As is the way with books in general this document is presented in the form of chapters (seven in number) devoted to individual topics relating to the overall topic of Gaia astrometric data processing. We progress logically from the satellite to the equations for the astrometry to the implementation of a software system to process Gaia observations. After this we look at a few key astrophysical issues for Gaia and explain tests which have been carried out, using the implementation, concerning these effects. A few appendices provide additional information. Here an overview paragraph is provided for each of the chapters: This introductory chapter Section 1 provides an overview of the work as well as an overview of the satellite hardware for the reader unfamiliar with Gaia. In Section 2 the equations underpinning the astrometric solution are explained and developed toward the algorithms actually coded in the system. Section 3 provides details of the Java software framework which hosts the equations previously described. The framework itself has been tuned to effectively process Gaia observations and is the main original content of the thesis. This system is known as the Astrometric Global Iterative Solution or AGIS. Having looked at the implementation, a few of the astrophysical effects and design decisions which influence the solution are described in Section 4. Although no data has yet been received from Gaia, extensive simulations have been performed in the Gaia community. Some of the AGIS tests relating to the astrophysical phenomena described in Section 4 are reported in Section 5. In this manner a demonstration of the effectiveness of AGIS is presented. A discussion and overview of the development approach adopted for A GIS is presented in Section 6. The eXtreme programming approach is particularly suited to science development and worked well for this project in the form presented. Brief conclusions are drawn in Section 7. Appendix A provides a primer on Quaternions which are used for attitude modelling. A complete list of the mind boggling acronyms used in this document appears in Appendix B. Finally some published papers are included in Appendix C.

Esta tesis presenta el marco numérico y computacional para la solución astrométrica Gaia. También cubre las consideraciones astrofísicas relativas a la solución y los aspectos relacionados con la gestión de la implementación de un sistema tan complejo.