Research On The Key Technologies Of Inter-satellite Precise Ranging For Satellite Gravity Measurement

The Earth’s gravity field can be recovered by measuring slight changes in distance between two LEO satellites in the same orbital plane. In order to recover the Earth’s gravity field precisely, the inter-satellite ranging precision needs to reach microns. Dual one-way ranging(DOWR) is an effective method of precise ranging. A fundamental requirement of DOWR is sampling time synchronization between the two satellites. However, each satellite is driven by its own clock, so the two’s sampling time cannot be synchronized strictly. As a result, ranging error is introduced. Aiming at reducing the ranging error caused by the two non-synchronous satellite time, this thesis studied four key technical problems of inter-satellite precise ranging as below:1. Ranging error model. Many error sources affect the inter-satellite ranging precision and some of them are coupled. To reduce the ranging error effectively, it is necessary to quantitatively describe the relationship between the ranging error and the error sources, which means modeling the ranging error. Therefore, the first problem studied in the thesis is how to model the ranging error correctly.2. Satellite time unification. Due to the essential demand of time-space continuum for the Earth’s gravity recovery, the two satellite time must be synchronized accurately at anytime and anywhere, by unifying the satellite time to a reference time system. However, it’s hard to unify the satellite time precisely by GPS without the support of GPS P(Y)-code. What’s more, the Chinese Bei Dou regional navigation system can only provide time service for the Asia-Pacific region at present. Consequently, how to realize accurate satellite time unification autonomously is the second problem studied in the thesis.3. Satellite time-tag offset correction. The Earth’s gravity filed recovery requires ranging values at given epoches in the reference time system and at corresponding latitude and longitude coordinates. Because there are time-tag offsets between satellite time and reference time, the measurement results are accumulated by the satellites at the epoches. It is necessary to correct the satellite time-tag offsets in the measurement results effectively to obtain precise ranging. Accordingly, how to correct the satellite time-tag offset effectively is another focus of the thesis.4. Ranging signal optimization. The ranging error has direct relationship with the parameters of ranging signal. In the parameters of the ranging signal, frequency is selectable in a certain range. Especially for dual-frequency ranging signal,ranging error can be reduced by designing the parameters optimally. Therefore, it is necessary to study the optimization of ranging signal and its realization. And it is the fourth problem studied in the thesis. ntTo solve the key technical problems above, the thesis established a non-relativistic ranging error model with unified satellite time, proposed a satellite time unification method based on TWTT(Two-Way Time Transfer) and Beidou Time local-trace and global-transfer, presented a multi-step satellite time-tag offset correction method using interpolation, and put forward a combinational optimization method for DOWR signal frequency. All these solutions were confirmed to be effective with theoretical analysis and simulation. And the feasibility of these techniques was proved by experiments.