Two years' worth of data from the European Space Agency's (ESA) Gaia spacecraft – which includes a camera with a billion pixels – is scheduled for public release on 14 September.
Gaia will give the most detailed map of the universe ever undertaken. The spacecraft, which has a camera comprised of a mosaic of 106 CCDs, is designed to pinpoint the positions, distances, motions and other properties of more than a billion stars.
It has three instruments collecting astrometric, photometric and spectroscopic data on stars in the Milky Way galaxy, as well as more distant galaxies and quasars, and nearby, but faint Solar System objects.
Located at the L2 Lagrange point, 1.5 million kilometres from Earth, Gaia surveys the entire sky as it spins on its axis. By repeatedly measuring the positions of the stars, Gaia is providing data that enables scientists to calculate their distances and motions through our Galaxy.
‘More than 50 billion focal plane transits, 110 billion photometric observations and 9.4 billion spectroscopic observations have been successfully processed to date,’ noted Fred Jansen, ESA's mission manager for Gaia.
The CCDs were manufactured by British company, e2v. David Morris, chief engineer for space imaging applications at e2v, told Imaging and Machine Vision Europe in an article just prior to the launch of Gaia that the scale of the focal plane array made it quite challenging to produce the detectors for the project.
Since its launch, Gaia has had to contend with water freezing on the optics, causing a reduction in the sensitivity of the telescopes, as well as stray light infiltrating the focal plane.
Stray light entered the focal plane from sunlight scattered by fibres around the edge of the insulating blanket that covers Gaia's 10 metre diameter sunshield. ‘This results in higher background noise in the data,’ explained Timo Prusti, ESA's project scientist for Gaia. ‘This is irrelevant for observations of brighter stars, but more significant for fainter stars. We can still easily detect stars of magnitude 20, but the stray light means that we can pinpoint locations of faint stars to an accuracy of 500 microarcseconds instead of the planned 300 microarcseconds.
'However, it is important to stress that, despite this noise, Gaia is still the most accurate star mapper ever built,' he added.
The past two years have been a steep learning curve for all of the Gaia team, especially the Data Processing and Analysis Consortium (DPAC), which has had to cater for the unexpected anomalies by developing additional software beyond that foreseen for the processing required for the first data release.
However, the team is happy with the condition of their spacecraft and confident that they can overcome the lingering observational problems to create the most accurate, detailed sky map ever made.
‘Although the mission has experienced a number of technical challenges, all of these have either been mitigated by additional software and analysis, or the mitigating mechanism is known and tested but full implementation is pending,’ said Jansen. ‘Overall, through the extensive efforts of ESA, DPAC, and prime contractor Airbus Defence and Space, these effects have had a limited impact on our ability to achieve the mission's original science objectives.’
‘We are confident that we shall still be able to analyse more than one billion stars, measuring each star's position and motion up to 100 times more accurately than Gaia's predecessor Hipparcos,’ added Prusti.
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