The Gaia spacecraft is composed of the payload module, the service module and the deployable sunshield. It has a launch mass of around 2 tonnes. The payload module is built around a toroidal-shaped optical bench (~3m diameter) which provides the structural support for the single integrated instrument that comprises three functions: astrometry, photometry and spectrometry. It further contains all necessary electronics for managing the instrument operation and processing the raw data. The service module comprises all mechanical, structural and thermal elements supporting the instrument and the spacecraft electronics. It includes the micro-propulsion system, deployable sunshield, payload thermal tent, solar arrays and harness. The service module offers support functions to the Gaia payload and spacecraft for pointing, electrical power control and distribution, central data management and radio communications with the Earth."
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Image appeared in Issue 18 of magazine "All About Space".