1. A self-calibrating visual sensor system, mounted on a mobile vehicle, comprising: a visual time-to-contact (TTC) sensor that determines a time before said sensor will contact an object in its path, said TTC sensor generating a plurality of image frames descriptive of a travel area in the direction of movement of the mobile vehicle; an image sensor processor, coupled to said visual TTC sensor, comprising an image memory for storing at least two image frames outputted by the visual TTC sensor; an image processing unit comprising an image grabber, coupled to the image memory and operable for reading the stored image frames from the image memory, and a visual control means for continuous calibration of the visual TTC sensor to point in the direction of focus of expansion (FOE) by adjusting pan and tilt angles of the visual TTC sensor; and a video bus between the image processing unit and the image sensor processor for transfer of image frames.