This paper discusses the transportation architecture for the round-trip exploration to Mars taking advantage of the combination of the "Deep Space Port" and "low-thrust propulsion." One of the merits of utilizing the Deep Space Port is the reusability of the interplanetary portion of the architecture. The main objective in this study is to verify the connectivity of the escape trajectory from Sun-Earth liberation point with the interplanetary trajectory. The paper divides the scenario into two segments; near Earth phase and interplanetary phase. Both ballistic trajectories and low-thrust trajectories are assessed. The low-thrust optimization is performed by DCNLP (Direct Collocation with Nonlinear Programming) which approximates the continuous problem with parameter optimization problem and provides precise results by simple formulation. This paper shows the connectivity of the escape trajectory from Sun-Earth liberation point with the interplanetary trajectory, and shows the usefulness for the round-trip exploration to Mars using Deep Space Port in combination with low thrust propulsion.