Update: satellite *might* fall on Friday at 22:00 UTC +/- 9 hours

By Phil Plait | September 22, 2011 11:40 am

NASA’s UARS satellite will almost certainly plunge back to Earth sometime Friday, September 23. The exact time is still not known, but the window for re-entry is centered at 22:00 UTC (6:00 p.m. Eastern US time) with a 9 hour uncertainty on either side. The Center for Orbital and Reentry Debris Studies puts the satellite off the west coast of South America at that time:

However, this is still very preliminary! In other words, if you live in that area, don’t panic (in fact, odds are you shouldn’t panic at all). The uncertainty is still pretty big, because it’s very difficult to pin down just when and where a satellite will come down. The +/- 9 hour window is a pretty clear indication of that. Atmospheric conditions play a big role, as does the fact that the satellite is tumbling; that means the amount of drag from our air that it feels as it orbits changes constantly, making the exact moment of re-entry too hard to determine this far out. As time goes on, it’ll get more precise.

The map shows several things. At the currently predicted re-entry time, the satellite is just west of Peru. The orange circle around it marks the area where re-entry would be visible. The blue track is the orbital position of the satellite over the Earth before the predicted re-entry, and the yellow after it; both are marked with tick marks at 5-minute intervals. The track moves across the Earth because the Earth is rotating under the satellite! That changes the apparent ground track. The white line marks the day-night boundary, so it’ll be late afternoon locally at the predicted re-entry location.

As of 07:00 Eastern US time, NASA was reporting UARS’s orbit being slightly elliptical at 185 x 195 km (115 x 120 miles). That’s very low, as you’d expect for a satellite about to come down. NASA has provided an RSS feed for updates if you want to stay on top of this, but I’ll note the CORDS site appears to be more current. They also have a nice discussion of how and why satellites come back down.

I’ll update this post as I hear news, but if there’s a significant change in the time or status, I’ll put up a new post.

MORE ABOUT: satellite, UARS

Comments (34)

Links to this Post

  1. El satélite UARS de 6 toneladas caerá mañana sobre la tierra | September 22, 2011
  1. There is an aviation warning for space debris, but they didn’t bother to give the location — maybe because they don’t know where.


  2. Imitation of “some” folks:

    Hey, this is a Politics and Religion Blog! Why have you posted two Astronomy/Science posts in a row! WHA! WHA! WHA! I demand you conform to my expectations, and don’t you dare disagree with me! WHA! WHA! WHA!

    Okay, done taking the mickey out of them. 😀

    Thank you for the update. Hopefully someone will manage to catch some good pictures of the event. Who knows, we coupld possibly learn something even from this. :)

  3. Mark

    I’d love for it to come down near where I live. Seriously, how cool would it be to say, “This is a chunk of NASA that landed in my back yard! Not only that, the odds of that happening were literally … *snicker* … astronomical!”

    I’d get a sickening amount of mileage out of that pun…

  4. RobT

    @Larian – I read this post since it interests me, not because it is simply about space/science/etc.

    What I don’t get is why people got so incensed about an article not about science or astronomy on this blog. Nobody forces them to read every blog Phil posts, especially ones that they feel don’t fit what (they think) this blog is about. I don’t always agree with Phil about everything he posts but it’s his blog and he ultimately decides what to write about. If you don’t like a post don’t read it, no one is making you.

    To the people that are angry at Phil – do you stop being friends with someone when they voice an opinion in opposition to your own? If so it must be a very lonely and boring world for you.

  5. I live in Brazil, and according to the map I must upgrade my status from “don´t worry at all” to “very tiny chance of a small lightshow”. If I read it correctly (I most certainly don´t) maybe the damn thing deorbits near the coast, where I am.

    Back in 1979 when Skylab made its reentry a prankster left a twisted piece of metal and a carboard with “piece of skylab” near Ipanema beach. Police, Firemen and scientists where called to verify if it was real, radioactive, etc.

    I´m having very dark thoughts right now. Time to find some scrap metal….

  6. Did you notice how this is happening at the Full Moon, +/- 15 days?

  7. Chris P

    So 25 minutes after the predicted re-entry point off the Peruvian coast, if it doesn’t come down exactly there, it will be over the UK in the middle of the night. Should I stay up to see the spectacular lightshow if it does come down over the UK?
    Actually there seems to be an awful lot of tracks crossing the UK, looks like the three passes after the predicted re-entry point will be visible from here. I might go out in the garden and keep my camera handy.

    Edit: heavens-above.com has the current position of UARS on their front page. I know what I’m doing friday night 😀

  8. Georg

    Looking at this curves I think that chance of coming down is much higher
    at the northermost/southernmost curve extrema (the envelope lines) than in
    equator regions. Is this right, or some optical illusion?

  9. Chris P

    It’s got the same chance of coming down anywhere (on the yellow/blue lines), but the chance of it coming down on a particular spot is higher if that particular spot is between 45 to 55 degrees north or south.
    Or so it seems to me, correct me if I’m wrong.

  10. Chris P

    Actually no, let me modify that.
    You have a much higher chance of seeing it come down if you are at a latitude of 45 to 55 degrees, than if you were on the equator.

