To enable real-time autonomous navigation, a mobile robot is equipped with on-board processing power, image-processing algorithms, and a fuzzy computation engine that allow the rover to safely navigate to a designated goal while avoiding obstacles and impassible terrains. The underlying architecture discussed in this paper utilizes real-time measurement of terrain characteristics and a fuzzy logic framework for onboard analysis of terrain traversability. The overall navigation strategy, consisting of terrain-traverse and goal-seeking behaviors, requires no a priori information about the environment, and uses the on-board traversability analysis to enable the rover to select easy-to-traverse paths to the goal autonomously. The rover navigation system is tested and validated with a set of physical rover experiments. These experiments demonstrate the real-time capability of the navigation system.