GAIA is an European (ESA) 5 year space mission to measure the positions of about 1 billion stars with unprecedented accuracy, to be launched at the end of 2011. GAIA's main goal is to considerably improve our knowledge of the distance to "nearby" objects: most stars measured by GAIA are close to us in astronomical terms.
GAIA’s two spinning telescopes will acquire images of the sky in optical light as well as measuring the spectrum of the brightest objects. GAIA represents a significant improvement respect to the previous astrometric mission: Hipparcos (http://www.rssd.esa.int/Hipparcos/), also an ESA mission launched nearly 20 years ago.
GAIA is unique in many ways: a) two telescopes whose light is collected into a very large composite digital camera (> 100 CCDs, about the size of a small coffee table [about 1m x 0.5m]), b) the observing mode, which will only transmit the data around the on-board detected stars (as opposed to the whole picture), c) the fact that it will be spinning all the time, which requires a great performance of its electronic controller and d) the location where it will make the observations: more than 4 times the average distance to the moon in the “night” side of the line which joins the Sun, and the Earth (the line where eclipses occur). This point or area of space is known as 'The second Lagrangian point of the Sun-Earth system' or 'L2'. Despite its fancy name, L2 is 'just' a zone of low gravity (caused by the pull of the Sun and Earth) where it is very easy to maneuver the satellite. In fact, GAIA will move 'around' L2 always avoiding the Earth’s shadow (no sunlight, no energy!)
Once launched, GAIA will collect data continuously and relentlessly, flooding the mission astronomers with data, which will require specialized treatment in order to achieve the final goal of measuring the positions of about 1 billion stars (each object observed an average of 80 times in five years). Handling this amount of information is a real challenge for the reduction software, which will be run in different data centres across Europe.
Knowing the distance to so many stars is a great improvement in our knowledge of the structure of our own galaxy: the Milky Way. In addition, GAIA will detect a large number of variable stars (variable in brightness), and because it observes from space, the accuracy achieved is much higher than from the ground.
GAIA’s mission is a cutting edge mission, involving the effort of scientists and technicians across Europe. The UK has a big role in it and the University of Leicester, with its vast experience in space missions and space instrumentation has been involved for several years already in understanding how the detectors (CCDs) will behave and be affected by a space environment quite different from the one found in low Earth orbit.