Maharashtra Board Class 10 Science Chapter 10 Space Missions Solutions

Space Missions

 

Question 1. Fill in the blanks and explain the statements with reasoning:
a. If the height of the orbit of a satellite from the earth’s surface is increased, the tangential velocity of the satellite will ................
b. The initial velocity (during launching) of the Mangalyaan must be greater than ............ from the earth.
Answer:
a. If the height of the orbit of a satellite from the earth’s surface is increased, the tangential velocity of the satellite will decrease.
Explanation: The gravitational force (F) exerted by the earth on the satellite will decrease if the height of the orbit of the satellite from the earth’s surface is increased. Hence, the tangential velocity of the satellite will decrease. The formula \( \frac{mv_c^2}{R + h} = \frac{GMm}{(R + h)^2} \) or \( v_c = \sqrt{\frac{GM}{R + h}} \) shows that critical velocity \( v_c \) decreases with increasing height \( h \). This mathematical relationship ensures that higher orbits require slower orbital speeds.

b. The initial velocity (during launching) of the Mangalyaan must be greater than the escape velocity from the earth.
Explanation: If a spacecraft is to travel beyond the gravitational pull of the earth, its velocity must be more than the escape velocity from the earth. This escape velocity is the minimum speed required to break free from Earth's gravity permanently.
In simple words: When a satellite is placed in a higher orbit, gravity is weaker, so it needs less speed to stay in orbit. To send a spacecraft like Mangalyaan to Mars, it must be launched faster than Earth's escape velocity so it can break free from Earth's gravity completely.

🎯 Exam Tip: Remember the formula for critical velocity \( v_c = \sqrt{\frac{GM}{R+h}} \). Since height \( h \) is in the denominator, increasing \( h \) will always decrease the velocity \( v_c \).

 

State with Reasons Whether the Following Statements are True or False

 

Question a. If a spacecraft has to be sent away from the influence of the earth’s gravitational field, its velocity must be less than the escape velocity.
Answer: False. The escape velocity of a body is the minimum velocity with which it should be projected from the earth’s surface, so that it can escape the influence of the earth’s gravitational field. This clearly shows that the given statement is false. To successfully break free from gravity, the spacecraft's velocity must actually be equal to or greater than this escape velocity.
In simple words: Escape velocity is the minimum speed needed to break free from Earth's gravity. If a spacecraft goes slower than this speed, it will not be able to escape into space and will fall back down.

🎯 Exam Tip: Always remember that "escape" requires a speed equal to or greater than the escape velocity. Any speed less than this will keep the object bound by gravity.

 

Question b. The escape velocity on the moon is less than that on the earth.
Answer: True.
Explanation: Escape velocity of an object from the earth,
\( v_{esc}(1) = \sqrt{\frac{2GM_1}{R_1}} \)
Escape velocity of an object from the moon,
\( v_{esc}(2) = \sqrt{\frac{2GM_2}{R_2}} \)
\( \therefore \frac{v_{esc}(2)}{v_{esc}(1)} = \sqrt{\frac{M_2}{M_1} \times \frac{R_1}{R_2}} \)
Now, \( \frac{M_1 \text{ (Earth)}}{M_2 \text{ (Moon)}} = 81 \) and \( \frac{R_1 \text{ (Earth)}}{R_2 \text{ (Moon)}} = 3.7 \)
\( \therefore \frac{v_{esc}(2)}{v_{esc}(1)} = \sqrt{\frac{3.7}{81}} < 1 \)
So, \( v_{esc}(2) < v_{esc}(1) \). This mathematical ratio confirms that the weaker gravitational pull of the moon makes it much easier to escape its surface than Earth's.
In simple words: The Moon is much smaller and lighter than Earth, so its gravitational pull is weaker. Because of this, you need much less speed to escape from the Moon than from Earth.

🎯 Exam Tip: When writing this proof, clearly state the values of the mass ratio (81) and radius ratio (3.7) to secure full marks in the explanation.

 

Question c. A satellite needs a specific velocity to revolve in a specific orbit.
Answer: True.
Explanation:
Centripetal force on the satellite \( \frac{mv_c^2}{R+h} \) = gravitational force exerted by the earth on the satellite \( \frac{GMm}{(R+h)^2} \)
\( \implies v_c^2 = \frac{GM}{R+h} \)
\( \implies v_c = \sqrt{\frac{GM}{R+h}} \)
where,
m: mass of the satellite
\( v_c \): critical velocity of the satellite
h: height of the satellite from the surface of the earth
This balance of forces ensures that the satellite remains stable in its designated path without falling or drifting away.
In simple words: For a satellite to stay in a stable orbit, its speed must perfectly balance the pull of gravity at that height. If it goes too fast or too slow, it will lose its orbit.

🎯 Exam Tip: Show the derivation step where mass of the satellite \( m \) cancels out, proving that the critical velocity depends only on the orbit's height and the planet's mass.

Critical Velocity of an Artificial Satellite

M: mass of the earth
R: radius of the earth
G: gravitational constant

\( \therefore v_c^2 = \frac{GM}{R+h} \)

\( \therefore v_c = \sqrt{\frac{GM}{R+h}} \)

Thus, if the value of h changes, the value of \( v_c \) also changes. It means a satellite needs to be given a specific velocity (in the tangential direction) to keep it revolving in a specific orbit.

Orbit of an Artificial Satellite (Diagram Labels)

• Satellite
• Critical velocity (\( v_c \))
• Height (h)
• Radius of Earth (R)
• Orbital radius (r)
• Earth
• Orbit of the satellite

 

Question d. If the height of the orbit of a satellite increases, its velocity must also increase.
Answer: False.
Explanation:
Centripetal force on the satellite \( \frac{mv_c^2}{R+h} \) = gravitational force exerted by the earth on the satellite \( \frac{GMm}{(R+h)^2} \)
where,
m : mass of the satellite
\( v_c \) : critical velocity of the satellite
h : height of the satellite from the surface of the earth
M : mass of the earth
R : radius of the earth
G : gravitational constant

\( \therefore v_c^2 = \frac{GM}{R+h} \)

\( \dots v_c = \sqrt{\frac{GM}{R+h}} \)
This mathematical relationship clearly demonstrates that critical velocity is inversely proportional to the square root of the orbital radius.
In simple words: As a satellite gets higher and further away from Earth, the pull of gravity becomes weaker, so it actually needs less speed to stay in its orbit.

🎯 Exam Tip: Always write down the final formula \( v_c = \sqrt{\frac{GM}{R+h}} \) to show the inverse relationship between velocity and height, which helps secure full marks.

Thus, if the value of \( h \) changes, the value of \( v_c \) also changes. It means a satellite needs to be given a specific velocity (in the tangential direction) to keep it revolving in a specific orbit.

Orbit of an Artificial Satellite (Diagram Labels):

• Satellite with tangential velocity \( v_c \)
• Orbit of the satellite
• Earth with radius \( R \)
• Height of satellite from Earth's surface \( h \)
• Radius of orbit \( r = R + h \)

As per the formula \( v_c = \sqrt{\frac{GM}{R+h}} \), if the value of \( h \) increases, the value of \( v_c \) decreases. Hence, if the height of the satellite from the surface of the earth increases, its velocity decreases.

 

Question 3. Answer the following questions:
a. What is meant by an artificial satellite? How are the satellites classified based on their functions?
(OR)
Write the importance of artificial satellites in your words. (Practice Activity Sheet - 3)
Answer: A manmade object orbiting the earth or any other planet is called an artificial satellite. Satellites work on solar energy and hence photovoltaic panels are attached on both sides of the satellite, which look like wings. Satellites are also installed with various transmitters and other equipment to receive and transmit signals between the earth and the satellites. They play a crucial role in modern communication and global positioning systems.

