The US space agency (Nasa) says that its out-of-control climate satellite is expected to crash to Earth sometime on Friday evening (GMT).
There is still much uncertainty over when and where the satellite will re-enter the atmosphere.
Experts say they will get a more precise idea in the last 12 hours before the satellite is due to return.
The US space agency says the risk to life from the Upper Atmosphere Research Satellite (UARS) is 1 in 3,200.
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.
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