# A Survey on Satellite Communication System Security
## 3 Background
### Satellite Constellation Characteristics  
In SCSs, the constellation is one of the most crucial elements. The orbit of a satellite greatly influences the area it can cover, which is also linked to the number of satellites. For example, as the satellite's orbit lowers, the propagation delay and error rate decrease, but  
Figure 3: Satellite architecture. the area a single satellite can cover on the ground is significantly reduced. A solution to this is deploying satellites that can fully cover the globe. However, this increases construction and maintenance costs considerably. Thus, a satellite's orbit has a significant impact on various aspects of the SCS network. In this section, we will explore the different orbits used in SCSs. Also, Table 2 summarizes the satellite constellation features [27]. **Geostationary Earth Orbit:** This orbit matches the Earth's rotational speed with the satellite's angular velocity. This means the satellite always faces the same region of the Earth's surface, which is an advantage utilized by various satellites. Geostationary orbits operate at a latitude of 0 degrees, directly above the equator, and are typically positioned at an altitude of approximately 36,000 km. Additionally, the typical communication latency is between 125 ms and 250 ms, resulting in a delay of nearly 0.5 s for communication between ground stations and satellites. The advantages of geostationary orbit (GEO) include, firstly, the satellite appears stationary from a specific point on Earth, which is advantageous for providing communication and broadcasting services. Secondly, a single GEO satellite can cover about one-third of the Earth's surface, allowing services to be provided over a wide area. Thirdly, because it is relatively stationary, the communication delay is consistent. Lastly, once Earth terminals or ground stations adjust their antennas, they can maintain a continuous connection with the satellite. However, there are disadvantages as well. Firstly, GEO satellites must be placed in high orbits, which increases launch costs and the technical complexity. Secondly, the longer travel time for communication signals to and from the satellite can result in a relatively high communication latency and potential data loss. Thirdly, GEO satellites are bigger and more expensive to deploy; the network operator can gradually add to their coverage as their business grows. Lastly, due to their fixed position relative to the Earth's surface and the Earth's tilt, GEO satellites struggle to cover polar regions [28]. **Medium Earth Orbit:** This orbit is located between 9000 and 11,000 km and is situated within the Van Allen radiation belt. MEO is at a lower altitude compared to geostationary orbit. Primarily, this orbit is used for navigation satellite systems like GPSs [27]. The advantages of medium Earth orbit (MEO) include, firstly, shorter communication delay times compared to GEO satellites, as MEO satellites operate in a lower orbit. This also allows MEO satellites to cover a wider area than LEO satellites, while requiring fewer satellites, thereby reducing system costs and complexity. However, there are disadvantages. Firstly, the communication delay is higher compared to LEO satellites, which can pose challenges for real-time communications. Secondly, satellites are visible for only 2 to 8 h from Earth, necessitating satellite tracking, due to their rotation. Lastly, signals become weaker when reaching the Earth compared to LEO, requiring more transmit power. **Low Earth Orbit:** This orbit refers to a range approximately 180 to 2000 km above the Earth's surface. In this orbit, there are various types of satellites, and due to the characteristics of LEO, it is primarily used in high-speed SCSs.