Textbook: Space Missions | Science and Technology Class 10 (Maharashtra SSC Board) PDF Download

 Page 1


135
  1.  What is the difference between space and sky? 
  2. What are different objects in the Solar system? 
  3. What is meant by a satellite?
  4. How many natural satellites does the earth have?
Which types of telescopes are orbiting around the earth? 
Why it is necessary to put them in space?
  
10. Space Missions 
  Man has always been curious about unknown places and he has always been eager 
to expand the horizons of his knowledge by exploring the unknown world. He must have 
had deep curiosity about the space and the many twinkling stars in the dark sky. He must 
have had dreams to fly to the space and must have been working for that.
Space missions
 Substantial developments in technology, specially space technology, in the later half 
of twentieth century resulted in the development of space crafts making space voyage 
possible. Since then, more than a thousand artificial satellites have been placed into orbits 
around the earth. Additionally, space missions have been undertaken for close observation 
of various objects in our solar system. We will learn about all this in this chapter.  
We can classify the space missions into two categories. In one type of missions, the 
objective is to put artificial satellites in orbits around the earth for research and various 
other useful applications. The objective of second type of missions is to send the spacecrafts 
to outer space for close observations and understanding of the objects in solar system, or 
even outside the solar system.
 The first person to go into the space in a spacecraft was Yuri 
Gagarin of the then USSR. He orbited the earth in 1961. The first 
person to step on the Moon (1969) was Neil Armstrong of USA. 
Rakesh Sharma of India orbited the earth in 1984 in a Russian 
spacecraft. Kalpana Chawla and Sunita Williams of Indian origin 
also participated in space explorations through missions organized 
by NASA (National Aeronautics and Space Administration) of USA.
Ø Space Missions            ØArtificial satellites 	
Ø Classification of artificial satellites  Ø Orbits of artificial satellites 
Ø Satellite launch vehicles 		 	 Ø Space missions away from the Earth 
    Where does the signal in your cell phone come from? 
Where from does it come to mobile towers? Where does the signal 
to your TV set come from? You may have seen photographs 
showing the position of monsoon clouds over the country, in the 
newspaper. How are these images obtained? 
Can you recall?
Can you recall
Can you tell?
Do you know ?
Page 2


135
  1.  What is the difference between space and sky? 
  2. What are different objects in the Solar system? 
  3. What is meant by a satellite?
  4. How many natural satellites does the earth have?
Which types of telescopes are orbiting around the earth? 
Why it is necessary to put them in space?
  
10. Space Missions 
  Man has always been curious about unknown places and he has always been eager 
to expand the horizons of his knowledge by exploring the unknown world. He must have 
had deep curiosity about the space and the many twinkling stars in the dark sky. He must 
have had dreams to fly to the space and must have been working for that.
Space missions
 Substantial developments in technology, specially space technology, in the later half 
of twentieth century resulted in the development of space crafts making space voyage 
possible. Since then, more than a thousand artificial satellites have been placed into orbits 
around the earth. Additionally, space missions have been undertaken for close observation 
of various objects in our solar system. We will learn about all this in this chapter.  
We can classify the space missions into two categories. In one type of missions, the 
objective is to put artificial satellites in orbits around the earth for research and various 
other useful applications. The objective of second type of missions is to send the spacecrafts 
to outer space for close observations and understanding of the objects in solar system, or 
even outside the solar system.
 The first person to go into the space in a spacecraft was Yuri 
Gagarin of the then USSR. He orbited the earth in 1961. The first 
person to step on the Moon (1969) was Neil Armstrong of USA. 
Rakesh Sharma of India orbited the earth in 1984 in a Russian 
spacecraft. Kalpana Chawla and Sunita Williams of Indian origin 
also participated in space explorations through missions organized 
by NASA (National Aeronautics and Space Administration) of USA.
Ø Space Missions            ØArtificial satellites 	
Ø Classification of artificial satellites  Ø Orbits of artificial satellites 
Ø Satellite launch vehicles 		 	 Ø Space missions away from the Earth 
    Where does the signal in your cell phone come from? 
