What is Satellite Communication?
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
FAQs on Satellite Communication Active and Passive Satellite
1. What are the two primary types of satellites used for communication?
The two main types of satellites used for communication purposes are active satellites and passive satellites. They are categorised based on whether they process and amplify the signal they receive before sending it back to Earth or simply reflect it.
2. What is the core difference between an active and a passive satellite?
The core difference lies in how they handle communication signals.
- A passive satellite acts like a large mirror in space. It simply reflects the incoming signal from a transmitter on Earth towards a receiver at another location. It does not amplify or process the signal, which results in significant signal loss.
- An active satellite, on the other hand, contains electronic equipment called a transponder. It receives the signal, amplifies it to boost its strength, often changes its frequency, and then re-transmits it back to Earth. This ensures a much stronger and more reliable signal at the receiving end.
3. How does satellite communication overcome the limitation of Earth's curvature?
Ground-based communication methods, like radio waves, travel in straight lines (line-of-sight propagation). Due to the Earth's curvature, these signals cannot travel over very long distances as the planet itself blocks their path. Satellite communication overcomes this by placing a relay station in space. The satellite receives a signal from a ground station, and because of its high altitude, it can re-transmit that signal to another ground station that is far away and well beyond the horizon, effectively bypassing the physical barrier of the Earth's curve.
4. Why are most modern communication satellites active rather than passive?
Most modern communication satellites are active because of signal strength and reliability. Passive satellites only reflect a small fraction of the energy they receive, leading to severe signal attenuation (weakening) over the vast distance. This requires extremely powerful ground transmitters and highly sensitive receivers. Active satellites solve this problem by using a transponder to amplify the signal before re-transmitting it, ensuring a high-quality, strong signal that is suitable for modern high-bandwidth applications like television broadcasting and internet services.
5. What is a transponder and why is it essential for an active satellite?
A transponder is an integrated receiver and transmitter unit within an active satellite. Its function is to receive uplinked signals from a ground station, amplify them to compensate for energy loss during travel, and then re-transmit them back to Earth on a different, lower frequency (the downlink). It is the key component that defines an active satellite, as it provides the crucial function of signal amplification, making long-distance communication viable and robust.
6. What is the significance of a geostationary orbit in satellite communication?
A geostationary orbit is a specific orbit approximately 35,786 km above the Earth's equator where a satellite's orbital period matches the Earth's rotational period (24 hours). This makes the satellite appear stationary in the sky from a fixed point on Earth. Its significance is immense for communication because ground-based antennas do not need to constantly track the satellite's movement. This greatly simplifies the ground equipment, making it ideal for services like Direct-to-Home (DTH) television and permanent communication links.
7. What are some key applications of satellite communication in our daily lives?
Satellite communication is integral to many modern technologies. Some key applications include:
- Broadcasting: Television and radio signals are broadcast over vast geographical areas.
- Telephony and Internet: Providing phone and internet services to remote or underserved regions.
- Navigation: The Global Positioning System (GPS) relies on a constellation of satellites to provide location and timing information.
- Weather Forecasting: Satellites monitor weather patterns and help in predicting climatic events.
- Military and Defence: Used for secure communications, surveillance, and reconnaissance.
- Emergency Services: Assisting in search and rescue operations in remote locations.
8. What are the main advantages and disadvantages of using satellite communication?
Satellite communication has distinct pros and cons as per the CBSE Class 12 Physics syllabus.
Advantages:
- The geographical coverage area is much larger than terrestrial systems.
- It can provide connectivity to remote and inaccessible areas.
- The network is flexible and can be easily scaled.
- The initial cost of building and launching a satellite is extremely high.
- There is a propagation delay (latency) because the signal has to travel to orbit and back.
- Repair and maintenance of a satellite in orbit are very difficult and expensive.
