All questions of Space Technology for BPSC (Bihar) Exam

C

Homi Bhabha was the founding chairman of the Department of Atomic Energy (DAE) in India, as mentioned in the provided text.

The primary driving force behind the expansion of the universe is Dark Energy.

Explanation:

1. Introduction:
The expansion of the universe refers to the phenomenon where the distance between galaxies and other cosmic structures is constantly increasing over time. This observation was first made by Edwin Hubble in the 1920s and has since been confirmed by various astronomical observations.

2. Dark Energy:
Dark Energy is a hypothetical form of energy that is believed to permeate all of space and is responsible for the accelerated expansion of the universe. It is called "dark" because it does not interact with light or other electromagnetic radiation, making it difficult to detect directly.

3. Discovery of Dark Energy:
The existence of Dark Energy was first proposed in the late 1990s when astronomers observed that distant supernovae were fainter than expected, indicating that the expansion of the universe is accelerating. This discovery was awarded the Nobel Prize in Physics in 2011.

4. Role of Dark Energy:
Dark Energy acts as a repulsive force that counteracts the gravitational attraction between galaxies and other cosmic structures. While gravity tends to pull objects together, Dark Energy pushes them apart, causing the expansion of the universe to accelerate over time.

5. Understanding Dark Energy:
Despite its importance, Dark Energy remains poorly understood. It is often associated with the cosmological constant, a term introduced by Albert Einstein in his general theory of relativity. The cosmological constant represents a constant energy density in space, which can drive the accelerated expansion.

6. Proportion of Dark Energy:
Dark Energy is believed to account for about 68% of the total energy content of the universe, with Dark Matter accounting for about 27% and ordinary matter making up the remaining 5%. This means that Dark Energy is the dominant factor influencing the expansion of the universe.

7. Future of the Universe:
The presence of Dark Energy and its acceleration of the universe's expansion have significant implications for the future of the cosmos. It is believed that as the universe continues to expand, galaxies will become more and more separated, eventually leading to a "Big Freeze" scenario where the universe becomes cold and dark.

Conclusion:
In conclusion, Dark Energy is the primary driving force behind the expansion of the universe. Its repulsive nature counteracts gravitational attraction and causes the acceleration observed in the expansion. While Dark Energy remains a mysterious phenomenon, further research and observations are ongoing to better understand its nature and implications for the future of the universe.

Liquid Propellants
Liquid propellant rocket engines store fuel and oxidizer separately in tanks and combine them in a combustion chamber to produce thrust. This type of propulsion system is commonly used in modern rockets due to its efficiency and controllability.

How it works
- In a liquid propellant rocket engine, the fuel and oxidizer are stored in separate tanks.
- The fuel and oxidizer are pumped into a combustion chamber where they mix and ignite to produce high-pressure gases.
- The gases are expelled through a nozzle at the back of the rocket, producing thrust that propels the rocket forward.

Advantages
- Liquid propellant engines offer precise control over thrust, allowing for greater maneuverability and efficiency.
- They can be throttled up or down during flight, providing flexibility in mission planning.
- Liquid propellants generally offer higher specific impulse compared to solid propellants, resulting in better overall performance.

Disadvantages
- Liquid propellant rocket engines are more complex and expensive to design and manufacture compared to solid propellant engines.
- They require more maintenance and ground support equipment due to the need for fueling and pressurization systems.
- Handling and storing liquid propellants can be hazardous and require careful safety measures.
In conclusion, liquid propellant rocket engines are a popular choice for modern rockets due to their efficiency, controllability, and performance advantages. They play a crucial role in space exploration and satellite deployment missions.

Reconnaissance Satellites:
Reconnaissance satellites are used for military purposes and have their performance and operation kept secret. These satellites are specifically designed to gather intelligence, surveillance, and reconnaissance data for military and national security purposes.

Key Points:
- Reconnaissance satellites can provide valuable information about potential threats, monitor enemy activities, and aid in strategic decision-making.
- These satellites are equipped with high-resolution cameras, radar systems, and other advanced sensors to capture detailed images and data.
- The information collected by reconnaissance satellites is crucial for military planning, intelligence analysis, and monitoring of global events.
- The performance and operation of reconnaissance satellites are classified to protect sensitive military information and prevent adversaries from accessing critical data.
- Governments and defense agencies around the world rely on reconnaissance satellites to maintain national security, gather intelligence, and monitor potential threats.
In conclusion, reconnaissance satellites play a vital role in military operations and national security efforts, with their performance and operation being kept secret to maintain their effectiveness and protect sensitive information.