Where from does it come to mobile towers? Where does the signal 
to your TV set come from? You may have seen photographs 
showing the position of monsoon clouds over the country, in the 
newspaper. How are these images obtained? 
Can you recall?
Can you recall
Can you tell?
Do you know ?
136
Need and importance of space 
missions:
The world has become a global 
village due to space missions. 
Today, we can contact a person in 
any part of the world within a 
second. We can gather information 
about worldwide events sitting at 
home. You all know the importance 
of internet.  Due to internet, every 
information is available at our 
fingertips. It has become possible to 
get advance alert about natural 
calamities and take proper 
precautions.
10.1 Communication by artificial satellite 
INSAT: Indian National Satellite
GSAT: Geosynchronous Satellite 
IRNSS: Indian Regional Navigation Satellite System 
IRS :  Indian Remote Sensing Satellite
GSLV: Geosynchronous Satellite Launch Vehicle
PSLV: Polar Satellite Launch Vehicle
Use of ICT
 Prepare a power point 
presentation  showing India’s 
contribution in space research 
and present it in the class.
10.2 Sputnik
 During war, it is possible to get information about the actions of the enemy through 
aerial surveillance using satellites. It is also possible to explore the fossil reserves  and 
minerals in the earth. Thus, there are unlimited applications of space missions. Today, 
space technology is an inevitable part for development of a nation. 
Artificial satellite  
 A natural satellite is an astronomical object orbiting the earth or any other planet. 
The moon is the only natural satellite of the earth. Some other planets in the solar system 
have more than one natural satellites. Similarly if a manmade object revolves around the 
earth or any other planet in a fixed orbit it is called an artificial satellite (fig 10.1).  
 The first artificial satellite ‘Sputnik’ was sent to 
space by Soviet Union in 1957(see figure 10.2). Today, 
more than thousand satellites are orbiting the earth. The 
satellites work on solar energy. So, solar photovoltaic 
panels are attached on both sides of these satellites like 
wings. Instruments are installed in the satellites to 
receive and transmit signals from and to the earth. 
 The satellites have various other types of instruments, depending on their functions. 
One such satellite is shown in figure 10.1. Signals transmitted from the earth to the satellite 
and from  the satellite to a mobile tower and mobile phone are also shown. These satellites 
are sent into the space to perform various functions. Depending on their functions, satellites 
are classified into following categories:
Page 3


135
  1.  What is the difference between space and sky? 
  2. What are different objects in the Solar system? 
  3. What is meant by a satellite?
  4. How many natural satellites does the earth have?
Which types of telescopes are orbiting around the earth? 
Why it is necessary to put them in space?
  
10. Space Missions 
  Man has always been curious about unknown places and he has always been eager 
to expand the horizons of his knowledge by exploring the unknown world. He must have 
had deep curiosity about the space and the many twinkling stars in the dark sky. He must 
have had dreams to fly to the space and must have been working for that.
Space missions
 Substantial developments in technology, specially space technology, in the later half 
of twentieth century resulted in the development of space crafts making space voyage 
possible. Since then, more than a thousand artificial satellites have been placed into orbits 
around the earth. Additionally, space missions have been undertaken for close observation 
of various objects in our solar system. We will learn about all this in this chapter.  
We can classify the space missions into two categories. In one type of missions, the 
objective is to put artificial satellites in orbits around the earth for research and various 
other useful applications. The objective of second type of missions is to send the spacecrafts 
to outer space for close observations and understanding of the objects in solar system, or 
even outside the solar system.
 The first person to go into the space in a spacecraft was Yuri 
Gagarin of the then USSR. He orbited the earth in 1961. The first 
person to step on the Moon (1969) was Neil Armstrong of USA. 
Rakesh Sharma of India orbited the earth in 1984 in a Russian 
spacecraft. Kalpana Chawla and Sunita Williams of Indian origin 
also participated in space explorations through missions organized 
by NASA (National Aeronautics and Space Administration) of USA.
