Early this morning, at 09:12 UTC, the cloudy pre-dawn sky above the coastal town of Kourou, French Guiana was brilliantly sliced by the fiery exhaust of a Soyuz VS06, which ferried ESA’s “billion-star surveyor” Gaia into space to begin its five-year mission to map the Milky Way.
Ten minutes after launch, after separation of the first three stages, the Fregat upper stage ignited, successfully delivering Gaia into a temporary parking orbit at an altitude of 175 km (108 miles). A second firing of the Fregat 11 minutes later took Gaia into its transfer orbit, followed by separation from the upper stage 42 minutes after liftoff. 46 minutes later Gaia’s sunshield was deployed, and the spacecraft is now cruising towards its target orbit around L2, a gravitationally-stable point in space located 1.5 million km (932,000 miles) away in the “shadow” of the Earth.
The launch itself was really quite beautiful, due in no small part to the large puffy clouds over the launch site. Watch the video below:
A global space astrometry mission, Gaia will make the largest, most precise three-dimensional map of our galaxy by surveying more than a billion stars over a five-year period.
“Gaia promises to build on the legacy of ESA’s first star-mapping mission, Hipparcos, launched in 1989, to reveal the history of the galaxy in which we live,” says Jean-Jacques Dordain, ESA’s Director General.
Repeatedly scanning the sky, Gaia will observe each of the billion stars an average of 70 times each over the five years. (That’s 40 million observations every day!) It will measure the position and key physical properties of each star, including its brightness, temperature and chemical composition.
By taking advantage of the slight change in perspective that occurs as Gaia orbits the Sun during a year, it will measure the stars’ distances and, by watching them patiently over the whole mission, their motions across the sky.
The motions of the stars can be put into “rewind” to learn more about where they came from and how the Milky Way was assembled over billions of years from the merging of smaller galaxies, and into “fast forward” to learn more about its ultimate fate.
“Gaia represents a dream of astronomers throughout history, right back to the pioneering observations of the ancient Greek astronomer Hipparchus, who catalogued the relative positions of around a thousand stars with only naked-eye observations and simple geometry. Over 2,000 years later, Gaia will not only produce an unrivaled stellar census, but along the way has the potential to uncover new asteroids, planets and dying stars.”
– Alvaro Giménez, ESA’s Director of Science and Robotic Exploration
Of the one billion stars Gaia will observe, 99% have never had their distances measured accurately. The mission will also study 500,000 distant quasars, search for exoplanets and brown dwarfs, and will conduct tests of Einstein’s General Theory of Relativity.
“Along with tens of thousands of other celestial and planetary objects,” said ESA’s Gaia project scientist Timo Prusti, “this vast treasure trove will give us a new view of our cosmic neighbourhood and its history, allowing us to explore the fundamental properties of our Solar System and the Milky Way, and our place in the wider Universe.”
Caption: Fully integrated Gaia payload module with nearly all of the multilayer insulation fabric installed. Credit: Astrium SAS
Earlier this month ESA’s Gaia mission passed vital tests to ensure it can withstand the extreme temperatures of space. This week in the Astrium cleanroom at Intespace in Toulouse, France, had it’s payload module integrated, ready for further testing before it finally launches next year. This is a good opportunity to get to know the nuts and bolts of this exciting mission that will survey a billion stars in the Milky Way and create a 3D map to reveal its composition, formation and evolution.
Gaia will be operating at a distance of 1.5 million km from Earth (at L2 Lagrangian point, which keeps pace with Earth as we orbit the Sun) and at a temperature of -110°C. It will monitor each of its target stars about 70 times over a five-year period, repeatedly measuring the positions, to an accuracy of 24 microarcseconds, of all objects down to magnitude 20 (about 400,000 times fainter than can be seen with the naked eye) This will provide detailed maps of each star’s motion, to reveal their origins and evolution, as well as the physical properties of each star, including luminosity, temperature, gravity and composition.
The service module houses the electronics for the science instruments and the spacecraft resources, such as thermal control, propulsion, communication, and attitude and orbit control. During the 19-day tests earlier this month, Gaia endured the thermal balance and thermal-vacuum cycle tests, held under vacuum conditions and subjected to a range of temperatures. Temperatures inside Gaia during the test period were recorded between -20°C and +70°C.
“The thermal tests went very well; all measurements were close to predictions and the spacecraft proved to be robust with stable behavior,” reports Gaia Project Manager Giuseppe Sarri.
For the next two months the same thermal tests will be carried out on Gaia’s payload module, which contains the scientific instruments. The module is covered in multilayer insulation fabric to protect the spacecraft’s optics and mirrors from the cold of space, called the ‘thermal tent.’
Gaia contains two optical telescopes that can precisely determine the location of stars and analyze their spectra. The largest mirror in each telescope is 1.45 m by 0.5 m. The Focal Plane Assembly features three different zones associated with the science instruments: Astro, the astrometric instrument that detects and pinpoints celestial objects; the Blue and Red Photometers (BP/RP), that determines stellar properties like temperature, mass, age, elemental composition; and the Radial-Velocity Spectrometer (RVS),that measures the velocity of celestial objects along the line of sight.
The focal plane array will also carry the largest digital camera ever built with, the most sensitive set of light detectors ever assembled for a space mission, using 106 CCDs with nearly 1 billion pixels covering an area of 2.8 square metres
After launch, Gaia will always point away from the Sun. L2 offers a stable thermal environment, a clear view of the Universe as the Sun, Earth and Moon are always outside the instruments’ fields of view, and a moderate radiation environment. However Gaia must still be shielded from the heat of the Sun by a giant shade to keep its instruments in permanent shadow. A ‘skirt’ will unfold consisting of a dozen separate panels. These will deploy to form a circular disc about 10 m across. This acts as both a sunshade, to keep the telescopes stable at below –100°C, and its surface will be partially covered with solar panels to generate electricity.
Once testing is completed the payload module will be mated to the service module at the beginning of next year and Gaia will be launched from Europe’s Spaceport in French Guiana at the end of 2013.