Newer update from NASA: Update #11
Fri, 23 Sep 2011 23:30:46 GMT

As of 7 p.m. EDT on Sept. 23, 2011, the orbit of UARS was 90 miles by 95 miles (145 km by 150 km). Re-entry is expected between 11 p.m. Friday, Sept. 23, and 3 a.m., Sept. 24, Eastern Daylight Time (3 a.m. to 7 a.m. GMT). During that time period, the satellite will be passing over Canada, Africa and Australia, as well as vast areas of the Pacific, Atlantic and Indian oceans. The risk to public safety is very remote.

The Center for Orbital and Reentry Debris Studies now says that the entry time is 4:04AM 23 September UTC (11:04 PM Central, US time). This is a VERY ROUGH estimate.

The location of reentry is the middle of the Pacific Ocean if the estimate is dead on, pretty near the Equator, with a northeasterly trajectory. If the estimate undershoots the time and the satellite comes in a bit later (minutes, up to a hour or so), the main landmass in the way is Canada, somewhere between the NW Coast and Hudson’s Bay, then the rest of Canada over the Maritimes, then traversing the North Atlantic to the southwest then over West Africa. If it comes in early, that orbit tracks between Australia and NZ, and across the Pacific.

Given the worst case scenario of the estimate being off by a couple/few hours, the major land masses that could be affected are: Canada, West Africa, Southwest Africa from Angola to South Africa (Namibia and western Botswana included) West-central Australia and the southern and northern coasts, eastern New Guinea, Europe, the United States and Mexico. One bit of the track takes it right down the Red Sea so a tiny bit of West Asia is under a possible de-orbiting location.

99.999 percent of Asia, Central America and South America may be off the hook. Unless, of course, the estimate is way off.

Oh, and the “reentry” location is where the satellite starts to become visible as one or more flaming meteor-like things. The land impact location would be down-stream from that, of course.

Update #10
Fri, 23 Sep 2011 09:45:08 AM CDT

As of 10:30 a.m. EDT on Sept. 23, 2011, the orbit of UARS was 100 miles by 105 miles (160 km by 170 km). Re-entry is expected late Friday, Sept. 23, or early Saturday, Sept. 24, Eastern Daylight Time. Solar activity is no longer the major factor in the satellite’s rate of descent. The satellite’s orientation or configuration apparently has changed, and that is now slowing its descent. There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent. It is still too early to predict the time and location of re-entry with any certainty, but predictions will become more refined in the next 12 to 18 hours.

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