Classification of satellites depending on their functions:
(1) Weather satellites: Weather satellites collect the information regarding weather conditions of the region. It records temperature, air pressure, wind direction, humidity, and cloud cover to help predict weather patterns.
In simple words: An artificial satellite is a human-made machine sent into space to orbit the Earth. It uses solar panels for power and helps us with tasks like predicting the weather and sending communication signals.

🎯 Exam Tip: Clearly define what an artificial satellite is first, and then list its classifications with their specific functions to secure full marks.

 

Question. Explain the functions of different types of artificial satellites.
Answer:
(1) Weather satellites: These satellites collect information about humidity, cloud cover, etc. This information is sent to the space research station on the earth and then with this information weather forecast is made.
(2) Communication satellites: In order to establish communication between different places on the earth through mobile phones or computer assisted internet, communication satellites are used. Many artificial satellites placed at various locations in the earth’s orbit are well interconnected and help us to have communication with any place, from anywhere, at any time and in any form including voicemail, email, photographs, audio mail, etc.
(3) Broadcasting satellites: Broadcasting satellites are used to transmit various radio and television programs and even live programs from any place on the earth to any other place. As a result, one can have access to information about current incidents, events, programs, sports and other events right from his drawing room with these satellites.
(4) Navigational satellites: Navigational satellites assist the surface, water and air transportation and coordinate their busy schedule. These satellites also assist the user with current live maps as well as real time traffic conditions.
(5) Military satellites: Every sovereign nation needs to keep the real time information about the borders. Satellites help to monitor all movements of neighboring countries or enemy countries. Military satellites also help to guide the missiles effectively.
(6) Earth observation satellites: These satellites observe and provide the real time information about the earth. These satellites also help us to collect information about the resources, their management, continuous observation about a natural phenomenon and the changes within it.
(7) Other satellites: Apart from these various satellites, certain satellites for specific works or purposes are also sent in the space. E.g. India has sent EDUSAT for educational purpose; CARTOSAT for surveys and map making. Similarly, satellites with telescopes, like Hubble telescope or a satellite like International Space Station help to explore the universe. In fact, ISS (International Space Station) provides a temporary residence where astronauts can stay for a certain short or long period and can perform scientific experiments in space.
In simple words: Artificial satellites are sent into space for different jobs like forecasting weather, helping us use mobile phones and internet, broadcasting TV shows, guiding navigation maps, protecting borders, and studying the Earth and outer space.

🎯 Exam Tip: Remember the key function of each satellite type (e.g., weather for forecasting, communication for internet/phones, navigational for maps) to easily write short notes on them in exams.

 

Question b. What is meant by the orbit of a satellite? On what basis and how are the orbits of artificial satellites classified?
Answer: Orbit of a satellite is its path around the earth. Orbits of artificial satellites can be classified on various bases. This classification helps in determining the specific path and purpose of each satellite.
(1) On the basis of the angle of the orbital plane: Orbital plane of a satellite can be the equatorial plane of the earth or it can be at an angle to it.
(2) On the basis of the nature of the orbit: Orbital plane can be circular or elliptical in shape.
(3) On the basis of the height of the satellite: Orbit of a satellite can be HEO, MEO or LEO.

(i) High Earth Orbit (HEO) satellite: A satellite orbiting at a height equal to or greater than 35780 km above the earth’s surface is called a High Earth Orbit satellite. The critical velocity (\( v_c \)) of a satellite revolving in an orbit at 35780 km above the earth surface is 3.08 km/s. Such a satellite will take about 23 hours 54 minutes to complete one revolution around the earth. The earth completes one rotation about its axis in the same time. The orbital plane of such a satellite is the equatorial plane of the earth. The satellite’s relative position appears stationary with respect to a place on the earth. This satellite is, therefore, called a geostationary satellite or geosynchronous satellite.

(ii) Medium Earth Orbit (MEO) satellite: A satellite orbiting at a height between 2000 km and 35780 km above the earth’s surface is called a Medium Earth Orbit satellite. The orbital path of such a satellite is normally elliptical and passes through the North and the South polar regions. These satellites take about 12 hours to complete one revolution.
In simple words: The orbit of a satellite is the path it takes to travel around the Earth. These orbits are grouped based on their angle, shape, and how high they are from the ground.

🎯 Exam Tip: Clearly define the three types of orbits (HEO, MEO, LEO) based on their heights and mention their respective revolution times to score full marks.

...revolution around the earth.

Orbits of Satellites

• Earth
• Low Earth Orbit
• Medium Earth Orbit
• High Earth Orbit

(iii) Low Earth Orbit (LEO) satellite:
A satellite orbiting at a height between 180 km and 2000 km above the earth’s surface is called a Low Earth Orbit satellite. Normally, these satellites take 90 minutes to complete one revolution around the earth. Weather satellites, space telescopes and International Space Station are Low Earth Orbit satellites.

 

Question c. Why are geostationary satellites not useful for studies of polar regions? (Practice Activity Sheet – 4)
(OR)
Explain the following statement. A geostationary satellite is not useful in the study of polar regions. (Practice Activity Sheet – 1)
Answer: Geostationary satellites have two distinct characteristics:
(1) Geostationary satellites are HEO satellites and are placed at 35780 km above the earth's equator.
(2) Their orbit lies entirely in the equatorial plane, which prevents them from having a proper line of sight to the polar regions due to the curvature of the earth.
In simple words: Geostationary satellites stay parked directly over the equator. Because the Earth is a round sphere, these satellites cannot "see" around the curve to look at the North and South poles.

🎯 Exam Tip: Clearly state that geostationary satellites orbit specifically in the equatorial plane, which prevents them from having a direct line of sight to the polar regions.

Orbit of a Geostationary Satellite (Diagram Labels):

• Axis
• Earth's rotation
• Earth
• Equator
• Geostationary satellite
• Orbit of a geostationary satellite

 

Question. Why are geostationary satellites not useful for studies of polar regions?
Answer: A geostationary satellite revolves in the equatorial plane of the earth, and thus, it can never fly above the polar regions. Hence, geostationary satellites are not useful for studies of polar regions. This limitation prevents them from gathering data directly over the North and South poles.
In simple words: Geostationary satellites stay fixed over the equator, so they cannot see or study the North and South poles.

🎯 Exam Tip: Clearly mention that geostationary satellites orbit specifically in the equatorial plane, which prevents them from having a line of sight to the polar areas.

 

Question d. What is meant by a satellite launch vehicle? Explain the satellite launch vehicle developed by ISRO with the help of a schematic diagram.
Answer: A rocket used to carry an artificial satellite to a desired height above the earth’s surface and then project it with a proper velocity so that the satellite orbits the earth in the desired orbit is called a launch vehicle. A satellite launch vehicle needs a specific velocity as well as a thrust to reach the desired height above the earth’s surface. The velocity and the thrust of a satellite launch vehicle depend on the weight and orbital height of the satellite. Accordingly, the structure of the launch vehicle is decided and designed. The weight of the fuel also contributes a major portion in the total weight of the launch vehicle. This also influences the structure of the launch vehicle. In order to use the fuel optimally, multiple stage launch vehicles are now designed and used. The Polar Satellite Launch Vehicle (PSLV) developed by ISRO is designed with multiple stages to efficiently place satellites into polar orbits.
In simple words: A satellite launch vehicle is a powerful rocket that carries satellites into space and places them into their correct orbits. It uses multiple stages of fuel to make the journey highly efficient.

🎯 Exam Tip: Define the launch vehicle clearly using key terms like 'thrust', 'velocity', and 'orbital height' to secure full marks.

