Gaia is an ambitious mission of the European Space Agency (ESA). Its main objective is to obtain a three-dimensional map of the Milky Way. Gaia will reveal the composition of the Galaxy and the way in which it was formed and has evolved. In order to do this, Gaia needs to measure with unprecedented accuracy the position, proper motions and radial velocities of a huge number of sources. These accuracies are needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population. In order to achieve these impressive accuracies, the most challenging technical developments have to be implemented, and controlling the orbit of Gaia is, perhaps, one of the most important issues. Gaia will orbit around the Lagrangian point L2 of the Sun-Earth system following a Lissajous orbit. This orbit allows a quite stable environment for the payload in terms of mechanical and thermal stability. Additionally a continuous scanning law has been adopted for Gaia as the optimal observation mode. The present master thesis is devoted to the study the scanning law of Gaia to characterize which will be the effects that a source of disturbances will cause. First of all we will reproduce the nominal scanning law for Gaia and, thereafter, a noise source modeled using a standard power spectral density law will be added. The effects of these disturbances will be studied in detail for the orbiting, precessional and scanning movements of Gaia. Finally we will evaluate the impact on the final astrometric performances and in the targeting process.