Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2023, Vol. 20, No. 4, pp. 89-97
Mathematical model of solar orientation sensor based on photodiodes
G.A. Avanesov
1 , B.S. Zhukov
1 , A.V. Nikitin
1 1 Space Research Institute RAS, Moscow, Russia
Accepted: 10.08.2023
DOI: 10.21046/2070-7401-2023-20-4-89-97
Solar orientation sensors based on photodiodes have been widely used in space technology since the mid-seventies of the past century, and have many design implementations. The article describes a mathematical model of a solar sensor based on single photodiodes located on the faces and upper base of three, four and six-sided regular truncated pyramids. The model assumes that the data from each photodiode is digitized and processed by a modern microprocessor device. The model calculates the key parameters of the device based on the given arrangement of photodiodes and their characteristics, as well as taking into account the optical elements that form the sensitivity diagram and the field of view of each of them. These elements include: protective glass in front of each photodiode, its microblend, aperture diaphragm and diffuser glass. Based on these data, the illumination produced by the Sun on the photodiodes is calculated at different viewing angles. The program embedded in the model determines the field of view of the device, calculates the angles of direction to the Sun, evaluates the measurement accuracy and displays the results. The following quantities are calculated in the program: the angles between the direction to the Sun and the sensitivity axes of the photodiodes, the dependence function of the voltage on the photodiodes on the angle between their sensitivity axes and the direction to the Sun. The resulting voltage values, taking into account noise, are used to calculate the direction cosines of the solar vector in the internal coordinate system of the device. The difference between the measured and calculated voltage value is used as an equation for calculating the direction to the Sun. The system of equations obtained for the entire set of photodiodes is solved by the method of successive approximations using the least squares method. The solution of the system is the direction angles to the Sun. The calculation results are compared with the values specified in the program, which makes it possible to determine the magnitude of the measurement error. If there are text files with a record of real measurements, the program can process them and evaluate the results.
Keywords: Sun orientation, photodiode, analog signal, coordinate system, lens hood, aperture diaphragm, signal/noise, digital accumulation
Full textReferences:
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