Indian Space Programme

Indian Space Programme

India has one of the world's most effective and active space programmes, with a diverse set of missions and accomplishments in the space sector. The Indian Space Research Organisation (ISRO) is India's primary space agency located in Bangalore. It has made significant contributions in areas such as satellite launch technology, remote sensing, and space exploration, from launching its very first satellite in 1975.

Different Types of Satellite Orbits:

Geosynchronous orbit:

• It is a path around the Earth where the orbital period matches the Earth’s rotation period.
• This path in high Earth orbit(as it is placed at an altitude of 35790 km) is known as a geosynchronous orbit.
• Telecommunications and remote sensing satellites are placed in this orbit.

Geostationary Orbit (GSO):

• It is a geosynchronous orbit with an inclination of zero, i.e. it lies on the same plane as that of the equator. It lies 35,786 km above earth’s equator.
• A satellite in this orbit appears to be stationary as seen from the earth. The geostationary satellite remains at the same position throughout the day.
• Thus, it is used for applications which requires a direct line of communication between the satellite and the receiver(for example-direct tv broadcast).

Geosynchronous Transfer Orbit:

• Geostationary transfer orbit is a temporary orbit. It is an elliptical orbit at a height of 35,786 km.
• Its inclination is nearly the same as the latitude of the location from where a spacecraft is launched.
• It is used to transfer a spacecraft from a low altitude orbit or flight trajectory to geosynchronous or geostationary orbit.

Semi-synchronous orbit :

• It is a path around the Earth where the orbital period is 12 hours.
• These orbits are at a height of 20,200 km(medium-earth orbit/MEO) above the earth’s surface.
• These are near circular orbits and Global Positioning System (GPS) satellites are placed in these orbits.

Polar orbits:

• Polar orbits are the ones that pass over the Earth from its  north pole to the south pole. These orbits mainly take place at low altitudes of between 200 and 1000 km.
• It usually takes around one and a half hours for one rotation. For a satellite in a polar orbit, the earth is rotating below it.
• Thus, it can cover the whole earth in 24 hours. They are used to monitor crops, remote sensing etc.

Sun synchronous Orbits:

• These are polar orbits are synchronous with the Sun. Thus, it passes over the same part of the earth at the same time of the day.
• A satellite in a sun synchronous orbit are usually at an altitude of between 600 and 800 km. Weather monitoring and spy satellites are usually placed in this orbit.

Low Earth Orbit:

• A low Earth orbit is normally at an altitude of less than 1000 km.

Earth Parking Orbit:

• An Earth parking Orbit is a temporary orbit used during the launch of a satellite before the satellite being boosted into its final orbit.

Launch Vehicle

Satellite Launch vehicles are the bedrock of space missions and satellite deployment in space. The satellite missions rely on powerful launch vehicles, also known as rockets, to carry satellites and payloads into space. 

• ISRO's journey into satellite launch vehicles began with the SLV, India's first experimental satellite launch vehicle, in 1980, and later with a more advanced Augmented Satellite Launch Vehicle.
• In 1994, ISRO launched its first PSLV and in 2001, ISRO further advanced the launch vehicle technology to build GSLV, which can take more heavy satellites in the Geosynchronous and Geostationary Orbit.

Sounding rockets

Are one- or two-stage solid-propellant rockets employed to explore the upper atmosphere as well as carry out space research.  Sounding rockets enabled the use of rocket-borne instrumentation to probe the atmosphere in situ.

• The first rockets were two-stage Russian (M-100) and French (Centaure) rockets. ISRO began launching indigenously built sounding rockets in 1965.
• The first sounding rocket was launched in 1963 from Thumba near Thiruvananthapuram, marking the beginning of the Indian Space Programme.
• The Rohini Sounding Rocket (RSR) Programme consolidated all sounding rocket activities in 1975.
• Currently, three operational sounding rocket versions are available, with payloads ranging from 8 to 100 kg and apogees ranging from 80 to 475 km.

Polar Satellite Launch Vehicle (PSLV)

• It is India's third-generation launch vehicle, first successfully launched in October 1994. It is the first Indian launch vehicle to have liquid stages.
• It is a four-stage vehicle with multiple satellite launch capabilities and multiple orbit capabilities.

• PSLV-XL, QL, and DL variants use 6,4,2 solid rocket strap-on motors to supplement the thrust provided by the first stage.
  • Strap-ons, on the other hand, are not used in the core-alone version of PSLV (PSLV-CA).
• Due to PSLV's unmatched reliability, numerous satellites, including satellites from the IRNSS constellation, have been launched into geosynchronous and GEO.
  • Thus, it is regarded as “the workhorse of ISRO” for Low Earth Orbits (LEO).
• Payload capacity: It can carry up to 1,750 kg of payload to 600 km altitude Sun-Synchronous Polar Orbits.
• Numerous Indian and foreign customer satellites have been launched by PSLV. 
  • It successfully launched Chandrayaan-1 in 2008 and Mars Orbiter Spacecraft in 2013.

