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Autonomous star trackers are optical-electronic devices used for attitude determination of artificial satellites, having as a reference for this computation the positions of stars. There is one autonomous star tracker in development at the Aerospace Electronics Division of the Brazilian National Institute for Space Research. The autonomous star tracker imager is a complementary metal-oxide-semiconductor active pixel sensor, consisting of an integrated circuit with an array of them. Each pixel has a photodetector and an active amplifier. Since it has many amplifiers, the active pixel sensor has an additional fixed pattern noise, therefore its characterization is different from the traditional method used for the charge coupled devices. With this experiment, it was observed that the mean value per columns of fixed pattern noise is ~100% greater than the mean value of the pixel one. Taking into account this result, modeling the pixel fixed pattern noise will not be important to improve the autonomous star tracker sensibility. Furthermore, the random noise value was less than 1% of the fixed pattern noise range data, being possible to estimate it. In this work, we presented the fixed pattern noise new parametric model, which has a good agreement when compared with the experimental data. It was calculated Pearson's product-moment correlation coefficient between the model and the observed data, in order to quantify the model accuracy and it was obtained 99% for flat field and 79% for dark current.

Determining the Fixed Pattern Noise of a CMOS Sensor: Improving the Autonomous Star Trackers Sensibility