Optical data are important data sources for operating state estimation of space targets. Inversion of the rotation rate of tumbling targets via light curves can help us perform on-orbit services. However, previous methods cannot estimate the precession and spin rates of tumbling targets from light curves simultaneously. To solve the problem, an efficient precession and spin rate estimation algorithm for tumbling targets is proposed in this paper. The method combines the variational mode decomposition (VMD) method and mutual information (MI). Specifically, VMD is utilized to decompose each light curve into discrete frequency intrinsic mode functions (IMFs). Then, the MI between each IMF and light curve is generated, and the IMF frequencies corresponding to the two maximum MI values are extracted as spin and precession frequencies. Finally, the two frequencies are converted into spin and precession rates. Experimental results show that the estimation accuracy of the precession and spin rates is no less than 97% for a small nutation angle (no greater than 20º). The method provides a simple way to invert a space target state and mine more information from light curves.
The traditional PLL (Phase-locked loop) is used to track the GPS signal carrier. However, an unavoidable contradiction between the bandwidth of PLL and the measurement accuracy occurs when PLL works in a high dynamic situation. Consequently some solutions have been studied since 1980s, which can be divided into two categories, namely with or without the aid of external data. The latter is always easy to realize and much cheaper. This thesis presents a review of the pure carrier tracking algorithms with no external aided data. And then examines various problems associated with these algorithms. Finally a corresponding comparison is made and a conclusion of these algorithms is given.
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