Space Missions Class 10 Science Notes Maharashtra State Board
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 a deep curiosity about 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, especially space technology, in the later half of the twentieth century resulted in the development of space crafts making space voyages 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 mission, the objective is to put artificial satellites in orbits around the Earth for research and various other useful applications. The objective of the second type of mission is to send the spacecraft to outer space for close observations and understanding of the objects in the solar system, or even outside the solar system.
The first person to go into 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 the 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 the USA.
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 the Internet. Due to the internet, every piece of information is available at our fingertips. It has become possible to get advance alerts 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 for space missions. Today, space technology is an inevitable part of the 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 satellite. 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 the Soviet Union in 1957 (see figure). Today, more than a 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 the figure. 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 space to perform various functions. Depending on their functions, satellites are classified into the following categories:
Types of Satellites
| Type of Satellite | Function of the Satellite | The Names of Indian Satellite Series and their Launch Vehicles |
| 1. Weather Satellite | Study and prediction of weather. | INSAT and GSAT Launcher: GSLV |
| 2. Communication Satellite | Establish communication between different locations in the world through the use of specific waves. | INSAT and GSAT Launcher: GSLV |
| 3. Broadcast Satellite | Telecasting of television programs. | INSAT and GSAT Launcher: GSLV |
| 4. 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 |
| 5. Military Satellite | Collect information for security aspects. | |
| 6. Earth Observation Satellite | Study of forests, deserts, oceans, and polar ice on the earth’s surface, exploration and management of natural resources, observation and guidance in case of natural calamities like floods and earthquakes. | IRS Launcher: PSLV |
- 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
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 the equator or make some angle with it. To put the satellite in its proper orbit at a 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 (vc) in a tangential direction to the orbit. The satellite then starts revolving around the Earth. The formula for the velocity vc can be derived as below.
If a satellite of mass ‘m’ is revolving around the earth in an orbit of height ‘h’ with speed ‘vc’, then as seen in the chapter on ‘Gravitation’, a centripetal force \(\frac{\mathrm{mv}_{\mathrm{c}}{ }^2}{\mathrm{r}}\) will act on it.
Here, ‘r’ is the orbital radius of the satellite from the center 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.
\(\frac{\mathrm{mv}_{\mathrm{c}}{ }^2}{\mathrm{R}+\mathrm{h}}=\frac{\mathrm{GMm}}{(\mathrm{R}+\mathrm{h})^2}\)
⇒ \(\mathrm{v}_{\mathrm{c}}^2=\frac{\mathrm{GM}}{\mathrm{R}+\mathrm{h}}\)
⇒ \(\mathrm{v}_{\mathrm{c}}=\sqrt{\frac{\mathrm{GM}}{\mathrm{R}+\mathrm{h}}}\) …….(1)
G = Gravitational constant = 6.67 × 10-11 Nm2/kg2
M = Mass of the earth = 6 × 1024 kg
R = Radius of the earth = 6.4 × 106 m = 6400 km
h = Height of the satellite above the earth’s surface
R + h = Radius of the orbit of the 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 concerning 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 around 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.
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 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 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. The figure shows various orbits of satellites.
A group of students from COEP (College of Engineering, Pune) made a small satellite and sent it to 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.
Satellite Launch Vehicles
Satellite launch vehicles are used, to place the satellites in their specific orbits. The functioning of the satellite launch vehicle is based on Newton’s third law of motion. The launch vehicle uses a specific type of fuel. The gas produced due to the combustion of the fuel expands due to its high temperature and is expelled forcefully through the nozzles at the rear side of the launch vehicle. As a reaction to this, a thrust acts on the vehicle, which drives the vehicle high into the space.
The structure of the launch vehicle is decided by the weight of the satellite and the type of satellite orbit. The fuel of the vehicle also depends on these factors. The fuel forms a major portion of the total weight of the launch vehicle. Thus, the vehicle has to carry a large weight of the fuel with it. To overcome this problem, launch vehicles with more than one stage are used. Due to this, the weight of the vehicle can be reduced step by step, after its launching. For example, consider a launch vehicle having two stages. For launching the vehicle, the fuel and engine in the first stage are used. This imparts a specific velocity to the vehicle and takes it to a certain height.
Once the fuel in this first stage is exhausted, the empty fuel tank and the engine are detached from the main body of the vehicle and fall either into the sea or on an unpopulated land. As the fuel in the first stage is exhausted, the fuel in the second stage is ignited. However, the vehicle now contains only one (i.e. the second) stage. The weight is now being reduced, the vehicle can move at a higher speed. Almost all vehicles are made of either two or more stages. As an example, the structure of a Polar Satellite Launch Vehicle (PSLV) developed by ISRO of India is shown in the figure.
The launch vehicles are costly because they can be used only once. USA has, therefore, developed a space shuttle (figure) that returns to the earth except for the fuel tank and can be reused in multiple launches. The ‘rocket’, a type of fire-cracker used in Diwali, is also a sort of launcher. In this rocket, the fuel is ignited using a fuse and the rocket is projected into the sky just like a satellite launcher. Similarly, if a balloon is blown and released with its end open, the air in the balloon is forcefully ejected and the balloon is pushed in the opposite direction. This can be explained using Newton’s third law of motion.
Space Missions away from Earth
As we have seen above, artificial satellites are being used to make our lives more and more enriched. However, in the previous standard, we have learned about how telescopes aboard artificial satellites are used to gather information about various objects in the universe. Similarly, some space missions are used to gain further knowledge about the universe. In these missions, spacecraft are sent to nearby objects in the solar system to observe them more closely. New information has been obtained from such missions and it is helping us to understand the creation and evolution of our solar system.
