Satellite systems - History, definition, functioning principles and application spheres

Table of contents

List of abbreviations

List of figures

List of tables

1 Introduction
1.1 Structure of Project

2 Basics Facts
2.1 Definition and History
2.2 Registration of satellites
2.3 Types of satellites
2.4 Satellite orbits
2.5 The advantages and disadvantages of satellite communication

3 Satellite working principles
3.1 Frequency bands
3.2 Satellite communication parts
3.3 Data distribution
3.4 The footprint of satellite
3.5 Signal Strength Decrement
3.6 Link Budget

4 Application
4.1 Television and Radio
4.2 Telephone Service
4.3 Internet Service
4.4 Very Small Aperture Terminals
4.5 Other applications

5 Conclusion

List of Literature

List of abbreviations

illustration not visible in this excerpt

List of figures

Figure 1: Satellites orbits

Figure 2: Electromagnetic wave

Figure 3: Global coverage by Intelsat

Figure 4: The Eutelsat HotBird position at 13 Degrees East and the footprint

Figure 5: Parbolic antenna

Figure 6: Satellite Antenna Patterns and Coverage Zones

Figure 7: Different polarizations

Figure 8: Eutelsat W1 regional coverage

Figure 9: Satellite and cellular telephones

List of tables

Table 1: Limitations of Frequency Bands Established by the ITU

Table 2: Data Dissemination Design Options

1 Introduction

One of the most important success factors today is quick and perfect communication. Such a communication is quite easy to ensure, when the communicators are near each other, but the difficulties arise as the distance increase. Already many years ago people used various means of communication between longer distances (smoke signals, sounds, different colors flags and etc.).

The age of wire – based communication began after the A. G. Bell first time transmitted his voice in 1875. The following inventions presented the two new ways of communication and networking, which are fiber-optic and satellite communications. Both opened the gates to innovative types and dimensions of services. Nevertheless the commonly known and used satellites’ function to broadcast television programs, many other services can be provided via these transmitters in the space. Nowadays satellites are used for various different reasons, such as weather forecasts, navigation systems, observation of other planets, scientific researches, military purposes, communication and etc.

Satellites and their systems play the significant role in our every day life and are used in places where it was even not imagined that they can be adapted (e. g. press).

Without satellites our life would be considerable different. Thus, the goal of this paper is to present this great invention of XX age, which enabled the society to speed – up the communication even more than before and opened the door to many new discoveries. The main focus is going to be concentrated on communication satellites and their main working principles as they are a part of nowadays used means of advanced communication.

1.1 Structure of Project

Firstly, the basic facts of satellites, including history, definition, types of satellites, their orbits and advantages as well as disadvantages, will be presented. Afterwards, the main functioning principles of communication satellites will be described in order to introduce the most important aspects, how the messages are transmitted. Finally, the application spheres of communication satellites will be listed and described more in detail.

2 Basics Facts

The background information about satellites is presented in this chapter, which is essential in order to understand their benefits for the communication of the world.

2.1 Definition and History

Usually, satellite is defined as a natural space body orbiting around the other natural space body. As for example, moon is the satellite of earth and earth is the satellite of sun. Nowadays the artificial spacecrafts are named satellites as well, because they are launched by a rocket to the space and are kept there by gravitational force revolving around the earth similarly as planets can orbit around the other planets. Satellites are highly specialized wireless receivers/transmitters, which main function is to relay the radio frequency waves and the encoded information in them from one corner of the world to another. Currently there are hundreds operating satellites above the earth.

The science fiction writer Arthur C. Clarke from England could be name the father of satellite communications, because he was the first who proposed to launch a satellite into the Earth orbit where satellite’s speed would match with the rotation of the Earth. That orbit, which is 35786 km height above the planet surface today, is known as geostationary orbit, but sometimes it is called Clarke orbit in honor of his work and ideas [Held91]. 1945 Mr. Clarke was analyzing different orbits and was stressing the possible high-speed global communication networks enabled by above the earth surface revolving satellites. Already at that time, he emphasized that it would be enough to have 3 satellites in order to cover the whole planet. The first world’s satellite Sputnik 1 as big as basketball was launched by Russia (former Soviet Union) in 1957 (October) with the aim to relay the signal of Morse code [Wiki06b].

The first commercial satellite PAS – 1 was launched by American satellite operator PanAmSat in 1984 as the governmental providers were able to offer quite poor services at the high cost.

2.2 Registration of satellites

Not all the countries are capable to launch satellites by themselves though lots of can design and build them, because of higher costs and required knowledge about launching. Recently various conjunctions (EU) and splits (Soviet Union) were made between different countries, which lowered the number of launching capable countries (Soviet Union, USA, EU, Israel and etc.) [Wiki06b].

