This weekend, there is one-in-3200 risk that the speeding debris of the defunct 6-tonne, 35-ft NASA satellite the size of a school bus would hit someone on Earth. What do you do if you got "lucky?"

NASA says, "Don't touch it."

NASA's dead spacecraft called Upper Atmosphere Research Satellite (UARS) is expected to shatter into pieces before plummeting into the Earth's atmosphere, showering about 800km of the planet with metal debris at the speed of eight kilometres per second.

The UARS was launched in 1991 from the space shuttle Discovery. It has completed its mission to explore chemicals in Earth's atmosphere in 2005, and since then has been gradually falling out of orbit. U.S. Strategic Command at Vandenberg Air Force Base, California, which tracks man-made objects circling the planet, expects UARS to plunge back to Earth during the last week of September. Latest estimates by experts point to Friday (Sept. 23) as the most probable date of UARS entry to Earth.

The 20-year-old spacecraft will be the biggest from NASA to fall uncontrolled from the sky in 32 years. Considering that over three-quarters of the planet is covered in water, NASA is expecting an ocean crash for the debris.

A scientist in the Orbital Debris Program Office at NASA's Johnson Space Center in Houston, Mark Matney, told Space.com, the odds that any of the 7 billion people on Earth will be struck by a piece of the UARS is 1 in 3,200. "The odds that you will be hit ... are 1 in several trillion." Getting struck by a lightning is even more probable than this.

Meanwhile, the European Space Agency said, "The annual risk of a single person to be severely injured by a re-entering piece of space debris is about 1 in 100 billion."

In a 75-year lifetime, the odds of getting injured by space junk would be a little less than one in 1 billion, said , Heiner Klinkrad, head of the ESA's Orbital Debris Office.

Space.com notes that in 1997, Lottie Williams from Tulsa, Oklahoma is so far the only person known to have been struck a piece of space debris. A piece of metal about the size of a DVD hit her shoulder while she was exercising at a park. She was lucky enough that she was not hurt by the metal piece, thanks to wind resistance at the time.

NASA will issue a 20-minute warning before the satellite debris hits the Earth's atmosphere. It would not hurt to have a thought in mind in case you find yourself hurt, or staring at satellite debris fresh from space.

NASA has warned the public through the media that the debris should not be touched. It has also stressed that these debris remains a property of NASA for their safe disposal. The agency stressed pieces of the UARS must not land on eBay. As Space.com reported, "The space agency wants to protect the public's safety, but also enforce the law. UARS remains U.S. government property, regardless of whether it is circling the Earth intact or lying on the ground in pieces."

The public has been informed and warned. Until the UARS has gone back to Earth, you are free to imagine what you would do if you are to be the one-in-3200.