A contact free optical position sensor for an inertial reference system. An optical sensor is adapted to generate image signals of a gas bearing supported inertial sensor assembly. The surface of the inertial sensor assembly is adapted with a reference surface pattern. A controller is coupled to receive the image signals from the optical sensor and is adapted with an image map of the reference surface pattern stored in a memory means that allows the controller to uniquely correlate an image captured by the optical sensor to an absolute position on the inertial sensor assembly. The controller is further adapted to determine the absolute position and attitude of the inertial sensor assembly based on the correlation between the imaged reference pattern features, the imaged reference pattern's angle of rotation, and the map of the reference pattern.