The Gaia satellite (ESA) evolves on a Lissajous orbit around the Sun-Earth L2 Lagrangian Point. To fully achieve the scientific objectives of the mission, and to completely eliminate effects such as aberration, the daily position and velocity vectors of the spacecraft have to be known to an accuracy respectively greater than 20 mas and 2.5mm/s. As these accuracies can not be reached by traditional techniques of spacecraft tracking (in particular in the normal plane to the line of sight) a Ground Based Optical Tracking (GBOT) of the satellite has been adopted. In this framework, we carried out a theoretical study with the aim of proving the feasibility of the GBOT project and optimizing the observational strategy by characterizing the astrometric precision limit for moving targets observed with digital-array detectors (Bouquillon et al, A&A 2017). This research led to useful results for planning astrometric observation of all kinds of moving bodies as meteors, satellites, space debris or asteroids.