Ø Space Missions            ØArtificial satellites 	
Ø Classification of artificial satellites  Ø Orbits of artificial satellites 
Ø Satellite launch vehicles 		 	 Ø Space missions away from the Earth 
    Where does the signal in your cell phone come from? 
Where from does it come to mobile towers? Where does the signal 
to your TV set come from? You may have seen photographs 
showing the position of monsoon clouds over the country, in the 
newspaper. How are these images obtained? 
Can you recall?
Can you recall
Can you tell?
Do you know ?
136
Need and importance of space 
missions:
The world has become a global 
village due to space missions. 
Today, we can contact a person in 
any part of the world within a 
second. We can gather information 
about worldwide events sitting at 
home. You all know the importance 
of internet.  Due to internet, every 
information is available at our 
fingertips. It has become possible to 
get advance alert about natural 
calamities and take proper 
precautions.
10.1 Communication by artificial satellite 
INSAT: Indian National Satellite
GSAT: Geosynchronous Satellite 
IRNSS: Indian Regional Navigation Satellite System 
IRS :  Indian Remote Sensing Satellite
GSLV: Geosynchronous Satellite Launch Vehicle
PSLV: Polar Satellite Launch Vehicle
Use of ICT
 Prepare a power point 
presentation  showing India’s 
contribution in space research 
and present it in the class.
10.2 Sputnik
 During war, it is possible to get information about the actions of the enemy through 
aerial surveillance using satellites. It is also possible to explore the fossil reserves  and 
minerals in the earth. Thus, there are unlimited applications of space missions. Today, 
space technology is an inevitable part for development of a nation. 
Artificial satellite  
 A natural satellite is an astronomical object orbiting the earth or any other planet. 
The moon is the only natural satellite of the earth. Some other planets in the solar system 
have more than one natural satellites. Similarly if a manmade object revolves around the 
earth or any other planet in a fixed orbit it is called an artificial satellite (fig 10.1).  
 The first artificial satellite ‘Sputnik’ was sent to 
space by Soviet Union in 1957(see figure 10.2). Today, 
more than thousand satellites are orbiting the earth. The 
satellites work on solar energy. So, solar photovoltaic 
panels are attached on both sides of these satellites like 
wings. Instruments are installed in the satellites to 
receive and transmit signals from and to the earth. 
 The satellites have various other types of instruments, depending on their functions. 
One such satellite is shown in figure 10.1. Signals transmitted from the earth to the satellite 
and from  the satellite to a mobile tower and mobile phone are also shown. These satellites 
are sent into the space to perform various functions. Depending on their functions, satellites 
are classified into following categories:
137
Orbits of Artificial Satellites 
 All artificial satellites do not revolve in similar orbits around the earth. The functions 
of the satellite decide the height of the satellite’s orbit from the earth’s surface, the nature 
of the orbit (circular/elliptical) and whether the orbit shall be parallel to equator or making 
some angle with it. To put the satellite in its proper orbit at specific height above the 
earth’s surface, the satellite is taken to that height using a satellite launcher. Then the 
satellite is given a specific velocity known as the critical velocity (v
c
) in a tangential 
Type of satellite Function of the satellite
The names of Indian 
satellite series and 
their launch vehicles
Weather satellite Study and prediction of weather.
INSAT and GSAT.
Launcher: GSLV.
Communication satellite
Establish communication between 
different location in the world 
through use of specific waves.
INSATand GSAT.
Launcher: GSLV.
Broadcast satellite Telecasting of television programs.
INSAT and GSAT.
Launcher: GSLV.
Navigational satellite
Fix the location of any place on the 
earth’s surface in terms of its very 
precise latitude and longitude.
IRNSS. 
Launcher : PSLV.
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. 
IRS.
Launcher : PSLV.                   
Types of satellites
direction to the orbit (fig 10.3). The satellite 
then starts revolving around the earth. The 
formula for the velocity v
c
 can be derived as 
below.
