Multiple Near Earth Asteroids rendezvous trajectories optimization with electric propulsion

In the recent past, space agencies moved towards the exploration of our local neighborhood, studying the asteroids. They are indeed very useful to understand the history and formation of our solar system. But, unfortunately, today few missions have been planned: the most important were the Hayabusa 1 and 2 by JAXA, and OSIRIS-REx by NASA. The growth of Near Earth Asteroids (NEA) discoveries, have increased the awareness and the probability of futures Earth impacts, causing the end of life on our planet. In recent years, numerous asteroids have been classified as potential hazards, and more informations are needed on their physical properties and their orbital parameters to better predict their future orbits. Inaf NEST mission aims to analyze three NEA, with Apophis the main target, with a spacecraft equipped with electric propulsion. This technology make possible to have more flexibility in departure dates and a considerably reduction in fuel consumption. The following thesis aims to determine the possible asteroids to be reached and the optimal trajectories that reduce the fuel consumption, by using the Optimal Control Theory, respecting the NEST mission constraints: departure in 2028; duration less than five years; rendezvous with three Near Earth Asteroids,(one must be Apophis). In particular, various departure dates from the Earth have been selected over the year 2028 and different departure and arrive dates from the asteroids have been selected, with multiple asteroids sequences. The best sequence was further analyzed, finding the best trajectories in terms of Delta V and duration.