This paper examines feasibility of a space robot system which captures a free-flying target. First, to examine it experimentally, we develop a berthing dynamics simulator (BDS) on which the space robot and the target behave as if they were on orbit. BDS measures force and torque operating on the real hardware, and it calculates the motion of the robot and the target using the detected force, then it drives the servo mechanisms so that they conform to the calculated posture. Next, to examine the feasibility by use of only numerical simulation, we propose a mathematical model. The validity of the model is verified in comparison with the experiments performed on BDS. Finally, it is confirmed that the space robot can automatically capture the free-flying target without yielding excessive force and oscillation by the experiments and the numerical simulation.