Structure of PSLV made by ISRO

• Place for a satellite
• Fourth stage using liquid fuel
• Third stage using solid fuel
• Second stage using liquid fuel
• First stage using solid fuel
• Engine using solid fuel which provides the initial thrust

 

Question e. Why is it beneficial to use a satellite j launch vehicle made up of more than one stage?
Answer: Earlier Satellite Launch Vehicles (SLV) used to be of a single stage vehicles. Such SLVs used to be very heavy as well as expensive in terms of its fuel consumption. As a result, SLVs with multiple stages were developed. In multistage SLVs, as the journey of the launch vehicle progresses and the vehicle achieves a specific velocity and a certain height, the fuel of the first stage is exhausted and the empty fuel tank gets detached from the main body of the launch vehicle and falls back into a sea or on unpopulated land. As the fuel in the first stage is exhausted, the engine in the second stage is Ignited. However, the weight of the launch vehicle is now less than what it was earlier and hence it can move with higher velocity, Thus, it saves fuel consumption. This step-by-step shedding of weight makes space exploration far more efficient and cost-effective. Hence, it is beneficial to use a multistage satellite launch vehicle.
In simple words: Using a rocket with multiple stages helps save fuel. As each stage runs out of fuel, its heavy empty tank is dropped off, making the rocket lighter so it can fly much faster with less energy.

🎯 Exam Tip: Clearly explain how detaching empty fuel tanks reduces the rocket's weight, allowing it to gain higher velocity with lower fuel consumption.

 

Question 4. Complete the following table:
Answer:

• IRNSS: Navigational Satellite — To fix the location in terms of precise latitude and longitude
• INSAT: Weather study and predict — Weather Satellite
• IRS: Earth observation satellite — Earth's observation

In simple words: This table matches different satellite systems with their main functions and types, like using IRNSS for finding locations and INSAT for weather forecasting.

🎯 Exam Tip: Memorize the full forms and primary functions of Indian satellite series like IRNSS, INSAT, and IRS as they are frequently asked in match-the-following questions.

 

Question 5. Solve the following problems:
a. If the mass of a planet is eight times the mass of the earth and its radius is twice the radius of the earth, what will be the escape velocity for that planet?
Answer: Given:
(1) The mass of the planet \( (M_p) = 8 \times M_e \) (where \( M_e \) is the mass of the earth, \( 6 \times 10^{24} \text{ kg} \))
(2) The radius of the planet \( (R_p) = 2 \times R_e \) (where \( R_e \) is the radius of the earth, \( 6.4 \times 10^6 \text{ m} \))
(3) \( G = 6.67 \times 10^{-11} \text{ N}\cdot\text{m}^2/\text{kg}^2 \)

Formula for escape velocity: \( v_{esc} = \sqrt{\frac{2GM}{R}} \)

For Earth, the escape velocity is \( v_e = \sqrt{\frac{2GM_e}{R_e}} = 11.2 \text{ km/s} \).

For the planet:
\( v_p = \sqrt{\frac{2G(8M_e)}{2R_e}} \)

\( \implies v_p = \sqrt{4 \times \frac{2GM_e}{R_e}} \)

\( \implies v_p = 2 \times \sqrt{\frac{2GM_e}{R_e}} \)

\( \implies v_p = 2 \times v_e \)

\( \implies v_p = 2 \times 11.2 \text{ km/s} = 22.4 \text{ km/s} \)

Thus, the escape velocity for the planet is \( 22.4 \text{ km/s} \).
In simple words: Since the planet is much heavier but also larger, its gravity works out to make its escape velocity exactly double that of Earth, which is 22.4 km/s.

🎯 Exam Tip: Instead of doing heavy calculations with actual values of G, M, and R, express the planet's parameters in terms of Earth's parameters to simplify the ratio and save time.

 

Question b. How much time would a satellite in an orbit at a height of 35780 km above the earth’s surface take to complete one revolution around the earth, if the mass of the earth were four times its original mass?
Answer:
Given:
Radius of Earth, \( R = 6400 \text{ km} = 6.4 \times 10^6 \text{ m} \)
Mass of Earth, \( M = 6 \times 10^{24} \text{ kg} \)
New Mass of Earth, \( M' = 4M = 4 \times 6 \times 10^{24} \text{ kg} = 24 \times 10^{24} \text{ kg} \)
Height of satellite, \( h = 35780 \text{ km} = 3.578 \times 10^7 \text{ m} \)
Gravitational constant, \( G = 6.67 \times 10^{-11} \text{ N}\cdot\text{m}^2/\text{kg}^2 \)

The time period \( T \) of a satellite revolving around the Earth is given by the formula:
\[ T = 2\pi \sqrt{\frac{(R+h)^3}{GM}} \]
For a satellite orbiting at a height of \( 35780 \text{ km} \) (which is a geostationary orbit), the standard time period to complete one revolution is \( T = 24 \text{ hours} \).

If the mass of the Earth becomes four times its original mass (\( M' = 4M \)), the new time period \( T' \) is:
\[ T' = 2\pi \sqrt{\frac{(R+h)^3}{GM'}} \]
\[ T' = 2\pi \sqrt{\frac{(R+h)^3}{G(4M)}} \]
\[ T' = \frac{1}{\sqrt{4}} \left[ 2\pi \sqrt{\frac{(R+h)^3}{GM}} \right] \]
\( \implies T' = \frac{1}{2} T \)
\( \implies T' = \frac{24}{2} \)
\( \implies T' = 12 \text{ hours} \)

Thus, the satellite would take 12 hours to complete one revolution around the Earth. This shows that an increase in the central mass results in a stronger gravitational pull, thereby increasing the orbital speed and reducing the revolution time.
In simple words: A satellite at this specific height normally takes 24 hours to orbit the Earth. If the Earth's mass becomes four times heavier, its stronger gravity pulls the satellite faster, cutting the orbit time exactly in half to 12 hours.

🎯 Exam Tip: Remember that the time period of a geostationary satellite is always 24 hours. Using the proportional relationship \( T \propto \frac{1}{\sqrt{M}} \) saves time and avoids tedious calculations during exams.

Calculation of Satellite Orbital Period
\( T = \frac{2\pi (R + h)}{v_c} \)
Now \( v_c = \sqrt{\frac{GM'}{R+h}} \)
\( \implies T = \frac{2\pi (R + h)}{\sqrt{GM'/(R+h)}} \)
\( \implies T = \frac{2\pi}{\sqrt{GM'}} (R+h)^{3/2} \)
\( \implies T = \frac{2\pi (6.4 \times 10^6 \text{ m} + 35.78 \times 10^6 \text{ m})^{3/2}}{\sqrt{6.67 \times 10^{-11} \text{ N}\cdot\text{m}^2/\text{kg}^2 \times 4 \times 6 \times 10^{24} \text{ kg}}} \)
\( \implies T = \frac{2\pi (42.18 \times 10^6)^{3/2}}{\sqrt{6.67 \times 24 \times 10^{13}}} \text{ s} \)
\( \implies T = \frac{2\pi \sqrt{(42.18)^3 \times 10^{18}}}{\sqrt{6.67 \times 2.4 \times 10^{14}}} \text{ s} \)
\( \implies T = 2 \times 3.142 \times \sqrt{\frac{(42.18)^3 \times 10^4}{6.67 \times 2.4}} \text{ s} \)
\( \implies T = \text{Approx } \frac{4.303 \times 10^4}{3600} \text{ hours} \)
\( \implies T = \text{Approx } 4.303 \times 10^4 \text{ s} \)
\( \implies T = \text{Approx } 11.95 \text{ h} \)
or 11 hours 57 minutes 10 seconds.

 

Question c. If the height of a satellite completing one revolution around the earth in T seconds is \( h_1 \) meters, then what would be the height of a satellite taking \( 2\sqrt{2} \) T seconds for one revolution?
Answer:
Given:
(1) Time: T seconds
(2) Height: \( h_1 \)
Let us assume the height of the satellite completing one revolution in \( 2\sqrt{2} \) T seconds as \( h_2 \). By Kepler's third law, the square of the orbital period is proportional to the cube of the semi-major axis, which allows us to determine the new height.
In simple words: We are given the time and height of one satellite and need to find the height of another satellite that takes longer to orbit. We can solve this using Kepler's laws of planetary motion.

