Submillimeter Wave Astronomy Satellite (SWAS, also Explorer 74 and SMEX-3) is a NASA submillimetre astronomy satellite, and is the fourth spacecraft in the Small Explorer program (SMEX). It was launched on 6 December 1998, at 00:57:54 UTC, from Vandenberg Air Force Base aboard a Pegasus XL launch vehicle. The telescope was designed by the Smithsonian Astrophysical Observatory (SAO) and integrated by Ball Aerospace, while the spacecraft was built by NASA's Goddard Space Flight Center (GSFC). The mission's principal investigator is Gary J. Melnick.