Sky
Skywatchers may be able to spot the falling UARS satellite sometime between Sept. 22 and 24. Image: Flickr / SIDS1 / CC-BY

The Upper Atmosphere Research Satellite has been in Earth’s orbit for 20 years. Six years ago, the satellite reached what NASA called the “end of a productive scientific life.” By Saturday, UARS is expected to come crashing back to Earth.

Life of UARS

The Upper Atmosphere Research Satellite was first put into orbit in 1991. The satellite was intended to study the Earth’s atmosphere, especially the ozone layer. Originally, UARS was intended to last about three years. After 14 years, UARS was operating with at least 60 percent of the instruments still working, but NASA chose to shut it down. UARS is about the size of a bus and is covered mostly in gold foil-like material.

NASA talks re-entry

The satellite has been in what NASA calls a “heavily decaying orbit,” and it estimates that UARS will re-enter Earth’s atmosphere sometime between Sept. 22 and 24. Most of the satellite is expected to break up in the atmosphere and burn up, but as many as 100 separate pieces won’t burn up entirely. Some of the pieces will be as heavy as 300 pounds. NASA estimates that there is a 1 in 3,200 chance of the pieces of UARS hitting land. The only continent that is not within the fall zone is Antarctica. The chance that each individual piece will hit a person is about 1 in 20 trillion.

Two hours’ warning

NASA is providing hourly updates on the status of the UARS satellite. Even with that, the best estimate is that NASA will be able to provide two hours’ warning on the UARS re-entry. Solar activity is blamed for the speed of UARS’s fall. The increased solar activity is also blamed for troubles with communications satellites. Though UARS is falling from the sky quickly, it is just one of the estimated 22,000 pieces of “space junk” orbiting the Earth.

Sources

MSNBC: http://www.msnbc.msn.com/id/44580262/ns/technology_and_science-space/#.Tneq2mOP-_0
NPR: http://www.npr.org/blogs/thetwo-way/2011/09/19/140598814/space-junk-will-fall-to-earth-this-week
NASA.gov: (PDF) http://www.nasa.gov/pdf/585584main_UARS_Status.pdf
Slatest: http://slatest.slate.com/posts/2011/09/19/uars_climate_satellite_expected_to_crash_into_earth_on_friday.html
LA Times: http://latimesblogs.latimes.com/nationnow/2011/09/space-junk-expert-on-why-nasa-needs-to-clean-up-space.html

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