🎯 Exam Tip: Clearly state Kepler's Third Law formula \( T^2 \propto r^3 \) and define all terms like orbital radius \( r = R + h \) to secure full marks in such derivation-based questions.

\( T = \frac{2\pi r}{v_c} \), i.e., \( T = \frac{2\pi (R + h_1)}{\sqrt{\frac{GM}{(R + h_1)}}} \)
\( \implies \therefore T = 2\pi \sqrt{\frac{(R + h_1)^3}{GM}} \) ... (1)
and \( 2\sqrt{2} T = 2\pi \sqrt{\frac{(R + h_2)^3}{GM}} \) ... (2)
From Eqs. (1) and (2),
\( \implies \therefore \frac{T}{2\sqrt{2} T} = \frac{2\pi \sqrt{\frac{(R + h_1)^3}{GM}}}{2\pi \sqrt{\frac{(R + h_2)^3}{GM}}} \)
\( \implies \therefore \frac{1}{\sqrt{8}} = \frac{\sqrt{(R + h_1)^3}}{\sqrt{(R + h_2)^3}} \)
\( \implies \therefore \frac{1}{2} = \frac{R + h_1}{R + h_2} \)
\( \implies \therefore R + h_2 = 2R + 2h_1 \)
\( \implies \therefore h_2 = R + 2h_1 \)

 

Project

 

Project 1. Collect information about the space missions undertaken by Sunita Williams.
Hints:
The following sources can be used to get the information on the above topic:
(1) Google Search Engine
(2) YouTube
(3) E-books on Sunita Williams
(4) English and other regional language books on Sunita Williams available in your library
(5) Newspaper clippings

Based on the information you have collected from the above sources, complete the project in about 5 pages. You can do value addition to your project with the help of suitable photos, clippings, charts, graphs and sketches.
Answer:
Page 1: Title Page & Introduction
• Title: Space Missions of Sunita Williams
• Introduction: Sunita Williams is an illustrious American astronaut and United States Navy officer of Indian-Slovenian descent. She formerly held the records for total spacewalks by a woman (seven) and most spacewalk time for a woman (50 hours, 40 minutes). She was assigned to the International Space Station as a member of Expedition 14 and Expedition 15, and later served as a flight engineer on Expedition 32 and commander of Expedition 33.

Page 2: First Space Mission (STS-116 and Expedition 14/15)
• Launch: December 9, 2006, onboard the Space Shuttle Discovery (STS-116).
• Role: Flight Engineer.
• Activities: During her stay at the ISS, she performed four spacewalks. She also ran the Boston Marathon while in space, completing it in 4 hours and 24 minutes on a treadmill.
• Return: June 22, 2007, onboard STS-117, setting a record at the time for the longest single spaceflight by a woman (195 days).

Page 3: Second Space Mission (Soyuz TMA-05M and Expedition 32/33)
• Launch: July 15, 2012, from the Baikonur Cosmodrome onboard Soyuz TMA-05M.
• Role: Flight Engineer for Expedition 32 and Commander for Expedition 33 (only the second woman to command the ISS).
• Activities: She performed three additional spacewalks to carry out repairs and maintenance on the ISS. She also became the first person to complete a triathlon in space using the station's exercise equipment.
• Return: November 19, 2012, after spending 127 days in space.

Page 4: Key Achievements and Records
• Total time spent in space: 322 days, 2 hours, and 15 minutes.
• Total spacewalk time: 50 hours and 40 minutes across 7 spacewalks.
• First astronaut to run a marathon and complete a triathlon in orbit.
• Recipient of prestigious awards including the Padma Bhushan (from the Government of India), NASA Space Flight Medal, and Congressional Space Medal of Honor.

Page 5: Conclusion & Bibliography
• Conclusion: Sunita Williams' extraordinary career serves as an inspiration to millions of young minds, especially girls worldwide, proving that dedication and hard work can help one reach the stars.
• Bibliography: NASA Official Website, Wikipedia, and regional library books on space exploration.
In simple words: Sunita Williams is a famous astronaut who went to space twice, spent over 322 days there, and did seven spacewalks. This project guide helps you write a 5-page report about her amazing space journeys and achievements.

🎯 Exam Tip: To score full marks in projects, organize your content page-by-page with clear headings and paste relevant pictures of Sunita Williams and the ISS to make it visually appealing.

Project 2. Assume that you are interviewing Sunita Williams. Prepare a questionnaire and also the answers.
Answer: Points to make a list of a questionnaire for the interview of Sunita Williams:
(1) Primary and higher education
(2) The source of inspiration to become an astronaut
(3) Information about her mentor
(4) General and specific training
(5) Initial experience of being an astronaut
(6) First space mission, its nature, duration and experience
(7) Nature of research carried out in space
(8) Some special memories
(9) Future plans
(10) Tips and guidance for the younger generation. These structured points help in conducting a comprehensive and engaging interview.
In simple words: To interview Sunita Williams, we should prepare questions about her school days, her training, her space journeys, and her advice for kids.

🎯 Exam Tip: When preparing an interview questionnaire, always organize your questions chronologically from early life to future plans to maintain a smooth flow.

 

Can You Recall? (Text Book Page No. 135)

 

Question 1. What is the difference between space and sky?
Answer:
1. The visible portion of the atmosphere and outer space seen by simple eyes, without any equipment from the earth, is known as the sky.
2. The infinite three-dimensional expanse in which the Solar system, stars, celestial bodies, galaxies and the endless Universe exist is known as space.
3. Both sky and space lack a definite boundary. However, the sky is a very tiny part of space. Understanding this distinction helps us appreciate the vastness of the universe beyond our immediate atmosphere.
In simple words: The sky is what we see when we look up from Earth, like the blue air and clouds. Space is the endless area beyond our atmosphere where stars, planets, and galaxies exist.

🎯 Exam Tip: Clearly define both 'sky' and 'space' separately before comparing them to secure full marks.

 

Question 2. What are different objects in the Solar system?
Answer:
1. Our Solar system is a very tiny part of a huge Galaxy-Milky Way.
2. It consists of the Sun, eight planets, their satellites, dwarf planets, and millions of smaller celestial bodies like asteroids and comets. All these diverse objects are bound together by the immense gravitational pull of the Sun.
In simple words: The solar system includes the Sun, the planets that orbit it, their moons, and other smaller rocks like asteroids.

🎯 Exam Tip: Remember to mention the Sun as the central body of the solar system along with planets and satellites.

 

Question 3. What is meant by a satellite?
Answer:
1. An astronomical object orbiting any planet of our Solar system is called a satellite. These celestial bodies do not have their own light and shine by reflecting sunlight.
2. Mercury and Venus have no satellites.
3. Some planets have more than one satellite. E.g. Jupiter has 69 satellites.
In simple words: A satellite is a natural object in space that travels around a planet. For example, the Moon is a satellite of the Earth.

🎯 Exam Tip: Remember to mention that some planets like Mercury and Venus do not have any satellites to score full marks.

 

Question 4. How many natural satellites does the earth have?
Answer: The earth has one natural satellite called the moon. It is the closest celestial body to our planet and shines brightly in the night sky.
In simple words: The Earth has only one natural satellite, which is the Moon.

🎯 Exam Tip: Always write the name of the satellite, 'the Moon', clearly in your answer.

 

Question 5. Which type of telescopes are orbiting around the earth? Why is it necessary to put them in space?
Answer:
(1) The following three types of telescopes are orbiting around the earth:
• Optical Refracting Telescope.
• Optical Reflecting Telescope.
• Radio Telescope.

