Onboard Ultra-Stable Oscillator Long-Term Drift Calibration for Tianwen-1 Mission
Objectives:The stability of ultra-stable oscillator(USO)which provides frequency standard and transmits downlink signal affects the accuracy of one-way Doppler measurements directly.It is a necessity to estimate the frequency bias during orbit determination with one-way Doppler measurements.Methods:First,the one-way Doppler observation model and observation partial derivative are deduced theoretically,and the main error sources affecting the accuracy are analyzed.Then,the frequency deviation is estimated and the USO long-term drift prediction model is constructed during the execution of Tianwen-1 precise orbit determination using the one-way Doppler measurements.Finally,the accuracy of frequency bias resolution is analyzed theoretically based on its key factors.Results:The USO drift rate is 0.075 75±0.006 20 Hz/d.Conclusions:This paper provides a feasible frequency drift calibration method for space-borne USO,and it constructs a priori frequency model for space-borne USO of Tianwen-1.
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