## 5 Experimental Progress
### Communication Test of User Terminals  
The user terminal is mainly used for high-precision satellite tracking, Ka-band signal transceiver and processing, baseband signal and communication protocol processing, etc. In order to facilitate user access, the vehicle-mounted Satcom on-the-move (STOM) phased array antenna with a 0.45 m equivalent aperture is adopted, as shown in Figure 8.  
After obtaining the satellite ephemeris, terminal location, and signal information, the STOM phased array antenna can precisely lock and track the satellite signal through beam switching. A STOM test (120 km/h) between the 0.45 m terminal and gateway station was conducted based on the LEO test constellation. The single-beam staring mode was adopted for remote sensing data transmission. The results in Table 2 showed that the transmission delay between the satellite communication terminal and the gateway station was about 40 ms (with maximum 47 ms and minimum 38 ms). The results in Table 3 showed that the average communication speed is about 45 Mbps (with maximum 45.4 Mbps and minimum 44.5 Mbps), which can meet the time-sensitive communication requirements of  
Figure 7: Illustration of TT&C stations that have cooperation with GalaxySpace.  
NRRS service, and can support the access of a large number of terminals, considering the broadband feature of the satellite.  
A long-range communication test of 1560 km from Chengdu to Beijing was conducted on 1 May 2022. The telemetry results of the satellite attitude and angular velocity are shown in Figure 9. The overlapped green and blue lines are close to zero. Due to the fact that the satellite mainly performs pitch maneuvers, the other two angles are kept as stable as possible. However, since disturbances exist in the system, there are steady-state errors in the attitude and angular velocity control. The angle evolution of the satellite feeder antenna and the terminal SNR results are illustrated in Figure 10 and Figure 11, respectively. It is shown that the maximum forward SNR is about 14 dB, and the maximum return SNR is about 7 dB, which can meet the demodulation threshold and link margin of the satellite communication. The communication time between the terminal and the satellite is nearly 5 min.  
\begin{table}
\begin{tabular}{c c} \hline
**From** & **Reply** \\ \hline
192.168.91.200 & Byte = 32; Time = 42 ms; TTL = 63 \\
192.168.91.200 & Byte = 32; Time = 39 ms; TTL = 63 \\
192.168.91.200 & Byte = 32; Time = 47 ms; TTL = 63 \\
192.168.91.200 & Byte = 32; Time = 44 ms; TTL = 63 \\
192.168.91.200 & Byte = 32; Time = 40 ms; TTL = 63 \\
192.168.91.200 & Byte = 32; Time = 38 ms; TTL = 63 \\ \hline \end{tabular}
\end{table}
Table 2: Latency results in STOM test.  
Figure 8: STOM phased array antenna produced by GalaxySpace.  
\begin{table}
\begin{tabular}{c c c} \hline
**Time** & **Data Volume** & **Speed** \\ \hline
25.00–26.01 s & 5.38 Mbytes & 45.0 Mbits/s \\
26.01–27.01 s & 5.38 Mbytes & 45.1 Mbits/s \\
27.01–28.01 s & 5.35 Mbytes & 45.0 Mbits/s \\
28.01–29.01 s & 5.30 Mbytes & 44.6 Mbits/s \\
29.01–30.01 s & 5.37 Mbytes & 45.1 Mbits/s \\
31.01–32.01 s & 5.43 Mbytes & 45.4 Mbits/s \\
31.01–32.01 s & 5.38 Mbytes & 44.8 Mbits/s \\
32.01–33.01 s & 5.32 Mbytes & 44.5 Mbits/s \\ \hline \end{tabular}
\end{table}
Table 3: Communication speed results in STOM test.