How and Why Did Two Satellites Collide This Week?

The collision this week involving an active U.S. commercial Iridium satellite and an inactive Russian Cosmos 2251 satellite in low Earth orbit has, if nothing else, raised public awareness of the growing problem of space debris. But how and why did this collision happen? If NORAD, the U.S. Air Forces’s Space Surveillance Network, NASA’s Orbital Debris Program Office and other entities are tracking space debris, did anyone know the collision was going to occur? Those who analyze data and track satellites say predicting collisions is difficult because of changes in satellite orbits which occur due to solar radiation and the gravitational effects of the Moon and Earth. Therefore, the orbit analysis is only as good as the data, which may be imprecise. “The main problem here is the data quality for the data representing the satellites locations,” said Bob Hall, Technical Director of Analytical Graphics, Inc. (AGI), the company that released video and images on Thursday recreating the collision event. “Given the uncertainty in the accuracy of the TLE orbital data, I do not believe anyone was predicting or necessarily expecting an event.”

AGI has tools that run automatically every day such as SOCRATES – (Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space) which is based on the current space catalog supplied by NORAD to look for close approaches.

“This analysis is performed automatically every day and you can easily go in and search it,” Hall told Universe Today. “Because the analysis is performed with the public two-line element (TLE) set satellite catalog, the analysis is only as good as that imprecise data is. So when it shows conjunctions on any given day (and for Tuesday this Iridium event was not even in the ‘top 10’ close approach predictions!) this has to be taken with some uncertainty.”

Hall said the closest approach predicted for last Tuesday’s Iridium-Cosmos event was predicted to be 584 meters. “Again, as close as that sounds (and it is), there were at least 10 other on-orbit conjunction predictions that day alone with smaller miss distances,” Hall said.

Simulation of the satellite debris break-up. Image courtesy of Analytical Graphics, Inc. (

The crash occurred on Tuesday 485 miles above northern Siberia in a crowded polar orbit used by satellites that monitor weather, relay communications and perform scientific surveys.

The International Space Station, as well as most satellites can be maneuvered out of harm’s way to avoid a possible collision, but a defunct satellite like the Russian Cosmos 2251 has no such ability.

Even with the uncertainties of tracking orbiting satellites, one group, the Secure World Foundation, is calling for the need to establish a civil space traffic control system.

“Unfortunately, it appears that there was data warning about the possibility of this collision beforehand,” noted Brian Weeden, Technical Consultant for Secure World Foundation. “However, it must be stressed that close approaches between satellites somewhere in Earth orbit occurs on almost a weekly basis…and until this event, have never before resulted in an actual collision.”

Weeden agreed that in every case it is impossible to give a definite answer on whether or not two objects will actually collide, only probabilities and potential risks.

“Getting the right information to the right authorities in time to make the right avoidance maneuver decision is a very complicated process that doesn’t entirely exist yet,” Weeden said. “The Secure World Foundation is working with many other organizations around the world to try and develop this process.”

The Secure World Foundation endorses the creation of a space traffic control system.

“This collision underscores in a dramatic way the importance of instituting an international civil space situational awareness (SSA) system as soon as possible,” said Dr. Ray Williamson Executive Director of Secure World Foundation.

Williamson said that such a civil SSA system could have been used to warn the Iridium operations managers of the danger of collision and allow them to take evasive action. “In the absence of reliable ways to clear debris from orbit, it will be increasingly important to follow all active satellites to prevent future preventable collisions,” he added.

Before this collision, another collision event happened in 1996, when a French spy satellite called Cerise was severely damaged by a piece of debris from the rocket that launched it.

The United States tracks debris or micro-meteorites down to 10 cm wide, but objects as small as a scrap of peeled-off paint can pose a threat once they start hurtling at orbital speeds through space.

