The tracking simulation for the control system of the Gemini 8-M Telescopes is a nonlinear time-domain model with six degrees of freedom. Structural elements representing the telescope pier, mount, and tube have been obtained with the NASTRAN finite element analysis package and these results used to create a state-space description. The state-space matrices are used in the control package Matlab 4.0 to model the interaction of the telescope structure with linear and nonlinear elements such as bearing friction, encoder quantization, motor torque cogging and various noise sources. Line of sight image motion equations are used to produce an RMS image centroid error which is the metric by which performance is evaluated. The simulation includes the cassegrain rotator and the associated errors caused by spatial separation of the guide object and science object. A fourth-order tip-tilt secondary is modeled to show the effect of tip-tilt upon the image smear induced by other system components. While the rest of the simulation operates in the continuous domain, the tip-tilt controller is modeled in the discrete domain to include the errors and limitations associated with sampling at 200 Hz.