CCD-based guiding sensor resolution enhancement

The paper presents the achievements in research and development of the compact optical CCD based guiding system. The ultimate goal of the project is a modest size, low mass and rugged systems to be applied for sub-arc second optical ground-space guiding and tracking. The system includes the optics, the CCD sensor with the readout and an image- processing algorithm. The optics consist of a diffraction limited objective, four-element lens system with eh effective input aperture 90 millimeters. The objective focal length 300 mm is extended by the additional relay optics. The resulting effective focal length is 3000 millimeters, the focal spot size is 65 micrometers Airy disc diameter. The combination of the diffraction limited objective design, focal extender and mechanical construction permitted to keep the overall length bellow 600 millimeters and the total mass bellow 5 kilograms while maintaining high ruggedness at one arc-second level. A sensor, the Texas Instrument CCD chip 192 X 164 pixels, 15 micrometers size is used. the custom designed readout and data processing hardware has been developed. Parallel communication maintains image download time 0.6 second with 12 bits amplitude resolution. The data acquisition and image processing software package running under MS Windows 95 or NT provide all functions for the camera control, data acquisition and image processing for precise target position evaluation. The position is evaluated as the center of mass of square neighborhood of the brightest CCD pixel. Indoor test of the ultimate position resolution using different diffraction limited images and sizes are described. The image position resolution +/- 0.03 pixel has been achieved. It corresponds to 0.03 arc seconds of angular resolution of the entire guiding sensor.