In this paper, the dynamic behavior of a satellite with an unactuated movable solar panel is examined as governed by two different controllers. This two-body system is dynamically underactuated because it has two outputs of concern, which are the angles of the satellite and the panel, but it has only one actuator, which is the reaction wheel attached to the main body of the satellite. Nevertheless, this system is still stabilizable owing to the spring supported joint of the panel. To describe and discuss the panel-satellite interactions plainly and clearly, a planar dynamic model is preferred. Thus, it has been possible to get an idea quickly about the effects of the stiffness of the panel joint spring and the type of the implemented controller on the attitude control of the satellite. However, a similar study can as well be extended without much difficulty to the general case of a multi-panel satellite with three-dimensional attitude control requirements. In this work, two different controllers are studied by assigning three different values to the stiffness of the spring between the panel and the satellite. With the support of the simulation results, this work has led to the conclusion that, if the spring is stiff enough, it is possible to implement the simple controller that requires feedback only from the satellite motion. On the other hand, if the spring is not very stiff, then it becomes advisable to implement the complicated controller that requires feedback not only from the satellite attitude but also from the relative panel motion, which further requires either extra sensors to use or an observer to implement. In this work, the complicated controller is implemented together with an observer.