Abstract
In order to improve the on-orbit measurement accuracy of star sensors, the effects of image-plane rotary error, image-plane tilt error and distortions of optical systems resulting from the on-orbit thermal environment were studied in this paper. Since these issues will affect the precision of star image point positions, in this paper, a novel measurement error model based on the traditional error model is explored. Due to the orthonormal characteristics of image-plane rotary-tilt errors and the strong nonlinearity among these error parameters, it is difficult to calibrate all the parameters simultaneously. To solve this difficulty, for the new error model, a modified two-step calibration method based on the Extended Kalman Filter (EKF) and Least Square Methods (LSM) is presented. The former one is used to calibrate the main point drift, focal length error and distortions of optical systems while the latter estimates the image-plane rotary-tilt errors. With this calibration method, the precision of star image point position influenced by the above errors is greatly improved from 15.42% to 1.389%. Finally, the simulation results demonstrate that the presented measurement error model for star sensors has higher precision. Moreover, the proposed two-step method can effectively calibrate model error parameters, and the calibration precision of on-orbit star sensors is also improved obviously.
Highlights
The improvement of the attitude accuracy of satellites has stressed the demand for high-precision attitude instruments [1]
The error factors of the main point drift, the focal length error, the image plane rotary-tilt errors and the distortions have been analyzed in this paper
A novel on-orbit measurement model of star sensors which considers the image-plane rotary-tilt errors and the distortions has been explored based on the incomplete traditional measurement model
Summary
The improvement of the attitude accuracy of satellites has stressed the demand for high-precision attitude instruments [1]. Sun [13] developed the Euler-axis-angle-based error model with six-degree-of-freedom image plane displacement errors, which considers the principal point drift, the focal length error and the tilt-rotary errors. Establishing a comprehensive error model including the principal point drift , the focal length error, the distortions as well as the image plane tilt and rotary errors, is important for high-precision star sensors [17,18]. Based on the above discussions, in this paper, a novel star sensor on-orbit calibration error model is suggested, which considers the principal point drift, the focal length error, the image plane tilt and rotary errors, and the lens distortions within a unified framework. The EKF is used to calibrate the main point drift, the focal length error and the distortions of the optical systems, while the LSM is used for estimating the plane rotary-tilt errors. A simulation study is performed to verify the effectiveness of the proposed on-orbit calibration method
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