If a satellite of mass ‘m’ is revolving 
around the earth in an orbit of height ‘h’ with 
speed ‘v
c
’, then as seen in the chapter on 
‘Gravitation’, a centripetal force 
mv
c
2
  r
will 
act on it.
Here, ‘r’ is the orbital radius of the satellite 
from the centre of the earth.
10.3 Orbit of an artificial satellite
Satellite
.
Satellite’s 
orbit
R
r
Vc
Earth
1.https://youtu.be/cuqYLHaLB5M
2. https://youtu.be/y37iHU0jK4s
Watch and share 
with others
Internet is my friend
h
Page 4


135
  1.  What is the difference between space and sky? 
  2. What are different objects in the Solar system? 
  3. What is meant by a satellite?
  4. How many natural satellites does the earth have?
Which types of telescopes are orbiting around the earth? 
Why it is necessary to put them in space?
  
10. Space Missions 
  Man has always been curious about unknown places and he has always been eager 
to expand the horizons of his knowledge by exploring the unknown world. He must have 
had deep curiosity about the space and the many twinkling stars in the dark sky. He must 
have had dreams to fly to the space and must have been working for that.
Space missions
 Substantial developments in technology, specially space technology, in the later half 
of twentieth century resulted in the development of space crafts making space voyage 
possible. Since then, more than a thousand artificial satellites have been placed into orbits 
around the earth. Additionally, space missions have been undertaken for close observation 
of various objects in our solar system. We will learn about all this in this chapter.  
We can classify the space missions into two categories. In one type of missions, the 
objective is to put artificial satellites in orbits around the earth for research and various 
other useful applications. The objective of second type of missions is to send the spacecrafts 
to outer space for close observations and understanding of the objects in solar system, or 
even outside the solar system.
 The first person to go into the space in a spacecraft was Yuri 
Gagarin of the then USSR. He orbited the earth in 1961. The first 
person to step on the Moon (1969) was Neil Armstrong of USA. 
Rakesh Sharma of India orbited the earth in 1984 in a Russian 
spacecraft. Kalpana Chawla and Sunita Williams of Indian origin 
also participated in space explorations through missions organized 
by NASA (National Aeronautics and Space Administration) of USA.
Ø Space Missions            ØArtificial satellites 	
Ø Classification of artificial satellites  Ø Orbits of artificial satellites 
Ø Satellite launch vehicles 		 	 Ø Space missions away from the Earth 
    Where does the signal in your cell phone come from? 
Where from does it come to mobile towers? Where does the signal 
to your TV set come from? You may have seen photographs 
showing the position of monsoon clouds over the country, in the 
newspaper. How are these images obtained? 
Can you recall?
Can you recall
Can you tell?
Do you know ?
136
Need and importance of space 
missions:
The world has become a global 
village due to space missions. 
Today, we can contact a person in 
any part of the world within a 
second. We can gather information 
about worldwide events sitting at 
home. You all know the importance 
of internet.  Due to internet, every 
information is available at our 
fingertips. It has become possible to 
get advance alert about natural 
calamities and take proper 
precautions.
10.1 Communication by artificial satellite 
INSAT: Indian National Satellite
GSAT: Geosynchronous Satellite 
IRNSS: Indian Regional Navigation Satellite System 
IRS :  Indian Remote Sensing Satellite
GSLV: Geosynchronous Satellite Launch Vehicle
PSLV: Polar Satellite Launch Vehicle
Use of ICT
 Prepare a power point 
presentation  showing India’s 
contribution in space research 
and present it in the class.
10.2 Sputnik
 During war, it is possible to get information about the actions of the enemy through 
aerial surveillance using satellites. It is also possible to explore the fossil reserves  and 
minerals in the earth. Thus, there are unlimited applications of space missions. Today, 
space technology is an inevitable part for development of a nation. 
Artificial satellite  
 A natural satellite is an astronomical object orbiting the earth or any other planet. 
