NASA satellite due to burn up some time in the next few days

By Phil Plait | September 21, 2011 6:27 am

[UPDATE: Alan Boyle at Cosmic Log is reporting that the satellite will definitely come down on Friday, though NASA is not sure yet exactly when and where.]

[UPDATE 2: Emily Lakdawalla at The Planetary Society blog has lots of detailed info now.]

By now you’ve probably heard that NASA’s Upper Atmospheric Research Satellite (UARS, pronounced YOO-arz, though in my head it’s always "You arse!") will burn up in our atmosphere some time between Thursday and Saturday. The satellite was decommissioned in 2005 and they used the remaining fuel to lower the orbit. It’s been slowly getting lower since then, but recently reached the part of our air where it slows and drops dramatically. As you can see from this plot (click to embiggen), it’s dropped from about 375 km to 200 in just the last few months, and down it’ll come later this week.

No one knows where or when it will hit, since the final flight path will depend on changing atmospheric conditions, orientation of the satellite, and so on. Most of the 6 ton satellite will burn up, but some two dozen or so pieces are expected to survive re-entry.

Speaking of which: I’m seeing some concern over people getting hit by this thing. The odds of that are extremely low. It’s possible — NASA rates the odds at about 1 in 3200 — but highly unlikely. Mind you, those are the odds of anyone getting hit by debris. The odds of a specific person, say me, getting hit are far lower — if I’m doing this math correctly, you’d multiply that number by the population of the Earth, nearly seven billion people. So the odds of me (or you, or pick someone) specifically getting hit are about 1 in 20 trillion. Pretty long odds.

In the meantime, on September, 15th, "amateur" astronomer Thierry Legault was able to capture video of the satellite while it passed over his location:

Cool, eh? You can see the rotation; it’s tumbling, apparently. Out of power, it can’t keep the correct attitude, and over time something has caused it to spin. Maybe it was a collision, or maybe it’s from other subtle but persistent forces over the years (solar wind, light pressure, drag through our tenuous upper atmosphere, slow fuel leak, what have you). Here are some stills from Thierry’s video to make that more clear:

Pretty cool. So stay tuned. I’ll update with more info when I get it; we’ll know the re-entry time and location much better as the week progresses. <a href="I’ll be tweeting about it as well as soon as I find anything out.

Credits: Orbit plot: Jonathan McDowell; UARS images: Thierry LeGault.

Related posts:

YouTube video where I explain a satellite re-entry
BREAKING: SpySat successfully hit by missile
The return of Stardust
Spy sat to come home… not too secretly


Comments (60)

  1. Hemogoblin

    Thierry’s pictures simply amaze me (I just wasted 15 minutes looking at his spy satellite and ISS videos). There is something utterly awe-inspiring in being able to find, track and take recognizable photos of objects man-made objects in space from the ground.
    With portable equipment, even.

  2. DennyMo

    How do they arrive at odds of 1 in 3200? And since the US has ~300,000 people, does that mean ~100 people in the US will be hit by debris? (I hated statistics class in college, my grade showed it, so I’m probably missing something really fundamental here…)

  3. alfaniner

    Another chapter for your book!

  4. blanton
  5. blanton

    Hi Phil,
    I think because people are clustered on the Earth, you don’t
    get to multiply by 7 billion, it has to be a smaller number by
    some factor, right? Since in the case that it hit >=1 person,
    the mean expected number of people hit would actually be
    substantially larger than 1.

    In the extreme, if we all were living in the same building, and
    the chances of hitting >=1 person were X, then the we’d each
    have a chance X (since we’d all be hit if one were hit). I guess
    I’m assuming something about how NASA’s quoted # was

    I think that’s right, though maybe I haven’t thought about it
    hard enough. Of course, the odds will still be long in any case.


  6. @DennyMo, I think you dropped a couple of zeros, and are only considering one landmass of the planet. It’s more like, there are 7 Billion humans on the planet that is 70% ocean. We don’t know where it will come down, so there is a small chance that someone will get hit. The odds that anyone in the US get’s hit would be much lower since we only account for ~4% of the world population.

