Previous trajectory proposals with the purpose of exploring the Kuiper Belt have been limited to identifying trajectories to fly by a single pre-selected Kuiper Belt Object (KBO). Furthermore, these proposals were often limited to high-velocity flybys that pass through the Kuiper Belt in a limited number of years, or are based on the assumption of significant and uncertain technological advances. This thesis investigates the existence of currently feasible trajectories which position a spacecraft inside the Kuiper Belt for a significantly longer period of time. The feasibility of these trajectories is based on the assumption of current technological capabilities and a launch date between the years 2025 and 2040. To model these unique trajectories the conventional MGA-1DSM trajectory model is adapted in order to optimize trajectory problems that aim to reach the Kuiper Belt. The use of powered flybys is excluded in these problems in order to reduce problem and mission complexity. Optimization of the trajectory problems was done by performing an interactive multi-objective optimization approach with four distinct objectives on a set of twenty planetary sequences. The high complexity of these problems in combination with conflicting multiple objectives was found to necessitate an iterative optimization process using the pooled results of several algorithms in order to obtain satisfactory results. The optimization algorithm performance was further enhanced using various encouragement methods. By using the established optimization method multiple routes were identified that all culminate in a long-duration flight through the Kuiper Belt. The best results were found with planetary flyby sequences VVEJS, EVEEJN, and JN. The required launch energy (C3) for these trajectories ranges from 16 km² /s² , for sequences utilizing multiple inner planet flybys, to 75.5 km²/s² , for solutions utilizing adirect Jupiter-Neptune route. The maximum onboard delta V capability required for these solutions is 400 m/s. The flight time to the inner boundary of the Kuiper Belt ranges from 14.6 to 24 years. All thesetrajectories feature a flight time through the Kuiper Belt of well over or close to 100 years. In addition, it was found that trajectories that conclude their planetary flyby sequence with a Jupiter-Neptune leg are found to be especially well suited for long-duration Kuiper Belt flight.