The SWAS Acousto Optical Spectrometer

M. Klumb, J. Frerick, R. Schieder, and G. Winnewisser

I. Physics Institute, University of Cologne

V. Tolls

Smithsonian Astrophysical Observatory, Cambridge, Ma

SPIE Proceedings of "Infrared Spaceborne Remote Sensing II", Vol. 2268, 1994


The first fully space qualified acousto-optical spectrometer (AOS) is described. It is built for the Submillimeter Wave Astronomy Satellite (SWAS) to be launched in July 1995. It has a very large bandwidth from 1400 to 2800 MHz covered by 1356 channels. This corresponds to a nearly 1 MHz channel spacing. The design is optimized for very high stability, which is demonstrated by means of Allan variance stability test. The Allan plot minimum time was found well above 800 seconds. The AOS can operate within a temperature range from -5 to +30 ° C (+5 to +25 ° C nominal) and with temperature variations of up to 2 ° C/h. The performance was verified also after environmental testing such as random vibration (10.2 G rms) and thermal cycling of -30 to +50 ° C. The lightweight mechanical design resulted in a total weight of 7.2 kg including electronics. A detailed optical design study was performed in order to achieve diffraction limited channel resolution, high efficiency and low sensitivity to mechanical distortion. The RF input power needed for full scale is 11 mW. The power consumption is 5.4 Watts (including data pre-averaging and DC-DC converter losses). The development has shown that AOSs are well suited for spaceborne applications.