Abstract
The operation and test of a multi-spot digital sun sensor for precise sun-line determination is described. The image forming system consists of an opaque mask with multiple pinhole apertures producing multiple, simultaneous, spot-like images of the sun on the focal plane. The sun-line precision can be improved by averaging multiple simultaneous measures. Nevertheless, the sensor operation on a wide field of view requires acquiring and processing images in which the number of sun spots and the related intensity level are largely variable. To this end, a reliable and robust image acquisition procedure based on a variable shutter time has been considered as well as a calibration function exploiting also the knowledge of the sun-spot array size. Main focus of the present paper is the experimental validation of the wide field of view operation of the sensor by using a sensor prototype and a laboratory test facility. Results demonstrate that it is possible to keep high measurement precision also for large off-boresight angles.
Highlights
Sun sensors are typically used to provide coarse-to-medium accuracy measurements of the sun line in the satellite-fixed axes
Once the average centroid coordinates on the FP have been determined, they are transformed into the sun-line α and β angles, respectively the horizontal and vertical off-boresight angles of the sun line in the sensor Field Of View (FOV), by means of a neural Calibration Function (CF) [12,16]
To get a quantitative estimate of the improvement achieved with the enhanced procedure, a comparison with the basic procedure has been performed in terms of the Signal-to-Noise Ratio (SNR)
Summary
Sun sensors are typically used to provide coarse-to-medium accuracy measurements of the sun line in the satellite-fixed axes. The mask has tiny slits or pinhole apertures to produce sun images on the focal plane from which the sun-line direction can be extracted These sensors offer medium-to-high measurement accuracy, depending on the optical head design and the algorithms used to process the sun images [4,5,6,7,8]. The degraded quality of the sun images acquired at large off-boresight angles may cause the image acquisition and processing procedure to fail in the identification of the correct number of sun spots on the focal plane The sensor wide-FOV operation is validated by using the available hardware model of the sensor and a dedicated test facility, in which in-orbit illumination conditions and variable sun-line orientation can be reproduced
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