Primary Purpose of Sounding Rockets:

Sounding rockets are suborbital rockets designed for scientific research and data collection in the upper atmospheric regions. They are typically used to probe and study various phenomena in the Earth's atmosphere and beyond.

Purpose of Sounding Rockets:

- Upper Atmospheric Research: The primary purpose of sounding rockets is to probe the upper atmospheric regions, including the ionosphere and thermosphere. These rockets carry scientific instruments and payloads to collect data on atmospheric conditions, radiation levels, and other phenomena.

- Data Collection: Sounding rockets are used to gather data on cosmic rays, solar radiation, magnetic fields, and other atmospheric properties. This data helps scientists better understand the Earth's atmosphere and space environment.

- Testing Instrumentation: Sounding rockets are also used to test new instruments and technologies in a space-like environment. Scientists can validate the performance of their instruments before using them on more expensive satellite missions.

- Quick and Cost-Effective Research: Sounding rockets provide a relatively quick and cost-effective way to conduct scientific research in space. They can be launched on short notice and do not require the long lead times associated with satellite missions.

- Educational Purposes: Sounding rockets are also used for educational purposes, allowing students and researchers to gain hands-on experience in space research and experimentation.

In conclusion, the primary purpose of sounding rockets is to probe the upper atmospheric regions and conduct scientific research to enhance our understanding of the Earth's atmosphere and space environment.

Transformation of INCOSPAR into ISRO
INCOSPAR (Indian National Committee for Space Research) was established in 1962 by the Department of Atomic Energy. It was responsible for coordinating space research activities in India. In 1969, INCOSPAR was transformed into ISRO (Indian Space Research Organisation) following the successful launch of the Indian Space Research Organisation (ISRO) with the vision of harnessing space technology for India's development.

Reasons for the transformation
1. Expansion of activities: With the successful launch of the Aryabhata satellite in 1975, INCOSPAR's activities expanded beyond research to include satellite development and launch capabilities. This expansion required a more structured organization, leading to the transformation into ISRO.
2. National importance: The growing importance of space technology for national development necessitated a dedicated space agency like ISRO to oversee and coordinate all space-related activities in India.
3. International recognition: The transformation into ISRO helped India gain international recognition as a space-faring nation with capabilities in satellite development, launch vehicles, and space exploration.
4. Organizational structure: The transformation into ISRO allowed for the establishment of a more streamlined organizational structure with specialized centers and facilities for various space-related activities.
In conclusion, the transformation of INCOSPAR into ISRO in 1969 marked a significant milestone in India's space exploration journey, leading to the establishment of a world-class space agency with a focus on harnessing space technology for national development.

Introduction:
India's first geostationary experimental communication satellite project was the APPLE (Ariane Passenger Payload Experiment) satellite. It was a collaborative effort between the Indian Space Research Organisation (ISRO) and the European Space Agency (ESA).

Background:
During the 1970s, India was making significant progress in space technology and was keen on launching its own satellite. The APPLE satellite project aimed to test and validate various communication technologies and systems that would be crucial for India's future communication satellites.

Details:
The APPLE satellite was designed to be a multipurpose satellite that would serve as a platform for testing and validating various communication technologies. It was based on the European Space Agency's experimental geostationary satellite, ECS-1.

Objectives:
The main objectives of the APPLE satellite project were as follows:
- To demonstrate and validate the technologies required for communication satellite systems.
- To test and evaluate various communication payloads, including transponders, antennas, and communication systems.
- To provide valuable data and insights for the development of future communication satellites by ISRO.

Launch and Specifications:
The APPLE satellite was launched on June 19, 1981, aboard the Ariane-1 rocket from the Kourou spaceport in French Guiana. It had a launch mass of approximately 670 kg and was placed in a geostationary transfer orbit. The satellite had a design life of one year.

Communication Systems:
The APPLE satellite carried various communication payloads, including a C-band transponder, a S-band transponder, and a Very Long Baseline Interferometry (VLBI) experiment. These payloads helped in testing and validating different communication technologies and systems.

Significance:
The successful launch and operation of the APPLE satellite marked a significant milestone for India's space program. It demonstrated India's capability to develop and launch its own communication satellites and paved the way for future advancements in satellite communication technology.

Conclusion:
The APPLE satellite was India's first geostationary experimental communication satellite project. It played a crucial role in testing and validating various communication technologies and systems, providing valuable data and insights for the development of future communication satellites. The successful launch and operation of APPLE marked a major achievement for India's space program and showcased the country's growing prowess in space technology.

