# Laser Inter-Satellite Link Visibility and Topology Optimization for Mega Constellation
## 5 Conclusions  
The term \"inter-satellite link\" refers to a wireless connection between two satellites in a network that acts as a conduit for data exchange between satellite nodes. The spatial location and duration of inter-satellite links of satellites in the mega-constellation are utilized to classify and number various types of LISLs between the constellation's satellites, and a basic model for satellite network topology analysis is created in this paper.  
Whereupon, with the usage of the optimization algorithm, the optimal phasing factors of the OneWeb and Starlink constellations with a large number of deployed satellites are determined to be F = 9 and F = 11, respectively. The comparison group is then set up, followed by the OneWeb constellation with F = 1 and F = 9, the Starlink constellation with F = 1 and F = 11, and the global coverage multiplicity map is obtained to demonstrate the efficacy of the F optimization algorithm proposed in this paper. Between the latitudes of 60\({}^{\circ}\) north and south, the coverage performance of the Starlink constellation is superior to that of the OneWeb constellation.  
Based on the coverage performance comparison results, the Starlink constellation with F = 11 is selected for the visibility and AER analysis of the LISLs, which is used to verify the link-building thresholds for co-orbital and hetero-orbital links, and the number of LISLs in different distance ranges is subsequently derived from the inter-satellite distance. Finally, based on the visibility and the number of links, the laser link connection strategy between co-orbital and hetero-orbital satellites is summarized, with the objective of theoretically constructing the static topology of 1584 satellites in the first phase of Starlink constellation  
Figure 17: Starlink constellation static topology.  
deployment and laying the foundations for the constellation's dynamic routing design and analysis.  
According to the constructed topology, when the Starlink constellation is observed in any area above the Earth, we can find out that half of the constellation's satellites orbit southeast, while the other half orbit northeast. These mission satellites generate a large number of intermittent LISLs in different directions among the intersecting satellites. A satellite can establish up to 94 permanent LISLs and 293 temporary cross-orbital interplane links with other satellites within 24 h under the condition of the maximum LISL distance range of 5016 km. While this connection state cannot remain for long, such links are critical for increasing constellation redundancy and survivability, improving routing options to reduce path delays, and more. Therefore, determining the regularity of the inter-orbital inter-satellite link at various times during the cycle is critical for increasing the flexibility of network communication.  
The following supporting information can be downloaded at: [[https://www.space-track.org/#catalog](https://www.space-track.org/#catalog)]([https://www.space-track.org/#catalog](https://www.space-track.org/#catalog)) (accessed on 15 April 2022).  
Conceptualization, Q.Z., H.T., Y.C. and X.L.; methodology, Q.Z. and Y.C.; software, Q.Z.; validation, H.T.; formal analysis, Q.Z.; investigation, Q.Z.; resources, X.L., Q.Z. and H.T.; writing--original draft preparation, Q.Z.; writing--review and editing, Q.Z., H.T.; visualization, Q.Z.; supervision, Y.C. and Q.Z. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
All data generated or analyzed during this study are included in this article.  
I would like to thank everyone who helped with this paper, especially my supervisor, and my colleagues who made this paper possible.  
The authors declare no conflict of interest.