# Analysis and Demonstration of First Cross-Support Interferometry Tracking in China Mars Mission
## 3 Results  
Six successful cross-support interferometry tracking sessions have been conducted by CLTC and ESOC in Tianwen-1 mission, especially before and after TCM and Mars orbit insertion during Earth-to-Mars transfer flying. A schedule of each session is suggested and validated by both agencies, and several principles are considered while making the schedule.  
1. Tianwen-1 is switched to one-way mode during the observation. In addition, DOR tone is frequency coherent with the downlink carrier, and frequency coherence ratios are 1/440 and 1/2200, respectively.
2. Sequence of spacecraft-quasar-spacecraft-quasar is adopted, where a cycle time of 10 min per scan.
3. For the spacecraft scan, the Doppler frequency computed with prediction orbit is added to the standard frequency from Tianwen-1, and then channels are allocated to record tones while the tones exist in the channel center. In total, four channels are recorded, including the carrier, +1 DOR, +2 DOR and \(-\)2 DOR. Figure 6 shows the signal distribution and channel setting in DeltaDOR measurements.
4. For the quasar scan, the same down-converting frequency of the channel is set, with a different sample rate.
5. The TTCP recording system is used at ESOC tracking stations, data are recorded with a nominal 4 MHz bandwidth for the quasar scan and 50 KHz bandwidth for the spacecraft scan, and the quantization is 2 bits and 8 bits for each case, respectively. The same bandwidth and quantization parameters are adopted in CLTC stations.  
A typical observation schedule is listed in the following table.  
Figure 7 shows the distribution of tracking stations in the cross-support DeltaDOR measurements, the average baseline is longer than 8000 km.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Key Steps** & **Complex Plus** & **Complex Multiply** \\ \hline \multirow{3}{*}{Traditional Method} & Fringe Rotation & 0 & F \(\times\) N \\  & FFT & F \(\times\) N \(\times\) log2N & F \(\times\) N \(\times\) log2(N/2) \\ \cline{1-1}  & Sub Bit Compensation & 0 & F \(\times\) N \\ \cline{1-1}  & Integration Time Spectrum & N \(\times\) M & 0 \\ \hline \multirow{3}{*}{This Paper} & Spectrum Compensation & 0 & N \\ \cline{1-1}  & FFT & N \(\times\) log2N & N \(\times\) log2(N/2) \\ \cline{1-1}  & Integration Time Spectrum & N \(\times\) M & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Computation burden of the two methods in each iteration.  
Figure 6: Channel configuration of DeltDOR measurement in cross support: the red frame means spacecraft scan and the black frame corresponds to quasar scan.  
CLTC develops a data converter, which complements the conversion parameters in order to satisfy generic and CCSDS standardized interfaces and provide consistency between that data acquired at the two agencies [40]. Besides raw data, other data such as tracking data message (TDM), meteo data, and orbit ephemeris message (OEM) are also exchanged among agencies.  
For a typical session in Table 2, the data quantity at one station is substantial up to 50 GByte (mainly from the quasar observations), and data are exchanged through the Internet.