The European Space Agency's 800 million pounds probe will become the Earth's first early warning system against asteroid impacts - even those that lie centuries ahead.
One of the key tasks of the telescope, featuring the most high-powered video camera ever built, is to stare at the space between the Earth and the Sun to plot the tracks of the thousands of asteroids lurking there.
Astronomers have not been able to spot such asteroids because they orbit between the Earth and the Sun, whose radiation blinds telescopes, but they are regarded as the most dangerous because their orbits often cross the Earth's.
"Gaia will measure all the asteroids including those between us and the sun which are the really nasty ones because we cannot see them," said Gerry Gilmore, professor of experimental philosophy at Cambridge University's Institute of Astronomy, who is a lead scientist on the project.
Gaia mission's other main task is designed to create the first 3D map of our Milky Way galaxy.
"Gaia is the biggest video camera with a sensor 1m long and 0.5m wide," Gilmore said.
"It will follow a billion stars for five or six years, plotting their movements 80 times so that we can work out their exact tracks. We can combine those movements with those of the Earth round the Sun to triangulate them - giving us the first accurate measurements across interstellar space," Gilmore added.
Gaia will let scientists build a network of 5,000 reference stars in the Milky Way plus 5,000 supernovae, exploded stars, whose distances will all be known. Scientists will use this to calculate the distances of other stars and galaxies.
The satellite completed final preparations in Europe last year and will take off from a launch site in French Guiana on November 20.


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