## 6 Conclusions  
Due to the particularity of its location in the terahertz frequency band, satellite terahertz communication technology has become one of the important technical means to achieve high-speed, large-capacity, and long-distance communication in space. Since the terahertz beam is narrow and the satellite is affected by the perturbation force in different directions in space, in order to achieve high-speed, large-capacity, and long-distance communication, it is necessary to study the pointing performance of the inter-satellite terahertz communication system. In this paper, the perturbation model of satellites in different orbits is established by analyzing the specific perturbation force and the specific direction of the antenna during the orbit of the satellite, and the inter-satellite terahertz communication link with and without pointing error is analyzed. Finally, a satellite terahertz communication system is designed, and the satellite perturbation orbit, pointing error angle, signal power attenuation and system signal-to-noise ratio are simulated and analyzed according to two hypothetical satellites. The simulation results show that the pointing error angle increases periodically with the increase of the satellite's running time. Therefore, it is necessary to  
Figure 14: Variation of signal-to-noise ratio with time at different communication frequencies in inter-satellite terahertz communication system: (**a**) uplink terahertz communication link for LEO-GEO; (**b**) downlink terahertz communication link for GEO-LEO.  
Figure 13: Variation of signal-to-noise ratio with time in inter-satellite terahertz communication system: (**a**) uplink terahertz communication link for LEO-GEO; (**b**) downlink terahertz communication link for GEO-LEO.  
take measures to suppress the influence of the perturbation force on the satellite to reduce the pointing error. By comparing the signal power attenuation without pointing error and the signal power attenuation with pointing error, it is found that the signal power attenuation caused by the pointing error reaches more than 100 dB. However, the current gain of high-gain terahertz antennas is mostly at the level of 60 dB, it is difficult to compensate for the huge loss caused by pointing error. Under the same pointing error, the higher the frequency, the lower the signal-to-noise ratio of the communication system and the worse the communication quality. This is also an important limiting factor for the development of current terahertz communication systems in the low terahertz frequency band. If the attitude control of the satellite is not carried out, signal distortion, communication quality degradation and even communication interruption will occur in a very short period of time.  
Conceptualization, Y.H. and C.M.; methodology, Y.H. and C.M.; software, C.M.; validation, Y.H. and C.M.; formal analysis, Y.H. and C.M.; investigation, Y.H.; resources, Y.H.; data curation, C.M.; writing--original draft preparation, C.M.; writing--review and editing, Y.H.; visualization, C.M.; supervision, Y.H.; project administration, Y.H.; funding acquisition, Y.H. All authors have read and agreed to the published version of the manuscript.  
The national key research and development program sponsored this work under grant number 2019 YFB1803201.  
Not applicable.  
The data presented in this study are available from the corresponding author upon reasonable request.  
The authors declare no conflict of interest.