UARS will crash on September 23rd, +/1 one day

According to the latest estimates from NASA, the Upper Atmosphere Research Satellite will re-enter the Earth’s atmosphere next Thursday, Friday or Saturday. It will strike somewhere between …. well, it will strike the earth somewhere, not likely near the poles. Could hit anywhere, really.


The satellite was launched in 1991 via Discovery, and has collected whopping huge piles of extremely important data. It weighs 5,668 kilograms. UARS was decomissioned on December 15th, 2005 and at that time, lowered into a “disposed orbit”

In case a piece of UARS falls near you, the following images may help you to identify the parts:


OSAT (the software that estimates satellite demise parameters) suggests that bits and pieces of the space craft will be spread over an area of about 1000 kilometers. Here is an interesting report on the re-entry.

It is expected that nothing will hit anything or anybody important.

If you find something you think may be a piece of UARS, do not touch it. Contact a local law enforcement official for assistance.

NASA updates will be posted here.

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21 thoughts on “UARS will crash on September 23rd, +/1 one day

  1. Wow, that NASA re-entry report is a bunch of defensive bureaucrat–double-speak. Why don’t they give some useful info? They must know the exact orbit, so they could at least have given the area over which the debris could fall. Any agency that writes a report as bad as that one loses a lot of credibility in my book.

  2. The don’t know the exact orbit because the process of putting a satellite into a decay orbit is messy, and orbital decay is messy. In the future, satellites will be better designed to crash with more precision or to vaporize more completely, but I don’t think this particular bird was designed with this in mind (I think the program to make de-orbiting cleaner may have started later than this satellite was launched, though I’m not sure).

  3. It seems unlikely that a local law enforcement officer would be helpful. Besides, I’d want a souvenir. I think I have enough sense to keep from burning myself.

  4. Lou @1: The issue is atmospheric drag. That is what is causing the satellite orbit to decay. But small variations in atmospheric drag have huge effects on the ground track, especially for a satellite which is about to reenter. The atmospheric drag will depend on, among other things, geomagnetic and solar activity, which we currently can’t forecast with enough precision to tell exactly where UARS will land. In my experience, even when a satellite that is not expected to reenter during my lifetime but has a perigee low enough for atmospheric drag to matter (below 400 km, in the case I am most familiar with), you can’t reliably predict the ground track with sufficient precision to tell whether it will be in view of your ground station more than about two weeks into the future.

    Greg @2: Yes, having a plan to de-orbit a satellite, particularly if it’s as big as UARS, is now a requirement for satellites in low-Earth orbit. I don’t know exactly when this requirement took effect, but it was sometime in the last decade. UARS is older than that.

  5. So, what IS the area that will be getting the bombardment of satellite pieces? That’s the important info. Or will we only find out after the fact?

    1 in 10,000 is a lot of `hurt’, when one figures a world of 7 billion people…

  6. oldebabe, I will post updated when I have them. The current area is exactly as it says on the post: Earth, but not near the poles! Hopefully this will get narrowed down a little. Maybe.

  7. The reason they are so vague about the impact zone is because they really can’t narrow it down. The satellite orbits in a particular plane in inertial space while the Earth rotates underneath it; the orbital plane does change, but the rate of that rotation for satellites in low earth orbit is typically about two orders of magnitude slower than the Earth’s rotation (e.g., for a satellite orbit which is designed to remain at a certain local time, the orbital plane will take a full year to precess in inertial space). So until they get a reasonably precise reentry time, they can’t say exactly where the impact zone will be. In particular, as long as the window is longer than 12 hours (and the original post indicates a window somewhere between 24 and 72 hours), it can land anywhere that is at least as close to the equator as the satellite’s orbital inclination, e.g., if the orbit is tilted 82 degrees out of the equatorial plane, the satellite can land anywhere that has a geographic latitude of 82 degrees or less.

  8. Jim Thomers:

    If it is decommissioned, is it no longer government property and available for salvage?

    No; NASA has been very clear on that matter. Actually, spacecraft do not ever become nobody’s property. There are special rules because decommissioning them doesn’t change the fact that their physical presence presents an ongoing hazard to other spacecraft, and because some of them can survive reentry. They remain property of their last operator, I believe (some satellites do change owners during their lifetimes), who is consequently responsible for any damage they cause.

    Most satellite operators won’t bother to assert ownership over recovered debris. NASA will, though. They are very protective of their stuff (perhaps too protective, for reasons which are too long to go into right now) and will actually pursue legal action against anybody who they find has retained bits of debris.

  9. The orbital inclination of the UARS satellite was 57 degrees. There are a few major world cities north of the 57 N parallel–Oslo, Stockholm, St. Petersburg, and Juneau jump out at me–but none south of 57 S. So easily 99.99% of the world’s population lives in an area that could include the impact zone.

  10. @Jim: It’s a bit more complex than the news articles would like people to think. If it falls within the US and its territories it remains property of the US government and all scraps, as a matter of courtesy, should be reported to the appropriate folks at NASA. If it falls outside US jurisdiction, the US government still claims ownership but in reality is not necessarily able to enforce that. However, even if you did retrieve bits of it you’d need to be careful about ever bringing it to the US and territories or attempting to sell it to anyone there because it is a federal offense to do so. Well, there are circumstances under which you can arrange to bring such scraps into the USA as in the case of SkyLab.

  11. @oldebabe: Yup, you get a report after the crash. NASA states that even the estimated time of impact made approximately 2H before impact may vary by half an hour. The variations depend on many things, but if you took the maximum +/- 25 minutes stated, that essentially means no one really knows where it will land. The PDF linked to at NASA seems to suggest that the largest parts expected to survive are a number of Beryllium components and the flywheels of the attitude management unit (the orientation of the spacecraft is adjusted by spinning up or slowing down gyroscopes). Beryllium is commonly used in the outer shell but it is not unusual to have internal components made from it; the metal can withstand very high temperatures.

  12. E-mails on it — ROTFL!!!

    Greg — if you find a piece and hold onto it, I won’t tell anyone. 😉 Enforcement of ownership is up to the satellite operator (and, as MadScientist pointed out, pretty much impossible to enforce outside of the US), so . . . what they don’t know won’t hurt you, right? 😀

  13. Calli: IANAL, but I suspect that if the satellite landed in a foreign country, their government would most likely be happy to cooperate with the US in enforcing NASA’s property rights, if only for the sake of reciprocity. (Likely exceptions include China, NK, Iran, Venezuela…) So while NASA would be unable to enforce their rights on their own, they’d likely have help from other states.

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