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.