Submillimeter Wave Astronomy Satellite Performance on the ground and in orbit

Abstract

The Submillimeter Wave Astronomy Satellite (SWAS), which was launched in 1998 December, is a NASA mission dedicated to the study of interstellar chemistry and star formation. SWAS is conducting pointed observations of molecular clouds throughout our Galaxy in either the ground state or a low-lying transition of five astrophysically important species: O 2, C I, H 2 18 O, 13 CO, and H 2 16 O at approximately 487, 492, 548, 551, and 557 GHz, respectively. The SWAS instrument is comprised of a 54cm×68cm off-axis Cassegrain telescope feeding two independent heterodyne receivers with Schottky barrier diode mixers, passively cooled to about 175 K. An Acousto-Optical Spectrometer (AOS) provides ~1 MHz (0.6 km s -1) frequency resolution and 1400 MHz (840 km s -1) total bandwidth with 350 MHz (210 km s -1) per line for spectral analysis. SWAS was fully characterized during ground-based testing, and all performance parameters were verified on-orbit. During its on-orbit operation, SWAS observed more than 200 astronomical objects with more than 5000 lines of sight. This paper describes the tests conducted and compares the ground-based test results with the on-orbit test results.