We spend our life knowing that many satellites orbit our planet every day and they are helping us in many ways. You will be surprised to know that there are about 8,377 active satellites orbiting the earth.
The most obvious question that comes to mind is that why are these satellites completely in different orbits? How does a satellite do all its functions and what are the components which helps them to complete their work. Let’s know the answer to all these questions in detail.
Working of Satellites
It is true that the satellite is in orbit due to the balance between the gravitational pull and the centrifugal force. The angular velocity force of the satellite is decided by the balance equation which balances the gravitational and centrifugal forces.
When the satellite is deployed, then it is given sufficient speed to balance these two forces. A satellite close to the Earth needs more speed to oppose the gravitational pull located further from the Earth.
Satellites never lose speed due to very low resistance in space. This means that satellites will continue their circular motion all around the Earth without any external energy source.
Satellites have a low Earth orbit, Medium Earth Orbit, or Geosynchronous Earth Orbit. These three orbits are illustrated here. There is an interesting region in space, which is called the Van Allen Belt. This region is full of highly energetic and charged particles, which can seriously damage an electronic section of a satellite. Normally in the Van Allen belt, it is advised not to park the satellites.
Placement of satellite
The decision of which orbit the satellite should be placed depends on the application and purpose of the satellite. If the satellite is made for Earth observation, weather forecasting, geographic area surveying, satellite phone calls, etc. then the near orbit of the Earth is chosen.
Low Earth Orbit
Leo(Low Earth Orbit) is closest to the Earth at a height of 160 to 2000 km and its orbital period is about 1.5 hours, But this type of satellite covers less area of the Earth. To get global coverage, many satellites are needed. That’s why high orbit like Geo is chosen in the case of broadcasting.
Geosynchronous Earth Orbit
In the geosynchronous orbit, satellites are at a height of 35786 km and rotate at the equal angular speed of the earth. This means that to complete one round of the satellite, 23 hours, 56 minutes, and 4 seconds.
In geosynchronous orbit, there is a special category of orbit, which is called a geostationary orbit, which is concentric for the equator of the earth. These satellites are stationary in relation to the Earth, so geostationary satellite is the ideal choice for television broadcasting because it means that you do not need to adjust the angle of your satellite dish repeatedly.
This is the reason why the geostationary belt is filled with satellites and it is managed by an international organization named ITU. Geosynchronous orbits are also filled with some navigation satellites. Geosatellites can cover one-third of the Earth’s surface, so three satellites are enough to cover the entire Earth.
Medium Earth Orbit
For GPS-like navigation applications, MEO is a wise option. Even if Leo is closest to Earth, In this orbit, satellites rotate at a very high speed. Because of this, Earth’s receivers fail to complete navigation calculations accurately.
Apart from the LEO needs a lot of satellites to cover the entire Earth. In this way, GPS uses the satellite MEO. In a typical GPS system, 24 satellites can cover the entire Earth. And the orbital period is 12 hours.
Let’s now look at the main components of a communication satellite. Along with their functions, there are transponders in the center of communication satellites. The main work of a transponder is to change the frequency of the received signal, remove any signal noise, and increase the signal power. On KU-band satellites, the transponder is converted from 14 GHz to 12 GHz and there can be 20 or more transponders in a single satellite.
It is clear that to handle all these functions, the transponder needs a lot of electrical power. For power supply, one satellite has the options of batteries and solar panels. The use of solar panels is done to power electronic equipment.
But battery is used during the eclipse. You can see a sun sensor on the satellite. This sun sensor helps the solar panels to give the right angle. so that more power can be extracted from the Sun.
Now, let’s see how the transponder receives input signal from the antenna. The most common antenna fixed in satellites is the reflector antenna.
A satellite should follow its intended smooth orbit. However, the gravitational field on all four sides of a satellite is not uniform due to the unequal mass distribution of the Earth, Moon, and the presence of the Sun. Because of this, sometimes the satellite is displaced from its intended orbital position. This is a dangerous situation because it will cause a total loss of signal.
Thrusters are used in satellites to avoid such situations. Thrusters are fired and the satellite is kept in the correct position. They also help satellites to avoid space junk. The necessary fuel for thrusters is kept in the satellite body tanks. The control of the satellite’s position and thrusters is continuously monitored by the Earth Station.
Apart from position controls, the Earth Station also keeps an eye on the satellite’s health and speed. This is done through tracking, telemetry and control systems. These systems continuously send signals to the Earth Station and keep a connection between Earth and the satellite. Usually, these signals are exchanged at different frequencies to separate them from other communication signals.
Lifespan of Satellite
Have you ever wondered what happens to a satellite when it is not functional? Or its lifespan is near its end? These satellites can harm other operational satellites or spacecraft.
To deal with this situation, inactive satellites are activated by thrusters and sent to graveyard orbit. Just by increasing the rotational speed of the satellite, we can transfer it to a high-radius orbit. This operation is explained in this animation.
Graveyard orbit is a few hundred kilometers above geostationary orbit. Thrusters use the same amount of fuel for this operation, as much as a satellite needs for station keeping for three months.
Now for some interesting information, in the satellites, you must have seen that they were covered with a gold-colored foil. What is the purpose of this foil? In reality, this is not a foil. If you take a cross-section of it, then you can know that it has a multi-layered structure.
Satellites have a heavy variation in the temperature in space, where the temperature varies from -150 to -200 degrees Celsius. Apart from this, satellites face heavy solar radiation from the sun. This material actually acts as a shield, which protects the satellite components from heavy temperature variations and solar radiation.
The satellites we have discussed so far are communication satellites. The most important component for GPS satellites is an atomic clock and antenna. In this type of satellite, an L-band navigation antenna is used, as explained here. Earth observation satellites, which are mostly in LEO, carry different types of sensors, imagers, etc. according to their mission.
We hope that you have got good information about different types of satellites and how they work. Please support our educational service by visiting on our website. Thank you!