Abstract
This paper describes the high precision digital sun sensor under development at the University of Naples. The sensor determines the sun line orientation in the sensor frame from the measurement of the sun position on the focal plane. It exploits CMOS technology and an original optical head design with multiple apertures. This allows simultaneous multiple acquisitions of the sun as spots on the focal plane. The sensor can be operated either with a fixed or a variable number of sun spots, depending on the required field of view and sun-line measurement precision. Multiple acquisitions are averaged by using techniques which minimize the computational load to extract the sun line orientation with high precision. Accuracy and computational efficiency are also improved thanks to an original design of the calibration function relying on neural networks. Extensive test campaigns are carried out using a laboratory test facility reproducing sun spectrum, apparent size and distance, and variable illumination directions. Test results validate the sensor concept, confirming the precision improvement achievable with multiple apertures, and sensor operation with a variable number of sun spots. Specifically, the sensor provides accuracy and precision in the order of 1 arcmin and 1 arcsec, respectively.
Highlights
Recent achievements and future trends in microengineering have identified micro/nanotechnologies as enabling technologies for future space programs
The paper is organized as follows: the sensor concept and operating principle are described in Section 2, the sensor hardware and software prototypes are presented in Section 3, the test facility is described in details in Section 4, and, Section 5 reports test campaigns and results
The sensor relies on CMOS technology and on an innovative design of the optical head which allows increasing precision in the determination of the sun illumination direction by exploiting a mask with up to 100 apertures
Summary
Recent achievements and future trends in microengineering have identified micro/nanotechnologies as enabling technologies for future space programs. High precision is achieved by exploiting an original design of the optical head in which an array of tiny apertures is created on the mask This particular design provides multiple simultaneous images of the sun disk on the focal plane, and, than multiple measurements of the sun line orientation, which can be averaged to filter out random noise components. The multi-aperture configuration improves precision with respect to classical configurations based on one single aperture [4,5,6,7], but, restricts the measurable range of sun line orientations of an amount depending on the number of exploited sun spots as in [3] To overcome this limitation, a major innovation is introduced, which consists in operating the sensor in an extended mode, i.e. by processing a variable number of spots, at the cost of reducing precision for increasing off-boresight angles. The paper is organized as follows: the sensor concept and operating principle are described in Section 2, the sensor hardware and software prototypes are presented in Section 3, the test facility is described in details in Section 4, and, Section 5 reports test campaigns and results
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