The primary goal of the HysIS satellite is to study the Earth's surface in various electromagnetic regions. The HysIS satellite, also known as the Hyperspectral Imaging Satellite, is an Indian satellite that was launched in November 2018. It is designed to capture images of the Earth's surface using hyperspectral imaging technology.

Hyperspectral imaging is a technique that allows the capture of images in many different wavelengths of the electromagnetic spectrum. Unlike traditional satellite imaging, which captures images in a few broad bands of the spectrum, hyperspectral imaging captures images in hundreds of narrow and contiguous bands. This enables more detailed analysis and interpretation of the data collected.

The HysIS satellite carries a payload of a hyperspectral sensor that captures images in the visible, near-infrared, and shortwave infrared regions of the spectrum. This sensor is capable of capturing images with a resolution of 30 meters and a swath width of 30 kilometers.

By studying the Earth's surface in various electromagnetic regions, the HysIS satellite aims to gather data on various aspects such as land use, vegetation, mineralogy, coastal zones, and snow or ice cover. This data can be used for a wide range of applications including agriculture, forestry, urban planning, disaster management, and environmental monitoring.

The hyperspectral imaging data collected by the HysIS satellite can provide valuable insights into the composition and health of the Earth's surface. For example, it can help identify different types of crops, detect changes in vegetation cover, monitor the health of forests, identify mineral deposits, and track changes in coastal regions.

In addition to its primary goal of studying the Earth's surface, the HysIS satellite also serves as a technology demonstrator for future Indian remote sensing satellites. It provides valuable data and experience that can be used for the development of more advanced satellite systems in the future.

Overall, the primary goal of the HysIS satellite is to study the Earth's surface in various electromagnetic regions using hyperspectral imaging technology. This data can be used for a wide range of applications and contribute to our understanding and management of the Earth's resources and environment.

Red Dwarfs make up about 90 percent of the stars in the universe.

- Red Dwarfs: Red Dwarfs are the most common type of star in the universe and are also known as M-type stars. They are relatively small and cool, with a mass that is less than half that of the Sun. Due to their small size and low mass, they have a low luminosity and emit most of their radiation in the infrared part of the electromagnetic spectrum. Red Dwarfs have a long lifespan, with some estimated to live for trillions of years.

- Abundance: Red Dwarfs are abundant in the universe, making up about 90 percent of all stars. They are found in all types of galaxies, from small dwarf galaxies to large spiral galaxies. Their abundance is due to the fact that they are long-lived and have a low mass, allowing them to form and exist for a longer period of time compared to other types of stars.

- Characteristics: Red Dwarfs have a relatively low surface temperature, ranging from about 2,200 to 3,500 Kelvin. This low temperature gives them a reddish appearance, hence the name "Red Dwarfs." They have a small size, typically less than half the size of the Sun, and a low luminosity. Their energy is generated through the fusion of hydrogen in their cores, but at a much slower rate compared to larger stars.

- Importance: Red Dwarfs are important in the study of exoplanets and the search for extraterrestrial life. Due to their long lifespan, they provide stable environments for orbiting planets to potentially develop life. The habitable zone around a Red Dwarf, where conditions may be suitable for liquid water to exist, is closer to the star compared to the habitable zone around a star like the Sun. This makes Red Dwarfs prime targets for the search for potentially habitable exoplanets.

In conclusion, Red Dwarfs are the most common type of star in the universe, making up about 90 percent of all stars. They are small, cool, and long-lived, and their abundance has significant implications for our understanding of the universe and the search for life beyond Earth.

Nebulae are primarily composed of hydrogen and helium gas, with some dust and other trace elements. These clouds of gas and dust are the birthplaces of stars.

The Big Bang Theory, as described in the text, states that the universe began as a single point of high-density and high-temperature and has been expanding in all directions ever since.

The primary objective of the Indian Department of Space (DOS) was to promote the development and application of space science and technology for national development, as mentioned in the provided text. DOS aimed to use space technology to assist in various aspects of the nation's growth and progress.

Explanation:

Sun Synchronous Orbit:
Sun-synchronous orbit is a type of polar orbit that allows a satellite to pass over a section of the Earth at the same local solar time each day. This means that the satellite will always cross the equator at the same time, providing consistent lighting conditions for imaging and data collection.

Characteristics of Sun Synchronous Orbit:
- The inclination of the orbit is typically around 98 degrees.
- The satellite crosses the equator at the same local solar time on each pass.
- The orbit precesses due to the gravitational effects of the Earth's oblateness, maintaining the same solar time for each pass.

