Overview:

The main goal of the Gaia mission is to make the largest, most precise three-dimensional map of our Galaxy by surveying an unprecedented one per cent of its population of 100 billion stars. Gaia will reveal the composition, formation and evolution of the Galaxy.

Objectives:

• measure the position of ~1 billion stars both in our Galaxy and other members of the Local Group, with an accuracy down to 20 µas.

• perform spectral and photometric measurements of all objects.

• derive space velocities of the Galaxy's constituent stars using the stellar distances and motions.

• create a three-dimensional structural map of the Galaxy.

Instrumentation:

• A dual telescope concept, with a common structure and a common focal plane. Both telescopes are based on a three-mirror anastigmat (TMA) design. Beam combination is achieved in image space with a small beam combiner.

• Silicon-carbide (SiC) ultra-stable material is used for mirrors and telescope structure.

• A highly robust measurement system for the Basic Angle between the two telescopes' poiting directions.

• A large common focal plane with an array of 106 CCDs. The large focal plane also includes areas dedicated to the spacecraft's metrology and alignment measurements.

• Three instrument functions:
  
  
  • Astrometry: accurate measurements, even in densely populated sky regions of up to 3 million stars/deg²
  
  
  • Photometry: continuous spectra in the band 320-1000 nm for astrophysics and chromaticity calibration of the astrometry
  
  
  • Spectrometry: high resolution, grating, narrow band: 847-874 nm