# SINDVis: User-Centered Dynamic Interactive Visualization System for Space Information Networks
## 2 Related Work
### SIN Concept and Architecture  
Researchers have presented various interpretations for SIN [2; 3; 4; 5; 6]. Combined with the main research plan of the National Nature and Science Fund of China, \"Space information networks based theory and key technology\", we define the concept of SIN as follows. **Definition 1**. : _SIN is an integrated information network system and network infrastructure that is carried by space platforms. It is composed of a satellite system (such as geostationary earth orbit (GEO) satellites, nonsynchronous medium earth orbit (MEO) satellites, nonsynchronous low earth orbit (LEO) satellites, mainly responsible for processing the load), other information systems HABs (Hot Air Balloons) or UAVs (L unmanned Aerial Vehicles) in near-space, or terminals (ground station, mainly responsible for control). It can support real-time data acquisition, transmission, and processing of mass data, and achieve systematic information service application through integrated network interconnecting. It provides integrated investigation, navigation,communications, and other services, and realizes battlefield situational awareness, such as communication broadcasting; investigation and surveillance; intelligence detection; navigation and positioning; missile warning; and weather, hydrology, and terrain._  
By analyzing the structure of its backbone network and other supporting facilities, we determined the specific components of SIN. According to its function and **Definition 1**, SIN should be mainly composed of four layers: the GEO layer satellite system, the MEO/LEO layer satellite system, the Near Space layer information system, and the Ground layer terminals. Each section will be discussed in detail in the following text. **Definition 2**. : _(GEO Layer Satellite System). GEO is a special geosynchronous orbit with zero inclination with an orbital height of 35786 km and the same orbital period as the Earth's rotation cycle. The satellite covering area of the orbit is large and static relative to the ground, so it is playing increasingly important roles in the civil and military fields, such as communication, navigation, warning, and meteorology. Therefore, in the SIN, we can rely on at least three GEO satellites to achieve the construction of the GEO layer satellite system, and the system can achieve 360\({}^{\circ}\) full-cycle coverage. The composition structure of the GEO layer satellite system is shown in Figure 1._  
**Definition 3**. : _(MEO/LEO Layer Satellite System). The MEO satellite orbital is 5000-20,000 km and the LEO satellite orbital is generally between 700 km and 1500 km. The satellites serving the MEO/LEO layer exist in the network form, and in the SIN, the MEO/LEO double-layer constellation network mode is adopted. Among them, the MEO satellites are mainly used as routing exchange stars and access stars. The LEO satellites are mainly used as access stars, and they can access the application stars and ground stations. The composition structure of the MEO/LEO layer satellite system is shown in Figure 2._  
**Definition 4**. : _(Near Space Layer Information System). The backbone networks of SIN are composed of satellite systems. However, the satellite systems cannot achieve all-weather, large-depth, and full-coverage. Therefore, it is necessary to rely on the Near Space layer aircrafts, including UAVs and HABs, to achieve the construction of the  
Figure 1: Composition structure of the geostationary earth orbit (GEO) layer satellite system. Figure 2: Composition structure of the nonsynchronous medium earth orbit/nonsynchronous low earth orbit (MEO/LEO) layer satellite system. Near Space layer information system. The Near Space layer is convenient for its condition, so the construction of Near Space layer information system is more flexible and more formal. The composition structure of the Near Space layer information system is shown in Figure 3.  
**Definition 5**. : _(Ground Layer Terminals).