    This all reminds me of the Skylab (and Mir) coming down days. I wonder if more “amateur” astronemers will catch this thing as it burns up?

  7. Bill3

    @DennyMo: No, the 1 in 3200 is the chance of hitting anyone at all, not per person.

    Still, if you had a 1 in 3200 chance of killing some random person on earth through your actions, would you consider that acceptable?

    If someone does get hit, can their family sue NASA for knowingly taking a chance at killing someone?

  8. STEVE

    I’ve tracked this satellite for more than 20 years.
    Several hundred positions for it have been recorded.
    It’s like an old friend, and I’ll be sorry to see it go.

  9. There is a diagram showing the drop in altitude over the last month plus modelled further drop the coming two days on my satellite blog:

  10. Robin

    @DennyMo (#1): If they’re doing it logically, then probability of hitting a person is a function of the presented area of a person, and the total area of the Earth pieces of the broken up satellite could strike. That fraction–the projected area of the person/the area of the Earth pieces could it–would be the probability. It would make sense that the probability would also be a function of the orbit at a given time. Of course, the amount of the satellite that makes it to the Earth should be defined by some probability, too.

    They, NASA, likely run Monte Carlo analyses to get a range of probabilities, but those Monte Carlo runs have to incorporate predefined probabilities for all the factors on which the overall probability is dependent….or at least the most influential factors. Technically, it’s not possible to account for every possible factor.

  11. Cindy

    What is reentry expected to look like and how wide of an area would be able to see it? Like if it went over my house would just people in my town be in the viewing area, or all of new hampshire or the whole eastern half of the US? I know we don’t have a location or time yet.

  12. But if you ARE that 1 person in 20 trillion, it’s gonna sting!

  13. Dragonchild

    Fearful people often forget the planet is 70% ocean, and even the vast majority of land is uninhabited.

    When people talk of overpopulation they’re specifically referring to resource depletion. We’re running out of fuel, soil, water. These are legitimate problems. But we take up very little space. A random rock falling out of the sky isn’t likely to hit anything.

    I mean, people gamble all the time hoping to defy odds on the order of 0.000001% or smaller. This thing has a 99.97% chance of landing on NOTHING and people are frightened??

  14. Bob

    Didn’t anyone else think “Focus” when watching the video?

  15. Chris

    Wouldn’t it have been smarter when they lowered the orbit to lower it some more so they’d know where it’d hit, or at least have a better idea?

    And somehow this seems appropriate, from Dead Like Me, when the toilet seat from the Mir space station came down.

  16. Pete Jackson

    When I click on the graph, it says that I have to be logged into Facebook to see it, but I don’t do Facebook. Youtube lets you see stuff without being logged in. Has Discover run out of disk space?

  17. K

    Oh! I hope it hits my old house! We haven’t been able to sell it for 6 years and now we can’t even rent it anymore (the market is so glutted, we can’t ask for anything NEAR the mortgage price. No point in letting it get wear and tear with a tenant).

    Too bad I can’t make a crashing satellite rod to put up on the roof.

  18. OtherRob

    Didn’t we see this on Northern Exposure?

  19. 1) Wet run for disposing of ISS FUBAR. Start circulating strongly-worded petitions: ISS FUBAR must be disassembled in orbit and brought back to Earth at inconceivable cost. This will create jobs!

    2) The Shire of Esperance farts in NASA’s general direction.

    3) The collapse of NASA’s Man in Space Potemkin village means huge tonnages of chlorine are not being directly injected into the stratosphere by Space Scuttle solid fuel boosters. The Ozone Hole will heal. The Greenhouse Effect, Global Warming, Climate Change will vanish. “Will whine about the Environment for food.”

  20. Would it be a fair hypothesis to say a tumbling object would burn/breakup more than a steady one?

    Bob – “enhance!”

  21. Sam H.

    I’m sure Phil has mentioned this site before:, which lets you get all kinds of data on astronomical viewing opportunities. Signing up for a free account lets you store your location without having to enter it on each visit.

