The defunct bus-size spacecraft is NASA's Upper Atmospheric Research Satellite (UARS), which launched in 1991 and was shut down in 2005 after completing its mission. The satellite was expected to fall to Earth sometime this year, with experts initially pegging a weeks-long window between late September and early October, then narrowing it to the last week of this month.
NASA expects at least 26 large pieces of the massive satellite to survive the scorching temperatures of re-entry and reach Earth's surface. Titanium pieces and onboard tanks could be among that debris, but the UARS satellite carries no toxic propellant (NASA used up all the fuel in 2005).

The debris is expected to fall over a swath of Earth about 500 miles (804 kilometers) long, NASA officials said. There is a 1-in-3,200 chance of satellite debris hitting a person on the ground, odds that NASA says are extremely remote. Outside experts agree.

"Look at how much of Earth is covered with water," Victoria Samson, the Washington Office Director of the Secure World Foundation, an organization dedicated to the peaceful use of outer space, told SPACE.com this week. "There's a really good chance it's going to go straight into the ocean."

http://www.space.com/12982-dead-nasa-satellite-falling-earth-sept-24.html