## 4 Ground Segment  
Satellite communication has the potential to gain a big share of communication market, as it enables services that are not achievable via cable, such as mobility or connection from remote or rural sites. As the demand for these services grows, the demand for broadbandsatellite communications is also growing, and this is one of the reasons why many new high-capacity satellites and constellations are now in the making.  
Considerable focus in Satcom technology is given to what happens in space, but what happens on earth is as important. Every satellite, no matter how advanced, is still only a part of a larger system and a satellite or constellation, and to be correctly exploited, it needs an adequate network of gateway ground stations and user terminals. In particular, the user terminal is key in the success of the satcom network, as it will impact the penetration into the market and will make the network successful and sustainable from an economic point of view.  
Many of these newer satellite systems we are seeing in development are NGSO constellations, made of smaller satellites but comprising hundreds or thousands of them, adding significant complexity to the communications system. While a GEO orbit is synchronized with the Earth rotation, and therefore the satellite appears static in the sky for an Earth-bounded observer, NGSO satellites arranged in constellations are constantly moving in the sky, adding tracking, Doppler shift and handover complexity to both the space and the ground segment. Moreover, NGSO constellations need to rely on extremely big networks of ground stations, as every satellite in the sky needs to be in view of a gateway ground station. Intersatellite links (either optical or RF) can ease the pressure on the ground network by removing the need for a satellite to be constantly connected to a ground station, but it is also adding complexity to the routing of the data and adding constraints and costs to the design of the satellite.  
This added complexity in NGSO satellites systems however comes with some advantages with respect to a GEO satellite, advantages that impact the design of the satellite itself but also, massively, the usability and effectiveness of user terminals. These main advantages are:  
1. The lower altitude in the sky means that the required performance to establish the link is lower, as the free space loss is drastically reduced. This means smaller satellites, less power and smaller antennas both on the ground and in orbit. A smaller antenna for a User Terminal represents a major advantage.
2. The lower altitude also reduces latency, thus making satcom networks comparable with ground networks (especially for LEO systems).
3. The fact that the satellites are constantly moving in the sky means that the look angle from Earth to the satellite is constantly changing, and most of the time, it is in an advantageous position, approximately overhead of a user. In a geosynchronous system, moving toward northern latitudes in the northern hemisphere (and the same southern for the southern hemisphere) means that the look angle reaches lower elevation values, making the link budget harder and harder to close.
4. Moving satellites in the sky means that the impact of blockage from buildings, mountains, terrains, etc., is massively reduced as the look angle constantly changes, naturally avoiding obstacles.  
Taking advantage of these assets of low orbit systems is key in the success of the constellation model and is where the satellite industry must invest to transform NGSO communication in a sustainable reality alongside the more mature and proven GEO Systems.