Introduction to Space Technology

Space technology refers to the set of tools, equipment, satellites, space stations, rockets, and systems developed to explore, utilize, and observe outer space. It includes all the applications that allow humans to understand space phenomena, communicate across the globe, and monitor Earth for science and security.

Applications span communication, navigation, Earth observation, environmental monitoring, weather forecasting, defense, and scientific exploration.

Orbits and Satellite Types

Understanding space technology begins with understanding orbits, because they define how satellites operate and what missions they serve.

Terms and Concepts related to Satellite Launches and Satellite Orbits

• The terms like Kepler’s laws, geosynchronous orbit, geostationary orbit, polar orbit, PSLV, GSLV, etc. keep on appearing in the news columns whenever there is a satellite launch.
• So, I thought it is better to keep all the related concepts at one place.

Titbit: Russia's Sputnik, the world’s first artificial satellite, was launched in 1957.

Kepler's laws of planetary motion (applicable to satellites also)

• Kepler’s First Law: The orbit of a planet is an ellipse with the Sun at one of the two foci.
• Kepler’s Second Law: A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
• In simple words, the speed of the planet increases as it nears the sun and decreases as it recedes from the sun.

The varying orbital speed of the earth (in the figure, the orbit of the earth is exaggerated)

• Kepler’s Third Law: The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

Hankwang, Wikipedia

• In simple terms,the distance of a planet from the sun determines the time it takes for that planet to revolve around the sun (farther the planet is, greater the orbital period).

Perigee and Apogee

• Most satellites orbit the earth in elliptical patterns.
• When a satellite is at its farthest point from the earth, it is at the apogee of the orbit.
• When a satellite is at its closest point to the earth, it is at the perigee of the orbit.
• In accordance with Kepler’s second law, the satellites are fastest at the perigee and slowest at the apogee.

Satellite Revolution and Orbital Mechanics

Why satellites revolve rather than staying still in space?

• There are two important forces acting on the satellite:
• the gravitational force which will pull the satellite towards earth and
• the centrifugal force (due to revolution) which counters the gravitational pull.

Source

• Revolution causes centrifugal force (the object tends to move away from the centre).
• Higher the speed of the revolving satellite (orbital velocity), higher the centrifugal force.
• Thus, by varying the speed (orbital velocity) of the satellite, we can make the satellite
• fall back to earth by decreasing the orbital velocity (centrifugal force < gravitational force)
• stay in its orbit by adjusting the speed so that the centrifugal force balances the gravitational pull (centrifugal force = gravitational force). (Lower the orbit, higher should be the orbital velocity).
• escape earth’s influence by keeping the orbital velocity above the required speed (centrifugal force > gravitational force).

Types of Satellite Orbits

Low Earth Orbit (LEO: 200-2000 km)

• International Space Station (400 km), the Hubble Space Telescope (560 km) and some observation satellites are all rotating the earth in Low Earth Orbit.
• LEO is high enough to significantly reduce the atmospheric drag yet close enough to observe the earth (remote sensing).
• In LEO, the satellite’s orbital period is much smaller than the earth’s rotational period (24 hours).
• That is, the satellites in LEO complete multiple revolutions in 24 hours (Lower the orbit, higher should be the speed).

Source

What is the speed required to keep a satellite in LEO?

• The speed is dependent on the distance from the centre of the Earth.
• At an altitude of 200 km, the required orbital velocity is a little more than 27,400 kmph.
• In the case of the space shuttle, it orbits the Earth once every 90 minutes at an altitude of 466 km.

Advantages of LEO

• Low Earth Orbit is used for things that we want to visit often, like the International Space Station, the Hubble Space Telescope and some satellites (usually spy satellites and other observation satellites).
• This is convenient for installing new instruments, experiments, and return to earth in a relatively short time.

Disadvantages of LEO

• Atmospheric drag will lead to more fuel consumption and constant speed adjustments.
• A satellite traveling in LEO do not spend very long over any one part of the Earth at a given time.
• Hence, satellites in LEO are not suitable for communication and weather observation and forecasting.

