[Lovers India] ANOTHER satellite to crash land soon...

ANOTHER satellite to crash land soon, and the odds of it hitting someone are even higher

By TED THORNHILL

Last updated at 5:13 PM on 30th September 2011

The world was gripped by the Nasa UARS satellite that fell back to Earth last Saturday – and now there's another that's plummeting back from orbit.

In late October or early November a Germany astronomy satellite – called ROSAT- will plunge uncontrolled back to Earth.

While slightly smaller than UARS, the German satellite is expected to have more pieces survive re-entry. The German space agency estimated that it has a 1-in-2000 chance of hitting someone - higher than the 1-in-3,200 odds NASA gave for UARS. 

Heavens above: An artist's impression of the ROSAT satellite, which is expected to plunge to Earth in the near future

The German ROSAT satellite was launched in 1990, 'died' in 1998 and weighs two and a half tonnes. 

The German space agency estimates that 30 pieces weighing less than two tons will survive re-entry. Debris may include sharp mirror shards.

The German space agency puts the odds of somebody somewhere on Earth being hurt by its satellite at 1-in-2,000 — a slightly higher level of risk than was calculated for the Nasa satellite. 

Again, it seems certain that information on when - or where - the satellite might land will be scant. 

Bus-sized: New U.S. Air Force calculations put the six-tonne satellite's death plunge on early Saturday thousands of miles from northwestern North America, where there were reports of sightings

But any one individual's odds of being struck are 1-in-14trillion.

Heiner Klinkrad, head of the Space Debris Office at the European Space Agency, said in a webcast posted on the German Aerospace Center's website: 'It is not possible to accurately predict ROSAT's re-entry.

'The uncertainty will decrease as the moment of re-entry approaches. It will not be possible to make any kind of reliable forecast about where the satellite will actually come down until about one or two hours before the fact.'

Experts believe that two dozen metal pieces from the bus-sized Nasa satellite fell over a 500-mile span in the Pacific Ocean.

It began hitting the water southwest of Christmas Island.

WHAT HAPPENS WHEN A SATELLITE FALLS TO EARTH?

Astronomer Dr Ian Griffin, from the UK Association of Science and Discovery Centres, says the Earth's atmosphere slows down falling satellites a great deal.

Much of any satellite crashing to Earth will be disintegrated by heat, caused by friction with the atmosphere. It's the reason we get shooting stars - created by meteors burning up in the upper atmosphere. 

Space vehicles experience incredible stress on re-entry. The load can be as much as 10Gs. An F1 car experiences around 5Gs with maximum braking from high speed.

The reason why the location of a crash site is so hard to predict is because the density of the atmosphere varies so greatly higher up, producing different amounts of drag.

A prediction that was wrong by even a few minutes would mean the satellite landing a huge distance away, owing to its speed.

http://www.dailymail.co.uk/sciencetech/article-2043846/ROSAT-ANOTHER-satellite-crash-land-weeks-time.html

M.Yusuf
Coonoor Nilgris

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