# Digital Twin Technology-Based Networking Solution in Low Earth Orbit Satellite Constellations
## 3 Phased Digital Twin System Design  
The satellite internet constellation system (LEO constellation) is a complex, large system composed of large-scale low-orbit satellites. Unlike high-orbit and terrestrial networks, it possesses the unique attributes of a low orbit, such as a highly dynamic satellite inter-satellite topology, the fast movement of satellite nodes, and the limited capacity of on-board payload platforms. The LEO constellation aims to meet the requirements of large-scale operation-level networking applications. As a result, its networking protocol is highly complex and specialized. The launch and deployment of the LEO constellation will be carried out gradually in stages. Taking into consideration the protocol design requirements and deployment implementation plan, the design of the digital twin architecture for the LEO constellation network's networking protocol needs to be divided into three stages: pre-construction, construction, and post-construction. Phase 1: Digital twin system before construction  
This stage belongs to the \"simulating reality and reflecting reality through simulation\" phase. To validate the effectiveness of the low-orbit constellation network's networking protocol, it is necessary to establish a simulated verification environment that closely resembles the real constellations and ground elements. This environment will enable functional implementation, design feasibility assessment, testing, and verification. This stage does not involve the physical system, and there is no actual data interaction between the digital twin system and the physical system, which is the internal closed-loop simulation verification of the pure digital twin system. Phase 2: Digital twin system under construction  
This stage belongs to the phase of the \"interconnection of the virtual and real, and the control of reality with virtuality\". On the basis of the first stage, the maturity level is further increased. Given the gradual verification requirements in constructing and deploying a satellite internet system, the strategy involves launching only a subset of satellites in the constellation, rather than deploying the entire network at once. It is necessary to build a digital twin system that can be interconnected with the physical system and directly deploy the routing protocols of satellites, information customs stations, and terminals that are actually used in the physical system to the digital twin system to build the corresponding twin nodes. At the same time, through the real-time two-way closed-loop interaction of virtual and real traffic, a semi-physical digital twin system based on the combination of on-orbit satellites and ground simulation is realized, which fulfills the requirements for functional performance verification, analysis, and evaluation throughout the construction phase. It also supports the continuous, iterative enhancement of networking technologies as the constellation progressively expands. Phase 3: Companion digital twin system after completion  
This stage belongs to the phase of \"using the virtual to accompany the real, and the virtual to accompany the real\". Twin rehearsal, optimization decision-making [15], and future deduction are accomplished through real-time, two-way, closed-loop state and data interaction between the digital twin system and the physical system. This interaction enables the near-real-time dynamic reflection of the current network status of the physical constellation system. The digital twin system involves three aspects: (1) completing the synchronous visual presentation; (2) predicting the network states that may occur in the future operation of the physical constellation system through the intelligent analysis of the obtained data, intelligently selecting the optimal network solution for the future, and finally implementing the intelligent management and control of the actual physical networking system; (3) carrying out the simulation and optimization of the new networking technology or protocol based on the current network state data.