Satellite Communication Active and Passive Satellite

Satellite communication can be depicted as the technique of transferring information from one place to another via a communication satellite in orbit around the Earth.

Our watching of television programs or any sports, or news with our friends and families would have been impossible without Satellite Communication.

A communication satellite that transfers the signal is an artificial satellite. It can be done through a transponder by generating a passage between the transmitter and the receiver pointed at dissimilar locations on the Earth. 

Electronic gadgets like telephone, radio, internet, television, and military services use satellite communications. About 2000 artificial satellites are there, revolving in space above our heads.

Need for Satellite Communication

As we recognize, there are many other ways to get connected, and the broadcast of these waves can go on in various methods. 

There are two methods, such as sky-wave propagation and ground wave propagation, where communication takes place for a given distance. The extreme distance covered by them is about 1500 km, and this was achieved by introducing satellite communication.

The figure given below is the block diagram of satellite communication.

History of Satellite Communication

The invention of the concept of artificial satellite communication has been credited to Arthur C. Clarke. He wrote an article describing the concepts behind artificial satellites for the first time in 1945. 

After this, on October 4, 1957, Sputnik 1, was launched on Earth’s orbit. This was the first artificial satellite ever launched. Mikhail Tikhonravov and Sergey Korolev developed this satellite together. The equipment of Sputnik 1 included an onboard radio transmitter. This radio transmitter worked on two frequencies and wavelengths as follows- 20.005 MHz and 40.002 MHz and 7 and 15 meters wavelength. The satellite’s purpose was not to send data from one point of the earth to another. The radio transmitter on this satellite was meant to examine and study the distribution of radio waves throughout the ionosphere. Another interesting fact about Sputnik 1 is that the launch of this satellite marked the beginning of the Space Age as it was a very important step towards scientific development.

Structure

The following subsystems altogether form a communication satellite. The parts are all listed below:

• The first part is the communication payload. This part consists of antennas, switching systems, and transponders. 

• Then comes the engine, which is the heart of the satellites. These engines are used to bring satellites to certain orbits.

• A station is another important part of the satellite. It keeps track of the satellite and keeps the satellite stable and on the right orbit. 

• The Power subsystem is the next essential subsystem of a satellite. As the name suggests, this subsystem powers the satellite enabling it to function. This subsystem is composed of solar cells and batteries.

• Next is the communications system which is known as the command and control subsystem. This subsystem is for maintaining communications with the control stations situated on the ground. This system monitors the various activities and phases of the satellites.

Active and Passive Satellite Communication

The requirement for satellite communication is obvious because we need to transmit the signal too far and wide places, where the curvature of the Earth interferes.

This obstacle is hurdled by setting communication satellites to dispatch the signals beyond the curvature in space. Satellite communication employs two types of artificial satellites to transmit the signals: active satellites and passive satellites.

Satellite Communication Active and Passive Satellite

1. Passive Satellites

If you put a hydrogen balloon up in the air, which has a metallic layer upon its surface, technically, it will become a passive satellite. This kind of balloon can reflect microwaves signals from different places.

In space, the passive satellites are alike. These satellites' objective is to reflect the signal to the Earth, deprived of amplification. As the satellites' orbit altitude can vary from 2000 to 35786 km, the reduction as a result of the atmosphere also interferes so that the received signal is a lot weaker.

2. Active Satellites

Unlike the passive satellites, active satellites intensify the transmitted signals before re-transmitting, it returns to Earth. The signal strength is excellent inactive satellites. 

Passive satellites were the most primitive communication satellite, but today, the majority of them are active satellites.

Every single consumer is allotted a specific frequency for transmitting the signal to skip the problems and interference of signals. The International Telecommunication Union allocates this frequency for each user. 

Geosynchronous satellites are some particular satellites. Geostationary orbit is available at the altitude of 35786 km above Earth's superficial. 

If you can point to such type of satellite with the help of a telescope from Earth, it will seem stationary to you. The rotational rate of the Earth and the orbital period of the satellite is occurring simultaneously.

Have a Look at This Gif About Geostationary Orbits

These were some of the distinctive orbits. Separately from these, we also have some orbits that report specific difficulties. The Russians tackled one such dispute. GEO satellites operated perfectly for the equatorial regions, but they had a very fragile coverage near the Poles. 

To solve this issue, the Russians invented an orbit with a very high inclination. The angle between the satellite's orbit and the equator is known as the inclination. This orbit was named the Molniya orbit.

The orbit possessed the outstanding coverage of the North pole for a little time. Molniya orbit had a period of 24 hours, but also, it would be nearer to Earth only about 6-9 hours. 

Russia propagated some more satellites in that particular orbit and a little while they had unremitting coverage.

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Applications of Satellite Communication Services

The application areas of satellite communication services are as follows:

• Tele-Medicine.

• Tele-Education. 

• Mobile Satellite Services. 

• Radio Networking. 

• Village Resource Centre. 

• Satellite Aided Search and Rescue. 

• Satellite Navigation Programme. 

• Satellite News Gathering and Dissemination.

Satellite Communication Services

There are two groups where satellite communication services can be categorized:

I. One-Way Satellite Communication

In regular satellite communication, the communication ordinarily occurs between either one or multiple earth stations via satellite support.

The communication obtains between the transmitters on the primary earth satellite to the receiver, which is the subsequent earth satellite. The transmission of the signal is one-way directed. Some common one-way satellite communications are:

• Tracking is a portion of space operations services

• Internet services obtain via broadcasting satellites

• Position location services are aided by the radio

The figure given below explains the one-way satellite communication

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ii. Two - Way Satellite Communication

Now the two-way satellite communication works via exchanging of the information between either two earth stations. It can be concluded that there is point-to-point connectivity.

The signal from the first earth station is transferred to the second earth station, just like there are two uplinks and two downlinks occurring between the earth stations and the satellite.

The figure given below has shown the two-way satellite communication:

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Advantages and Disadvantages of Satellite Communication

The Benefits of Satellite Communication Are

a. Arrangements of circuits are easy.

b. The elasticity of these circuits is outstanding.

c. The operator entirely operates the network.

d. Via satellite communication, every angle of the Earth can be covered.

The Drawbacks of Satellite Communication Are

a. Preliminary expenses are costly.

b. Probabilities of the obstacle of the frequencies.

c. Difficulties in the propagation and interference of the frequencies