## 3 Influence of Physical Properties of NS on Communication, Navigation, and TT&C Integration  
### Theoretical Loss of Signal Propagation in NS  
NS vehicles have time-varying free-space propagation loss, the estimation of free-space loss can be calculated according to the Friis Equation, and the calculation equation converted into the dB form is as follows [65],  
\[L_{p}=32.45+20\text{lg}d(\text{km})+20\text{lg}f(\text{MHz})\quad(\text{dB}) \tag{2}\]  
where the unit of \(d\) is km, and the unit of \(f\) is MHz.  
For the NS, the loss of the K/Ka band signals (18 GHz-40 GHz) is shown in Figure 1. When the elevation angle is 90\({}^{\circ}\), as the frequency increases, the loss also increases, the range of the path loss is roughly between 143 dB and 165 dB.  
Since the distance between the NS vehicle and the receiving end changes in real time, the magnitude of the transmission loss also changes accordingly. The linear distance between the NS vehicle and the ground is approximately 20-100 km. Assuming that the communication elevation angle is between 0 and 90\({}^{\circ}\), without considering the influence of the Earth's curved surface, the calculation of the inclined path of the signal propagation is as follows [66],  
\[D=\left\{\begin{array}{ll}\frac{H_{\text{ns}}-H_{0}}{\sin\theta}&(\theta\geq 5 ^{\circ})\\ \frac{2(H_{\text{ns}}-H_{0})}{\sqrt{\sin^{2}\theta+\frac{2(H_{\text{ns}}-H_{0} )}{\text{Re}}+\sin\theta}}&(\theta<5^{\circ})\end{array}\right.\qquad(\text{ km}) \tag{3}\]  
where \(H_{\text{ns}}\) is the height (km) of the NS vehicle in the NS; \(H_{0}\) is the height of the ground station above mean sea level (km); \(\theta\) is the elevation angle (\({}^{\circ}\)); Re = 8500 (km), which is the effective radius of the Earth.  
According to Equation (2), the propagation distance range between the NS vehicle and the receiving end can be obtained, which is approximately 20 km to 1303.841 km. Figure 2 shows the simulation results of the attenuation estimation values at different elevation angles when the NS vehicle is located at the bottom and top layers of the NS, respectively.  
\begin{table}
\begin{tabular}{c c c} \hline
**Comparison Items** & **K/Ka Frequency Band** & **L/S/C Frequency Bands** \\ \hline Power efficiency & There is a large path loss, and a high-power amplifier is required. & The path loss is small, and the power efficiency is high. \\  & & Suitable for high-throughput \\  & & scentors, & Suitable for long-distance \\  & & short-distance/space-to-ground links & communication, scenarios with high \\  & & (rain attenuation needs to be & penetrability requirements, and \\ Typical application & Advantages & compensated), and miniaturized terminals. & low-cost wide-coverage scenarios. \\  & & Cases: Starlink user terminals, & Cases: Satellite television \\  & & Airborne radars, and urban 5G hotspots. & broadcasting, GPS navigation, \\  & & 1. Communication in rainy areas; & 1. Scenarios with high-capacity \\ Disadvantages & & 2. Long-distance transmission & requirements; \\  & & 2. Scenarios with high spectrum \\  & & & reuse. \\ \hline \end{tabular}
\end{table}
Table 2: Cont.  
According to Figure 2a, from the simulation results, it can be found that at the elevation angle of \(\theta=90^{\circ}\), for the path at the bottom layer, the loss ranges from 143.5 dB to 150.5 dB; for the path at the top layer, the loss ranges from 157.5 dB to 164.4 dB. In addition, according to the simulation results of Figure 2b,c, as the elevation angle decreases, the path loss becomes greater. When the elevation angle is \(\theta=0^{\circ}\), the maximum attenuations of the bottom layer and the top layer are close to 180 dB and 187 dB, respectively, and the attenuation difference between the two is almost 7 dB.