(2) Visible light and radio waves emitted by celestial bodies in space pass through the atmosphere before reaching the earth's surface. During this journey, some light is absorbed by the atmosphere. Hence, the intensity of the light reaching the earth's surface decreases. Besides, temperature and air pressure cause the atmospheric disturbance. Placing these telescopes in space completely avoids these atmospheric interferences, allowing us to capture extremely sharp and clear images of deep space.
In simple words: We put telescopes in space because the Earth's atmosphere blocks and distorts light from stars. In space, there is no air to block the view, so we get much clearer pictures.

🎯 Exam Tip: Clearly list the three types of telescopes first, and then explain the atmospheric interference factor in the second part of your answer.

turbulence. Hence, light rays change their path, resulting in a change in the position of the image of a celestial body.

City lights during night, and bright sunlight during day also put limitations on usage of optical telescopes on the earth. To minimize these problems, optical telescopes are situated on mountain top, away from inhabited places. However, limitations caused by the atmosphere still persist.

To get rid of these problems scientists have successfully launched telescopes in space. Images obtained by these telescopes are brighter and clearer than those obtained by the telescopes located on the earth’s surface.

Can You Recall? (Text Book Page No. 135)

 

Question 1. Where does the signal in your cellphone come from?
Answer: In nearby area of our residence, many mobile towers are installed at various places. Cellphones receive signals from one of these mobile towers. This network of towers ensures we stay connected while moving around.
In simple words: Cellphone signals come from mobile towers set up in our neighborhoods.

🎯 Exam Tip: Mention "mobile towers" as the primary source of signals for cellphones to secure full marks.

 

Question 2. Where from does it come to mobile towers?
Answer: All mobile towers are connected to satellites. Cellphone signal reaching the nearest mobile tower in our vicinity is first transmitted to the satellite. The satellite transmits the signal to the mobile tower near the destination. This satellite link allows long-distance communication across the globe.
In simple words: The signals travel from mobile towers to satellites in space, which then send them back down to other towers near the person you are calling.

🎯 Exam Tip: Clearly explain the role of satellites in transmitting signals between different mobile towers.

 

Question 3. Where does the signal to your TV set come from?
Answer: (1) Television Centre or Studio transmits the TV program which first reaches the satellite. The dish antenna of the cable operator in our area receives these signals. The TV programs reach our TV set through a cable connected between the cable operator’s receiving station and our TV set. This ensures high-quality transmission of video and audio directly to our homes.
In simple words: TV signals are sent from a studio to a satellite, then received by a local cable operator's dish, and finally sent to our TV through cables.

🎯 Exam Tip: Remember to list the sequence: Studio -> Satellite -> Cable Operator's Dish -> TV Set to show a complete understanding of the signal path.

 

Question 4. You may have seen photographs showing the position of monsoon clouds over the country in the newspaper. How are these images obtained?
Answer: Weather satellites take photographs of the sky above the earth’s surface at regular intervals. Some satellites, capable of receiving radio signals, also collect the information of weather conditions and finally images of the sky are built with computers. Territorial boundaries of the states and the country are drawn later on these images. Such satellite images with imposed boundaries are printed in media or shown on the television. These advanced space technologies help meteorologists predict weather patterns more accurately.
In simple words: Special weather satellites orbiting the Earth take pictures of the clouds and sky. Computers then process these pictures and add map borders so we can see them on TV or in newspapers.

🎯 Exam Tip: Remember to mention 'weather satellites' and 'computers' as the key tools used to capture and process these cloud images to score full marks.

 

Fill in the blanks:

 

Question 1. A man-made object revolving around the earth in a fixed orbit is called .............
Answer: A man-made object revolving around the earth in a fixed orbit is called an artificial satellite. These satellites are launched into space using powerful rockets.
In simple words: Any object made by humans that goes around the Earth in a set path is called an artificial satellite.

🎯 Exam Tip: Always underline the filled-in word in your answer sheet to make it stand out clearly for the examiner.

 

Question 2. Chandrayaan-I discovered the presence of ............. on the moon.
Answer: Chandrayaan-I discovered the presence of water on the moon. This groundbreaking discovery changed our understanding of the lunar environment.
In simple words: India's first moon mission, Chandrayaan-1, found actual proof of water on the moon's surface.

🎯 Exam Tip: Make sure to spell 'Chandrayaan-I' correctly with the Roman numeral 'I' as given in the textbook.

 

Question 3. Apart from launching a satellite around the earth, India has been able to launch a satellite around .............
Answer: Apart from launching a satellite around the earth, India has been able to launch a satellite around Mars. This mission is famously known as the Mangalyaan mission.
In simple words: Besides Earth, India has successfully sent a spacecraft to orbit the planet Mars.

🎯 Exam Tip: Remember that Mars is the correct planet name here, and always capitalize the first letter 'M' as it is a proper noun.

 

Question 4. All satellites work on ............... energy.
Answer: All satellites work on solar energy, which is captured using large solar panels attached to the sides of the spacecraft.
In simple words: Satellites use energy from the sun to power their instruments and stay active in space.

🎯 Exam Tip: Remember that solar energy is the primary source of power for almost all active satellites orbiting Earth.

 

Question 5. ............... are used to carry and place a satellite in a specific orbit.
Answer: Satellite launchers are used to carry and place a satellite in a specific orbit. These powerful rockets overcome Earth's gravity to deliver payloads safely into space.
In simple words: Satellite launchers are big rockets that carry satellites from Earth and put them into their correct paths in space.

🎯 Exam Tip: Always use the term "satellite launchers" or "launch vehicles" when describing the rockets that carry satellites.

 

Question 6. USA has developed ............... as an alternative to space launch vehicles.
Answer: USA has developed space shuttles as an alternative to space launch vehicles. These reusable spacecraft can carry astronauts and cargo to and from orbit.
In simple words: Space shuttles are reusable spacecraft designed by the USA to carry people and equipment into space and return safely.

🎯 Exam Tip: Highlight the reusability aspect of space shuttles as it is their main advantage over traditional launch vehicles.

 

Question 7. Hubble telescope is a ............. satellite.
Answer: Hubble telescope is a Low Earth Orbit (LEO) satellite. It orbits at an altitude of about 540 kilometers above Earth, allowing it to capture clear images of deep space.
In simple words: The Hubble telescope is a space telescope that orbits close to Earth to take clear pictures of stars and galaxies.

🎯 Exam Tip: Be sure to write both the full form and abbreviation "Low Earth Orbit (LEO)" for complete clarity.

 

Question 8. ............... executed the first ever mission to the moon in the world.
Answer: Russia executed the first ever mission to the moon in the world. This historic milestone was achieved with the Luna 2 spacecraft in 1959.
In simple words: Russia was the first country to successfully send a spacecraft to reach the moon.

🎯 Exam Tip: Remember that Russia (then USSR) sent the first unmanned mission to the moon, while the USA sent the first manned mission.

 

Question 9. ........... executed the first manned mission to the moon in the world.
Answer: USA executed the first manned mission to the moon in the world. This was the famous Apollo 11 mission in 1969 where Neil Armstrong walked on the moon.
In simple words: The USA was the first country to send astronauts to walk on the moon.

🎯 Exam Tip: Do not confuse the first unmanned mission (Russia) with the first manned mission (USA).

 

Select the Appropriate Answer From Given Options:

 

Question 1. Which one of the following is a Low Earth Orbit (LEO) satellite?

Question 1. Which of the following is an example of a space station?
(a) Navigational satellite
(b) Geostationary satellite
(c) International Space Station
(d) All of the options
Answer: (c) International Space Station
In simple words: The International Space Station is a large spacecraft in orbit where astronauts live and conduct scientific research, unlike regular satellites which are unmanned.

🎯 Exam Tip: Remember that space stations are designed for humans to live in space, whereas other satellites are unmanned instruments used for communication or navigation.

 

Question 2. Which of the following satellite launchers is developed by India?
(a) INSAT
(b) IRNSS
(c) EDUSAT
(d) PSLV
Answer: (d) PSLV
In simple words: PSLV stands for Polar Satellite Launch Vehicle, which is a rocket designed by India to carry satellites into space.

