The European Space Agency has launched an advanced telescope designed to detect a billion stars and provide a detailed map of the Milky Way.
The Gaia telescope was successfully hoisted by a Soyuz-STB-Fregat rocket from the ESA base in Kourou, French Guiana, at 6.12am (local time) on Thursday.
"All is functioning normally," an ESA commentator said.
The satellite was to be deployed 42 minutes after launch.
The plan is to build a census of a billion stars, or around 1% of all the stars in the Milky Way.
By repeating the observations as many as 70 times throughout its mission, Gaia can help astronomers calculate the distance, speed, direction and motion of these stars and build a 3D map of this section of the galaxy.
It will also help in the search for planets beyond our solar system.
ESA chief scientist Mark McCaughrean said the mission holds the key to unlocking the secrets of the galaxy.
Gaia will also observe the asteroid belt between Mars and Jupiter for any rocks that may one day threaten Earth.