Kamis, 22 September 2011

New Images Of UARS Satellite

An amateur astronomer has recorded images of the out-of-control US satellite as it tumbles back to Earth.

Theirry Legault, from Paris, captured the video as the satellite passed over northern France on 15 September.

The six-tonne, 20-year-old spacecraft has fallen out of orbit and is expected to crash somewhere on Earth on or around 24 September.

The US space agency says the risk to life from the Upper Atmosphere Research Satellite (UARS) is 1 in 3,200.

Mr Legault, an engineer, used a specially designed camera to record the tumbling satellite through his 14-inch telescope, posting the footage on his Astrophotography website.

UARS could land anywhere between 57 degrees north and 57 degrees south of the equator - most of the populated world.

Nasa says that most of the satellite will break or burn up before reaching Earth.

But scientists have identified 26 separate pieces that could survive the fall through the atmosphere. This debris could rain across an area 400-500km (250-310 miles) wide. 

Robust, spherical satellite components such as fuel tanks are often most likely to survive the fiery plunge to Earth, say space experts.

Nasa said scientists would only be able to make more accurate predictions about where the satellite might land two hours before it enters the Earth's atmosphere.

The 1 in 3,200 risk to public safety is higher than the 1 in 10,000 limit that Nasa aims for.

But agency officials stress that nobody has ever been hurt by objects re-entering from space.

Mark Matney, a scientist with Nasa's Orbital Debris Program Office, told Space.com that there was "always a concern". 

But, he added: "Populated areas are a small fraction of the Earth's surface. Much of the Earth's surface has either no people or very few people. We believe that the risk is very modest."

UARS is one of the biggest American satellites to make an uncontrolled re-entry in more than 30 years. However, the Skylab space station, which also made an uncontrolled plunge through the atmosphere in 1979, was about 15 times heavier than the tumbling satellite.

Experts say that a recent expansion in the Earth's atmosphere due to heating by ultraviolet radiation has been causing UARS to fall to Earth faster than expected. The expansion increases the atmospheric drag on satellites in space, hastening re-entry.

The US satellite was deployed in 1991 from the space shuttle Discovery on a mission to study the make-up of Earth's atmosphere, particularly its protective ozone layer.

Nasa has warned members of the public not to touch any pieces of the spacecraft which may survive the re-entry, urging them to contact local law enforcement authorities.

by "environment clean generations"

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