The moon is the only natural satellite of the earth. Some other planets in the solar system 
have more than one natural satellites. Similarly if a manmade object revolves around the 
earth or any other planet in a fixed orbit it is called an artificial satellite (fig 10.1).  
 The first artificial satellite ‘Sputnik’ was sent to 
space by Soviet Union in 1957(see figure 10.2). Today, 
more than thousand satellites are orbiting the earth. The 
satellites work on solar energy. So, solar photovoltaic 
panels are attached on both sides of these satellites like 
wings. Instruments are installed in the satellites to 
receive and transmit signals from and to the earth. 
 The satellites have various other types of instruments, depending on their functions. 
One such satellite is shown in figure 10.1. Signals transmitted from the earth to the satellite 
and from  the satellite to a mobile tower and mobile phone are also shown. These satellites 
are sent into the space to perform various functions. Depending on their functions, satellites 
are classified into following categories:
137
Orbits of Artificial Satellites 
 All artificial satellites do not revolve in similar orbits around the earth. The functions 
of the satellite decide the height of the satellite’s orbit from the earth’s surface, the nature 
of the orbit (circular/elliptical) and whether the orbit shall be parallel to equator or making 
some angle with it. To put the satellite in its proper orbit at specific height above the 
earth’s surface, the satellite is taken to that height using a satellite launcher. Then the 
satellite is given a specific velocity known as the critical velocity (v
c
) in a tangential 
Type of satellite Function of the satellite
The names of Indian 
satellite series and 
their launch vehicles
Weather satellite Study and prediction of weather.
INSAT and GSAT.
Launcher: GSLV.
Communication satellite
Establish communication between 
different location in the world 
through use of specific waves.
INSATand GSAT.
Launcher: GSLV.
Broadcast satellite Telecasting of television programs.
INSAT and GSAT.
Launcher: GSLV.
Navigational satellite
Fix the location of any place on the 
earth’s surface in terms of its very 
precise latitude and longitude.
IRNSS. 
Launcher : PSLV.
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. 
IRS.
Launcher : PSLV.                   
Types of satellites
direction to the orbit (fig 10.3). The satellite 
then starts revolving around the earth. The 
formula for the velocity v
c
 can be derived as 
below.
If a satellite of mass ‘m’ is revolving 
around the earth in an orbit of height ‘h’ with 
speed ‘v
c
’, then as seen in the chapter on 
‘Gravitation’, a centripetal force 
mv
c
2
  r
will 
act on it.
Here, ‘r’ is the orbital radius of the satellite 
from the centre of the earth.
10.3 Orbit of an artificial satellite
Satellite
.
Satellite’s 
orbit
R
r
Vc
Earth
1.https://youtu.be/cuqYLHaLB5M
2. https://youtu.be/y37iHU0jK4s
Watch and share 
with others
Internet is my friend
h
138
High Earth Orbits : (Height from the earth’s surface  > 35780 km) 
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. The geostationary satellites orbit 
above the equator. These are, therefore, not useful in the study of polar regions. For this 
purpose, elliptical medium earth orbits passing over the polar region are used. These orbits 
are called polar orbits. In these orbits, the satellites complete one revolution in 2 to 24 
hours.
Some of these satellites revolve in circular orbits at  a height of around 20,200 km 
above the earth’s surface. Global positioning satellites revolve in such 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. The satellites used for scientific 
experiments and atmospheric studies revolve in low earth orbits. Depending on the height 
of their orbits, they complete one revolution in around 90 minutes. International Space 
Station and Hubble telescope also revolve in Low earth Orbits. 
Figure 10.4 shows various orbits of satellites.
 It can be seen that the critical velocity does not depend on the mass of the satellite. As 
the height of the satellite’s orbit from the earth’s surface increases, the critical velocity 
decreases. Depending on the height of the satellite’s orbit above the earth’s surface, the 
satellite orbits are classified as below:
G = Gravitational constant  = 6.67 × 10
-11 
N m
2
/kg
2
M = Mass of the earth = 6 × 10
24 
kg
R = Radius of the earth = 6.4 × 10
6
 m = 6400 km
h = Height of the satellite above earth surface 
R + h = Radius of the orbit of satellite.