Solution

• One solution is to put a satellite in a highly elliptical orbit (eccentric orbit ― non-geosynchronous).
• The other is to place the satellite in a geosynchronous orbit.

Highly Elliptical Orbits

• Kepler's second law: an object in orbit about Earth moves much faster when it is close to Earth than when it is farther away.
• Perigee is the closest point and apogee is the farthest.
• If the orbit is very elliptical, the satellite will spend most of its time near apogee (the furthest point in its orbit) where it moves very slowly.
• Thus, it can be above a specific location most of the time.

Disadvantages of Highly Elliptical Orbits

• In a highly elliptical orbit, the satellite has long dwell time over one area, but at certain times when the satellite is on the high speed portion of the orbit, there is no coverage over the desired area.

Solution

• We could have two satellites on similar orbits but timed to be on opposite sides at any given time.
• In this way, there will always be one satellite over the desired coverage area at all times.

• If we want continuous coverage over the entire planet at all times, such as the Global Positioning System (GPS satellites are in Medium Earth Orbit though), then we must have a constellation of satellites with orbits that are both different in location and time.
• In this way, there is a satellite over every part of the Earth at any given time.

Satellite constellation (Source)

Geosynchronous Orbits (GSO)

• Another solution to the dwell time problem is to have a satellite whose orbital period is equal to the period of rotation of the earth (24 hrs) (satellite’s revolution is in sync with the earth’s rotation).
• In this case, the satellite cannot be too close to the Earth because it would not be going fast enough to counteract the pull of gravity.
• Using Kepler's third law it is determined that the satellite has to be placed approximately 36,000 km away from the surface of the Earth (~42,000 km from the centre of the Earth) in order to remain in a GSO orbit.
• By positioning a satellite so that it has infinite dwell time over one spot on the Earth, we can constantly monitor the weather in one location, provide reliable telecommunications service, etc.
• The downside of a GSO is that it is more expensive to put and maintain something that high up.

Geostationary Orbit or Geosynchronous Equatorial Orbit (GEO)

• A geostationary orbit or geosynchronous equatorial orbit is a circular geosynchronous orbit above Earth's equator and following the direction of Earth's rotation.
• Because the satellite stays right over the same spot all the time, this kind of orbit is called "geostationary."

Geostationary vs Geosynchronous

Medium Earth Orbits (MEO: 2000-36,000 km)

• Medium Earth Orbits (MEO) range in altitude from 2,000 kms up to the geosynchronous orbit at 36,000 km which includes part of the lower and all of the upper Van Allen radiation belts.
• The Van Allen Radiation Belt is a region of high energy charged particles moving at speeds close to that of light encircling the Earth which can damage solar cells, circuits, and shorten the life of a satellite or spacecraft.
• Practical orbits therefore avoid these regions.

Polar Orbits (PO)

• Satellites in these orbits fly over the Earth from pole to pole in an orbit perpendicular to the equatorial plane.
• This orbit is used in surface mapping and observation satellites since it allows the orbiting satellite to take advantage of the earth's rotation below to observe the entire surface of the Earth as it passes below.
• Pictures of the Earth's surface in applications such as Google Earth come from satellites in polar orbits.

Sun-synchronous orbits (SSO)

• Polar orbit and sun-synchronous orbits are low earth orbits.
• Sun-synchronous orbit is a near polar orbit in which the satellite passes over any given point of the planet's surface at the same local mean solar time.
• When a satellite has a sun-synchronous orbit, it means that the satellite has a constant sun illumination.
• Because of the consistent lighting, the satellites in sun-synchronous orbit are used for remote sensing applications (image the Earth's surface in visible or infrared wavelengths) like imaging, spying

Geostationary Orbits (GEO)

• Satellites in geostationary orbit are located at an altitude of approximately 35,786 km (22,236 miles) above the Earth's equator.
• Their orbital period matches the Earth's rotational period (approximately 23 hours, 56 minutes, 4 seconds), causing them to appear stationary relative to a fixed point on the Earth's surface.
• This unique characteristic makes them ideal for communication satellites (television broadcasting, telephone, internet services) and weather monitoring, as they provide continuous coverage over a large geographical area.
• A single geostationary satellite can cover roughly one-third of the Earth's surface, and three such satellites strategically placed can provide near-global coverage.
• Ground stations can maintain a constant line of sight with these satellites, simplifying antenna tracking.

