Gigapixel array to map Milky Way

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The largest focal plane array ever sent into space is under construction by the European Space Agency (ESA) as part of its galaxy mapping mission, Gaia. A mosaic of 106 large area, high performance e2v CCD91-72 imaging sensors will make up the focal plane array.

Due to launch in 2012, Gaia's goal is to map the positions, parallaxes and proper motions (movement across the sky) of around 1 billion objects in our galaxy, the Milky Way. For the brightest objects, radial velocities (movement towards and away from the satellite) will be measured and photometric data taken to determine the composition of the objects. The result of this will be the most detailed map of the Milky Way ever produced which will improve our understanding of our galaxy.

The focal plane array is at the heart of these astrometric, spectroscopic and photometric instruments onboard Gaia. The CCDs will be operated synchronously in TDI mode, effectively working as a near Gigapixel array.

There are three variants of the CCD91-72, each optimised for different wavelengths in the range 250 to 1,000nm. e2v's specialist technology has been implemented into each CCD, with functionalities like charge injection, anti-blooming and TDI gate structures to meet the specific needs of the mission. The CCD package is three sided buttable, to minimise the dead space between CCDs when they are tiled together in the mosaic. All CCDs have also been through e2v's, back thinning process.

Having completed the design and extensive evaluation of these CCDs, e2v is now close to completing manufacture and test. More than 150 devices have now been delivered during the flight phase of the project, comprising of flight models, flight spares and engineering models. These are currently being integrated by the satellite prime contractor, EADS Astrium, to form the array ahead of the proposed 2012 launch.

Giuseppe Sarri, project manager of Gaia at ESA, said: 'Gaia continues a European tradition for pioneering astrometry, building on the expertise generated by the first space-based astrometry mission, Hipparcos. Gaia will outdo its predecessor in terms of accuracy, limit magnitude and number of objects. It will pinpoint the position of stars with accuracy in the order of 10-300 microarcseconds (10 microarcseconds is the size of ten-cent coin on the Moon, when viewed from Earth). All this is thanks to companies like e2v, who are able to push technology to the extreme.'

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