This paper presents a discrete-time stable tracking control scheme for an underactuated vehicle modeled as a rigid body. This energy-based control scheme guarantees discrete-time stability of the feedback system. The underactuated vehicle is characterized by four control inputs for the six degrees of freedom of rigid body motion. These control inputs actuate the three degrees of freedom (DOF) of rotational motion and one degree of freedom of translational motion in a vehicle body-fixed coordinate frame. The actuated translational DOF corresponds to a body-fixed thrust direction. The stability analysis of translational and rotational motion of the vehicle are addressed separately, and it is shown that the total energy-like quantity of the system is decreasing in discrete time. This leads to discrete-time control laws that achieve asymptotically stable tracking of desired position and attitude trajectories.