    I regularly use the site to get info on ISS passes so I can go outside and watch it fly over. It also showed me that I will not even be able to see the re-entry of UARS, much less get smushed by it, here in Billings, MT.

    When I checked yesterday, the closest (and also soonest) visible pass of UARS to me was to be on Saturday the 24th, passing over central Wyoming (the ground map feature is super-cool). It would have been visible; I think the elevation was 40 degrees or so. As of today, that pass is not even showing up for me any longer since confidence is growing that UARS will be down by the 23rd.

  22. tmac57

    “Coming soon!!! UARS!!! It’s outta gas,out of a job,it’s comin’ down…HARD,and it has…ONE…BAD…ATTITUDE!!! “

  23. tmac57

    #9 Bob says:”Didn’t anyone else think “Focus” when watching the video?”
    Actually,I was thinking ‘Hey! It’s Bigfoot!’

  24. Brian

    With the satellite spinning, is there any chance that it will skip across the atmosphere for a while? I’m thinking kind of like a stone skipping across a pond — it doesn’t skip unless it is spinning.

  25. Pete Jackson

    @19UncleAl: Actually, ISS needs to be fitted with ion thrusters and gently nudged into an equatorial orbit where it can really serve as a rendezvous-assembly station for deep space exploration. The Russians will understand, they are now launching from French Guyana.
    Eventually, the ion thrusters can then move it gently into interplanetary space and finally nestled into a final resting place on Deimos for space tourists to visit.

  26. Titan

    Phil, could you use your platform to try to get people to track the UARS satellite (Heavens-Above, N2YO) so they know when to point their video cameras up. Obviously we don’t know when it will burn up, but if enough people are recording the sky there is a good chance that someone will get it on video.

  27. Our local news radio folks have been reporting this, saying a person’s chance of getting hit by a piece of UARS 1 in 3200. They even compared that chance to a person’s chance of getting hit by lightening or dying in a plane crash. I called in to correct that, they told me that NASA says it’s the way they reported it. I tried telling them that if it were true they could expect hundred of victims in the Seattle area, and that there are not enough pieces to do what they claim, even asked that they check the NASA web site. They said there was no way NASA was wrong and I was right. I gave up.

    I really hope this comes over our area, I would love to see it.

  28. Daffy

    My concern here is that—at a time when NASA is facing budget cuts anyway—this will be seen by most people as NASA taking risks with people’s lives. Yes, I understand the statistics—almost certainly no one will be hurt; but this will be an emotional reaction and emotions are not influenced very well by statistics.

  29. Chris S

    Will the big decay graph image be moved somewhere besides Facebook so that we can all see it?

  30. Matt

    Shouldn’t the odds of this thing hitting anyone be next to impossible? Columbia comes up a lot in this conversation, but its flight path was intentionally directed over populated areas as it was on its descent for landing.

    This thing could come down anywhere over about 80% of the earth’s surface supposedly…so the odds of it even hitting a populated area are probably less than one in 3200,let alone hitting a PERSON.

  31. Messier Tidy Upper

    @19. Uncle Al : 2) The Shire of Esperance farts in NASA’s general direction.

    Nice one. :-)

    Or, maybe, they’re preparing to fine NASA for littering again as they did after Skylab‘s fall? 😉

    1) Wet run for disposing of ISS FUBAR. Start circulating strongly-worded petitions: ISS FUBAR must be disassembled in orbit and brought back to Earth at inconceivable cost. This will create jobs!

    Building it – and building more like it will also create jobs and provide us with marvellous platforms to learn and accomplish more. If Obama wants a job program he can do worse than making a Babylon-5 type space station become something real rather than fictional.

    3) The collapse of NASA’s Man in Space Potemkin village means huge tonnages of chlorine are not being directly injected into the stratosphere by Space Scuttle solid fuel boosters. The Ozone Hole will heal. The Greenhouse Effect, Global Warming, Climate Change will vanish. “Will whine about the Environment for food.”

    The ozone hole has been healing ever since the Montreal protocol banned CFCs – a rare case of an international treaty actually being beneficial and working as planned.