Advantages of Sun Synchronous Orbit:
- Allows for consistent lighting conditions for Earth observation satellites.
- Provides a predictable and repeatable ground track for data collection.
- Enables efficient use of onboard power systems due to consistent solar illumination.

Applications of Sun Synchronous Orbit:
- Earth observation and remote sensing for environmental monitoring, agriculture, and disaster response.
- Climate research and monitoring of ice caps, oceans, and forests.
- Weather forecasting and atmospheric studies.

In conclusion, a Sun Synchronous Orbit is the type of orbit that allows a satellite to pass over a section of the Earth at the same time of day, making it ideal for various Earth observation and scientific missions.

Explanation:

Astronomical Satellites
Astronomical satellites are specifically designed and used for the observation of distant stars and other objects in space. These satellites are equipped with powerful telescopes and sensors that can capture images and data from great distances in space.

Key points:
- Astronomical satellites orbit in higher altitudes than other types of satellites, allowing them to have a clear view of distant celestial bodies.
- They are used by astronomers and scientists to study the universe, gather data on stars, planets, galaxies, and other cosmic phenomena.
- These satellites play a crucial role in advancing our understanding of the universe and expanding our knowledge of space beyond what is observable from Earth.
- Examples of astronomical satellites include the Hubble Space Telescope, Chandra X-ray Observatory, and James Webb Space Telescope.
By using astronomical satellites, scientists can explore the mysteries of the universe and make groundbreaking discoveries in the field of astronomy.

The primary service area of the IRNSS navigation system developed by India extends up to 1500 km from its boundary, as mentioned in the provided text.

Antrix Corporation: Marketing Space Products and Services
Antrix Corporation is the commercial arm of the Indian Space Research Organisation (ISRO) and is responsible for marketing space products and services on behalf of the Indian government. Here is a detailed explanation of how Antrix Corporation operates:

Role of Antrix Corporation:
- Antrix Corporation acts as the marketing arm of ISRO, promoting and selling products and services related to space technology.
- It facilitates international collaborations and partnerships for ISRO, enabling the organization to expand its reach globally.
- The corporation plays a crucial role in commercializing ISRO's space capabilities by offering satellite launch services, transponder leasing, and satellite imagery to customers worldwide.

Services Offered by Antrix Corporation:
- Antrix Corporation provides satellite launch services through ISRO's Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV) platforms.
- The corporation also offers transponder leasing services for communications, broadcasting, and broadband applications.
- Additionally, Antrix Corporation provides remote sensing data and satellite imagery for various applications such as agriculture, disaster management, and urban planning.

International Collaborations:
- Antrix Corporation has established partnerships with several international space agencies, organizations, and commercial entities to enhance cooperation in the space sector.
- Through these collaborations, ISRO and Antrix Corporation have been able to undertake joint satellite missions, technology transfers, and capacity-building initiatives.

Conclusion:
In conclusion, Antrix Corporation plays a vital role in marketing space products and services on behalf of the Indian government. By leveraging ISRO's expertise and capabilities, the corporation facilitates the commercialization of space technology and fosters international collaborations in the space sector.

The electron has an antiparticle called the antielectron (positron) with the same mass but opposite electrical charge.

Accumulation of material from a companion star

In a binary star system, a nova event on the surface of a white dwarf is triggered by the accumulation of material from a companion star. This process occurs in a close binary system where the white dwarf and the companion star are gravitationally bound to each other.

Binary Star System:
- A binary star system consists of two stars orbiting around a common center of mass. In a close binary system, the stars are located in close proximity to each other.
- The more massive star in the system evolves faster and eventually becomes a white dwarf, while the less massive star may still be in its main sequence phase.

Accretion of Material:
- The white dwarf in a close binary system has a strong gravitational pull. As the companion star evolves, it expands and starts transferring material onto the white dwarf.
- The transferred material forms an accretion disk around the white dwarf, composed of gas and dust.
- This material gradually spirals inward due to the gravitational attraction of the white dwarf.

Thermonuclear Runaway:
- As the accreted material accumulates on the surface of the white dwarf, it increases the pressure and temperature in the layer.
- When the temperature reaches a critical point, a thermonuclear runaway reaction is triggered. This reaction involves the fusion of hydrogen into helium.
- The sudden release of a large amount of energy from the thermonuclear reaction causes an explosive eruption on the surface of the white dwarf.

Nova Event:
- The explosion, known as a nova, results in a temporary increase in brightness of the white dwarf by several magnitudes. The nova event can last for a few days to several weeks.
- The explosion ejects the accumulated material into space, forming a shell of gas and dust around the white dwarf.
- After the nova event, the white dwarf gradually returns to its normal state and starts accumulating material again for future eruptions.

