Miami ( CNN ) -- A defunct satellite plummeting toward Earth is expected to re-enter the atmosphere between 11:45 p.m. Friday and 12:45 a.m. Saturday ET , NASA reported late Friday evening . `` During that time period , the satellite will be passing over Canada and Africa , as well as vast areas of the Pacific , Atlantic and Indian oceans . The risk to public safety is very remote , '' the space agency said . The United States is once again an unlikely but potential target for the 26 pieces of the Upper Atmosphere Research Satellite , expected to survive the descent . Those pieces , made of stainless steel , titanium and beryllium that wo n't burn , will range from about 10 pounds to hundreds of pounds , according to NASA . `` There is a low probability any debris that survives re-entry will land in the United States , '' NASA headquarters said , `` but the possibility can not be discounted because of this changing rate of descent . '' Mark Matney of NASA 's Orbital Debris team in Houston said there 's no way to know exactly where the pieces will come down . `` Keep in mind , they wo n't be traveling at those high orbital velocities . As they hit the air , they tend to slow down . ... They 're still traveling fast , a few tens to hundreds of miles per hour , but no longer those tremendous orbital velocities , '' he explained . Because the satellite travels thousands of miles in a matter of minutes as it orbits -- even just before it begins re-entry -- it will be impossible to pinpoint the exact location the pieces will come down . On top of that , Matney said , the satellite is not stable . `` Part of the problem is , the spacecraft is tumbling in unpredictable ways , and it is very difficult to very precisely pinpoint where it 's coming down even right before the re-entry . '' Because water covers 70 % of the Earth 's surface , NASA has said that most if not all of the surviving debris will land in water . Even if pieces strike dry land , there 's very little risk any of it will hit people . However , in an abundance of caution , the Federal Aviation Administration released an advisory Thursday warning pilots about the falling satellite , calling it a potential hazard . `` It is critical that all pilots/flight crew members report any observed falling space debris to the appropriate ( air traffic control ) facility and include position , altitude , time and direction of debris observed , '' the FAA statement said . The FAA said warnings of this sort typically are sent out to pilots concerning specific hazards they may encounter during flights such as air shows , rocket launches , kites and inoperable radio navigational aids . NASA says space debris the size of the satellite 's components re-enters the atmosphere about once a year . Harvard University astrophysicist Jonathan McDowell noted that the satellite is far from being the biggest space junk to come back . `` This is nothing like the old Skylab scare of the '70s , when you had a 70-ton space station crashing out of the sky . So , I agree with the folks in Houston . It 's nothing to be worried about , '' McDowell said . Pieces of Skylab came down in western Australia in 1979 . The only wild card McDowell sees is if somehow a chunk hits a populated area . `` If the thing happens to come down in a city , that would be bad . The chances of it causing extensive damage or injuring someone are much higher . '' NASA said that once the debris hits the atmosphere 50 miles up , it will take only a matter of minutes before the surviving pieces hit the Earth . CNN 's Mike Ahlers contributed to this report .
Re-entry is expected between 11:45 p.m. Friday and 12:45 a.m. Saturday. The space agency still ca n't say with certainty where the satellite 's remnants will land . About 26 pieces , some weighing hundreds of pounds , are expected to survive reentry .