Fast low thrust trajectories for the exploration of the outer solar system

Low thrust missions to destinations in the outer solar system are quite common since several years. In the majority of cases they are based on solar electric ion propulsion. Owing to the low available power, they are mostly long duration missions, in which the travel time is of the order of many years, sometimes decades, even if extensive use of gravity assist maneuvers is made.. The aim of the present paper is that of investigating which are the technological requirements to decrease drastically the travel time for low thrust missions to the outer solar system, in view not only of robotic exploration but also of future human exploration of the satellites of the giant planets. In the latter case low thrust spacecraft may be used at least as cargo ship to prepare the human presence in such distant places.