    The Greenhouse effect keeps Earth’s global average temperature above minus eighteeen degrees (Celsius?) and it isn’t disappearing as long as our atmosphere contains water vapour and some important trace gases.

    Climate has always changed naturally – and has recently been changing artificially too due to excessive human emissions of carbon dioxide and other additional greenhouse gases plus deforestation and other escalating feedback mechanisms. That won’t go away because of reduced space travel either.

    Oh & btw. you misspelled Space Shuttle – it wasn’t built by Dr Zoidberg’s people ( 😉 ) but instead was constructed by rocket scientists who created one of the former wonders of the modern world.

    Oh well, some of your comment there was accurate and amusing (in my view natch) anyhow.

    UARS~wise how do these odds compare with being hit by lightning or eaten by a shark? I’m guessing there’s more chance of being killed those things happening than being killed by this falling artificial moon. Am I mistaken about that?

  32. QuietDesperation

    And since the US has ~300,000 people


    Well, he did put the ~ there.

    it wasn’t built by Dr Zoidberg’s people

    And why *not* Zoidberg’s people, hmmm?

  33. Eric

    Launching this satellite was the only shuttle launch that I got to see live. My father had some instruments on the satellite, so we went to see it go up.

  34. Wayne on the Plains

    @15 Chris,

    Yes, a planned deorbit WOULD have been smarter. I used to work with the PI of one of the UARS sensors, and I recall back in 2002 or 2003 some idiot ordered much of the reserve fuel dumped, I think in a failed bid to force the Shuttle program to retrieve it (UARS was designed to be Shuttle serviced or returned to Earth in the payload bay). There was lots of dumb politics going on with this mission around that time.

  35. @Chris #15: I don’t think they could have lowered it any further – it sounds like they used up all the remaining fuel to get it as far as they did.

  36. Krish

    Would it be a fair hypothesis to say a tumbling object would burn/breakup more than a steady one?

  37. DennyMo

    Oops, yeah, I left out a comma…

  38. Chris A.

    @Bill3 (#7):
    “If you had a 1 in 3200 chance of killing some random person on earth through your actions, would you consider that acceptable?”

    What are the odds of killing someone simply by getting behind the wheel of an automobile daily?

  39. Megan McC

    Phil, You should run a You Arse! sweepstake of impact zones. Closest to within 50 nautical miles is the winner. Anywhere between 57 degrees North or South of the equator. In honour of Douglas Adams my money is on it coming down somewhere around Belgium man, Belgium.

  40. TStein

    I did a back of the envelope calculations when the number of 1 out of 3200 first appeared, because it seemed way too big of a chance to me. I assumed 6 billion instead of 7 billion people if I recall correctly. Nonetheless, reverse engineering that value I arrived at a 1 square meter cross section for each person. This means, again if I calculated correctly, that the average person in this model had a square meter of area around them such that if the center of any one of the debris pieces struck within this square meter it would hit them. This roughly corresponds the center of the debris pieces being within a 2 foot (radius) circle from the center of the person. This would agree with a degree piece that is roughly 2-3 feet across.

    I am curious how people being inside of buildings affect this.

  41. @ Phil, Regarding update #1: “Friday” in terms of US local time: expressed in UTC, early Saturday is however definitely still in the picture.

  42. Ribert

    @Megan McC – Apparently a number of bookmakers have already opened betting lines on where UARS will come down. Pacific Ocean is currently odds-on (like that should be a real surprise).

  43. Das Boese

    Hm, isn’t it possible that the “tumble” is intentional?

    A lot of spacecraft are intentionally sent tumbling for atmosheric reentry to help break them up and maximize drag.

  44. Jay Fox

    My wife and I saw that thing go by in daylight, about two hours before sunset, a couple weeks ago. The sunlight reflected off it right at us, and it was SOOOO bright. We could easily make out the shape and the fact that it was tumbling. It did appear a lot lower than most of the other satellites that we see going overhead. It was the first time I’ve seen an orbiting object in daylight (besides the moon). I had to stare at it until it went out of view. Wish I’d had a camera with me at the time.