Conclusion:
In a binary system, a nova event on the surface of a white dwarf is triggered by the accumulation of material from a companion star. The transferred material forms an accretion disk, which eventually leads to a thermonuclear runaway reaction and an explosive eruption on the surface of the white dwarf.

C-band is known for being less susceptible to rain fade compared to other satellite frequency bands such as S-band, L-band, and Ku-band. Rain fade refers to the attenuation or loss of signal strength that occurs when rain or other atmospheric conditions interfere with the transmission of electromagnetic waves between the satellite and the ground station.

The reasons why C-band is less susceptible to rain fade are as follows:

1. Lower Frequency:
- C-band operates at a lower frequency range of around 4 to 8 GHz.
- Lower frequencies have longer wavelengths, which allows them to penetrate raindrops more effectively.
- Raindrops have a smaller impact on the signal at lower frequencies, resulting in less attenuation.

2. Absorption by Oxygen:
- C-band experiences less absorption by atmospheric gases, particularly oxygen.
- Oxygen molecules in the atmosphere absorb electromagnetic waves at higher frequencies, such as Ku-band and Ka-band.
- This absorption leads to a higher level of attenuation, especially during heavy rainfall.

3. Scattering Effects:
- C-band experiences less scattering of the transmitted signal due to raindrops.
- Scattering occurs when the electromagnetic waves interact with the raindrops and deviate from their original path.
- At higher frequencies, such as Ku-band, scattering is more significant, leading to increased signal loss.

4. Availability of Backup Frequencies:
- In addition to the above factors, C-band is also advantageous as it has a larger bandwidth allocation.
- This allows for the provision of backup frequencies within the C-band spectrum.
- If rain fade occurs on a particular frequency, the satellite operator can switch to a different frequency within the C-band to maintain signal continuity.

Overall, the combination of lower frequency, reduced absorption by atmospheric gases, minimal scattering effects, and availability of backup frequencies make C-band less susceptible to rain fade compared to other frequency bands commonly used for satellite communications.

The answer is option 'B', L-band.

The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to users all around the world. It relies on a network of satellites orbiting the Earth to transmit signals that can be received by GPS receivers.

GPS carriers use the L-band frequency band for transmitting their signals. Here is an explanation of why L-band is chosen for GPS carriers:

Frequency Band Characteristics:
- Different frequency bands have different characteristics in terms of signal propagation, interference, and antenna size requirements.
- The L-band frequency range falls between 1 to 2 GHz, which is in the microwave region of the electromagnetic spectrum.
- Microwave frequencies are commonly used for satellite communication due to their ability to penetrate the Earth's atmosphere and experience less interference from weather conditions.

Advantages of L-band for GPS:
1. Signal Penetration: L-band signals have a good ability to penetrate through various obstacles such as buildings and tree canopies. This makes them suitable for providing accurate positioning information even in urban areas or dense forests.

2. Interference: L-band signals experience less interference from atmospheric conditions, such as rain or fog, compared to higher frequency bands. This ensures reliable signal reception and reduces the chances of signal degradation.

3. Antenna Size: The wavelength of L-band signals is relatively large compared to higher frequency bands. This allows for the design of smaller and more compact GPS antennas, making them easier to integrate into handheld devices or vehicles.

4. Availability of Frequencies: The L-band frequency range is allocated specifically for satellite navigation and positioning systems like GPS. This ensures that the frequencies are reserved and not heavily congested with other communication systems.

5. Global Coverage: The GPS system is designed to provide global coverage, and L-band signals are capable of traveling long distances without significant degradation. This allows GPS receivers to obtain accurate positioning information anywhere on Earth.

In conclusion, the L-band frequency band is used by GPS carriers due to its advantages in signal penetration, interference resistance, compact antenna design, availability of frequencies, and global coverage capabilities.

Primary Application of X-band Satellite Frequency
The X-band frequency, which ranges from 8 to 12 GHz, is widely utilized in various applications, but its primary use is in military radar systems.

Military Radar
- X-band frequencies are particularly effective for military radar due to their ability to provide high-resolution imaging.
- These frequencies allow for precise target detection and tracking, which is crucial in defense operations.
- The shorter wavelength of X-band enables better performance in adverse weather conditions, making it suitable for tactical applications.