 This centripetal force is provided by the gravity of the earth.
 Therefore, centripetal  force=gravitational force between the Earth and the satellite.
mv
c
2
R+h
= 
 GMm
(R+h)
2
  GM
  R+h
v
c
2 
=
GM
R+h
v
c
 =                             .......... (1)
  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. As we will see in the next solved example, 
a satellite revolving in an orbit 35780 km above the earth’s surface, will take around 24 
hours to complete one revolution. We know, that the earth also takes almost 24 hrs for one 
revolution. If the satellite is revolving in an orbit parallel to the equator, the time of revolution 
for the earth around itself and that for the satellite to revolve around the earth being the 
same, the satellite will appear to be stationary with respect to the earth. For a passenger in 
one vehicle, another vehicle, moving parallel to him with equal velocity, appears to be 
stationary. This is what happens here also. These satellites are, therefore, called 
geosynchronous satellites. Since, these satellites are stationary with reference to the earth, 
they can observe a specific portion of the earth, continuously. Therefore, they are used in 
applications like meteorology and for carrying signals for telephone, television, radio etc. 
Page 5


135
  1.  What is the difference between space and sky? 
  2. What are different objects in the Solar system? 
  3. What is meant by a satellite?
  4. How many natural satellites does the earth have?
Which types of telescopes are orbiting around the earth? 
Why it is necessary to put them in space?
  
10. Space Missions 
  Man has always been curious about unknown places and he has always been eager 
to expand the horizons of his knowledge by exploring the unknown world. He must have 
had deep curiosity about the space and the many twinkling stars in the dark sky. He must 
have had dreams to fly to the space and must have been working for that.
Space missions
 Substantial developments in technology, specially space technology, in the later half 
of twentieth century resulted in the development of space crafts making space voyage 
possible. Since then, more than a thousand artificial satellites have been placed into orbits 
around the earth. Additionally, space missions have been undertaken for close observation 
of various objects in our solar system. We will learn about all this in this chapter.  
We can classify the space missions into two categories. In one type of missions, the 
objective is to put artificial satellites in orbits around the earth for research and various 
other useful applications. The objective of second type of missions is to send the spacecrafts 
to outer space for close observations and understanding of the objects in solar system, or 
even outside the solar system.
 The first person to go into the space in a spacecraft was Yuri 
Gagarin of the then USSR. He orbited the earth in 1961. The first 
person to step on the Moon (1969) was Neil Armstrong of USA. 
Rakesh Sharma of India orbited the earth in 1984 in a Russian 
spacecraft. Kalpana Chawla and Sunita Williams of Indian origin 
also participated in space explorations through missions organized 
by NASA (National Aeronautics and Space Administration) of USA.
Ø Space Missions            ØArtificial satellites 	
Ø Classification of artificial satellites  Ø Orbits of artificial satellites 
Ø Satellite launch vehicles 		 	 Ø Space missions away from the Earth 
    Where does the signal in your cell phone come from? 
Where from does it come to mobile towers? Where does the signal 
to your TV set come from? You may have seen photographs 
showing the position of monsoon clouds over the country, in the 
newspaper. How are these images obtained? 
Can you recall?
Can you recall
Can you tell?
Do you know ?
136
Need and importance of space 
missions:
The world has become a global 
village due to space missions. 
Today, we can contact a person in 
any part of the world within a 
second. We can gather information 
about worldwide events sitting at 
home. You all know the importance 
of internet.  Due to internet, every 
information is available at our 
fingertips. It has become possible to 
get advance alert about natural 
calamities and take proper 
precautions.
10.1 Communication by artificial satellite 
INSAT: Indian National Satellite
GSAT: Geosynchronous Satellite 
IRNSS: Indian Regional Navigation Satellite System 
IRS :  Indian Remote Sensing Satellite
GSLV: Geosynchronous Satellite Launch Vehicle
PSLV: Polar Satellite Launch Vehicle
Use of ICT
 Prepare a power point 
presentation  showing India’s 
contribution in space research 
and present it in the class.
