London, Oct 22: A big German spacecraft is about to make an uncontrolled fall from the sky.
 The Roentgen Satellite (Rosat) is due to come back to Earth at some stage over the weekend - possibly Sunday.
 Just as for Nasa's UARS satellite, which plunged into the atmosphere in September, no-one can say precisely when and where Rosat will come in.
 What makes the redundant German craft's return interesting is that much more debris this time is likely to survive all the way to the Earth's surface.
 Experts calculate that perhaps as much as 1.6 tonnes of wreckage - more than half the spacecraft's launch mass - could ride out the destructive forces of re-entry and hit the planet.
 In the case of UARS, the probable mass of surviving material was put at only half a tonne (out of a launch mass of more than six tonnes).
 The difference is due to some more robust components on the German space agency (DLR) satellite.
 Rosat was an X-ray telescope mission and had a mirror system made of a reinforced carbon composite material. This mirror complex and its support structure are expected to form the largest single fragment in what could be a shower of some 30 pieces of debris to make it through to the surface.
 But again, as was the case with UARS, any Rosat wreckage is strongly tipped to hit the ocean, given that so much of the Earth's surface is covered by water.
 UARS' final resting place was tracked to a remote region of the Pacific, north-east of the Samoan islands.
 Rosat could come down anywhere between 53 degrees North and South latitude - a zone that encompasses the UK in the north and the tip of South America in the south.
 Future spacecraft sent into orbit may have to meet stricter guidelines that limit the amount of debris likely to fall back on to the planet, but these rules are still some way from being introduced said Prof Richard Crowther, an expert on space debris and adviser to the UK Space Agency. BBC

Lastupdate on : Sat, 22 Oct 2011 21:30:00 Makkah time
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