Geosynchronous Orbits (GSO)

• A geosynchronous orbit is an orbit around Earth with an orbital period that matches Earth's sidereal rotation period (one sidereal day).
• While geostationary orbits are a specific type of geosynchronous orbit (circular and equatorial), a geosynchronous orbit can be inclined or elliptical.
• Satellites in GSO appear to trace a figure-eight pattern in the sky from an observer on Earth, rather than remaining stationary.
• These orbits are also used for communication, especially for providing coverage to higher latitudes where geostationary satellites are less effective due to their equatorial position.

Other Important Orbits

• Molniya Orbit: A highly elliptical orbit with a high inclination (around 63.4 degrees) and a long orbital period (typically 12 hours). It allows satellites to spend a significant amount of time over high-latitude regions, making it suitable for communication and remote sensing in polar areas where GEO satellites are not effective.
• Tundra Orbit: Similar to Molniya but with a higher apogee and a 24-hour period, allowing the satellite to spend even more time over specific high-latitude regions.
• Lagrange Points (L-points): These are five positions in an orbital configuration where a small object, under the influence of two large orbiting bodies, can maintain a stable position relative to them. They are not orbits in the traditional sense but stable points in space.
  • L1: Located between the two large bodies, useful for solar observation (e.g., SOHO, DSCOVR).
  • L2: Located beyond the smaller body, useful for space telescopes as it offers a stable, cold environment away from Earth's heat and light (e.g., James Webb Space Telescope, Planck).
  • L3: Located on the opposite side of the larger body from the smaller body.
  • L4 and L5: Located 60 degrees ahead and behind the smaller body in its orbit, known as Trojan points, often stable for long periods.

Applications of Space Technology

Space technology has permeated various aspects of modern life, offering solutions and advancements across numerous sectors. Its applications are crucial for governance, economic development, and scientific research.

• Communication:
  • Satellite Telephony & Internet: Providing connectivity to remote areas, disaster zones, and for mobile platforms (ships, aircraft).
  • Direct-to-Home (DTH) Television & Radio Broadcasting: Delivering entertainment and information services across vast geographical regions.
  • VSAT (Very Small Aperture Terminal) Networks: Used for corporate communication, banking, and data transfer.
• Navigation and Positioning:
  • Global Navigation Satellite Systems (GNSS): Such as GPS (USA), GLONASS (Russia), Galileo (Europe), BeiDou (China), and India's NavIC (IRNSS). These systems provide precise location, velocity, and time information for various applications including transportation, surveying, mapping, and emergency services.
• Remote Sensing and Earth Observation:
  • Agriculture: Crop health monitoring, yield estimation, precision farming, drought assessment.
  • Forestry: Forest cover mapping, deforestation monitoring, wildfire detection.
  • Water Resources: Glacier monitoring, flood mapping, reservoir management, groundwater exploration.
  • Urban Planning: Urban sprawl analysis, infrastructure development, land use mapping.
  • Environmental Monitoring: Pollution tracking (air, water), biodiversity assessment, climate change studies (sea-level rise, ice cap melting).
  • Geology & Mineral Exploration: Mapping geological structures, identifying potential mineral deposits.
  • Disaster Management: Early warning systems (cyclones, tsunamis), damage assessment, relief operations coordination.
• Meteorology and Climate Studies:
  • Weather Forecasting: Tracking weather patterns, cyclones, and storms, providing crucial data for short-term and long-term forecasts.
  • Climate Research: Monitoring atmospheric composition, ocean temperatures, and ice cover to understand climate change.
• Defense and Security:
  • Surveillance & Reconnaissance: Monitoring borders, strategic installations, and troop movements.
  • Missile Early Warning Systems: Detecting missile launches.
  • Secure Communication: Providing encrypted communication channels for military operations.
  • Navigation for Military Operations: Guiding precision-guided munitions and troop movements.
• Space Exploration and Scientific Research:
  • Planetary Science: Studying other planets, moons, and celestial bodies (e.g., Mars Orbiter Mission, Chandrayaan).
  • Astrophysics: Observing distant galaxies, stars, and phenomena using space telescopes (e.g., Hubble, James Webb).
  • Fundamental Research: Studying microgravity effects, cosmic rays, and the origins of the universe.
• Disaster Management:
  • Early Warning: For cyclones, floods, and tsunamis.
  • Damage Assessment: Rapid mapping of affected areas to guide relief efforts.
  • Resource Mobilization: Aiding in the deployment of rescue teams and resources.