10.2 Sputnik
 During war, it is possible to get information about the actions of the enemy through 
aerial surveillance using satellites. It is also possible to explore the fossil reserves  and 
minerals in the earth. Thus, there are unlimited applications of space missions. Today, 
space technology is an inevitable part for development of a nation. 
Artificial satellite  
 A natural satellite is an astronomical object orbiting the earth or any other planet. 
The moon is the only natural satellite of the earth. Some other planets in the solar system 
have more than one natural satellites. Similarly if a manmade object revolves around the 
earth or any other planet in a fixed orbit it is called an artificial satellite (fig 10.1).  
 The first artificial satellite ‘Sputnik’ was sent to 
space by Soviet Union in 1957(see figure 10.2). Today, 
more than thousand satellites are orbiting the earth. The 
satellites work on solar energy. So, solar photovoltaic 
panels are attached on both sides of these satellites like 
wings. Instruments are installed in the satellites to 
receive and transmit signals from and to the earth. 
 The satellites have various other types of instruments, depending on their functions. 
One such satellite is shown in figure 10.1. Signals transmitted from the earth to the satellite 
and from  the satellite to a mobile tower and mobile phone are also shown. These satellites 
are sent into the space to perform various functions. Depending on their functions, satellites 
are classified into following categories:
137
Orbits of Artificial Satellites 
 All artificial satellites do not revolve in similar orbits around the earth. The functions 
of the satellite decide the height of the satellite’s orbit from the earth’s surface, the nature 
of the orbit (circular/elliptical) and whether the orbit shall be parallel to equator or making 
some angle with it. To put the satellite in its proper orbit at specific height above the 
earth’s surface, the satellite is taken to that height using a satellite launcher. Then the 
satellite is given a specific velocity known as the critical velocity (v
c
) in a tangential 
Type of satellite Function of the satellite
The names of Indian 
satellite series and 
their launch vehicles
Weather satellite Study and prediction of weather.
INSAT and GSAT.
Launcher: GSLV.
Communication satellite
Establish communication between 
different location in the world 
through use of specific waves.
INSATand GSAT.
Launcher: GSLV.
Broadcast satellite Telecasting of television programs.
INSAT and GSAT.
Launcher: GSLV.
Navigational satellite
Fix the location of any place on the 
earth’s surface in terms of its very 
precise latitude and longitude.
IRNSS. 
Launcher : PSLV.
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. 
IRS.
Launcher : PSLV.                   
Types of satellites
direction to the orbit (fig 10.3). The satellite 
then starts revolving around the earth. The 
formula for the velocity v
c
 can be derived as 
below.
If a satellite of mass ‘m’ is revolving 
around the earth in an orbit of height ‘h’ with 
speed ‘v
c
’, then as seen in the chapter on 
‘Gravitation’, a centripetal force 
mv
c
2
  r
will 
act on it.
Here, ‘r’ is the orbital radius of the satellite 
from the centre of the earth.
10.3 Orbit of an artificial satellite
Satellite
.
Satellite’s 
orbit
R
r
Vc
Earth
1.https://youtu.be/cuqYLHaLB5M
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138
High Earth Orbits : (Height from the earth’s surface  > 35780 km) 
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. The geostationary satellites orbit 
above the equator. These are, therefore, not useful in the study of polar regions. For this 
purpose, elliptical medium earth orbits passing over the polar region are used. These orbits 
are called polar orbits. In these orbits, the satellites complete one revolution in 2 to 24 
hours.
Some of these satellites revolve in circular orbits at  a height of around 20,200 km 
above the earth’s surface. Global positioning satellites revolve in such 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. The satellites used for scientific 
experiments and atmospheric studies revolve in low earth orbits. Depending on the height 
of their orbits, they complete one revolution in around 90 minutes. International Space 
Station and Hubble telescope also revolve in Low earth Orbits. 
