Maharashtra Board Class 10 Science Part 1 Chapter 10 Space Missions PDF Download

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.

Teacher's Note

Space missions help us learn about planets and stars. Just like when you see weather news on TV about rain coming, that information comes from satellites in space.

Exam Trick

Remember: First space person = Yuri Gagarin (1961), First moon person = Neil Armstrong (1969), First Indian = Rakesh Sharma (1984). Write these three names and years in your exam.

Points to Remember

Man wanted to know about space and stars for a long time.
Two types of space missions: satellites around earth and spacecrafts going far away.
Yuri Gagarin was the first person in space in 1961.
Neil Armstrong was the first person on the moon in 1969.
Rakesh Sharma was the first Indian in space in 1984.

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.

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.

Teacher's Note

Space satellites help us know about weather and talk with people far away. In India, satellites help us see monsoon rains coming so we can prepare for floods.

Exam Trick

Remember: Satellites = phone calls + TV + weather news. Write these three uses in your exam to get full marks.

Points to Remember

World became a global village because of space missions.
We can talk to people anywhere in the world now.
Satellites give us weather information and news.
Internet works because of satellites.
Satellites help us know about floods and earthquakes before they happen.

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.

The first artificial satellite 'Sputnik' was sent to space by Soviet Union in 1957. 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:

Teacher's Note

Different satellites do different jobs. Weather satellites tell us if rain is coming, communication satellites help us make phone calls, and TV satellites give us programs to watch.

Exam Trick

Remember: INSAT = Indian National Satellite. Write this full form in your exam. Each satellite type has a different job - weather, TV, phone calls, finding location.

Points to Remember

Sputnik was the first artificial satellite sent in 1957.
The moon is a natural satellite, not man-made.
Artificial satellites have solar panels like wings to get power from sun.
Weather satellites help predict rain and storms.
Communication satellites help us make phone calls and watch TV.

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 direction to the orbit. 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 \(\frac{mv_c^2}{r}\) will act on it.

Here, 'r' is the orbital radius of the satellite from the centre of the earth.

This centripetal force is provided by the gravity of the earth. Therefore, centripetal force = gravitational force between the Earth and the satellite.

\[\frac{mv_c^2}{R+h} = \frac{GMm}{(R+h)^2}\]

\[v_c^2 = \frac{GM}{R+h}\]

\[v_c = \sqrt{\frac{GM}{R+h}} \text{ .......... (1)}\]

Where:

\(G\) = Gravitational constant = \(6.67 \times 10^{-11}\) N m\(^2\)/kg\(^2\)

\(M\) = Mass of the earth = \(6 \times 10^{24}\) kg

\(R\) = Radius of the earth = \(6.4 \times 10^6\) m = 6400 km

\(h\) = Height of the satellite above earth surface

\(R + h\) = Radius of the orbit of satellite.

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:

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. 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.

Teacher's Note

Geosynchronous satellites stay in one place above earth. This is like a fan that turns with the ceiling - both move together at the same speed so the fan looks like it is not moving.

Exam Trick

Remember: Geosynchronous satellite = 24 hours = one day. The satellite takes 24 hours to go around earth, just like earth takes 24 hours to turn around itself. So the satellite looks still.

Points to Remember

Critical velocity does not depend on the mass of satellite.
As height increases, critical velocity decreases.
Geosynchronous satellites stay in same place above earth.
Geosynchronous satellites take 24 hours for one orbit.
High earth orbits are above 35780 km height.

This is a preview of the first 3 pages. To get the complete book, click below.