Indian Space Program (ISRO)

India's space program, spearheaded by the Indian Space Research Organisation (ISRO), has made significant strides, establishing India as a major spacefaring nation. Its focus has been on self-reliance and using space technology for national development.

• Founding Principles: Established in 1969, ISRO's vision is to harness space technology for national development while pursuing planetary exploration and space science research.
• Key Milestones:
  • Aryabhata (1975): India's first satellite, launched by the Soviet Union.
  • SLV-3 (1980): India's first indigenous satellite launch vehicle, successfully launched Rohini satellite.
  • ASLV (Augmented Satellite Launch Vehicle): Developed to demonstrate technologies for future launch vehicles.
  • PSLV (Polar Satellite Launch Vehicle): India's workhorse rocket, known for its reliability and ability to launch multiple satellites into various orbits (LEO, SSO). It has successfully launched Chandrayaan-1, Mars Orbiter Mission, and numerous foreign satellites.
  • GSLV (Geosynchronous Satellite Launch Vehicle): Designed to launch heavier communication satellites into GTO/GEO. GSLV Mk-III (now LVM3) is India's most powerful rocket, capable of launching 4-ton class satellites into GTO and is crucial for Gaganyaan.
• Major Missions and Achievements:
  • INSAT Series: India's largest domestic communication satellite system, providing services for telecommunications, broadcasting, meteorology, and search and rescue.
  • IRS Series: Indian Remote Sensing satellites, forming one of the largest constellations of remote sensing satellites globally, providing data for various applications.
  • Chandrayaan-1 (2008): India's first lunar mission, which confirmed the presence of water molecules on the Moon.
  • Mars Orbiter Mission (MOM) / Mangalyaan (2013): India's first inter-planetary mission, successfully entering Mars orbit on its first attempt, making ISRO the fourth space agency to achieve this.
  • Chandrayaan-2 (2019): India's second lunar mission, comprising an orbiter, lander (Vikram), and rover (Pragyan). The orbiter is fully functional, while the lander had a hard landing.
  • Chandrayaan-3 (2023): Successful soft landing of Vikram lander and deployment of Pragyan rover on the lunar south pole, making India the fourth nation to achieve a soft landing and the first to reach the lunar south pole.
  • NavIC (Navigation with Indian Constellation): India's independent regional navigation satellite system, providing accurate real-time positioning and timing services over India and a region extending up to 1,500 km around it.
  • Aditya-L1 (2023): India's first solar mission, designed to study the Sun from a halo orbit around the Sun-Earth L1 Lagrange point.
  • Gaganyaan (Upcoming): India's first human spaceflight mission, aiming to send astronauts into low Earth orbit.
  • NISAR (NASA-ISRO Synthetic Aperture Radar) (Upcoming): A joint Earth-observing mission with NASA, designed to observe and measure changes in Earth's ecosystems, ice mass, vegetation biomass, sea level rise, and natural hazards.
• Recent Policy Initiatives:
  • Indian Space Policy 2023: Aims to liberalize the space sector, encourage private sector participation, and enable ISRO to focus on R&D, advanced technologies, and human spaceflight.
  • IN-SPACe (Indian National Space Promotion and Authorisation Centre): An autonomous nodal agency under the Department of Space to promote, authorize, and supervise private sector space activities.
  • NewSpace India Limited (NSIL): A Public Sector Undertaking (PSU) under the Department of Space, mandated to transfer ISRO's technologies to industry and promote commercialization of Indian space products and services.

Challenges and Future Directions in Space Technology

Despite rapid advancements, space technology faces several challenges, while also opening up new avenues for innovation and exploration.

