NASA has released the final update on the UARS bird that burned up in re-entry last week: it came down in the Pacific, west of the US.

The Earth’s atmosphere is not a lid over us, but gets thinner with height, so it’s hard to define exactly what it means to say that the satellite burned up at such-and-such a spot. However, at 04:01 UTC on September 24th, the satellite’s motion became dominated by the Earth’s atmosphere, and for all intents and purposes that can be called the point where it came back in… or at least, where it started. The forward motion of the satellite took the pieces along a track 500 – 1300 km (300 to 800 miles) long, which is still safely out in the ocean.

Thus ends the UARS tale.

… but we’re not quite done yet. The venerable German astronomical satellite ROSAT is due to come back down in about a month or so. Smaller than UARS — a little over 2 tons, as opposed to over 6 — ROSAT will probably have more pieces survive the ride down because its mirrors had to be shielded from heat to operate. That means the odds of it hitting someone will be slightly higher than from UARS, about 1 in 2000. Bear in mind that’s still really small odds! The chance of a specific individual getting hit are still something like only 1 in 14 trillion.

ROSAT is an X-ray satellite, designed to study high-energy radiation from astronomical sources. Years ago, I looked briefly at ROSAT data of a supernova remnant while putting together an educational activity about exploding stars. I don’t feel the same connection to the satellite as I do to, say, Hubble, but still, it’s a little sad to see it come down. However, it did provide years of outstanding service to the astronomical community, and gathered a vast amount of data about the high-energy Universe around us.

Image credits: NASA; German Aerospace Center (DLR)

NASA has confirmed that the Upper Atmosphere Research Satellites, UARS, burned up over the Pacific Ocean last night, September 24, between 03:23 and 04:09 a.m. UTC (11:23 p.m. and 12:09 Eastern US time). I have no other reliable information on it, but I expect we’ll get more updates soon. There were lots of reports last night of it falling over Canada, but those were mistakes or hoaxes. Apparently some people were fooled by meteors, Chinese lanterns, and possibly even the planet Jupiter. That’s happened before.

If I find photos or such I’ll try to post them, but I’ve heard no reports of witnesses, and I’ll be away this afternoon for my TEDxBoulder talk, so if any pictures turn up I may not be able to get to them. I imagine SpaceWeather will post any if they crop up.

Thus ends that saga. If you’re curious, you can read about the history of the UARS and what we learned from its 15 year mission to investigate our planet’s atmosphere.

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now 9/24 (tonight!) at 05:10 UTC (01:10 Eastern US time), which puts it over the southern Indian ocean:

See Related posts below for information and background. Note the uncertainty is once again smaller, at +/- 2 hours!

[UPDATE to the update (22:00 UTC): a new prediction just came out: tonight, September 23/24, at 04:04 UTC (midnight Eastern US time). The uncertainty is down to +/- 3 hours, and the location is the middle of the Pacific. Clicking the links below to CORDS or the image itself will take you to the most current prediction.]

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now 9/24 (tonight!) at 03:16 UTC, which puts it over the Sahara:

Note that again this is later than the last estimate. As the satellite has gotten lower, aerodynamic drag — the wind blowing on it, tenuous as it is — has changed its orientation, creating less drag, slowing the descent.

Please note that the time is still uncertain, though now it’s only +/- 5 hours. Still, that’s a wide swath of Earth in that range, so we’re still not sure where it’ll burn up.

Check the Related posts links below for more info on the satellite, why it’s coming down, and how to read that map. Again, the danger from this is pretty minimal. You may note that the three predictions we’ve had have put re-entry over the ocean or otherwise largely uninhabited areas, and that’s not a coincidence: most of the Earth is like that! That’s why the odds of someone getting hit are so low.

I’m sure we’ll get another update or two in the next few hours, so stay tuned. You can also check the CORDS site for updates, and the NASA page as well.

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now three hours later than before: 9/24 at 00:58 UTC, which puts it in the middle of the south Pacific:

Mind you, the uncertainty on this is still +/- 7 hours, so we’re a long way from knowing just where it will come down.

For more details, please read this earlier post (and you might as well read this one as well for the background info).

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.

[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. I’ll be tweeting about it as well as soon as I find anything out.

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