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Gaia blasts off to begin mapping the Milky Way

Paul Sutherland, Feature writer
Dec 19, 2013, 8:00 UTC

Sen—A Soyuz rocket soared into the sky from Kourou, French Guiana, today carrying a space probe that will measure a billion stars to produce the most detailed 3D map of our galaxy ever made.

The two-tonne Gaia spacecraft was carried aloft by a Soyuz-STB/Fregat launch vehicle from the European Spaceport. Then 118 seconds after liftoff, the rocket’s four boosters were jettisoned, followed by the fairing that protected the probe during its turbulent ascent, at 220 seconds.

Separation of the rocket’s second and third stages were followed by two burns of the Fregat upper stage, before it too separated from Gaia 42 minutes after launch. This activated Gaia’s automatic sequence, including switching on its transmitters, setting its attitude with respect to the Sun, and deploying the 10.5 metre-wide sunshield, 88 minutes after launch.

The whole sequence ended 101 minutes after launch, after which mission controllers confirmed completion of the most critical part of the ‘launch and early orbit’ phase of the mission.

During five years of scheduled operations, the spacecraft will observe each of its target stars about 70 times, producing an accurate picture of each one’s brightness and motion around the centre of the galaxy.

By building this 3D picture over time, scientists expect to find clues to help them understand how our home spiral galaxy formed and evolved. The data will provide the most precise measurements ever for the stars’ astrometry, or positional data.

Europe’s Gaia mission is set to survey around one billion stars in the Milky Way, or one per cent of the galaxy’s 100 billion stellar population.


An artist's impression of the Gaia spacecraft at work. Credit: ESA/ATG medialab; background image: ESO/S. Brunier

But the powerful observatory is also expected to discover new planets around other stars, asteroids and icy bodies in the outer reaches of our Solar System, “failed” stars called brown dwarfs, and remote supernovae and quasars.

The Gaia spacecraft is formed of the payload module, a service module and a deployable sunshield to protect it from brilliant sunlight. The Payload module holds the single integrated observing tool which will carry out the astrometry, photometry to measure brightness and spectrometry to analyse starlight and tell what the star is made of.

The service module includes the micro-propulsion system to orient the spacecraft plus essential mechanics and electronics including a system to radio data back to Earth.

Gaia is heading for an orbit around the Sun at a stable point 1.5 million km (930,000 miles) away that is called the second Lagrange point (L2). There it can orbit the Sun in concert with the Earth. ESA’s now defunct Herschel and Planck satellites also operated from the L2 point.

Gaia originally stood for Global Astrometric Interferometer for Astrophysics. The instrumentation was redesigned but it kept its name. It will follow in the footsteps of a previous European mission to map the stars, called Hipparcos - the High Precision Parallax Collecting Satellite.

A replay of the launch of Gaia from Kourou. Credit: ESA

Hipparcos produced a primary catalogue with detailed data for about 118,000 stars, and a secondary, less precise catalogue, called Tycho, which included more than two million stars. Gaia’s two telescopes will be able to collect more than 30 times the light of Hipparcos, allowing it to make measurements 200 times more accurate.

A problem for scientists that is common for many of the new astronomical surveys is how to handle the enormous amount of information that the satellite will send back. It is estimated that over its five-year lifetime, Gaia will collect enough data to fill more than 1.5 million CD-roms!

University College London’s Mullard Space Science Laboratory is one institution that has played a major part in developing Gaia’s observing instrument over 12 years. Professor Mark Cropper explained: “If we know the positions of all of the stars, we can map the Milky Way. And if we know their movements, we can work out the forces on the stars.

“Because gravity is the main force controlling stellar movement, and its strength and direction depends on the location of matter, including mysterious dark matter, we can weigh the Milky Way and work out where all the mass is. This controls the entire shape of the Milky Way to make it look as it does.”

A video animation shows Gaia's launch and journey to its operating orbit. Credit: ESA – C. Carreau / ATG medialab