Advantages of X-band for Military Use
- **High Resolution**: The X-band radar can produce detailed images, essential for identifying and distinguishing between different targets.
- **Penetration Capabilities**: It can penetrate through certain obstacles like foliage, making it effective for surveillance and reconnaissance.
- **Mobility**: X-band systems are often deployed on mobile platforms, such as ships and aircraft, enhancing their operational flexibility.

Other Applications
While military radar is the primary application, X-band frequencies are also used in:
- **Satellite Communication**: Used for transmitting data over short distances.
- **Weather Forecasting**: Employed in meteorological satellites for gathering data on atmospheric conditions.
- **Radio Communications**: Utilized in some forms of terrestrial and satellite communications, though less commonly than other bands.
In summary, although X-band frequencies serve multiple purposes, their distinct advantages make them vital for military radar applications, ensuring effective surveillance, target tracking, and operational readiness.

The Indian Space Research Organization (ISRO) is responsible for India's space endeavors, as mentioned in the provided text.

Purpose of ISRO's Chandrayaan Mission
The Indian Space Research Organisation (ISRO) initiated the Chandrayaan mission with a clear focus on lunar exploration. The mission is primarily aimed at advancing scientific knowledge about the Moon, making option 'C' the correct choice.
Key Objectives of Chandrayaan Mission
- Unmanned Lunar Exploration: Chandrayaan aims to conduct detailed surveys of the Moon's surface, including its topography, mineral composition, and the presence of water ice in polar regions.
- Understanding Lunar Geology: The mission seeks to study the Moon's geological features and processes, providing insights into its formation and evolution.
- Search for Water: One of the standout objectives is to locate and analyze water deposits, which are crucial for future lunar exploration and potential human habitation.
- Conducting Experiments: Chandrayaan carries scientific instruments to perform experiments that will enhance our understanding of the Moon's atmosphere and exosphere.
Significance of Lunar Missions
- Technological Advancements: The Chandrayaan mission allows ISRO to develop and refine advanced technology for space missions, contributing to India's growing capabilities in space exploration.
- International Collaboration: The mission fosters opportunities for collaboration with other space agencies, enhancing global scientific knowledge.
- Inspirational Impact: Successful lunar missions inspire the next generation of scientists and engineers in India, promoting interest in STEM fields.
In conclusion, the Chandrayaan mission is a pivotal step in India's space exploration efforts, focusing on unmanned lunar missions to enhance our understanding of the Moon and lay the groundwork for future exploration initiatives.

Explanation:

The correct answer is option 'C', the Main Sequence Star.

A star goes through several stages in its life cycle, starting from its formation as a protostar to its eventual death as a white dwarf, neutron star, or black hole. The stage characterized by the fusion of hydrogen to form helium in the star's core is known as the Main Sequence.

Main Sequence Star:
- A main sequence star is a stable phase in the life cycle of a star, where it spends the majority of its lifetime.
- During this stage, a star is in a state of hydrostatic equilibrium, where the inward gravitational force is balanced by the outward pressure generated by nuclear fusion in its core.
- The main source of energy in a main sequence star is the fusion of hydrogen nuclei (protons) to form helium through a process called nuclear fusion.
- In the core of a main sequence star, high temperatures and pressures cause hydrogen atoms to collide and fuse together, releasing a tremendous amount of energy in the form of light and heat.
- This fusion process, known as hydrogen burning, occurs through a series of nuclear reactions called the proton-proton chain.
- The fusion of hydrogen to form helium in the core of a main sequence star provides the star with a stable source of energy, which keeps it shining brightly and maintains its gravitational equilibrium.
- The energy generated by nuclear fusion in the core is radiated outwards, providing the star with the necessary pressure to counteract the inward force of gravity.
- The mass of a star determines its position on the main sequence. More massive stars have higher core temperatures and pressures, allowing them to fuse hydrogen more rapidly and burn through their fuel supply at a faster rate.

Other Stages in the Life Cycle:
- Protostar: The initial stage of a star's formation, where a dense cloud of gas and dust collapses under its own gravity to form a hot, condensed object.
- Red Giant: A phase that occurs later in a star's life when it exhausts its hydrogen fuel in the core and starts burning helium. The star expands and becomes much larger and brighter.
- White Dwarf: The final stage for low to medium-mass stars, where the exhausted core collapses and the outer layers are expelled, leaving behind a dense, hot core composed mainly of carbon and oxygen.

In conclusion, the stage characterized by the fusion of hydrogen to form helium in the core of a star is the Main Sequence.

Primary Function of Neutrinos in the Study of the Universe: Probing the Early Universe

Neutrinos play a crucial role in the study of the universe, particularly in probing the early universe. They are subatomic particles that are extremely lightweight, electrically neutral, and interact only weakly with matter. Due to these properties, neutrinos can provide valuable information about the early stages of the universe and help scientists understand various phenomena and processes.

