far more reasonable to de-orbit bodies at the end of their usefulness.

 

[drwayne]

I wonder what the covariance was on the states during the period of time when the probability of
collision was nominally so high?

Wayne

 

[silylene]

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.

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.

I (aka silylene) still maintain that it is time to de-orbit Iridium now.

 

[DrRocket]

I wonder what the covariance was on the states during the period of time when the probability of
collision was nominally so high?

Wayne

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 ?

 

[Mee_n_Mac]

I wonder what the covariance was on the states during the period of time when the probability of
collision was nominally so high?

Wayne

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 ?

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.

http://celestrak.com/SOCRATES/AIAA-03-548.pdf

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.

 

[DrRocket]

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.

http://celestrak.com/SOCRATES/AIAA-03-548.pdf

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.

There are couple of issues here.

First, it quite possible for an event of probability zero to occur and it is possible for an event of probability 1 to not occur, within the rigorous rules of measure-theoretic probbility theory. To understand this you have to think of events as sets, certain subsets of fixed probability space, and of the probability of an event as a function defined on the class of events that assigns to a set a number between 0 and 1 inclusive, called the "measure" of the set, that obeys some relatively intuitive rules (such as the measure of a countable union of disjoint sets is the sum of their measures). In that setting, which is the setting for modern probability theory, an event of probability zero is simply a set of measure zero, and it need not be an empty set. For instance if you consider the typical continuous probability density functions encountered in many engineering or physics applications, the probability of any singleton event (any specific number) is zero -- which is nothing more than the statement that the usual Riemann integral of a function over a single point is zero.

Another way to think about that is with the law of large numbers. Roughly speaking the probability of an event is the number of times K and event occurs in N trials, divided by N (i.e. K/N) in the limit as N grows without bound. If and event occurs only a finite number of times, or even on average sqet(N) times then the limit as N goes to infinity is zero and the probability of that event is zero even though it occurs occasionally.

But more importantly, when in an application like the prediction of collisions probabilities are quoted, what is being described is not really a random event but rather the error surrounding a calculation based on data of limited accuracy. If you actually had sufficiently accurate orbital parameters you could calculate trajectories precisely and make an absolute prediction as to whether or not there would be a collision -- no probabilities requires and a completely deterministic prediction. The use of probabilistic language is simply a code for uncertainty in the data, not randomness in the physics. Basically they assume that the input parameters are random variables with a mean value equal to the measures value and some ASSUMED probability distribution. Based on that assumption one can calculate the probability of the bodies coming within some distance of one another, a sphere sufficiently small as to constitute a collision. Now, it should be quite clear that if there is any real level of uncertainty at all that a reasonable model cannot result in a probability of 1. Further if it does, then the probability is 1, not 1,00000000 with the implication that the uncertainty is covered by a number of "significant figures". If you have some uncertainty then the proper way to describe it is to show the probability as something like 0.99999999x. It damn sure is not 1.000000001.

The real reason that a collision can be quoted as having probability 1 and not happen is not, however, due to any of the above, and certainly not to an occurrence of probability zero. It is due to the simple fact that the quoted probabilities are quite simply nonsense. They are based on false assumptions and bad data. GIGO.

In short the probabilities quoted are not the probability of a collision, but the probability that the forecaster knows what he is talking about.