Similar as all the ships should be registered in central register, satellites has to be recorded as well. The registration process starts in the own country (where launched or produced - I think produced), e. g. in Germany responsible is Bundesamt für Luftfahrt (Braunschweig) (approx. 100 satellites were registered till 1997) and the company forwarded the registration further to UNO in New York, which list the satellites of the entire world. Speaking only about satellites, which broadcast TV and radio signals, there are more than 100 such a communication satellites today placed in the space. Much more complicated taking much more time is the transmission frequency (Funkanmeldung) registration, which is made by in scope of United Nations working agency called International Telecommunications Union the Radiocommunication department (ITU - R), located in Genf, in Switzerland. The main responsibility of this organization is to ensure the possibility to transmit and administer the limited resources of orbits in space as well as the spectrum of radio frequency (RF). Thus, the orbit position, the frequency spectrum from 9 kHz till 1000 GHz (terrestrial and via satellite) and also the wire line connected communication is in charge of ITU organization. It regulates and administrates everything, what can radiate starting from garage door opener and ending with high capacity radar. Registrations are made through signatory states (eg. In Germany: RegTp = Regulierungsbehörde für Telekommunikation und Post) according principle “First come, first Served”. The first step of the registration of transmission equipment (Funkanlage) is the so called Advanced Publication, where the operator should describe for the society the characteristics of his new service, such as desired orbit position, frequency band, the power of transmitter, modulation, bandwidth and etc. This information is printed in the ITU – Weekly Circular. So, the other operators, who think that such parameters will harm their services, have 4 months time to deliver their reclamation. In case there is one or a few operators, who are not satisfied about delivered characteristics of new comer, they can directly discuss or through ITU moderator discuss the problem and find the salvation suitable for both. Quite often such a decision is to reduce the sending power or the position relocation of the new operator. Only afterwards follows the so called Notification step, where ITU considers the characteristics of new comer and ratifies them if find correct. ITU acts as a guardian for the new operator against the other comers [cp.

Dodel99].

2.3 Types of satellites

Nowadays there are hundreds various types of satellites used for different services. They are categorized in the following types:

- Communication satellites

Their purpose of them is to serve as a relay station in the space using radio frequency waves to transmit the signal and information with it.

- Navigation satellites

The radio line signals sent from navigation satellites with the help of regularly developed electronic equipment enables the signals receiver on the earth to identify its position with pretty high accuracy.

- Earth observation satellites

These satellites are constructed with the goal to observe the earth from the space in order to monitor environmentally, make maps, use for meteorology, but usually not for military purposes.

- Astronomical satellites

The galaxies, other planets and other space bodies can be tracked and studied with the help of these satellites.

- Reconnaissance satellites

They are similarly as Earth Observation satellites are also used to watch the earth, but for military and intelligence (e. g. espionage) purposes. Governments do not provide much information about the power of these satellites as it used for various secret purposes.

- Solar power satellites

They use the radio frequency waves to transmit the power of sun to a huge antenna on the earth. The solar power afterwards can be used as a resource instead of traditional power.

- Space stations

The purpose of man shaped space stations is to create an environment for more and longer different scientific researches in comparison with other spacecrafts to measure the effects for human beings of a longer stay in the space.

- Weather satellites

Space vehicles are used to observe the weather and in some case the global climate.

- Miniaturized satellites

These satellites have uncommonly light weight and are very small (e.g. 500 – 10 kg compared with traditional satellites, which can weight about 5000 kg, like PAS 1 – R made by PanAmSat Corp.). The advantage of such spacecrafts is the much lower requirements for equipment in order to launch them into space, which leads to much lower costs. Besides that, they are also used for the missions, which usual satellites are not able to execute, like the low data rate transmission constellations, inspection of traditional space vehicles and etc.

- Biosatellites

In order to conduct the scientific tests and various experiments with the different living forms, the biosatellites were created.

- Killer Satellites

They are also named Anti-Satellite Weapons and are used for destruction of rival satellites or other weapons in orbits [Wiki06b].

2.4 Satellite orbits

In general, orbit is described as a pathway, which one space body makes around the other space body, because they are both influenced by gravity and centripetal force [Wiki06a]. The orbits, where satellites are launched by rockets, differ according their altitude above the surface of Earth and are most often categorized into the following classes (Figure 1):

illustration not visible in this excerpt

Figure 1: Satellites orbits [Walke00]

- Low Earth Orbit (LEO)

LEO finds its place from 200 km to 1200 km height above the earth. The advantage of this orbit is the shorter signal traveling time and lower possibility to loose its path. On the other hand, the coverage zone is quite small (in comparison with GEO) and the connection to satellite from ground station time is shorter, because the satellite moves quicker as the earth is turning. The increased interest in mobile communications via satellites over the last years motivated the augmentation of LEO usage and development of them.

- Medium Earth Orbit (MEO)

MEO is located between 1200 km and 35286 km altitude above earth surface. Some literature sources indicate that the Medium Earth Orbit is located between 5000 km and 13000 km height or between two Van Allen belts [Walke00]. Van Allen belts are two high intensity radiation zones of the earth, where highly charged particles and high energy neutrons take place. For this reason, the two belts are communication satellites damaging [ Fehler! Verweisquelle konnte nicht gefunden werden. ]. Thus, it is avoided to place the satellite in the Van Allen belts zones.

- Highly Elliptical Orbit (HEO)

The name of the HEO arise form its elliptical form, which is helpful in order to achieve a better coverage of higher populated zones or usually not reachable parts of earth (such as poles) without the interruption of lower orbits [Walke00].

- Geostationary Orbit (GEO)

GEO is placed 35786 km above Earth's surface. The orbit is called geostationary orbit, because satellites’, placed in this orbit, speed is matched with earth turning speed so that the satellite moves always together with the earth. In other words to say, if the one would be able to see the satellite from the earth, the satellite would always stay in the same point of the space from the earth perspective. Most of the communication satellites are place in GEO.

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