This paper deals with the force control of a space manipulator for a sample-return mission. There are two difficulties in force control of this class of space manipulator: One is that a space robot has no fixed point in space and moves when its manipulator exerts force on the environment. The other is that physical properties of the environment on which the manipulator exerts force are not well known. In order to overcome these difficulties, a hierarchical controller is proposed in this paper. The controller manages attitude control of the main body and force control of the manipulator. The end effector is attached to the manipulator by a passive compliance mechanism. The performance of the proposed controller is verified by numerical simulations and hardware experiments.