• Space Debris:
  • Increasing number of defunct satellites, rocket stages, and fragments pose a significant collision risk to operational satellites and spacecraft.
  • Mitigation strategies include designing satellites for de-orbiting, active debris removal, and improved space situational awareness.
• Space Traffic Management:
  • Congestion in popular orbits (LEO, GEO) due to mega-constellations (e.g., Starlink) and increasing number of launches.
  • Need for robust international regulations and coordination mechanisms to prevent collisions and ensure sustainable use of space.
• Funding and Resources:
  • Space missions are capital-intensive, requiring substantial financial investment and skilled human resources.
  • Balancing national priorities with ambitious space exploration goals remains a challenge for many nations.
• International Cooperation and Competition:
  • Space is increasingly a domain of geopolitical competition, with nations vying for technological superiority and strategic advantage.
  • However, complex missions often necessitate international collaboration (e.g., ISS, NISAR).
• Dual-Use Technology:
  • Many space technologies have both civilian and military applications, raising concerns about weaponization of space and arms control.
• Cybersecurity in Space:
  • Vulnerability of satellite systems to cyberattacks, which could disrupt critical services (communication, navigation) or compromise national security.
• Sustainability and Environmental Impact:
  • Environmental impact of rocket launches (emissions) and the disposal of space hardware.
  • Need for greener propulsion systems and responsible space debris management.

Way Forward / Conclusion:

• Promoting International Collaboration: Foster global partnerships for large-scale missions, resource sharing, and addressing common challenges like space debris and climate change monitoring.
• Strengthening Domestic Capabilities: Invest in R&D, skill development, and infrastructure to build a robust indigenous space industry, reducing reliance on foreign entities.
• Developing Sustainable Practices: Prioritize the development and implementation of eco-friendly propulsion systems, active debris removal technologies, and responsible satellite deployment strategies.
• Establishing Clear Space Governance: Work towards international treaties and norms for the peaceful and responsible use of outer space, addressing issues like weaponization and resource exploitation.
• Leveraging Space for Socio-Economic Development: Continuously explore and expand the applications of space technology for societal benefits, including disaster management, rural connectivity, education, and healthcare.
• Ensuring Cybersecurity: Develop robust cybersecurity frameworks and technologies to protect critical space assets from malicious attacks.

Frequently Asked Questions (FAQs):

Q1: What is the primary objective of India's Gaganyaan mission?

A1: The primary objective of the Gaganyaan mission is to demonstrate India's capability to send humans to low Earth orbit (LEO) on an Indian launch vehicle and bring them back safely to Earth.

Q2: How does space technology contribute to disaster management?

A2: Space technology aids disaster management through satellite-based remote sensing for early warning (e.g., cyclones, floods), monitoring disaster-affected areas, assessing damage, and facilitating communication in disrupted regions.

Q3: What are the main challenges in space debris management?

A3: The main challenges include the sheer volume of debris, the high velocities at which they travel (posing collision risks), the difficulty and cost of tracking small objects, and the lack of universally agreed-upon international regulations for active debris removal.

Multiple Choice Questions (MCQs):

1. Which of the following is NOT a direct application of remote sensing technology?

   1. Crop yield estimation
   2. Weather forecasting
   3. Global Positioning System (GPS) navigation
   4. Forest cover mapping

   Answer: c) Global Positioning System (GPS) navigation

2. Consider the following statements regarding India's space program:

   1. PSLV is primarily used for launching heavier communication satellites into Geostationary Transfer Orbit (GTO).
   2. GSLV is known as the 'workhorse' launch vehicle for launching Earth Observation Satellites into Low Earth Orbit (LEO).

   Which of the statements given above is/are correct?

   1. 1 only
   2. 2 only
   3. Both 1 and 2
   4. Neither 1 nor 2

   Answer: d) Neither 1 nor 2 (PSLV is the workhorse for LEO/SSO, GSLV for GTO/heavier satellites)

Mains Practice Question:

Discuss the multi-faceted contributions of space technology to India's socio-economic development. What are the key challenges that need to be addressed to further harness its potential? (250 words)