🎯 Exam Tip: Do not confuse satellite names like INSAT or EDUSAT with launch vehicles like PSLV or GSLV; launchers are the rockets that carry the satellites.

 

Question 3. Which of the following astronauts travelled through space shuttle 'Discovery' first time? (Practice Activity Sheet – 4)
(a) Kalpana Chawla
(b) Rakesh Sharma
(c) Sunita Williams
(d) Neil Armstrong
Answer: (c) Sunita Williams
In simple words: Sunita Williams made her first space journey aboard the Space Shuttle Discovery to join the crew of the International Space Station.

🎯 Exam Tip: Keep a list of famous astronauts of Indian origin and their specific space missions to easily answer such historical trivia questions.

 

Considering the Correlation Between the Words of the First Pair, Pair the Third Word Accordingly with Proper Answer. (OR) Considering the First Correlation, Complete the Second.

 

Question 1. IRNSS : Direction showing satellite :: INSAT : ............. (Practice Activity Sheet – 1)
Answer: IRNSS : Direction showing satellite :: INSAT : Weather satellite. This classification helps in understanding the primary function of different satellite series launched by ISRO.
In simple words: Just like IRNSS is used for finding directions (navigation), the INSAT series of satellites is used for monitoring weather and climate.

🎯 Exam Tip: In correlation questions, identify the exact relationship (like name and its function) in the first pair to correctly complete the second pair.

 

Question 2. Hubble telescope : 569 km high from the earth’s surface :: Revolving orbit of Hubble telescope :.......... (Practice Activity Sheet – 2; March 2019)
Answer: Hubble telescope : 569 km high from the earth’s surface :: Revolving orbit of Hubble telescope : Low Earth Orbit. This orbit is relatively close to Earth's surface, allowing for easier maintenance and data transmission.
In simple words: The Hubble telescope travels in a path close to Earth called the Low Earth Orbit, which is about 569 kilometers high.

🎯 Exam Tip: Remember that satellites or telescopes orbiting between 180 km and 2000 km above Earth's surface are classified under Low Earth Orbit (LEO).

Match the Column:

 

Question 1. Match the columns:

Column A	Column B
(1) Clouds over India	(a) Low Earth Orbit
(2) Global communication	(b) PSLV
(3) Launch vehicle made by ISRO	(c) Communication satellite
(4) International Space Station	(d) EDUSAT
(5) Navigational satellite	(e) Weather satellite
	(f) Medium Earth Orbit

Answer:
(1) Clouds over India – Weather satellite
(2) Global communication – Communication satellite
(3) Launch vehicle made by ISRO – PSLV
(4) International Space Station – Low Earth Orbit
(5) Navigational satellite – Medium Earth Orbit. These matches correctly pair each space technology or mission with its corresponding category or orbit type.
In simple words: This table matches different space objects and tasks with their correct orbits or vehicle types. For example, weather satellites help us see clouds, and the PSLV is a rocket made by ISRO.

🎯 Exam Tip: When matching columns, write the complete correct pair side-by-side in your final answer sheet to make it easy for the examiner to grade.

Answer the Following Questions in One Sentence Each:

Question 1. What do you mean by the orbit of a satellite?
Answer: Orbit of a satellite is its path around the earth. It is the specific trajectory followed by the satellite due to gravitational forces.
In simple words: The orbit is the circular or oval path that a satellite takes as it travels around the Earth. It is like a track in space.

🎯 Exam Tip: Remember to define the orbit clearly as the specific path around the Earth to score full marks.

 

Question 2. Which factor decides the orbit of a satellite?
Answer: The function of a satellite decides the orbit of the satellite. Depending on what the satellite is designed to do, its height and speed are chosen accordingly.
In simple words: What the satellite is used for determines where it needs to fly. For example, weather satellites need different paths than communication satellites.

🎯 Exam Tip: Focus on the word "function" as it is the key term the examiner looks for in this answer.

 

Question 3. What is a High Earth Orbit satellite?
Answer: A satellite orbiting at a height equal to or greater than 35780 km above the earth’s surface is called a High Earth Orbit satellite. These satellites take about 24 hours to complete one revolution around the Earth.
In simple words: If a satellite flies very high up, at least 35,780 kilometers above us, it is called a High Earth Orbit satellite.

🎯 Exam Tip: Always write the exact number "35780 km" clearly, as numerical accuracy is crucial for scoring full marks.

 

Question 4. Give two examples of Low Earth Orbit satellites.
Answer: Weather satellite and International Space Station are Low Earth Orbit satellites. They orbit much closer to the Earth's surface compared to other satellites.
In simple words: Two examples of satellites that fly close to Earth are weather satellites and the International Space Station where astronauts live.

🎯 Exam Tip: Memorize both examples (Weather satellite and ISS) as questions asking for examples usually require both for full credit.

 

Question 5. What is a launch vehicle?
Answer: A rocket used to carry an artificial satellite to a desired height above the earth’s surface and then project it with a proper velocity so that the satellite orbits the earth in the desired orbit is called a launch vehicle. It works on the principle of Newton's third law of motion.
In simple words: A launch vehicle is a powerful rocket that carries a satellite from Earth up into space and places it into its correct path.

🎯 Exam Tip: Make sure to include both key actions: carrying the satellite to a height and projecting it with the correct velocity.

 

Question 6. Name the launch vehicle developed by India.
Answer: The launch vehicle developed by India is known as PSLV, i.e., Polar Satellite Launch Vehicle. It has been highly successful in launching numerous national and international satellites.
In simple words: India's main rocket used to send satellites into space is called the PSLV, which stands for Polar Satellite Launch Vehicle.

🎯 Exam Tip: Write both the abbreviation (PSLV) and its full form (Polar Satellite Launch Vehicle) to ensure you get full marks.

 

Question 1. Write the proper name of the orbits of satellites shown in the following figure with their height from the earth's surface. (Practice Activity Sheet – 4)
Answer: The proper names and heights of the orbits shown in the figure are as follows:
(a) Low Earth Orbit (LEO): height above the earth's surface: 180 km to 2000 km
(b) Medium Earth Orbit (MEO): height above the earth's surface: 2000 km to 35780 km
(c) High Earth Orbit (HEO): height from the earth's surface > 35780 km
In simple words: Satellites circle the Earth at different heights depending on their job. Low orbits are closest to Earth, medium orbits are in the middle, and high orbits are the farthest away.

🎯 Exam Tip: Remember the specific altitude ranges for each orbit type, as examiners frequently ask for these exact numbers in diagram-based questions.

 

Question 2. Explain the need and importance of space missions.
Answer: Man has always been curious about the sun, moon, stars and the world beyond the Earth. Space missions are essential to satisfy this curiosity, help us understand the origin of our solar system, and provide real-time data for weather forecasting, global communication, and national security.
In simple words: Space missions help us explore the universe and learn about other planets. They also make our daily lives easier by powering our GPS, internet, and weather reports.

🎯 Exam Tip: Divide your answer into two parts—scientific exploration and daily-life applications—to make it structured and easy to read.

 

Question 3. What are space expeditions? Explain their need and importance in your own words. (Practice Activity Sheet - 2)
Answer: A mission planned (i) for establishing artificial satellites in the earth’s orbit, using them for research or for the benefit of life, or (ii) for sending a spacecraft to the various components of the solar system or outside is called a space expedition.
Man has always been curious about the sun, moon, stars and the world beyond the earth. Initially, man tried to observe space with the help of telescopes. However, later he dreamt to fly into space and finally succeeded to reach into space. Space missions are now essential to understand the origin and evolution of our solar system as well as to study the Universe beyond the Solar system.
Space missions have given us many benefits and made our life simpler. It is because of space missions that the real-time immediate communication and exchange of information across the globe is now possible. We can receive the abundant information at the desk at our home or office. We also get information about any topic at any time and anywhere at fingertips through the Internet. Besides, the advanced alerts about some natural calamities like cyclones or storms are received through satellites sent as a part of space missions. Satellites have also helped us in entertainment. Programmes, sports events, etc., can be telecast live and can reach millions at a time throughout the world. These advancements have truly transformed human society into an interconnected global community.
Satellite surveillance of the enemy, exploring the reserves of various minerals resources, access to various activities like trade, tourism and navigation, and easy global reach to make world a global village is all possible due to the space missions. Thus, space missions are extremely important in defence, communication, weather forecast, observation, direction determination, etc.
In simple words: A space expedition is a planned journey into space, either by sending satellites to orbit Earth or sending spacecraft to other planets. These missions are important because they help us understand the universe, improve global communication, predict weather disasters, and strengthen national security.

