The European Space Agency (ESA) launched its €940 million ($1.3 billion) Gaia star-mapping spacecraft Dec. 19 after postponing the mission one month due to technical issues involving a component flying on another satellite already in orbit.

Equipped with twin silicon-carbide telescopes built around a single, 1-billion-pixel focal array, Gaia is designed to survey a billion stars in the Milky Way, providing a precise 3-D map to better understand the galaxy’s composition, formation and evolution.

The Gaia mission blasted off at 6:12 a.m. local time atop a Soyuz ST-B rocket from Europe’s equatorial spaceport in Kourou, French Guiana. About 10 min. later, after separation of the first three stages, the Fregat upper stage ignited, delivering Gaia into a temporary parking orbit at an altitude of 175 km. A second firing 11 min. later took Gaia into its transfer orbit, followed by spacecraft separation at 42 min. after liftoff. With the 2,034-kg Gaia on its way to the L2 Lagrange point 1.5 million km (930,000 mi.) from Earth, ESA says it has established ground telemetry and attitude control from the agency’s operations center in Darmstadt, Germany, and that the spacecraft is now activating its systems.

On Dec. 20 engineers will command Gaia to perform the first of two critical thruster firings to ensure it is on the right trajectory toward L2. About 20 days after launch, a second critical burn is expected to insert the spacecraft into its operational orbit, beginning a four-month commissioning phase during which all of the systems and instruments will be turned on, checked and calibrated before beginning its five-year mission.

Built by satellite manufacturer EADS-Astrium under a €317 million contract awarded in May 2006, Gaia will measure the angular position of stars between 7-300 microseconds of arc — 100 times the accuracy of ESA’s 1989 Hipparcos mission and equivalent to a terrestrial measurement of an astronaut’s thumbnail on the lunar surface. The resulting census will allow astronomers to determine the origin and evolution of the galaxy while uncovering tens of thousands of previously unseen objects, including extrasolar planets, brown dwarfs, quasars, asteroids and comets, and other galaxies, monitoring each target object up to 100 times to precisely chart its characteristics. Over the course of its five-plus year mission, Gaia will observe more than 40 million objects per day, collecting 100 terabytes of raw data and yielding 1 petabyte of processed and archived data.

More than a decade in the making, Gaia is running two years behind schedule due to technical issues with the satellite’s instruments and delays imposed by a crowded manifest in Kourou. The latest technical glitch that slipped the mission from Nov. 20 to Dec. 19 involved faulty transponder components built by Thales Alenia Space of Italy that generate timing signals for downlinking science data. ESA did not identify the in-orbit satellite with the faulty transponder component that prompted the agency to delay the mission one month, but said it would replace the parts prior to Gaia’s launch as a precautionary measure.

Gaia is the second consecutive Soyuz launch from French Guiana to be delayed in 2013. Earlier this year O3b Networks postponed a planned late-September Soyuz launch of four communications satellites built by Thales Alenia Space due to a technical problem discovered on four similar O3b satellites launched earlier this year. The four spacecraft are now slated to launch in 2014.