SWAS (Submillimeter Wave Astronomy Satellite) is a NASA satellite, launched in December 1988, that is equipped with a 0.6-meter telescope for making observations in the 490–550 gigahertz submillimeter range, and also with an acousto-optical spectrometer. It enable studies of the cooling of molecular cloud cores – the sites of star formation in the Galaxy – by measuring spectral lines of molecular oxygen and water. SWAS was the fourth SMEX (Small Explorer) mission. It is currently in an extendedperiod of hibernation.