Mission-oriented Micro-Sun-Sensor Laboratory Testing in Real-Time Operation Mode

This paper describes the digital sun sensor under development at the University of Naples. The sensor optical head exploits a CMOS photodetector and a mask with multiple holes. This original design allows forming multiple simultaneous images of the sun on the focal plane, which, once processed, produce multiple measurements of the sun line orientation. These are then averaged to improve sensor precision. To achieve high accuracy in sun line determination a calibration function based on neural networks is developed. The sensor can be operated either with a fixed number or with a variable number of sun spots, depending on the required field of view and sun-line measurement precision. This improves sensor flexibility and operation range but, at the same time, increases the computational load when multiple spots are used. Specific techniques are developed to minimize the computational load needed to process multiple acquisitions and to extract the sun line orientation with high accuracy and precision, and adequate updating frequency. These techniques have been tested by extensive test campaigns, carried out by using a laboratory test facility reproducing sun spectrum, apparent size and distance, and variable illumination directions. Specifically, tests reproducing the in-orbit planned experiment profile in terms of a sequence of sun line orientations are performed. Test results validate the sensor concept, confirming the precision improvement achievable with multiple apertures, and the sensor capability of operating with a variable number of sun spots.