Question

Answer the following questions:
a. What is meant by an artificial satellite? How are the satellites classified based on their functions?
b. What is meant by the orbit of a satellite? On what basis and how are the orbits of artificial satellites classified?
c. Why are geostationary satellites not useful for studies of polar regions?
d. What is meant by satellite launch vehicles? Explain a satellite launch vehicle developed by ISRO with the help of a schematic diagram.
e. Why it is beneficial to use satellite launch vehicles made of more than one stage?

Answer 1

a. A man made object revolving around a planet in a fixed orbit is known as artificial satellites. Based on their functions, satellites are classified as following:

Type of satellite	Function of satellite
Weather satellite	Study and prediction of weather
Communication satellite	Establish communication between different location in the world through use of specific waves
Broadcast satellite	Telecasting of television programs
Navigational satellite	Fix the location of any place on the Earth’s surface in terms of its very precise latitude and longitude
Military Satellite	Collect information for security aspects
Earth Observation Satellite	Study of forests, deserts, oceans, polar ice on the earth’s surface, exploration and management of natural resources, observation and guidance in case of natural calamities like flood and earthquake

b. An orbit is a specific path (elliptical or circular) or trajectory around a planet in which a satellite revolves. ​Depending on the height of the satellite’s orbit above the Earth’s surface, the satellite orbits are classified as below:

• High Earth Orbits (Height from the earth’s surface > 35780 km): If the height of the satellite’s orbit above the earth’s surface is greater than or equal to 35780 km, the orbit is called High earth Orbit
• Medium Earth Orbit (Height above the earth’s surface 2000 km to 35780 km): If the height of the satellite orbit above the earth’s surface is in between 2000 km and 35780 km, the orbits are called medium earth orbits.
• Low Earth Orbits (Height above the earth’s surface: 180 km to 2000 km): If the height of the satellite orbit above the earth’s surface is in between 180 km and 2000 km, the orbits are called Low earth Orbits.

c. The geostationary satellites orbit above the equator. Thus, these are not useful for studies of polar regions.

d. Satellite launch vehicles are used to place the satellites in their specific orbits. The structure of polar satellite launch vehicle (PSLV) developed by ISRO is shown below. It is a vehicle with 4 stages using solid and liquid fuels. The weight of the vehicle decreases after each stage because of consumption of fuel at that stage and detachment of that stage (i.e. the empty tank) from its body. Thus, the vehicle moves with higher speed after every stage.



e. The major portion of weight in satellite launch vehicles is contributed by fuel. Thus, vehicles have to carry a large weight of fuel during their course of journey. To overcome this problem of launch vehicles carrying heavy load during its entire journey, it is provided with more than one stage. Because to this, the weight of the vehicle can be reduced step by step, after its launching. For example, consider a launch vehicle having two stages. For launching the vehicle, the fuel and engine in the first stage are used. This imparts a specific velocity to the vehicle and takes it to a certain height. Once the fuel in this first stage is exhausted, the empty fuel tank and the engine are detached from the main body of the vehicle and fall either into a sea or on an unpopulated land. As the fuel in the first stage is exhausted, the fuel in the second stage is ignited. However, the vehicle now contains only one (i.e. the second) stage. The vehicle can move with higher speed as the weight has reduced.