Final Activity Report Summary - ELSA (European Leadership in Space Astrometry) The ELSA network has recruited 10 ESRs and 5 ERs to work on scientific preparations related to the European Space Agency (ESA) satellite Gaia, which is planned to be launched in 2012. Gaia will survey about one million stars and a few hundred thousand asteroids by measuring their positions, motions, distances, and spectra. Investigations undertaken by ELSA fellows concern both methods to derive the astronomical information (by processing the raw data transmitted from the satellite to the ground) and the subsequent astrophysical interpretation of the results. Many of the results obtained in the network have an important and direct impact on the development of data processing methods for Gaia, including improved algorithms to solve extremely large systems of equations and detailed physical modelling of the damage caused by cosmic radiation on the optical detectors in Gaia. Other results will help to maximise the scientific return from the Gaia data, for example though improved modelling of stellar properties and the distribution of stars in our galaxy.
