After a couple weeks of uncertainty, NASA has announced that its bus-sized Upper Atmosphere Research Satellite (UARS) will fall to Earth tomorrow afternoon, Eastern daylight time.

According to agency officials, the 6.5-ton satellite is one of the largest to make an uncontrolled re-entry into Earth's atmosphere in over 30 years.

Aerospace engineers from Analytical Graphics Inc have created the video up top, showing the satellite on its current orbital track, its potential fall zone, and models for its burn-up and breakup.

Most of the derelict satellite is expected to burn up in our atmosphere, but the agency estimates that up to a half-ton of debris could make it to Earth's surface, in chunks weighing up to 150kg (~300 pounds).

The latest updates from NASA still contain no information on the ultimate location of the fall zone, but they have a pretty good idea of where it won't be, noting that "the satellite will not be passing over North America" when it de-orbits. In other words: if you're in the US, you're in the clear — but what are your odds of getting beaned by space junk everywhere else?

NASA's massive derelict satellite will re-enter Earth's atmosphere tomorrow afternoon

According to NASA, the chances are beyond slim. A half-ton of debris may sound like a lot, but given the vast quantities of Earth's surface that are uninhabited — or uninhabitable — the agency isn't losing any sleep over the possibility of human casualties, and neither should you. Nicholas Johnson, head of NASA's Orbital Debris Program Office, estimates that the chances of any pieces of UARS debris hitting anybody are roughly 1 in 3,200, which translates into a 1-in-20 trillion risk for any individual person.

"Throughout the entire 54 years of the Space Age," said Johnson, "there has been no confirmed report of anybody in the world being injured or severely impacted by any re-entering debris."

You'll find updates on the satellite's status over at NASA, who will be be issuing updates on the timing of the satellite's re-entry starting this afternoon, with updates at T-minus-12, T-minus-6, and T-minus-2 hours before the predicted fall.

[Via SPACE.com, Cosmic Log, and agiBlogs]
Image of UARS via NASA Marshall Space Flight Center