The GAIA mission, approved as one of ESA's next two "cornerstones," aims to provide positional and radial velocity measurements with unprecedented accuracy, enabling a stereoscopic and kinematic census of about one billion stars in our Galaxy and the Local Group. The primary scientific goal is to clarify the origin and history of the Galaxy, including the timing of star formation, the assembly process, and the distribution of dark matter. GAIA will achieve this through astrometric measurements, photometry, and spectroscopy, providing data on stellar populations, chemical abundances, and distances. Key scientific goals include understanding the structure and dynamics of the Galaxy, determining the star formation history, and studying stellar astrophysics, variability, binaries, brown dwarfs, planetary systems, and the Solar System. GAIA will also contribute to extragalactic astronomy, fundamental physics, and cosmology, offering precise tests of general relativity and cosmological models. The mission design includes two astrometric viewing directions, each with a three-mirror telescope, and a spectrometric instrument for radial velocity measurements and photometry. The optical design ensures high accuracy and stability, with a compact structure suitable for the Ariane 5 launcher.The GAIA mission, approved as one of ESA's next two "cornerstones," aims to provide positional and radial velocity measurements with unprecedented accuracy, enabling a stereoscopic and kinematic census of about one billion stars in our Galaxy and the Local Group. The primary scientific goal is to clarify the origin and history of the Galaxy, including the timing of star formation, the assembly process, and the distribution of dark matter. GAIA will achieve this through astrometric measurements, photometry, and spectroscopy, providing data on stellar populations, chemical abundances, and distances. Key scientific goals include understanding the structure and dynamics of the Galaxy, determining the star formation history, and studying stellar astrophysics, variability, binaries, brown dwarfs, planetary systems, and the Solar System. GAIA will also contribute to extragalactic astronomy, fundamental physics, and cosmology, offering precise tests of general relativity and cosmological models. The mission design includes two astrometric viewing directions, each with a three-mirror telescope, and a spectrometric instrument for radial velocity measurements and photometry. The optical design ensures high accuracy and stability, with a compact structure suitable for the Ariane 5 launcher.