Types of satellites

Types of satellites based on purpose and size

Satellites are classified into different types based on the purpose and size. The various types of satellites include

 1. Weather satellites
 2. Communication satellites 
 3. Navigation satellites
 4. Earth observation satellites
 5. Astronomical satellites
 6. Miniaturized satellites.

1. Weather satellites

Weather satellites are mainly used to check the climate and weather conditions of the earth. Weather satellites are also called as meteorological satellites. They continuously measure the amount of heat energy released from the earth surface. This information helps the meteorologists to predict the weather conditions. Weather satellites use sensors called radiometers for measuring the intensity of radiation (heat energy) released from the earth surface.  

The weather satellites capture the mass of cloud covered in the sky. This information helps to predict rain. Weather satellites also predict the dangerous storms such as hurricanes. 

The first weather satellite was launched on February 17, 1959. However, it is failed to collect the accurate weather information from the earth. The first successful weather satellite (TIROS-1) was launched by NASA on April 1, 1960. 

Types of weather satellites 

Weather satellites are launched into two types of orbits: geostationary orbit and polar orbit.

Geostationary weather satellites

The weather satellites that are placed in geostationary orbit are called geostationary weather satellites or geostationary meteorological satellites. Geostationary weather satellites revolve around the earth at a height of 35,880 km. 

The orbiting speed of the geostationary weather satellite is equal to the speed of earth rotation (spinning of the earth on its own axis). Hence, when we look the earth from the geostationary satellite, earth looks like it is at rest position. Thus, weather satellites easily capture the images of the earth with their sensors.

Polar weather satellites

The weather satellites that are placed in polar orbit are called polar weather satellites or polar meteorological satellites. Polar weather satellites revolve around the earth at a height of 850 km. The polar weather satellites are also called as sun-synchronous weather satellites. 

The orbiting speed and direction of the polar weather satellite is different from the earth rotational speed and earth rotational direction. Hence, earth does not look stationary from the polar weather satellites.

2. Communication satellites

The communication satellite is a satellite that transmits the signals such as telephone, television, radio, internet signals over long distances. 

Electrical signal is used to transmit the information through the wire. However, electrical signal or electric current is not transmitted wirelessly because air is a pure insulator. Hence, it resists the flow of electric current or electrical signal. 

In order to transmit the information wirelessly, light signals or electromagnetic waves are used. However, light signals or electromagnetic waves cannot bend around the curvature of the earth. Hence, in order to transmit the information or signal over long distances, a single satellite or multiple satellites are used to redirect the signals.

Types of communication satellites 

Communication satellites are of two types: passive satellites and active satellites. 

Passive satellites 

Passive satellites receive the electromagnetic signal from the source or transmitter and redirect it towards the receiver or destination. 

The electromagnetic signal transmitted from the source collides continuously with the atmospheric particles. Because of this continuous collision, the signal strength is reduced. Hence, the receiver will receive a weak signal.

Active satellites 

An active satellite is a satellite that receives the signal from the source, amplifies the signal, and redirects the signal towards the receiver. 

The electromagnetic signal transmitted from the source collides continuously with the particles of the atmosphere. Because of this continuous collision, the signal strength is reduced. However, the active satellite amplifies the signal to a desired level and redirects the signal towards the receiver.

3. Navigation satellites

Generally, navigation refers to a process by which geographical location of an object is determined. The navigation satellites determine the geographic location of ships, aircrafts, or any other object.

The navigation satellite system with global coverage is called Global Navigation Satellite System (GNSS). The United States GPS (Global Positioning System), the Russian GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema), Galileo, and compass are the examples of Global Navigation Satellite System (GNSS). 

4. Earth observation satellites 

Earth observation satellites are mainly used to observe the earth from its orbit. These satellites detects the changes in the earth vegetation, ocean color, radiation from the earth surface. These satellites are also used to map the terrain. The various earth observation satellites include proba-1, proba-2, ERS-1, ERS-2, and Environmental Satellite (Envisat). 

5. Astronomical satellites 

Astronomical satellites are used to observe the distant galaxies, stars, planets, natural satellites, and other objects in the space. Astronomical satellites are mainly used to find the new planets, stars, and galaxies. 

Hubble space telescope is one of the most famous and largest astronomical satellites. It captures extremely high-resolution images from the space. 

5. Miniaturized satellites 

The miniaturized satellites revolve around the earth just like the normal satellites. However, these satellites have low mass and small physical size. The mass of a miniaturized satellite is below 600 kg. The cost required to launch the miniaturized satellites is very less compared to the heavier satellites.