UARS animation from BBC
Between now and next weekend, a 20-year-old satellite – the Upper Atmosphere Research Satellite (UARS) – will make an uncontrolled re-entry through the Earth’s atmosphere. Pieces of the 6.5-ton satellite are expected to survive the fiery plunge and hit our planet. Trouble is, no one knows exactly where.
The chances of being hit by a falling satellite are small. Nick Johnson, chief scientist with NASA’s Orbital Debris Program, told Universe Today:
Numerically, it comes out to a chance of one in 3,200 that one person anywhere in the world might be struck by a piece of debris.
When you think about the seven billion people on Earth today, you see how vanishingly small the probability of being struck really is. After all, most of Earth is ocean, so chances are UARS will go from the fires of re-entry directly to a watery grave in the ocean depths. It’s also important to note that no injury has ever been caused by orbital debris during the half-century that we humans have been placing objects in Earth orbit.
NASA says the satellite is likely to begin re-entry on September 23, 2011, give or take a day. Hurtling at five miles (eight kilometers) per second, they say it could land anywhere between 57 degrees N. latitude and 57 degrees S. latitude – basically, most of the populated world.
The satellite was launched in 1991 by the space shuttle Discovery. Designed to operate for three years, six of its ten instruments are still functioning, according to NASA’s UARS page. However, the satellite was officially decommissioned in 2005, at the same time that other satellites took over its work.
This isn’t the first time a massive satellite left orbit and made an uncontrolled re-entry back to Earth. In 1979, Skylab re-entered the atmosphere, causing some nail-biting before it finally struck safely in Australia.
Bottom line: Around September 23, 2011, NASA’s Upper Atmosphere Research Satellite (UARS) will make an uncontrolled re-entry through the Earth’s atmosphere. Pieces of the 6.5-ton satellite are expected to survive the fiery plunge through the atmosphere and hit our planet, but the precise location it will strike is unknown. NASA says there is a one in 3,200 chance that a person anywhere in the world might be struck by a piece of debris.