Options for a mission to Pluto and beyond

In this paper several options for a potential mission to the limits of the solar system are presented. Starting from a direct launch to Jupiter used to boost the spacecraft toward Pluto the paper analyses several other possibilities using both chemical and nuclear electric propulsion, multiple gravity assist maneuvers and aero-gravity assist maneuvers. Some scenarios include a combined mission to a closer system or a return mission. The wide range of possibilities has been obtained using two different global approaches to span the solution domain for a possible transfer to Pluto and beyond. The most promising solutions have been refined and fully optimized using a direct method. INTRODUCTION Currently most of our knowledge about Pluto and its moon Charon comes from indirect clues. No spacecraft has ever visited either of them, and from the Earth (or its proximity) its angular size is close about resolving limit of the most capable ground and space-based observatories. However, there is unanimity on the scientific interest of the Pluto-Charon system and that of the Kuiper Belt Objects, to which they probably belong or are closely related to. The latter is a family of bodies outside of Neptune's orbit that have been identified to be a source of short-period comets. Currently many KBO have been observed, and some of them have extremely interesting features variability (e.g. Chiron), strong absorption of blue light (maybe indicating that they are completely covered by complex organic molecules), diversity, etc. A mission to the Pluto-Charon system and to a Kuiper Belt Object (KBO) will significantly increase our knowledge of the formation and evolution of the Solar System as well as the origin of volatiles and organic molecules that enabled the appearance of life on our own planet. The mission therefore has a strong exobiological interest, which could be increased exponentially by adding new elements like a Europa or Titan microprobe deployment on route to the final destination, taking advantage of the opportunities provided by the gravity assist at the giant planets. In this paper some possible mission scenarii for a mission to Pluto and the Kuiper belt are proposed: these include the utilization of advanced propulsion systems (nuclear electric propulsion) and power technologies and the possibility to deploy a probe while a gravity assist maneuver in the vicinity of Jupiter is performed. If the Jupiter option is selected the possibility of a swing-by of one of the moons is investigated. In particular a swing-by of Ganymede can be performed to brake the probe while the main spacecraft continues on its way to Pluto. In addition the possibility of advanced missions using chemical propulsion ad gravity or aero-gravity assist maneuvers have been studied. Analyses available in the literature propose to carry out a very quick flyby of Pluto and Charon with a large relative velocity, thus enabling a limited science return. Another option is therefore to study the possibility to alter the mission analysis concept in such a way that the flyby velocity can be reduced. The design of the NEP trajectories has been performed with a direct transcription method by finite elements in time. However the problem presents quite e number of possible solutions dependent on launch window, transfer time and combination of planetary encounters, therefore in order to find favorable launch windows and the optimal sequence of swing-bys a global optimization strategy has been used to procure sets of promising initial guesses. Then, these initial guesses have been optimized using direct transcription and Paper AAS 03-210