  11. Carey

    @6 Harold: Well done :) I chuckled.

  12. Chris A.

    @Georg and Chris P
    Notice, however, that the space between tick marks is a lot wider the further you are from the equator. So no, the odds are no better there than anywhere else–it’s just due to the distortion of displaying the spherical earth as a rectangle.

  13. Jason

    Well it doesn’t look like the track takes it over me at all, Guess I won’t need a hardhat after all…
    Just saw on Reuters, that the headline is “NASA space junk to crash to Earth this week.”

    How about “Successful NASA satellite ends its mission in a blaze of glory”

  14. Chris

    Oh crap, that’s right over my house!

  15. Viadd

    It’s a scandal that we don’t understand satellite drag well enough to predict this better.

    What NASA should have done is put up some sort of research satellite to study the upper atmosphere.

    If NASA had done that back in the 1990’s then we wouldn’t have to worry now.

  16. Gary

    @Chris A, Chris P, and Georg

    The chance of it coming down in any particular spot is the same anywhere on the orbital path but you have a much better chance of being in the debris field or seeing the reentry the further from the equator you get.

    If you look at the Northeastern region of Canada the satellite makes several passes over the same general area. It’s a little hard to tell but it looks like at least 3 or 4 passes would be within the area of the viewable circle. If you’re closer to the equator the lines don’t intersect. If you’re in the Southeastern part of the United States you have one pass that is in the viewable area. This isn’t due to distortion of the map but the rotation of the Earth. In fact due to map distortion the viewable circle would get bigger the further from the equator you get.

  17. dcsohl

    Right, Gary… if you look at the track as being a sine wave with an amplitude of 55 degrees, then it will spend half its time between 39 S and 39 N; one quarter of its time between 39 N and 55 N, and one quarter of its time between 39 S and 55 S. To put this another way, nearly 80 degrees of latitude account for half the satellite’s time, and a total of 32 degrees of latitude (at the north and south extremes) account for the other half of the satellite’s time.

    Now, it isn’t actually a sine wave but I *think* as an approximation this will do. Anybody know what sort of curve it is, if you plot the satellite’s latitude vs time?

  18. QuietDesperation

    If it lands within the borders of the Desperation compound, can we keep it? Well, the bits, at least.

    Will we have G-men sniffing around with their sniffy government noses?

    Hey Sweaty! Angry! Go oil up the shotguns. What? Yeah, the death ray, too, I guess.

    Oh, and you missed a chance for another song title, Phil!

    (screaming like a boss) “Danger Zone!”

  19. QuietDesperation

    It’s a scandal that we don’t understand satellite drag well enough to predict this better.

    If you google it, you’d see how much work has been done, and how complicated an issue it is. There’s a lot of variables.

  20. @dcsohl: I think that, for a circular orbit, it’s the arcsin of the product of some constant depending on orbital inclination, and a sine wave. (If the orbit were completely polar, the constant would be 1 and you’d just get a linear variation in latitude, with the formula breaking down as it goes over the poles. If the inclination is small, it’s very close to a sine wave.)

  21. Keith Bowden

    @QD – I think Viadd’s comment was a joke. (That’s how I took it.)

    Speaking of jokes, well done, Harold! :)

  22. So if it waits four full orbits after the predicted time it will happen over head here in the Pacific Northwest, and I’ll miss it anyway because of thick cloud cover and rain.

    Hopefully it happens somewhere that someone has a video camera pointed up.

  23. Chris P

    Oh bravo sir, bravo!

    Thanks, that was what I was trying to say.

  24. Brian

    If this satellite comes down about 20 minutes before the expected reentry time it will come down right over central New Zealand. And I live in central New Zealand. I will definitely be looking out for it at this time. That will be around 9-30am Saturday local time.

  25. Wzrd1

    So far this year, it’s been cloudy for every meteor shower and interesting celestial event here.
    Indeed, it’s supposed to be raining hard tomorrow through the weekend.
    Interestingly enough, I noticed that kook neighbor up the street just finished his boat and animals were getting on board…

  26. Kim

    What does this satellite have to make its reentry so interesting? Doesn’t rocket modules and old satellites come down all the time?

  27. Pete Jackson

    Now they’re saying 00:58 UTC on Sept 24 +/- 7 hours.

  28. Wzrd1

    My numbers show 46.1° S, 112.7° E at 00:43 GMT, +/- 15 hours. Federal source that is FOUO.
    Next data run is at 05:00 GMT.

    @Kim, #28, see http://www.nasa.gov/pdf/585584main_UARS_Status.pdf for full details on why it’s interesting. Things DO come back in all the time, the vast majority are better controlled and fully burn up on the way in.
    This one is coming down like a large load of buckshot. The prior article has the approximate Earth ballistic impact data compared to what is coming in.
    HIGHLY doubtful that a human will be injured, but one should always be prepared. :)

  29. QuietDesperation

    yeah. i was tired. ah well.

  30. DLC

    The odds of being struck by a falling satellite chunk are so small as to be negligible.

  31. Paul

    @16: Well played, sir. Well played.


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