1. Neutrinos and the Big Bang
The study of neutrinos can shed light on the early universe, specifically the period immediately following the Big Bang. Neutrinos were produced abundantly during the first few seconds after the Big Bang when the universe was extremely hot and dense. As the universe expanded and cooled, these neutrinos became "frozen" and have persisted since then. By studying the properties of these relic neutrinos, scientists can gain insights into the conditions and dynamics of the early universe.

2. Neutrinos as Cosmic Messengers
Neutrinos can act as cosmic messengers, carrying information about distant astrophysical objects and phenomena. Unlike other particles, neutrinos are not easily absorbed or scattered by matter, allowing them to travel vast distances through space without being significantly affected. This property makes them valuable for studying distant sources such as supernovae, active galactic nuclei, and gamma-ray bursts.

3. Neutrinos and Supernovae
Supernovae, the explosive deaths of massive stars, release an enormous amount of energy and produce a wide range of particles, including neutrinos. Neutrinos are the earliest messengers of a supernova explosion, as they can escape the dense stellar core before other particles. By detecting these neutrinos, scientists can gain crucial information about the inner workings of supernovae, such as the core collapse process and the formation of neutron stars or black holes.

4. Neutrinos and Dark Matter
One of the greatest mysteries in astrophysics is the nature of dark matter, which constitutes a significant portion of the universe's mass. Neutrinos, being weakly interacting particles, were initially considered as potential candidates for dark matter. However, extensive experimental observations have shown that neutrinos have very little mass, making them unsuitable for explaining the observed dark matter. Despite this, studying neutrinos can still provide valuable insights into the properties and behavior of dark matter.

In conclusion, the primary function of neutrinos in the study of the universe is to probe the early universe, providing information about the conditions and dynamics shortly after the Big Bang. Neutrinos also act as cosmic messengers, carrying information about distant astrophysical objects and phenomena. By studying neutrinos, scientists can deepen their understanding of various processes in the universe, including supernovae, dark matter, and the overall evolution of the cosmos.

The Final Stage in the Life Cycle of a Star like the Sun is a White Dwarf

The life cycle of a star like the Sun can be divided into several stages: formation, main sequence, red giant, and white dwarf. The final stage in this life cycle is a white dwarf.

Formation of a Star
Stars like the Sun are formed from massive clouds of gas and dust called nebulae. The force of gravity causes the nebula to collapse, and as it collapses, it forms a dense core called a protostar.

Main Sequence Stage
Once the protostar reaches a certain temperature and density, nuclear fusion begins, and the star enters the main sequence stage. During this stage, the star steadily fuses hydrogen into helium in its core, releasing a tremendous amount of energy. This energy counteracts the gravitational force, maintaining the star's stability.

Red Giant Stage
After spending billions of years in the main sequence stage, a star like the Sun eventually exhausts its hydrogen fuel. As a result, the core contracts and heats up, causing the outer layers of the star to expand and cool. The star then enters the red giant stage. In this stage, the star becomes much larger and brighter, as it starts fusing helium into heavier elements like carbon and oxygen.

White Dwarf Stage
Once the red giant stage ends, the outer layers of the star are expelled into space, forming a beautiful cloud of gas and dust called a planetary nebula. What remains is a hot, dense core known as a white dwarf.

A white dwarf is about the size of the Earth but incredibly dense, with the mass of a star compressed into a small volume. It is composed mainly of carbon and oxygen, and its high temperature is sustained by residual heat from the red giant stage. Without nuclear fusion, the white dwarf gradually cools over billions of years, eventually becoming a cold, dark object known as a black dwarf. However, no black dwarfs have been observed yet, as the universe is not old enough for any white dwarfs to have completed this transition.

In conclusion, the final stage in the life cycle of a star like the Sun is a white dwarf. It is formed after the star goes through the main sequence and red giant stages, and it represents the remnant core of the star after it has shed its outer layers.

