**2. The apparition of communications satellites**

Satellites have always been bounded to broadband telecommunications thanks to their large visibility of the Earth. This capability is inherited from their natural

*From Monolithic Satellites to the Internet of Satellites Paradigm: When Space, Air… DOI: http://dx.doi.org/10.5772/intechopen.97200*

movement. Satellites are celestial bodies which constantly move tracing an elliptical trajectory around another larger celestial body. The broadband telecommunications satellites orbit around the Earth. This distinctive motion is defined by means of the Keplerian orbital parameters or elements. These six parameters determine the shape and size of the ellipse, the orientation of the orbital plane with respect to the Earth, the orientation of the ellipse in this plane, and the location of the satellite along this trajectory.

Satellite orbits are gravitationally curved trajectories which can be represented in a two-dimensional trajectory located in a plane. This plane is known as orbital plane, and two Keplerian elements determine its orientation with respect to the Earth: (1) the longitude of the ascending node (Ω) corresponds to the horizontal angle between the plane and the origin of the longitudes (the Greenwich meridian or prime meridian); (2) the inclination angle (*i*) determines the vertical orientation of the plane with respect to the origin of the latitudes (the equator). The orbit shape traced in this plane is determined by (3) the semi-major axis (*a*) that corresponds to half the distance between the periapsis and apoapsis of the orbit, and (4) the eccentricity (*e*) which describes how much the ellipse is elongated compared to a circle. The resulting ellipse can be rotated in the same plane determined by (5) the angle known as argument of periapsis (*ω*). A satellite travels this elliptical curve over time, moving periodically among numerous locations. The position of a satellite in this ellipse is represented by the (6) the true anomaly (*ν*) which corresponds to the angle of the satellite location at a specific epoch or time with respect to the direction of the periapsis.

The ensemble of Keplerian elements allow the characterization of the satellite position, and its complete trajectory. **Figure 1** represents these parameters to clarify their meaning.

Numerous orbits exist depending on the values of the Keplerian elements, which laid the foundation of different classifications. Among them, the classification based on satellite altitude prevails, which determines implicitly the orbit semi-major axis. In this classification, satellite orbit are structured in three main blocks: (1) Low Earth Orbits (LEO) are identified by altitude values between 200 km and 2000 km; (2) Medium Earth Orbits (MEO) correspond to those orbits with an altitude encompassed between 2000 km and 35,786 km; Finally, (3) Geosynchronous Equatorial Obrits (GEO), also known as geostationary orbits, are determined by a specific altitude of 35,786 km. Is in this last type of orbit, indeed, in which

#### **Figure 1.**

*Representation of the Keplerian elements that represents the orbit trajectory of a satellite (gray sphere), and its plane (yellow surface) with respect to the equatorial plane (gray surface).*

telecommunications operators identified potential characteristics to deploy satellites that broadcast multiple services.

Satellites that orbit following GEO trajectories are characterized to be deployed in an orbit plane located at the equator of the Earth, and following a circular orbit (i.e. inclination 0° and eccentricity 0). This combination of inclination, eccentricity and altitude allows a satellite to constantly move at the same velocity than the Earth rotation. Therefore, a GEO satellite constantly observes the same region of the Earth, and remains them as fixed points in the sky. These characteristics are ideal to provide broadband services for specific geo-political regions, such as television delivery, military applications, or generic telecommunications.

Since the launch of the Syncom 3 satellite at 1964 [1], geostationary largesatellites became the standard configuration to provide these services. This was the first GEO satellite deployed to provide television coverage of the Summer Olympics. Its launches promoted the apparition of other GEO satellites, such as the Intelsat I (nickname Early Bird) satellite at 1965. In paritcular, this satellite was developed by the company Intelsat to demonstrate that communications through this kind of orbit were feasible. It was used during four years and four months to provide multiple services among different missions, standing out the first live television coverage and its participation in the Apollo 11 mission.

This satellite was the first one to provide direct communications contact between Europe and North America, handling telephone, television, and telefacsimile transmissions. This satellite paved the way to develop such kind of backhaul systems to communicate around the glove, and it was the first of a large family of Intelsat satellite that reaches current epoch with Intelsat 39 launched in 2019.

Over the different missions, the developments on these satellites have been focused on the optimization and adjustment of the Internet mechanisms, techniques, and protocols to enhance the throughput over satellites. With the advent of the different versions of the Digital Video Broadcast - Satellite (DVB-S) protocols [2], the television broadcast over satellites was also investigated as part of the digitalization of this service. The outcome of all these efforts was the development of the high throughput satellites, so-called next-generation satellites [3].

These GEO satellites has coped the broadband telecommunications activity during the last years with the mission development from companies like Hughes Space and Communications, Space Systems/Loral (SSL), Orbital Science Corporation, Lockheed Martin, Thales Alenia Space, and Airbus-Astrium. They are currently part of our space environment, and keep providing telecommunication service to interconnect fixed regions in the globe. This interconnection is also characterized by having a considerable delay transmission, around 900 ms (approximatelly). Although its static relative position becomes ideal for coverage region, this large delay values may not be suitable for services deployed in the Internet. Therefore, new approaches emerged to compensate this long delay with lower-altitude regions, and to integrate Internet services in these satellite systems.
