How do satellites work?

When you gaze at the sky, you are actually looking at the empty space over the earth and many satellites are orbiting around it. Among them, there are broadcasting satellites, communication satellites, weather satellites, navigation satellites and many more. Most of today's technology is based on satellite communication which has provided wireless connection in the whole world. But what actually a satellite is?

What is a satellite?

Simply, satellites are those objects which move around to their host planet. For example, moon is a natural satellite of earth. But, we humans have sent some artificial satellites for different purposes. Sputnik 1 was the first man made satellite launched by Russia On 4 October, 1957. From that, the journey of space race started among different countries.

Artificial Satellites are basically some communication devices which receive signals from the earth and re-transmit it back to the earth station with the help of transponder. They can be placed in different altitude on the basis of their applications. They orbit their host celestial body by using its gravity.

How satellites are placed in orbit?

Like an aircraft, satellites cannot fly directly to space. It needs a launching rocket to place it in the right distance from the earth. For that, mathematical calculations are required. The design, construction and speed of the launching rocket depends on those mathematical equations.

The famous rocket principle is Newton's 3rd law of motion. According to this law, every forces have their equal and opposite directions. That means, the greater the force in one direction, same amount of force will be done by that body in the opposite direction. That is why, using fuels and propulsion engines, large amount of force is applied in the bottom. This force helps to react in the opposite direction with the same amount of force. This results in the movement of the rocket in upward direction. For more information about working of rocket check this How do rockets work?

After reaching the escape velocity, that means when the speed of the rocket reaches 11.2 Km/sec, then the rocket escapes from the gravitational pull of the earth and travels to the space. During this time, the rocket keeps separating itself one stage with another and thus, it place the satellite into the perfect destination.

Orbit of satellite:

After firing the satellite into space, it needs to be rotating around the earth for sustaining it's orbit. Otherwise, it will fall back to earth just like throwing a ball into air and come back to the ground. Though they are placed in space, every satellite has their own orbit depending on their applications. There are mainly three categories of satellite orbits-

1. Low Earth Orbit (LEO)
2. Medium Earth Orbit (MEO)
3. High Earth Orbit (HEO)

1. Low Earth Orbit (LEO):

These types of satellites are placed only a few hundred kilometers up (~3000-4000 km). They follow almost circular path of the orbit. As, they are very close to earth, they have to move very fast to sustain their positions. Due to this reason, they cover a very long distance in a very few time. Scientific satellites are placed in Low Earth Orbit. ISS (International Space Station) is also orbiting around the earth in this region of space.

2. Medium Earth Orbit (MEO):

Such types of satellites are placed almost 10 times higher up than the Low Earth Orbit, that means above almost 20,000 km. As, they are in higher atmosphere than the LEO satellites, they move slowly compared to that of the satellites. They take almost 12 hours to loop the whole planet. Their orbit is semi-synchronous. That means, their position do not remain same while passing over our heads. GPS navstar satellites are placed in Medium Earth Orbit.

3. High Earth Orbit (HEO):

Such types of satellites are placed above 36,000 km from the surface of the earth. They take exactly one day to loop the whole planet and come back to their same position. Such types of satellites are also called Geostationary or Geosynchronous satellites as they are synchronized with the earth's rotation. As, they are the far most satellites of the earth, they move very slowly compared to all other satellites and stay a longer position in a current place compared to the others. Communication satellites, weather satellites are often placed in this region of space. 

Satellite Construction:

For satellite construction, mainly the following systems are taken in use-

1. Body:

For making a satellite, body is most important part. Because, it protects the whole electronic system from the radiation emitted by the sun and also from some space particles. The anti-radiation material protects the electronic systems from harmful UV radiation. 

2. Power supply:

For continuous functioning of the electronic components of the satellite system power supply is needed. For power supply system, solar panels and high performance batteries are needed. 

3. Transmitter:

Transmitter transmits the radio frequency signals to the destination. The transmitter consists of oscillator, modulator, amplifier and antenna. Oscillator generates a high frequency carrier sine wave which is then combined with the main information with the help of a technique called Modulation. Then this modulated signal is amplified and transmitted by antenna.

4. Receiver:

Receiver receives the EM waves transmitted by transmitter. It consists of receiving RF antenna, de-modulator, tuner and amplifier. The receiving antenna receives the transmitted signal. The de-modulator extracts the original message signal by demodulation process. The tuner is used here to particularly tune a signal. The amplifier amplifies the signal to a desired amplitude and we get the output from the message signal.

5. Tracking Telemetry & Control system:

It controls and monitors all the parameters of satellite system, stores and analyze the data and also communicate with other satellites. Here the data are any scientific information or telecommunication signal, position and health of the satellite system etc.

What does actually a satellite do?

Satellites are used for many purposes. They do many jobs for us. Though they are placed in space, they are not only used in space application, but also in other fields. They are used as following ways-

1. Communication:

Due to the curvature of the earth, long distance communication cannot be possible in a straight line from one antenna to another antenna directly. So, to avoid this problem satellite communication is taken in use. It uses radio waves to send information from one point to another. They catch signals from one of the ground station to the receiver of the satellite. Then the receiver of the satellite receives the signal and with the help of transmitter, the signals are sent back to the destination ground station. This technique eliminates the limitations of direct communication between the antennas which are shoot in a straight line.

With the help of this technique, various communications are done across the globe. TV broadcasting, radio communication, mobile communication, internet connection are done with the help of satellite communication. This also limits the use of physical wires for long distance communication, specially in some remote areas. INMARSAT, INSAT, INTELSAT are some of the modern communication satellites used today.

a) Uplink:

When transmission is done from ground station to the satellite in space, that is called Uplink.

b) Downlink:

After Uplink, the satellite amplifies the signal to a desired value and reroutes it on a different frequency and send back to ground station. This is called Downlink.

2. Scientific analysis and imaging:

These satellites are used for analysis of scientific data and imaging. Such kind of satellites continuously report about the weather condition of a particular area, sea levels, upcoming disasters etc. They also take scientific information of all the areas across the globe and publish it all over the internet with the help of inbuilt search engine.

Poseidon, Jason, RISAT-1, IRS are some examples of scientific analysis and imagine saatellites.

3. Navigation:

Such kind of satellites are used for navigation. Most of the day, to find a place or finding the best rout we use GPS. The GPS works due to navigation satellites. 

GPS, IRNSS (Indian Regional Navigation System) are used for navigation process which are operated by the navigation satellites.

Next generation satellites:

The conventional satellites uses heavy payloads and electronic equipment, which make the satellites more bulky and heavy. Due to this, heavy rockets are taken in use to place the satellite in the orbit. More the weight of the rocket, more power is required. This entire process cost sometimes millions of dollars. If the launch fails, then all the money, effort and passions gets wasted. 

So, if the size of a satellite system is made small, then it would require very less amount of power to lift off with a small rocket to space. This will reduce the cost of the entire process. The main candidate of building a small and compact satellite is the Nanotechnology. However, engineers were trying to build such small and compact satellites for almost last two decades. In 2017, NASA launched world's smallest picosat made by an Indian student Rifath Sharook weighing only 64g. It was made by using 3D printer.

If nano satellites were made, the cost, failure risk, effort would be very very less. So, by using nanosats, may be we will explore the whole universe very soon.