SWAS-AOS: The first acousto-optical spectrometer in space

On December 5, 1998, the Submillimeter Wave Astronomy Satellite has been launched with a PEGASUS carrier after more than 3 years delay. SWAS is observing molecular line signals (H2O, (CO)-C-13, Cl, O-2, and (H2O)-O-18) from astronomical sources at frequencies between 487 and 557 GHz. SWAS is the first sub-millimeter heterodyne space mission, end, for the spectral analysis of the received signals, it carries the first acousto-optical spectrometer (AOS) in space. The AOS has been build at University of Cologne, and it covers 1.4 GHz bandwidth with approximately 1400 frequency channels. The total weight is 7.5 kg and the power consumption is 5.5 Watts only. The very stable temperature conditions on SWAS allow longtime integrations at total observing times far above 100 hours still with radiometric performance. So fat, the AOS-spectra have not been degraded by particle hits, particularly the CCD detector of the AOS does not exhibit any visible effect due to cosmic rays. SWAS has already observed many interstellar sources in our galaxy. Emission of water is seen to be very abundant, while signals of molecular oxygen seem to be too weak to be observable.