A NASA satellite launched on 6 December 1998 to study the chemical composition of interstellar gas clouds and the processes that lead to the formation of stars and planets. It carries a telescope with an elliptical mirror 0.55 m by 0.71 m, and detectors which are sensitive to the submillimetre spectral lines emitted by water molecules, oxygen, carbon, and carbon monoxide. SWAS used its instruments to map giant molecular clouds in the Galaxy's spiral arms, the sites of current star formation. The satellite was placed in hibernation in July 2004 then reactivated in June to provide support for the Deep Impact mission. SWAS data showed that there was no excessive release of water due to the impact event. After the three-month mission, in September 2005 SWAS was once again placed into hibernation, and remains on standby.