Figure 10.4 shows various orbits of satellites.
 It can be seen that the critical velocity does not depend on the mass of the satellite. As 
the height of the satellite’s orbit from the earth’s surface increases, the critical velocity 
decreases. Depending on the height of the satellite’s orbit above the earth’s surface, the 
satellite orbits are classified as below:
G = Gravitational constant  = 6.67 × 10
-11 
N m
2
/kg
2
M = Mass of the earth = 6 × 10
24 
kg
R = Radius of the earth = 6.4 × 10
6
 m = 6400 km
h = Height of the satellite above earth surface 
R + h = Radius of the orbit of satellite.
 This centripetal force is provided by the gravity of the earth.
 Therefore, centripetal  force=gravitational force between the Earth and the satellite.
mv
c
2
R+h
= 
 GMm
(R+h)
2
  GM
  R+h
v
c
2 
=
GM
R+h
v
c
 =                             .......... (1)
  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. As we will see in the next solved example, 
a satellite revolving in an orbit 35780 km above the earth’s surface, will take around 24 
hours to complete one revolution. We know, that the earth also takes almost 24 hrs for one 
revolution. If the satellite is revolving in an orbit parallel to the equator, the time of revolution 
for the earth around itself and that for the satellite to revolve around the earth being the 
same, the satellite will appear to be stationary with respect to the earth. For a passenger in 
one vehicle, another vehicle, moving parallel to him with equal velocity, appears to be 
stationary. This is what happens here also. These satellites are, therefore, called 
geosynchronous satellites. Since, these satellites are stationary with reference to the earth, 
they can observe a specific portion of the earth, continuously. Therefore, they are used in 
applications like meteorology and for carrying signals for telephone, television, radio etc. 
139
A group of students from COEP 
(College of Engineering, Pune) made a 
small satellite and sent it to the space 
through ISRO in 2016. The name of the 
satellite is ‘Swayam’ and it weighs around 
1 kg. It is orbiting the earth at a height of 
515 km. The main objective of the satellite 
was to provide point to point messaging 
services using a special method.  
10.4 Orbits of satellites
LEO
HEO
MEO
GM
R+h
v = 
(6.67 x 10
-11
 ) x ( 6 x 10
24
)
      42180 × 10
3
 m
 = 
Example 2. In the previous example, how 
much time the satellite will take to complete 
one revolution around the earth?
Given: Height of the satellite above the 
earth’s surface= 35780 km.
Velocity of the satellite=3.08 km/sec
Solution: Suppose, the satellite takes T 
seconds to complete one revolution around 
the earth. The distance travelled during this 
one revolution is equal to the circumference 
of the circular orbit. If r is the radius of the 
orbit, the satellite will travel a distance 2pr 
during one revolution. Thus, the time 
required for one complete revolution can 
be obtained as follows:
v =                = 
distance
time
circumference
time
        = 
2 p r
  T
= 23.89 hrs.  = 23 hrs 54 M.
40.02 x 10
13
42180 x 10
3
 = 
40.02
42180
 = × 10
10
=
0.0009487909 × 10
10
= 9487909
= 3.08 km/s
v = 3080.245 m/s
2 × 3.14 × (6400 + 35780)
             3.08
=
86003.38 sec
=
(Here, since the velocity is taken in the unit of 
km/s, the radius is also taken in unit of km)
T  =                    
2 p (R+h)
        v
2 p r
   v
=
Solved Example
Do you know ?
Example 1. Suppose the orbit of a satellite 
is exactly 35780 km above the earth’s 
surface. Determine the tangential velocity 
of the satellite.
Given : G = 6.67 × 10
-11  
N m
2
/kg
2  
, 
M = 6×10
24 
kg (for earth)
R = 6400  km (for earth) = 6.4 × 10
6
 m , 
h = height of the satellite above the earth’s 
 surface 35780 km. 
v = ?
R + h = 6400 + 35780 = 42180 × 10
3
 m
MEO