Submillimeter Wave Astronomy Satellite

Abstract

The Submillimeter Wave Astronomy Satellite (SWAS) mission will study galactic star formation and interstellar chemistry. To carry out this mission, SWAS will survey dense (n H2 > 10 3 cm -3 ) molecular clouds within our galaxy in either the ground-state or a low- lying transition of five astrophysically important species: H 2 O, H 2 18 O, O 2 , CI, and 13 CO. By observing these lines SWAS will: (1) test long-standing theories that predict that these species are the dominate coolants of molecular clouds during the early stages of their collapse to form stars and planets and (2) supply heretofore missing information about the abundance of key species central to the chemical models of dense interstellar gas. During its two-year mission, SWAS will observe giant and dark cloud cores with the goal of detecting to setting an upper limit on the water abundance of 3 X 10 -6 (relative to H 2 ) and on the molecular oxygen abundance of 2 X 10 -6 (relative to H 2 ). SWAS is designed to carry all elements of a ground based radiotelescope. The telescope is a highly efficient 54 X 68-cm off-axis Cassegrain antenna with an aggregate surface error less than or equal to 11 micrometers rms. The receiver system consists of two independent heterodyne receivers with second harmonic Schottky diode mixers, passively cooled to approximately equals 150 K. The spectrometer is a single acousto-optical spectrometer (AOS) with 1400 1-MHz channels enabling simultaneous observations of the H 2 O, O 2 , CI, and 13 CO lines.