NASA says a six tonne satellite has fallen out of orbit and is expected to crash somewhere on Earth on or around 24 September.
NASA says the risk of it hitting someone is higher than usual and it could land anywhere.
However, the BBC reports most of the satellite will break or burn up on entering the atmosphere.
The Upper Atmosphere Research Satellite was launched in 1991 by the Discovery space shuttle and was decommissioned in 2005.
It is much smaller than Skylab, a satellite that re-entered the earth's atmosphere in 1979 and crashed in Western Australia.
Sputnik 2 crashed on Earth in 1958.