CAPE CANAVERAL, Fla. – A pair of NASA astronauts face the final and most important part of their SpaceX test flight: returning to Earth with a rare splashdown.Doug Hurley and Bob Behnken took part in a farewell ceremony Saturday at the International Space Station, several hours ahead of their planned departure on a SpaceX Dragon capsule.Despite approaching Hurricane Isaias, NASA said the weather looks favorable for a Sunday afternoon splashdown in the Gulf of Mexico near Panama City, Florida.