Updated: September 28: Although rumours suggested that few of NASA’s UARS satellite debris have finally hit the country Canada, NASA says that any debris have fallen into open waters of Pacific Ocean.
UARS (Upper Atmosphere Research Satellite) was an orbital space observatory. The 5,900 kg (13,000 pounds) spacecraft was deployed in 1991. $750 million mission was sent to study the Earth’s atmosphere, particularly the ozone layer.
For 20 years, satellite was passing over anyone living south of Alaska or north of New Zealand. UARS has been dead in orbit since 2005 – it was shut down because of the newer, better satellites operating in orbit.
When and where UARS will fall? The current (september 21) UARS orbit is about 190 km by 205 km and it is decreasing every day. In September of 2011 UARS, about the size of a school bus (11 meters long and 4,5 meters wide), will hit the Earth’s atmosphere, moving at speed of 5 miles per second! Re-entry is expected late Friday, September 23, or early Saturday, September 24, Eastern Daylight Time. 26 large pieces (total weight 530 kg, 1,170 pounds) of the NASA satellite can reach the Earth’s surface. The largest “bomb” could weigh nearly 300 pounds (150 kg).
The satellite will not be passing over North America during that time period, but neither NASA nor russian scientists know where the dead spacecraft will fall until around two hours before it happens. The actual date of re-entry is difficult to predict because it depends on solar flux, the spacecraft’s orientation as its orbit decays, the atmosphere changes on a daily basis. As re-entry draws closer, predictions on the date will become more reliable.
Pieces of UARS will fall within a zone between 57 degrees north latitude and 57 degrees south latitude. It is estimated that debris footprint will be about 500 miles long.
What are your chances of being hit by debris from UARS? About one in 21 trillion! It means 1 of 3 200 chance that a human on Earth could be hit by falling satellite debris. Seventy percent of the surface is water. Most of the rest is mountain, desert, tundra or open farmland. Humans really use only about 5 percent of the land on the planet Earth. On average one piece of debris fells back to Earth each day, but throughout the entire 54 years of the Space Age nobody was injured by space debris. In 1979, 15 times heavier than the UARS, Skylab space station crashed in Australia and the USA had to pay clean-up costs. Newer satellites use their last fuel to ditch themselves in the Pacific ocean.
How to watch UARS entering the atmosphere?
If the UARS satellite will fall over a populated region, it should be a magnificent sight to observers on the ground. Probably, it would be visible even in daylight! Now UARS is slowly rotating with a period of 17 seconds. Its magnitude changes from -4.0 to 3.5 mag (so it can be easily seen by naked eye like a bright moving star). It also can be observed with binoculars but even for small telescopes it is flying to fast. Satellite revolts the Earth 16 times per day. It is better to look for UARS in the early evening or before dawn, because at night it dissapear in Earth’s shadow. Visability vary with the observers latitude. For a star chart and other pass details we recommend to visit http://www.heavens-above.com
UARS Break up model (video)
It is also confirmed that another NASA’s ROSAT satellite is heading to Earth at the end of October, and 400 kg debris could survive re-entry.