Sources: Email exchange with Bob Hall of AGI, Secure World Foundation press release, Reuters

32 Replies to “How and Why Did Two Satellites Collide This Week?”

  1. Thank very much for the article from someone in the field of expertise. It explains a awful lot;
    However worrying is the statement;
    “Impossible to give a definite answer on whether or not two objects will actually collide, only probabilities and potential risks.”
    What is the probability and potential risk is the million dollar question.
    Also worrying “…objects as small as a scrap of peeled-off paint can pose a threat once they start hurtling at orbital speeds through space.”
    This indicate that collisions and damage could occur at anytime, whose origins will remain uncertain. This confirms various Universe Today articles in the last year – and some of the comments.
    The question remains. what can be done to improve the situation that is not already being done?

  2. Conspiracy Theory: Now that the USA and China have displayed the ability to knock out a satellite in orbit for the ground, Russia has completed a test that displays its ability to kill out a satellite too. Taking it out over Northern Siberia gave them a perfect view.

    The fact that the “event was not even in the ‘top 10’ close approach predictions” adds weight to the theory that it was a deliberate kill rather than a random event.

    Thoughts anyone?

  3. The major point of concern, in my view, is that the idea of setting a space traffic control system, international as is necessarily has to be, will always be sabotaged by all nations with an invested interest in having some satellite activity secret. I.e., anyone with spy satellites up there. I.e., just about everyone.

    The only way they’ll accept space traffic control is if they are forced to. And that, I’m afraid, will not happen with the mere destruction of an iridium satellite. Something much more serious will need to happen.

    Things tend to get much worse before they get better.

  4. My feeling is that these are going to become much more common. As the satellites and debris increases the instances will rise exponentially. I fear this is a start of a trend.
    Biggest disappointment will be the impact on science and exploration. Hope this does not happen.

  5. Craig Miller, I have the very same gut feeling about this collision. The mere coincidence that it happened directly over Russia, gives high credibility to the purposeful knock down as a test.

    Considering the real power by Putin in Russia, and his desire to re-establish the old KGB, this is almost without a doubt.

  6. Craig Miller and Bill J
    Absolute incredulous bull. Russia has just as much to lose as America has.
    All this sound like absolute paranoia because of America’s fast decent in space exploration and the rise of many other countries interest in the region. Sure, blame everyone else for your own decrepitude, but the fact is you have no evidence for your claims.
    Recommend you read the article in the Sydney Morning Herald from the Russian (whose view are at least seem reasonably partisan to reality) at;
    No wonder much of the world despises the U.S. for its arrogance and stupidity… WAKE UP !!!

  7. “Russia has completed a test that displays its ability to kill out a satellite too. Taking it out over Northern Siberia gave them a perfect view.”

    Russia (as the Soviet Union) demonstrated a rendezvous-and-explode ASAT capability many years ago. They have nothing to prove, especially at this particular time…

    …This satellite collision is just what it seems to be, take it at face value.

  8. Dear Mr. Miller,

    you created not only a conspiracy theory but also an “inspiracy” theory 😉

    It inspired me to imagine that not Cosmos 2251 was the killer but the victim. It was dead already, unable to move. But the Iridium sat was under full control and was reshaped into a weapon. From whom? I guess you will find the name of the backer in one of Michael More’s works or in Simon Hersh’s articles. They wanted to test the ability of transforming civil satelites into battle stars in case of a future space war.

    I’m just kidding. So don’t worry. Be happy.


  9. While I would not reject the possibility of secret government at work, limited budget and/or a series of unlikely events was more likely the culprit. Each active satellite has a limited amount of fuel for course correction and a limited budget for the decision making to correct or not correct.
    Human error is also possible, and that human’s career is being protected, by others who suspect a human error was made.
    In the case of Indium, I believe it is presently owned by the USA government and a course correction to avoid possible collisions are likely as not to reduce the overall reliability of the indium system.
    Redundancy, and more advanced equipment can decrease the likelihood of another collision of large and medium size objects, but both are expensive, and there is a tendency to think the insurance company loses in the case of commercial satellites.
    If I understand correctly, the optical search with telescopes is done at only one USA location. Obviously several locations and sharing the data would decrease the probability of a close approach not being predicted and the error bars would be narrowed at least slightly. Some items and some passes of 10 cm items are more likely to be detected by RADAR. Newer and more powerful Radar should push the minimum size detected down to about one centimeter, which would possibly require a new computer as the number of detections could increase by 100. I’m mostly guessing, so don’t hesitate to rebut. Neil

  10. Hummmm, I have a gut feeling that Craig Miller may be on to something.
    After the invasion of Georgia and the missile defense issues in Poland or where ever maybe this was a warning shot.

