PROCYON (PRoximate Object Close flY by with Optical Navigation) is world's first mission aimed to demonstrate the technology of a micro spacecraft deep space exploration and proximity flyby to asteroids. The mission is developed by the University of Tokyo in collaboration with ISAS, JAXA. The spacecraft is scheduled to be launched as a secondary payload in late 2014 with Hayabusa 2 spacecraft. PROCYON will first target back to the Earth using its miniature ion engine; then it will transfer to the target asteroid using Earth gravity assist; finally it will use optical navigation to perform proximity flyby of the asteroid. Due to the very low thrust and limited propellant of the mission, it is therefore important to ensure that the mission objective and requirements can still be satisfied under different conditions and parameters. In this paper, we present the results of a broad sensitivity study of PROCYONs trajectory due to various launch dates and mission parameters.