Explanation:
Space-based Navigation:
- The GAGAN system in India stands for GPS Aided GEO Augmented Navigation System.
- It is a space-based augmentation system developed by the Indian Space Research Organization (ISRO) in collaboration with the Airports Authority of India (AAI).
- The primary purpose of the GAGAN system is to provide accurate, real-time positioning information for civil aviation.
- It enhances the accuracy and reliability of GPS signals by providing corrections and integrity monitoring over the Indian airspace.
Key Functions:
- Accuracy: GAGAN enhances the accuracy of GPS signals to within a few meters, which is crucial for safe and efficient air navigation.
- Integrity: The system provides integrity information to ensure the safety of the aircraft during critical phases of flight.
- Reliability: GAGAN increases the reliability of GPS signals, reducing the risk of signal degradation or loss.
Benefits:
- Improved Air Navigation: GAGAN helps in improving air navigation by providing precise positioning information to pilots.
- Increased Efficiency: The system enables more efficient routing and landing procedures, leading to fuel savings and reduced emissions.
- Enhanced Safety: By providing accurate and reliable navigation information, GAGAN enhances the safety of air travel in Indian airspace.
Conclusion:
The GAGAN system in India plays a crucial role in space-based navigation, particularly in the aviation sector. Its accurate positioning information, integrity monitoring, and reliability enhancements contribute to safer and more efficient air travel in the Indian airspace.

The main purpose of the Indian National Satellite (INSAT), as mentioned in the text, is to provide telecommunication, television broadcasting, and meteorological services. It plays a vital role in communication and weather forecasting.

Dark Matter is a type of matter that interacts with gravity but does not emit, absorb, or reflect light. It is "dark" because it is invisible to electromagnetic radiation, including light.

Solid propellants are not a type of liquid propellant. They are a separate category of rocket propellants, consisting of a solid mixture that burns to produce thrust.

Negative Matter is a hypothetical type of matter that, if it exists, would have negative mass and negative energy. It is believed to repel normal matter under gravity.

The primary objective of the Indian Department of Space (DOS), as mentioned in the text, is to promote the development and application of space science and technology for national development. It focuses on using space technology for the benefit of the nation.

In Europe, the Ku-band downlink is primarily used for direct broadcast satellite services, such as Astra. This frequency band is commonly associated with satellite television services.

X-band radar frequency sub-bands are primarily used in civil, military, and government institutions for applications such as air traffic control, weather monitoring, maritime vessel traffic control, defense tracking, and more.

The primary purpose of a launch vehicle in space exploration is to transport spacecraft and satellites into space. This allows for various space missions, including satellite deployment, planetary exploration, and scientific research.

The main advantage of hypergolic propellants is that they ignite spontaneously on contact with each other and do not require an ignition source. This feature makes them ideal for spacecraft maneuvering systems.

India launched its GSAT-6 satellite in the S-band to enable multimedia applications for strategic military purposes and societal uses in case of emergencies.

Solid propellant rockets are easier to store and handle compared to liquid propellant rockets. They do not require complex systems for fuel and oxidizer management and can be kept ready for launch for extended periods.

GSLV Mk III has the advantage of being able to launch heavier payloads to Geosynchronous Transfer Orbit (GTO). It can carry payloads of up to 5,000 kg to GTO, making it suitable for launching larger communication satellites.

The Satellite Instructional Television Experiment (SITE), as mentioned in the text, was a large-scale sociological experiment using satellite broadcasting to educate people in Indian villages. It aimed to harness the power of satellite technology for educational purposes.

Aryabhata was the first Indian satellite to be launched into space, as mentioned in the provided text. It was launched on April 19, 1975.

Developing reusable launch vehicles with air-breathing propulsion systems can significantly reduce launch costs and increase efficiency in accessing space. This technology has the potential to make space exploration more cost-effective and accessible.

The Satellite Launch Vehicle (SLV) was the first Indian launch vehicle to achieve successful satellite deployment in orbit. It successfully launched the Rohini satellite in July 1980.

The first satellite launched by ISRO for meteorological purposes was METSAT, which was later named 'Kalpana.' It provided meteorological data and was a precursor to the INSAT systems.

The Ka-band for satellite communication operates in the frequency range of 26–40 GHz. It is used for close-up, high-resolution applications and is commonly employed for communications satellites.

The Polar Satellite Launch Vehicle (PSLV) is often referred to as the "workhorse of ISRO." It has successfully launched missions to the Moon (Chandrayaan-1) and Mars (Mars Orbiter Mission) and numerous other satellites.

The discovery of cosmic microwave background radiation, as mentioned in the text, was crucial evidence in favor of the Big Bang Theory. It provided strong support for the theory's explanation of the universe's origin.

The Space Commission is responsible for formulating policies and overseeing the implementation of the Indian space program, as mentioned in the provided text. It plays a crucial role in guiding the direction of India's space activities.

The purpose of the Thumba Equatorial Rocket Launching Station (TERLS), as mentioned in the text, is to launch sounding rockets and study the upper atmosphere. It is primarily focused on atmospheric research.