[Omah]

Originally Posted by Shardlake

You would think that with all their supposed technology and 'experts' they could give us a better time frame than ' the most likely time for re-entry could be after 23:00 GMT Friday, and as late as 03:00 GMT on Saturday.'

http://www.bbc.co.uk/news/science-environment-15021323

Satellite and space expert Dr Stuart Eves stressed the large uncertainties involved in tracking the "decay" of satellite orbits (their slow fall back into the Earth's atmosphere).

Using the most recent determination of UARS' orbit - taken in the early hours of this morning - Dr Eves and a colleague have come up with their own projections of the satellite's final descent. But he explained that a spacecraft's orbit lifetime could only be estimated to about 10% accuracy.

This translates to a six-hour window either side of the expected decay which is based on a range of probabilities. Calculations using the data available on Thursday afternoon suggested a splash down in the Southern Ocean. But this is likely to change as tracking specialists get a better fix closer to Friday evening.

Given the 10% accuracy figure, and the fact that UARS takes about one-and-a-half hours to complete an orbit of Earth, the satellite could come down during one of four possible orbits of Earth on Friday evening/Saturday morning.

And a number of different estimates could be produced depending what software is used to model the satellite's decay, explained Dr Eves, who is lead mission concept engineer at Surrey Satellite Technology Limited (SSTL).

Satellite decays can be affected by a number of different factors, such as the shape of the spacecraft and its unpredictable tumbling, as well as heating of the Earth's atmosphere by ultraviolet radiation from the Sun.

This can make the atmosphere expand, causing UARS to fall to Earth faster than expected.

But other conditions could see the satellite stay in space for longer than anticipated.