🎯 Exam Tip: Clearly define 'space expedition' first, then list at least 3-4 distinct benefits like communication, weather forecasting, and defense to secure full marks.

Space missions have given us many benefits and made our life simpler. It is because of space missions that the real-time immediate communication and exchange of information across the globe is now possible. We can receive the abundant information at the desk at our home or office. We also get information about any topic at any time and anywhere at fingertips through the Internet. Besides, the advanced alerts about some natural calamities like cyclones or storms are received through satellites sent as a part of space missions. Satellites have also helped us in entertainment. Programmes, sports events, etc., can be telecast live and can reach millions at a time throughout the world.

Satellite surveillance of the enemy, exploring the reserves of various minerals resources, access to various activities like trade, tourism and navigation, and easy global reach to make world a global village is all possible due to the space missions. Thus, space missions are extremely important in defence, communication, weather forecast, observation, direction determination, etc.

 

Question 4. What are the objectives of the space mission?
Answer: Man initially tried to satisfy his curiosity to know the world and universe beyond the earth with the help of telescopes. However, it has some obvious limitations and to overcome these limitations, man later ventured into space missions. These endeavors have greatly expanded our understanding of the cosmos. Space missions carried out by man were aimed at four specific objectives:
1. To launch artificial satellites in the earth’s orbit for study and research.
2. To launch artificial satellites in the earth’s orbit for various purposes like telecommunication, weather forecast, radio and TV programme transmission, etc.
3. To send artificial satellites beyond the earth’s orbit to observe, study and collect the information from other planets, meteors, meteoroids, asteroids and comets.
4. To sense and understand space beyond the solar system.
In simple words: Space missions help us put satellites into orbit to study Earth, improve communication, and explore other planets and deep space.

🎯 Exam Tip: Clearly list all four objectives of space missions in bullet points or numbered lists to ensure you get full marks.

 

Question 5. Write on significant space missions carried out by man.
Answer: Man has carried out many space missions within and beyond the earth’s orbit. Significant space missions are as follows:
(1) Space missions within the earth’s orbit: Man has so far sent many artificial satellites of various types in the earth’s orbit. These satellites have made the life of man simpler. Besides, it has also helped us in resource management, communication, disaster management, etc.

(2) Moon missions : Moon is the natural satellite , of the earth and it is the nearest celestial body to us. Naturally, our initial space missions were directed to the moon. As of now, only Russia, USA, European Union, China, Japan and India have successfully undertaken . moon missions. Russia executed 15 moon missions between 1959 and 1976. Of these, last 4 missions brought the stone samples from the moon for study and analysis. However all these missions were unmanned. USA executed moon missions between 1962 and 1972. Some of these missions were unmanned.

However, the historic moon mission took place on 20^th July, 1969, when American astronaut Neil Armstrong became the first human to step on the moon. India has undertaken the moon mission. Indian Space Research Organisation (ISRO) successfully launched Chandrayaan-I and placed it in orbit of the moon. It sent useful information to the earth for about a year. The most important discovery made during the mission was the presence of water on moon’s surface. India was the first country to discover this.

(3) Mars mission: The second nearest celestial object to the earth is Mars and many nations sent spacecraft towards it. But only few of them have been successful. However, the performance of Mangalyaan, the Indian spacecraft sent by ISRO towards Mars, was remarkable. Mangalyaan was launched in November 2013 and was placed in the orbit of Mars successfully in September 2014. This historic mission made India the first nation to reach Mars orbit on its very first attempt. It has obtained useful information about the surface and atmosphere of Mars.

(4) Space missions to other planets: Other than moon and Mars missions, many other space missions were undertaken for studying other planets. Some spacecraft orbited the planets, some landed on some planets, and some just observed the planets,
In simple words: Humans have sent many spacecraft into space to study our solar system. These missions include satellites orbiting Earth, landing on the Moon, reaching Mars, and exploring other distant planets to gather valuable scientific data.

🎯 Exam Tip: To score full marks, clearly categorize the missions into four groups: Earth's orbit, Moon, Mars, and other planets, and remember to highlight India's unique achievements in these missions.

 

Question 6. Bring out the contribution of India’s space missions.
Answer: Successful space missions as well as scientific and technological accomplishments by India in space technology have made a significant contribution in the national and social development of our country. These advancements have placed India among the leading nations in space exploration.

India has indigenously built various launchers and these launchers can put the satellites having the mass up to 2500 kg in orbit. Indian Space Research Organisation (ISRO) has designed and built two important launchers: Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV).

Many satellites in INSAT and GSAT series are active in telecommunication, television broadcasting, meteorological services, disaster management and in monitoring and management of natural resources. EDUSAT is used specifically for education while satellites in IRNSS series are used for navigation. Thumba, Sriharikota and Chandipur are Indian satellite launch centers.

Vikram Sarabhai Space Centre at Thiruvananthapuram, Satish Dhawan Space Research Centre at Sriharikota and Space Application Centre at Ahmedabad are space research organizations of India.
In simple words: India has made great progress in space technology by building its own rocket launchers and satellites. These satellites help us with TV, weather reports, education, and maps, making daily life much easier.

🎯 Exam Tip: Mention key launchers like PSLV and GSLV, and highlight satellite series like INSAT and GSAT to score full marks.

 

Question 7. What is meant by space debris? Why is there need to manage the debris? (March 2019)
Answer: Space debris refers to non-functional man-made objects in space, primarily in Earth's orbit, which no longer serve any useful purpose. This includes non-functional satellites, parts of launcher rockets, and pieces of debris left behind after collisions. Developing technologies to clean up this clutter is becoming a global priority.

There is an urgent need to manage space debris because these floating pieces travel at very high speeds. Even a tiny piece of debris can collide with functional satellites or spacecraft, causing severe damage or destroying them completely. As the amount of debris increases, it poses a major threat to future space missions and communication networks.
In simple words: Space debris is the junk left behind by humans in space, like broken satellites. We need to clean it up because it can crash into working satellites and destroy them.

🎯 Exam Tip: Clearly define what space debris consists of and explain the risk of collision with active satellites as the main reason for management.

In a space nonessential objects such as the parts of launchers and satellites, revolving around the earth are called the debris in space.

The debris can be harmful to the artificial satellites. It can collide with the satellite or spacecrafts and damage them. Therefore the future of artificial satellites or spacecrafts are in danger. Hence, it is necessary to manage the debris.

Solve the Following Examples/Numerical Problems:

[Note: See the textbook for the relevant data.]

