Our solar system is positioned near the centre of the Milky Way, not far from the galactic core. It's a nice part of town, sure, but it doesn't allow for a very clear view of the rest of the galaxy. That's prevented us from studying many of the Milky Way's fundamental aspects, like whether it has two arms or four, how big it is, how fast it's moving, and whether we're someday going to ram headfirst into the Andromeda galaxy.
However, the Gaia project is about spend five years mapping the whole of the Milky Way, answering our most basic questions about its evolution and structure. "It's going to be phenomenal," says astronomer Barry F. Madore of the Carnegie Observatories in Pasadena, Ca. "It will change everything."
Developed by the European Space Agency, and currently being built by EADS Astrium SAS, the €700 million Gaia spacecraft is just the second such satellite dedicated to astrometry to be put in orbit. Astrometry itself has been practised for centuries, but the accuracy of ground-based telescopes is limited by atmospheric turbulence. To date, we know the distance to fewer than 1000 stars with a precision of 1 per cent. But with the Gaia, researchers estimate they'll be able to measure more than 10 million stars with the same fidelity. As mission scientist Timo Prusti quipped to IEEE, "It's going to really be a sledgehammer in fundamental astronomy."
The Gaia will launch later this year from Kourou, French Guiana and enter into orbit at Lagrange 2 (L2), some 1.5 million kilometres from earth from Earth, always facing away from the Sun. This position not only guarantees that the observation platform will always have a view unobstructed by the Sun, Earth, or moon, it will continually expose the craft's solar panel "skirt" to its power source.
Gaia is expected to process nearly 8000 star positions per second over the course of its five-year mission. In all, the positions and velocities of more than a billion stars will be mapped. No, literally, the Gaia project will create an incredibly accurate three-dimensional map of more than a thousand million galactic stars by the time it's through. What's more, while the spacecraft is mapping stellar positions, it's also studying the composition of each star it sees, generating a massive new data set for astronomers to utilise.
The Gaia spacecraft itself measures about 11 metres wide, weighs 2030kg, and uses a two-module design with propulsion, avionics and communications devices stored in the service module while the crafts pair of optical telescopes reside in the payload module under a "thermal tent". Each telescope will focus incoming light onto a shared 106 CCD array, 4500 x 1966 pixels in size. This array is split into three areas, each associated with the three primary goals of the survey: measuring a star's position, chemical composition and velocity.
These telescopes offer unparalleled precision down to magnitude 20 (that's 400,00 times fainter than what your naked eye can see) which will allow researchers to spot the numerous brown dwarves, distant supernovae and other super-faint celestial occurrences. At magnitude 15, the craft will measure stars with an accuracy of 24 microarcseconds — roughly the width of a human hair if viewed from 1000km away or the size of your thumbnails on the moon as seen from the Earth. That's so precise that the distance nearby galaxies will be measured with 0.001 per cent accuracy and those as far as 30,000 light-years will be measured with 20 per cent accuracy.
All of the data that the array collects is transmitted to the ESA's most sensitive ground stations in Cebreros, Spain, and New Norcia, Australia, over the course of eight hours every day at the surprisingly quick throughput of 5Mbit/s. At that rate, it's only a matter of time before the secrets of the Milky Way are revealed to us in full. [IEEE - ESA - Wikipedia]