  11. Mr. Miller,
    I’m sitting here wondering -why- you would say such a thing without -any- facts to support it at all. Are you simply that pathetic and paranoid that you have to go looking for “conspiracies”? What…no terrorists attacks on your home town and you feel the need blame somebody for something regardless of any truth, facts or who it may hurt? Is your little life really that lost without something like the “cold war” to give you purpose??

    The problem with making comments such as you have here is that there are other folks who are just dumb enough to believe you….and apparently people such as yourself -never- seem to take that into consideration. Skepticism and having an “opinion” are one thing but publicly proposing a conspiracy such as this is without any facts what so ever another thing completely.

    Let’s think about this for a moment. The Russian satellite is “inactive” and here you are claiming that they used it to prove they could take out an active American satalilite…WHY??? This is like turning a blind, crippled poodle loose on someone’s 2 year old Rottweiler! Beyond that, as other’s have said, activities such as this are going to be just as problematic and detrimental to the Russians as it would be to anyone else…there is no advantage to it strategically or otherwise for anyone. In addition, there have been several other proposed theories that would easily explain this incident…including simple human error…yet in your mind you jumped right to conspiracy. Living your life in fear and paranoia is no way to live there dude and it’s very wrong to expect others to do the same.

    Mindless dribble such as this -ALWAYS- does more harm than good. Ooh, ooh…the Russians may be attacking…we all better start building bomb shelters again and the country needs to start building up those nuclear weapons….don’t people have anything better to do with their lives?

    I’m sorry, but that needed to be said.

  12. Alan, Mr. Miller,

    experience teached me to associate gut feelings with women. It is their way to decide what they want, I guess.

    If you don’t like the Russians than say it. Don’t express it like chicks would.

  13. OK lets go through some “things”

    1) Who says the russian satellite was inactive? How do they know?

    2) what do we do with the debris now? Is it dispersing? Will it “clutter” up areas that will make it impossible or expensive to position satellites there?

    3) I thought this was a science (thus rational) forum and not a forum of namecallling when someone voices their thoughts? But ofcourse, it shows just who the easily offended are.

    4) a number of questions remain… One why didn’t Iridium move the Sat, What is their “close call” tolerance level and finally what are the options of clean up? will the objects orbit degrade and thus burn up?
    with the inferiority of the RADARs trajectory predictions, what now happens with all thos other thousands of pieces that it has to track and calculate?

    Now if we can dispense with the immature namecalling, it would be soooo refreshing. What r u..? children? So the guy didn’t document his thoughts…. Gee, I don’t see where documentation really matters in a case such as this where pretty much every theory could be plausible.

  14. Dear Tareece,

    the use of the expression “like chicks” is like calling names, but to suspect a partner on the ISS of doing a warlike action is a notable “theory” for you?

    Give us a break, please!

  15. Dear Nancy Atkinson,

    you should have your points of contact at AGI. They are experts. Won’t you contact them and interview them about the plausibility of those conspiracy theories here? Don’t you have any interest in damming up this practice here?

  16. Firstly, I don’t buy into the deliberate collision idea. My experience is that errors, ignorance, and negligence are far more likely explanations. Plus this seems like a poor choice for a test. I believe the US and Chinese intercepts were much lower than this.

    Next, it would seem to me from the numbers on the near miss that we collectively don’t have a good handle on the prediction errors. To me that says we need to get a better handle and define a range of potential collisons and then investigate anything inside that range to get better data. The figure of about 600 meters really surprised me.

    We also need to get a good sense of how long in advance we need to predict these things and what can be done about it.

    I doubt it’s as simple as making two course corrections to avoid a collision and get back on course. You don’t just swerve around an obstacle like you would in a car. Any changes you make will have implications with all kinds of potential future collisions. Those probably won’t need to be addressed right at the point of correction but it will make things interesting.

    What is clear is this is a big wake up call. And we need to look at this in a lot more detail.

