Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the consideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of centroid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid location and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows' centroid estimation are less than 2×10 −3 pixels and 2×10 −4 pixels respectively. star tracker, star image location, subpixel centroid estimation, centroid algorithm, frequency domain analysis, systematic error compensation
Citation:Jia H, Yang J K, Li X J, et al. Systematic error analysis and compensation for high accuracy star centroid estimation of star tracker.
A peroxy lithium titanate sol was prepared with low-cost and easily available titanyl sulfate as the titanium source, lithium acetate as the lithium source, and aquae hydrogenii dioxidi as the complexing agent using an inorganic precipitation-peptization method. The sol system was aged, centrifugal-washed, dried and calcined to obtain a pure precursor, Li 2 TiO 3 , followed by pickling with hydrochloric acid to obtain the H 2 TiO 3 -lithium adsorbent. The effects of aging time and calcination temperature on the target product were investigated. The results indicate that the sol-system is stable, which is beneficial for loading on a suitable carrier, such as ceramic foams. Centrifugal-washing, instead of vacuum filtration-washing, is conducive to product formation. The most suitable aging time of precursor sol is 24 h and the appropriate calcination temperature is 750 C. The lithium drawn-out ratio of samples synthesized in this condition reaches 89.50% after pickling with 0.2 M hydrochloric acid for 8 h at 70 C. Moreover, the Li + uptake of the adsorbent (adsorption capacity) reaches 29.96 mg g À1 and 33.35 mg g À1 when the adsorption time is 1 h and 8 h, respectively.
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