Billion-pixel camera

What will it be used for? [Link]

According to ESA, the Gaia satellite will operate at the Earth-Sun L2 Lagrange point, 1.5 million kilometers behind the earth, when looking from the sun.  "As the spinning Gaia's two telescopes sweep across the sky, the images of stars in each field of view will move across the focal plane array, divided into four fields variously dedicated to star mapping, position and motion, color and intensity and spectrometry," the space agency stated.

Gaia is expected to map a billion stars within the Milky Way Galaxy over the course of its five-year mission, charting brightness and spectral characteristics along with their three-dimensional positions and motions.

From the ESA on Gaia's mission:

• Gaia's transmitter is weak, much less powerful than a standard 100 W light bulb. Even so, this equipment will be able to maintain the transmission of an extremely high data rate (about 5 Mbit/s) across 1.5 million km. ESA's most powerful ground stations, the 35 m-diameter radio dishes in Cebreros, Spain, and New Norcia, Australia, will intercept the faint signal transmitted by Gaia.
• The numbers foreseen in Gaia's celestial census are breathtaking. Every day it will discover, on average, 10 stars possessing planets, 10 stars exploding in other galaxies, 30 'failed stars' known as brown dwarfs, and numerous distant quasars, which are powered by giant black holes.
• Estimates suggest that Gaia will detect about 15, 000 planets beyond our Solar System. It will do this by watching for tiny movements in the star's position caused by the minute gravitational pull of the planet on the star.