Space-qualified wideband and ultrawideband acousto-optical spectrometers for millimeter and submillimeter radio astronomy

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Abstract
Acousto-optical techniques are particularly well suited for wide band spectroscopy in astrophysical and geophysical applications using millimeter and sub-millimeter heterodyne radiometers aboard spacecraft. An illustration is given by the 1 GHz AOS built for the ODIN, sub-millimeter telescope in Earth's orbit. We describe the spectrometer, including the IF down converter, AO processor, data acquisition and pre- processing sub-systems. The used technology, space qualification of the critical components as well as relevant environmental and electrical results are presented. The acousto-optical technique can also be used for compact, ultra wide band spectrometers (2000 to 4000 channels over 4 GHz bandwidth or more). Scientific applications include sub- millimeter missions in Astronomy (FIRST) as well in Geophysics (Microwave Limb Sounding programs). Performances obtained on prototypes built in Meudon Observatory are presented and the characteristics achievable for near future systems are analyzed. They fit well with the presently retained design of the heterodyne (HET) instrument on FIRST, based on a font-end system made of a four band, dual polarization receiver, allowing for full frequency coverage from 480 to 1250 MHz.

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