  17. Correction according to the article in the Syndey Herald the Chinese intercept was near the same altitude. (I knew it was higher than the US one, but didn’t realize it was this high).

  18. Hmmm, interesting forum.

    I’ve read articles on this site for years now and have LOVED all aspects of space science since early childhood. I tend to avoid forums in general because, and I’m disappointed to see it applies here too, there are too many people who express unreasonable opinions (if science & rationality are guiding principles) such as those of Craig Miller & Bill J. Sadly, they then get support from others such as alan.

    It is worsened then by others who actually let themselves be goaded into emotionally reacting (to postings that are obviously intended to be inflammatory (likely because Miller, J & alan have a lot of spare time on their hands)) .

    Salacious B. & James Walczak – blaming Americans for conspiracy theories? You’re both too funny & like Miller, J & alan you both have a lot of spare time on your hands.

    dollhopf – your HILARIOUS!!! Loved your comment!

    Wang: the most reasonable by far!

    Me: A med student who just finished up a neurology block exam Fri and am doing NOTHING but surfing the net and going to the gym this weekend have really been enlightened by this forum. I won’t be back to check on replies, etc so take care all of you and try to enjoy the science offered the site – which is outstanding, and fine chatrooms to pursue your various & sundry interests if you can’t stick to the science in a ‘science forum’ for the sake of everyone else…lol.


    Cronos D

  19. opps, some typos above…”science offered *on the site” and “…*find chatrooms”…lol…take care again everyone!!

  20. Filling space with our debris is no different than the polluting we’ve done on Earth, it is dangerous to the health of any living species. The Russians are likely guilty only of being irresponsible, as we Americans have as well. As to the comment made by dollhopf, one can only assume his vast collection of “experience’ coincides with the onset of some form of dementia. That is assuming he ever possessed manners. Either way, the comment he was referring to seems to have been made by a man, and was therefore totally inappropriate, and completely unscientific.

  21. I suggest that in the future all satellites (of course except classified sats) have to be equipped with GPS. The sat then could itself issue the information of its position and direction with unmatched accuracy. And the sat itself is expected to report its position to the space control tower operator. Navigation systems do not weight much, so launch costs would hardly suffer an increase by it.

    But of course as soonas a sat goes into “dead mode” then the navi would also power off. But for operational sats this should work with excellence.

    And “kymmy_cat”, just relax 🙂 Thanks in advance! Dollhopf

  22. Dear Mang, I am noticing that noone besides “Cronos D” did rate your February 15th, 2009 at 2:16 pm comment positive in an own comment till now. I am sorry about that.

  23. How many other facts and figures that we live by are a result of poor data quality?

  24. The GPS thing would work for commercial satellites but I doubt the military would agree to it since their satellite could then be easily tracked, although surely all governments technologically advanced enough to pose a threat already know our military satellite orbits. MOK

  25. would the collision have anything to do with my garmin gps is wacky like determining that for a 50 mile trip it will take 5.5 hours to drive 50 miles.

  26. My gps says more like; 80.467 kilometres trip takes 5.5 hours to drive 80.457 kilometres
    Clearly not the same problem!


  27. Salacious B. Crumb- you are right, there’s no reason for anyone to ‘crash’ their vehicles with anyone else, as the ending results and the ‘gains’ by the ‘offending’ collider will be zero when their vehicle eventually collides with the junk pieces they created. Anyone believing in a ‘conspiracy’ theory should realize there’s no such thing as ‘quick’ manuvering of any vehicles in Earths’outer space with the current proplusion technology available, besides, any craft has a very limited amount of fuel/power available.
    The manuvering ability of any ‘remote controlled ‘ satillites makes the ultra-large petroleum supertankers seem like a 1 person powered craft!. GPS after the fact! We have to find some ways to get rid of the space junk. .

