1. A detector for measuring sub-pixel pointing jitter comprising: a coherent light source; an electro-optical sensor able to move relative to the light source; an optical element between the light source and the sensor; the optical element operative to project a speckle field on the sensor when the optical element is illuminated by the light source; the sensor operative to acquire at least a first data frame representing a first speckle pattern; and, speckle pattern analysis operative to indicate relative motion between the electro-optical sensor and the light source.