  45. Jorge Laris

    I hope i can watch it at Yucatan

  46. Robin

    @Das Boese (#43): Not really. This thing ran out of fuel a while ago, so there’s been no fuel for a while for orbit adjust maneuvers.

  47. Wzrd1

    @Jorge, probably. The latest projections put it coming down over French Guiana and Brazil, so you might get to see its track in the distance.
    Current risk assessments (I have the .pdf file from NASA) shows 26 components arriving at the surface, out of those, a dozen could strike you and not leave a bruise. Of the rest, three components would impact with 95, 102 and 153 kJ kinetic energy.
    Of course, if the sun excites our atmosphere by any significant amount, Space-Track predictions will be in the toilet.

  48. Wzrd1

    @Procyan #48, interesting that you are angry over a satellite coming in, yet you are happily complacent over meteors smacking into you. You’re gleefully tolerant over the HIGH risk of being killed or injured in a traffic accident, with orders of magnitude probability higher chance of occurring. You’re smugly satisfied with the higher probability that an aircraft part or even a chunk of “blue ice” hitting you.
    And that you would wish harm upon a blogger’s family is shocking and tells much about you, your upbringing and culture.
    “Smug USA attitude” indeed!

  49. Wzrd1

    The NASA risk assessment is at:
    For comparison to the kinetic energy of impactors, a 9mm pistol has a muzzle energy of 470-500 joules. An M-16 has around 1600-1700 joules muzzle energy. A .308 caliber rifle has about 3800 joules of muzzle energy. A .50 caliber Browning machine gun has about 15 kilojoules muzzle energy.

  50. Folks, don’t bother replying to people who are obviously either a) trolls, or b) breaking my “Don’t be a jerk” rule. If you see something like that, please drop me an email and I’ll take care of it.

    I deleted Procyan’s comment.

  51. Wzrd1

    My apologies, Phil. Bad day here, so my a and b filters failed.
    Our inclement weather has my back and knees beyond enraged. It’s what I get for violating my warranty and putting too many miles and interesting years of life on… :/
    Oh, thanks for moderating in the risk assessment. I know that quite a few folks out there would be put off by ballistics information, but it’s the closest real world energy exchange information I could think of. I don’t have energy exchange data for a 2 year old running into you vs a Buick or high speed train and I’m too lazy to do that simple calculation for each. 😉
    But, for those with more time and energy to pursue it, it’s E=1/2mv^2. 😀

  52. Guy Ferguson

    How does anyone so obviously intelligent manage to use a ridiculous word , (click to embiggen)!
    Could he possibly mean ENLARGE?

  53. DennyMo

    Guy, I hope you’re kidding. Either that, or you haven’t hung around here long enough to get the joke. BA frequently (i.e “nearly always”) makes up new words as replacements for enlarge. Usually the new word is related to the topic. “Embiggen” is actually a retread: he’s used it several times before.

  54. Jon Hanford

    @#43 Das Boese

    “Hm, isn’t it possible that the “tumble” is intentional?”

    In November of 2007, the UARS satellite was struck by an unknown object (space junk or a meteoroid) that probably sent it tumbling. It also broke 4 small pieces off UARS which eventually reentered on their own:

    Of course, interactions with the upper atmosphere since then have probable contributed to the satellites’ gyrations as well.

  55. tmac57

    Thanks DennyMo. That was enlightiating 😉

  56. Robin

    “Embiggen” is a synonym for “galactinate” and is derived from “humor”.

  57. Wzrd1

    @Guy, #52, erm, I rather LIKE enbiggen. It’s more gooder. 😉

  58. Obi-Jon

    Embiggen was also used in The Simpsons if my memory serves me correctly. A noble spirit, embiggens the smallest man.’ by Jebediah Springfield. I heard UARS would come down about 1 or 2 am local time somewhere near Ireland. That was on BBC TV in the UK.

  59. Joseph G

    @59 Obi-Jon:
    It’s a perfectly cromulent word!

    /Sorry, someone had to say it.

    Personally, I love playing word games and making up whimsical new words. It makes me squee when Phil shows the same proclivity.


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