  28. Salacious B. Crumb-I’ve read an interesting previous link you’rve posted on how satillites just ‘corrodes’ due to the solar winds,cosmic-rays.etc- with over 10-11K pieces ‘detectable’ junk pieces with todays technology, it is impossible with the keep tabs of all-the only orbitiing vehicles that will be monitored for possilbe hits are manned, high priority satilites then other priority satillites. It appeared the US already had ‘redundant’
    Iridium satellites ready to take the place of the destroyed one quickly. Ground control do make mistakes, just human nature,what ground control looks for is some satillite or ‘junk’ that appeared to change orbits and something unexpected except to know it may be a possible ‘satilitte killer’. Again, it takes quite a period of time and distance for any satillite or ‘junk’ to manuver- forget about what you see in these SiFi Movies, those don’t exist — a manned vehicle fully powered by nuclear power-still a distant dream!!!!!

  29. “although surely all governments technologically advanced enough to pose a threat already know our military satellite orbit”

    Dear Mike,

    since science is funded by government in most cases, who should have more advanced methods than any governmental agency?

    I would like to remind you on what is possible already on tracking objects in earth’s vicinity. Do you remember the article “A Possible Answer to Flyby Anomalies” (January 20th, 2008) here on this UT webserver?

    “So, when Galileo completed gravity assist past Earth on December 8, 1990, to speed it toward Jupiter, you can imagine NASA’s surprise to find that Galileo had accelerated suddenly, andÂ for no apparent reason. This small boost was tiny, but through the use of the Deep Space Network, extremely accurate measurements of the speeding craft could be made. Galileo had accelerated 3.9 mm/s.”

    Crazy, isn’t it?


    you could try to break down the problem. There are fully operational vehicles, there are dead satellites, there is debris larger than 10, there is debris smaller than 10 cm. And there is every possible combination of collision. The main problem is the collison of a fully operational space vehicle – be it a sat or a shuttle or the ISS – with any other one. Thus, if only the orbit of fully operational vehicles would be determined more accuratelly then the need for a path correction or not would be more obvious.

    I wonder how small you do think that the possibilities of GPS are!

  30. So – given there are some pro- and some anti- conspiracists out there, and a bunch of people who said “hey, it couldn’t have been predicted but it wasn’t guided, how about another thought altogether.

    Think of a person in a field with a butterfly net, catching butterflies. After that person is finished, the butterfly population of the field is greatly reduced.

    Then, think of a company (or group of companies) that would like to make a lot of money by somehow, metaphorically of course, doing something similar in space around the earth.

    First off, you say: well, butterflies are light. They don’t fly very fast. Their paths, although somewhat chaotic are reasonably predictable in the short run.

    The bits of crud in space can be anything from something very tiny to something very large. In either case, it is the relative speed that counts for the most part: you immediately think of momentum – “the product of a body’s mass and its velocity”. Therefore, a fleck of paint going extremely fast can, in fact have an enormous momentum. The “net” you’ve got has to be something in a class of “things” or “materials” we haven’t created yet.

    In a sense, mass per se isn’t a huge problem: that is, if you are in an exactly matching orbit. Nonetheless, it will almost certainly take special _handling_ that a fleck of paint wouldn’t. And where do you put it once you’ve grabbed it?

    I could elaborate on this theme further, but I believe by now you’ve got the basic point. An organization that could “clean up space” in an effective manner might well have an incredible ROI once they’ve done their research properly.

    So – they watch the skies, they know that collisions and near-collisions tend not to be terribly predictable. BUT: that isn’t quite the problem. What they’d look for is the probable NEGATIVE CONSEQUENCES of “fairly close” or “definite” collisions.

    I seem to remember everyone evacuating to the Soyuz for a while for protection. The shuttle has been moved about several times for the same reason, The nearly invaluable Hubble telescope is basically in that rather perilous portion of space. Gosh. Who cares WHAT goes boom or who did it or how. The real question is what might happen afterward.

    Oh – space civil control is just fine for launching new stuff and controlling those devices that are controllable.

    But the incredibly expensive rates charged by the space janitors and prognosticators: I’d think that -could- be big bucks.

    Just a thought.

  31. I forgot to mention: obviously, prognostication isn’t enough. The spaceships with the red crosses on them that have a cask of rum hanging off of their nose who are somewhat like ambulance chasers, but they do their work in advance of a possible accident (ah! the entrails of the chicken are green! your spaceship may encounter terrible luck!), might be a part of the whole deal.

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