Spacecraft & Instruments

Exploded view of Gaia

copyright: ESA/ATG-medialab

The Gaia spacecraft is comprised of three major functional modules:

• The payload module containing the optical instrument and all electronics required to manage its operation and process its raw data. For this purpose the Payload Module includes the Video Processing Unit, the Clock Distribution Unit (housing the atomic clock references) and the Payload Data Handling Unit in charge of data storage between two downlink sessions.

• The mechanical service module made of all mechanical, structural and thermal elements supporting the instrument and the spacecraft electronics. In addition, the mechanical SVM comprises Micro-Propulsion system, Deployable sunshield, Payload thermal tent, Solar arrays and Harness.

• The electrical 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.

Payload & Instruments

Gaia's payload carries two identical telescopes, pointing in two directions separated by a 106.5° basic angle and merged into a common path at the exit pupil. Three instruments detect the light collected by these telescopes.

• The astrometric instrument is devoted to measuring stellar positions on the sky. By combining all measurements of a given star over the mission period, it will be possible to deduce its parallax and thus its distance, as well as the velocity of the star as it moves accross the plane of the sky.

• The photometric instrument provides colour information for celestial objects by generating two low-resolution spectra, one in the blue and one in the red range of the optical spectrum. These data help to determine key stellar properties such as temperature, mass and chemical composition.

• The Radial Velocity Spectrometer reveals the velocity of the star along the line of sight by measuring the Doppler shift of absorption lines in a high-resolution spectrum covering a narrow wavelength range.