• orbit determination
• conjunction events
• collision avoidance
• celestial mechanics
• space debris

Since the last decades, solutions devoted to space debris issues have been investigated. Indeed, several investigations came up with the same conclusion done by the 'Kessler syndrome': the increase of this population could lead to an unstoppable cascade effect of collisions of objets in the near-Earth environment.
The research in this thesis focuses on the orbit determination problem and the identification of conjunctions of these objects.
A new algorithm is introduced and consists in determining preliminary orbits for objects in Low Earth Orbit based on correlation of radar observations.
Using the evolution of the trajectories, a procedure is developed to select the pairs that have potential close encounters.