For such missions, the spacecraft must escape the earth’s gravitational force to travel into outer space. To achieve this, the initial velocity of the moving object must be greater than the escape velocity of the earth as we have learnt in the Chapter on Gravity. Escape velocity on a planet can be obtained using the following formula:
\(\mathrm{v}_{\mathrm{esc}}=\sqrt{\frac{2 \mathrm{GM}}{\mathrm{R}}}\)
G = Gravitational constant = 6.67 × 10-11 Nm2/kg2
M = mass of the planet = 6 × 1024 kg (for earth)
R = Radius of the planet = 6.4 × 106 m (for earth)
\(v_{\text {esc }}=\sqrt{\frac{2 \times 6.67 \times 10^{-11} \times 6 \times 10^{24}}{6.4 \times 10^6}}\)
= 11.18 × 103 m/s
= 11.18 km/s
Thus, if a spacecraft is to escape the earth’s gravitational force to travel to outer space, it must have a minimum velocity of 11.2 km/s.
The astronomical object closest to us is the moon. Light takes 1s to reach from the moon to the earth. It means that if we travel with the speed of light, it will take 1s to reach the moon. However, since a spacecraft travels at a much smaller speed, it takes a longer time to reach the moon. The shortest time taken by a spacecraft to reach the moon, so far, is 8 hours and 36 minutes.
Moon Missions
Since the moon is the closest astronomical object to us, the first space missions to objects in the solar system were the missions to the moon. Such missions have so far been executed by the USA, Soviet Union, European countries, China, Japan, and India. The space crafts in the Luna series sent by the Soviet Union reached near the moon. Luna 2, launched in 1959 was the first such craft. After that, till 1975, 15 space crafts made chemical analyses of the moon and also measured its gravity, density, and radiation. The last four crafts even landed on the moon and brought samples of stones to the moon for analysis in the laboratories. All these missions were unmanned.
America also executed moon missions from 1962 to 1972. The specialty of these missions was that some of these were manned missions. In July 1969, Neil Armstrong became the first human to step on the moon. In 2008, the Indian Space Research Organization (ISRO) successfully launched Chandrayaan-1 and placed it into an orbit around the moon. It sent useful information to Earth for about a year. The most important discovery made during the mission was the presence of water on the moon’s surface. India was the first country to discover this.
Mars Missions
Next to the moon, the astronomical object nearest to the Earth is Mars. Many nations sent spacecraft to Mars. Mars mission is difficult and almost half the missions were unsuccessful. However, ISRO’s performance in this mission is remarkable and we all must be proud of it. The spacecraft ‘Mangalyaan’ made by ISRO using minimum expenses was launched in November 2013 and was placed into orbit around Mars in September 2014. It obtained very useful information about the surface of Mars and the atmosphere around it.
Rakesh Sharma was the first Indian to travel to space. He went into space along with two Russian astronauts under the joint Indo – USSR space program. He stayed in space for 8 days.
Kalpana Chawla obtained her Engineering in Aeronautics degree from Punjab and 1988 obtained her doctorate from the University of Colorado. She was in space for 336 hrs during a research mission. While returning to Earth from space, on 1st February 2003, the Columbia spacecraft exploded and Kalpana perished.
Sunita Williams traveled to the International Space Station in the space shuttle Discovery in 2006. She worked for 29 hrs outside the space station. She created a record by staying for 192 days in space.
Missions to Other Planets
Many missions have been executed to study other planets. In some of these missions, the spacecraft orbited the planets, some landed on the planets and some just passed near the planet and observed them. Additionally, spacecraft have been sent to observe asteroids and comets and they have successfully collected some dust and stones from the asteroids and brought them back to Earth. We are getting very useful information from all these missions clarifying our concepts about the origin and evolution of the solar system.
India and Space Technology
India also has made remarkable progress in the science and technology of launch vehicles. Various types of launch vehicles have been developed to put satellites weighing weight upto 2500 kg, into all types of orbits. PSLV and GSLV are two important launchers. The scientific and technological feats achieved by India in this field have a significant contribution to national and social development. INSAT and GSAT satellite series are activities working in the fields of telecommunication, television broadcasting, and meteorological services. Availability of television, telephone, and internet services all over the nation has been possible due to these satellites only. EDUSAT satellite in this series is used especially in the field of education. IRS satellite series is working for monitoring and management of natural resources and disaster management. To exactly locate the position of any place on the earth’s surface in terms of its precise latitude and longitude, the IRNSS satellite series has been established.
Vikram Sarabhai is considered the father of the Indian space program. His efforts led to the foundation of the Physical Research Laboratory (PRL) at Ahmedabad. In 1962, the Indian government constituted the ‘Indian National Committee for Space Research’ under his Chairmanship, and the first satellite launch center was established at Thumba in 1963. The launching of India’s first satellite ‘Aryabhatta’ into space, was the result of his efforts. He played an important role in the establishment of the Indian Space Research Organization (ISRO).
Space Debris and its Management
In addition to the artificial satellite, some other objects are also revolving around the Earth. It includes non-functional satellites, parts of the launcher detached during launching, and debris generated due to the collision of a satellite with another satellite or any other object in space. According to one estimation made in 2016, there are about 2 crore pieces of length more than 1 cm, revolving around the earth! All this is nothing but the debris in space. This debris can be harmful to artificial satellites. It can collide with these satellites or spacecraft and damage them. This debris is increasing day by day. Soon, it will be difficult to launch new spacecraft. It is, therefore, very essential to manage the debris. Some studies and experiments are being done with this in view. Hope that soon we will have a solution for this problem and that future satellites and spacecraft will not be in danger anymore.
Good Maharashtra State Board Class 10 Science Notes Space Missions can simplify complex concepts and make studying more efficient.