# Real-Time State Evaluation System of Antenna Structures in Radio Telescopes Based on a Digital Twin
## 2 DTs Framework of the Radio Telescope  
The current DT technology lacks a common reference model. The DT five-dimensional model system proposed by the Beihang University team has been proven to have good practicability and universality through experimental exploration, and its model structure is shown in Equation (1):  
\[M_{DT}=(L_{PE},L_{VE},L_{CN},L_{DD},L_{SS}) \tag{1}\]  
where \(L_{PE}\) represents the physical entity layer, \(L_{VE}\) represents the twin model layer, \(L_{CN}\) represents the information transmission layer, \(L_{DD}\) represents the twin data layer, and \(L_{SS}\) represents the application service layer [18].  
Therefore, to realize the monitoring and evaluation of the real-time state of the radio telescope, this paper constructs the DTs of the radio telescope based on the above model framework system and the actual working state of the antenna. The system's framework is shown in Figure 2.  
1. Physical entity layer The physical entity layer is the foundation of the DTs, which mainly includes the radio telescope entity, sensor, and control system. The entity is mainly composed of the primary reflector, the subreflector, the backup structure, the panel, the elevation gear,the center body, the alidade, and so on. The sensor includes an acceleration sensor, wind speed and direction sensor, temperature and humidity sensor, etc. The control system includes servo motors and control algorithms that drive the elevation and azimuth motion of the antenna.
2. Twin model layer The twin model layer is the mapping of physical entities in the virtual space, which mainly includes the geometric model, kinematics model, and mechanism model of the radio telescope. The geometric model is obtained by modeling the real size of the entity in equal proportion, and the lightweight twin model is constructed by mesh simplification technology and mesh reconstruction algorithm. The kinematics model reflects the position, attitude, trajectory, and other motion state information of the radio telescope during operation, as well as the internal constraints of the system. The mechanism model contains the mechanical behavior and state information of the radio telescope in the coupled physical field.
3. Twin data layer The data layer is the key to ensuring the stable operation of the entire DT, including physical data and virtual data. Physical data comprise to the static attribute data and dynamic pose data of the radio telescope, sensor monitoring data, environmental data, etc. Virtual data comprise finite element simulation data, surrogate model prediction data, etc.
4. Information interaction layer The information interaction layer aims to realize efficient and accurate data interaction between physical entities and twin models. It mainly includes a communication module and database management module, which can realize the functions of data collection, processing, analysis, and storage in the system.
5. Application service layer The application service layer is the integration of various functions of the DTs. Based on the Unity3D visualization engine, this layer can realize core functions such as monitoring, evaluation, and human-computer interaction of the motion state and structural state in the DTs of the radio telescope.  
Figure 2: DT framework of radio telescope.  
Based on the above description, the construction of a real-time monitoring and evaluation system for radio telescopes mainly applies three key technologies: surrogate model technology, twin model lightweight technology, and virtual-real mapping. The surrogate model technology realizes the rapid and accurate prediction of the structural state by constructing a high-fidelity mathematical model based on finite element data. The lightweight twin model is the basis for realizing the rapid interaction between virtuality and reality. The virtual-real mapping realizes the interaction between real physical entities and twins through intelligent algorithms, data communication, data storage, etc.