 

Question 1. If the mass of a planet is 8 times that of the earth and its radius is twice the radius of the earth, what will be the escape velocity for that planet? (Escape velocity for the earth = 11.2 km/s) (Practice Activity Sheet – 2)
Answer:
Given:
Mass of the planet \( (M_P) = 8M_E \)
Radius of the planet \( (R_P) = 2R_E \)
Escape velocity for the earth \( (v_{escE}) = 11.2 \text{ km/s} \)
Escape velocity for the planet \( (v_{escP}) = ? \)

Formula:
\( v_{esc} = \sqrt{\frac{2GM}{R}} \)

Calculation:
\( v_{escP} = \sqrt{\frac{2GM_P}{R_P}} \)
\( \implies v_{escP} = \sqrt{\frac{2G(8M_E)}{2R_E}} \)
\( \implies v_{escP} = \sqrt{4 \times \frac{2GM_E}{R_E}} \)
\( \implies v_{escP} = \sqrt{4} \times \sqrt{\frac{2GM_E}{R_E}} \)
\( \implies v_{escP} = 2 \times v_{escE} \)
\( \implies v_{escP} = 2 \times 11.2 \)
\( \implies v_{escP} = 22.4 \text{ km/s} \)
The escape velocity for the planet is \( 22.4 \text{ km/s} \). This shows that a higher planetary mass significantly increases the escape velocity despite a larger radius.
In simple words: Escape velocity is the speed needed to break free from a planet's gravity. Since this planet is much heavier, its gravity is stronger, meaning an object must travel twice as fast (\( 22.4 \text{ km/s} \)) to escape it compared to Earth.

🎯 Exam Tip: Always write down the given values with their respective symbols first, as this helps in choosing the correct formula and prevents calculation errors.

 

Question 2. Calculate the critical velocity (\(v_c\)) of the satellite to be located at 35780 km above the surface of the earth.
Answer:
Given:
Height of the satellite above the earth's surface \( (h) = 35780 \text{ km} = 3.578 \times 10^7 \text{ m} \)
Radius of the earth \( (R) = 6400 \text{ km} = 6.4 \times 10^6 \text{ m} \)
Mass of the earth \( (M) = 6 \times 10^{24} \text{ kg} \)
Gravitational constant \( (G) = 6.67 \times 10^{-11} \text{ N}\cdot\text{m}^2/\text{kg}^2 \)

Formula:
\( v_c = \sqrt{\frac{GM}{R+h}} \)

Calculation:
First, find the orbital radius \( (r = R + h) \):
\( r = 6400 \text{ km} + 35780 \text{ km} = 42180 \text{ km} = 4.218 \times 10^7 \text{ m} \)
Now, substitute the values into the formula:
\( v_c = \sqrt{\frac{6.67 \times 10^{-11} \times 6 \times 10^{24}}{4.218 \times 10^7}} \)
\( \implies v_c = \sqrt{\frac{40.02 \times 10^{13}}{4.218 \times 10^7}} \)
\( \implies v_c = \sqrt{9.4879 \times 10^6} \)
\( \implies v_c \approx 3.08 \times 10^3 \text{ m/s} = 3.08 \text{ km/s} \)
The critical velocity of the satellite is approximately \( 3.08 \text{ km/s} \). This speed ensures that the satellite remains in a stable geostationary orbit without falling back to Earth.
In simple words: Critical velocity is the exact speed a satellite needs to maintain to stay in its circular orbit around Earth. For a satellite high up at 35,780 km, it needs to travel at about 3.08 kilometers every second to stay in space.

🎯 Exam Tip: Remember to convert the height \( h \) and radius \( R \) from kilometers to meters before substituting them into the formula to keep all units in the SI system.

Question 2. Calculate the critical velocity of a satellite orbiting the Earth at a height of 35780 km.
Answer:
Given:
\( G = 6.67 \times 10^{-11} \text{ N}\cdot\text{m}^2/\text{kg}^2 \)
\( M\text{(Earth)} = 6 \times 10^{24} \text{ kg} \)
\( R\text{(Earth)} = 6.4 \times 10^6 \text{ m} \)
\( h = 35780 \text{ km} = 35780 \times 10^3 \text{ m} \)
\( v_c = ? \)

Critical velocity of the satellite is given by:
\( v_c = \sqrt{\frac{GM}{R+h}} \)

Substituting the values:
\( \implies v_c = \sqrt{\frac{6.67 \times 10^{-11} \times 6 \times 10^{24}}{6.4 \times 10^6 + 35780 \times 10^3}} \)

\( \implies v_c = \sqrt{\frac{6.67 \times 6 \times 10^{13}}{10^3(6400 + 35780)}} \text{ m/s} \)

\( \implies v_c = \sqrt{\frac{40.02 \times 10^{10}}{42180}} \text{ m/s} \)

\( \implies v_c = \sqrt{\frac{400200 \times 10^6}{42180}} \text{ m/s} \)

\( \implies v_c = \sqrt{9.488} \times 10^3 \text{ m/s} \)

\( \implies v_c = 3.08 \times 10^3 \text{ m/s} \)

\( \implies v_c = 3.08 \text{ km/s} \)
This calculated speed ensures that the gravitational pull of the Earth acts precisely as the necessary centripetal force.
In simple words: The critical velocity is the exact speed a satellite needs to maintain in its orbit so that it stays in a stable circular path around the Earth without falling down.

🎯 Exam Tip: Always convert the height \( h \) from kilometers to meters before adding it to the Earth's radius \( R \) to avoid calculation errors.

 

Question 3. In the above example (2) how much time will the satellite take to complete one revolution around the earth?
Answer:
Given:
\( R = 6400 \text{ km} = 6.4 \times 10^6 \text{ m} \)
\( h = 35780 \text{ km} = 3.5780 \times 10^7 \text{ m} \)
\( v = 3.08 \text{ km/s} = 3.08 \times 10^3 \text{ m/s} \)
\( T = ? \)

The time required for the satellite to complete one revolution around the earth is given by:
\( T = \frac{2\pi(R+h)}{v} \)

Substituting the values:
\( \implies T = \frac{2 \times 3.14 \times (6.4 \times 10^6 + 35.78 \times 10^6)}{3.08 \times 10^3} \)

\( \implies T = \frac{2 \times 3.14 \times 42.18 \times 10^6}{3.08 \times 10^3} \)

\( \implies T = \frac{264.89 \times 10^6}{3.08 \times 10^3} \)

\( \implies T \approx 86000 \text{ s} \)

\( \implies T \approx 23.9 \text{ hours} \approx 24 \text{ hours} \)
This specific orbital period is characteristic of geostationary satellites used widely in modern telecommunications.
In simple words: It takes the satellite approximately 24 hours to complete one full round around the Earth, which is the same time the Earth takes to rotate once on its axis.

🎯 Exam Tip: Remember that a satellite with an orbital period of 24 hours is a geostationary satellite, which appears stationary relative to a point on the Earth's surface.

 

Problem 4. Calculate the critical velocity (\(v_c\)) of the satellite to be located at 2000 km above the surface of the earth.
Answer: Refer to the example (2) above. Here, \(h = 2 \times 10^6\text{ m}\) (since \(2000\text{ km} = 2 \times 10^6\text{ m}\)). The critical velocity is calculated using the standard orbital formula, which gives \(v_c = 6902\text{ m/s}\). This specific speed keeps the satellite in a stable circular path around the Earth.
In simple words: Critical velocity is the exact speed a satellite needs to travel so it stays in its circular orbit without falling back to Earth. For a satellite at this height, that speed is 6902 meters per second.

🎯 Exam Tip: Always convert the altitude \(h\) from kilometers to meters (\(1\text{ km} = 10^3\text{ m}\)) before starting your calculations to ensure your units are consistent.

 

Problem 5. In the above example (4), how much time will the satellite take to complete one revolution around the earth?
Answer: Refer to example (3) above. The time period \(T\) is calculated using the orbital period formula, which gives approximately \(7647\text{ s}\). This is equal to \(2\text{ hours } 7\text{ minutes } 27\text{ seconds}\). This duration represents the time required for one complete orbit at this altitude. [Note: For more solved problems and problems for practice, refer Chapter 1 (Gravitation)]
In simple words: This is the time the satellite takes to make one complete trip around the Earth. At 2000 km high, it takes about 2 hours and 7 minutes to go all the way around.

🎯 Exam Tip: To convert seconds into hours, divide by 3600, then convert the remainder into minutes and seconds to get the final formatted time.