Geosynchronous Satellite Launch Vehicle (GSLV)

• It is a 4th generation launch vehicle designed to place communication satellites in geostationary transfer orbit using a cryogenic third stage. It was used for launching Chandrayaan-2.
• It is a three-stage vehicle with four liquid strap-ons. Initially, cryogenic stages from Russian GK were used; later, it was developed indigenously.

• Payload capacity: GSLV is capable of placing up to 6 tonnes of payloads in Low Earth Orbits, from heavy satellites to multiple smaller satellites.
  • Further, it is capable of putting a 2,250 kg satellite into Geosynchronous Transfer Orbit (GTO), such as the INSAT and GSAT communication satellites.
• GSLV with indigenous Cryogenic Upper Stage made possible the launch of communication satellites weighing up to 2 tonnes.
  • In comparison to solid and earth-storable liquid propellant rocket stages, a cryogenic rocket stage is more efficient and provides more thrust per kilogramme of propellant burned.

LVM3 (Geosynchronous Satellite Launch Vehicle Mk III)

It is a next-generation launch vehicle of ISRO. Previously it was known as Geosynchronous Satellite Launch Vehicle Mk III (GSLV MkIII).

It is a three-stage vehicle with two solid strap-on motors, one liquid core stage and a high-thrust cryogenic upper stage.

Payload capacity: It is capable of putting the GSAT series' 4-tonne satellites into Geosynchronous Transfer Orbits.

LVM3's powerful cryogenic stage allows it to place payloads of up to 8000 kg into 600 km Low Earth Orbits. Recently, it was used for launching the Chandrayaan-3 mission.

Under Development

ISRO has been advancing its technology to build new satellites according to the need and future prospects such as space stations, manned missions and the launching of small satellites. Following are the satellite launch vehicles of ISRO under development:

• Human Rated Launch Vehicle (HRLV):
  • It will be the modified version of the current heavy-weight LVM-3 launch vehicle.
    • It will be capable of launching the Orbital Module into a 400 km Low Earth Orbit.
  • It will include a Crew Escape System (CES) powered by quick-acting and high-burn rate solid motors.
• Small Satellite Launch Vehicle (SSLV):
  • It is a three-stage launch vehicle with three solid propulsion stages and a terminal stage based on liquid propulsion called the Velocity Trimming Module.
  • It is capable of launching nano, micro and mini satellites up to 500 kg satellite in a 500km planar orbit.
• Reusable Launch Vehicle - Technology Demonstrator (RLV-TD):
  • The RLV-TD's configuration resembles that of an aircraft because it combines the complexity of launch vehicles and aeroplanes.
  • It comprises a nose cap, a fuselage (body), two delta wings, and two vertical tails. Elevons and Rudder, which are symmetrically placed active control surfaces, are also included.
  • In future, it will be scaled up to become the first stage of India’s reusable two-stage orbital launch vehicle.
  • SpaceX has the Falcon 9, one of the most important heaviest reusable launch vehicle.
• Scramjet Engine - TD:
  • A scramjet engine outperforms a ramjet engine by operating at hypersonic speeds and allowing supersonic combustion. The engine uses Hydrogen as fuel and Oxygen from the atmospheric air as the oxidiser.
  • The first experimental mission of the Scramjet Engine towards the realisation of an Air Breathing Propulsion System was successfully conducted in 2016 by ISRO. 
  • India is the fourth country to demonstrate the flight testing of a Scramjet Engine.

Notable Foreign Launch Vehicles

The ISRO has utilised various foreign launch vehicles for launching satellites. Some of the notable foreign launch vehicles are given below:

• Arien 5: It is one of the heavy-lift launchers used by European Space Agency. It is capable of carrying payloads weighing more than 20 metric tons into LEO and over 10 metric tons to geostationary transfer orbit. India has used Arien 5 launch vehicles for launching manby communication and earth observation satellites such as INSAT-3D and GSAT 30.
• Falcon 9: It is the world's first orbital class reusable rocket with two-stages designed and manufactured by SpaceX. It is capable of launching payload of 22 metric tonnes to the Low Earth Orbit and 8 metric tonnes to Geostationary orbit.
• Space Launch System (SLS): It is a super heavy-lift rocket developed by NASA. It is capable of launching a payload of 70 metric tonnes to LEO.
  • It is the only rocket capable of transporting the Orion spacecraft, four astronauts, and large cargo to the Moon in a single mission.
  • It includes both crew and service modules and a launch abort system.
• Soyuz 5: It is one of heaviest launch vehicle of the Russian Space Agency, with capability of launching 17 metric tonnes to the LEO.

Types of satellite

Communication Satellites

Communication satellites are artificial satellites that are used for communication purposes such as telecommunication, broadcasting, etc. They are equipped with a transponder, which relays and amplifies radio telecommunication signals from Earth and retransmits them back to Earth.

Orbits of Communication Satellites

To meet the specific objectives, communication satellites can be placed in different orbits - in Geostationary Earth Orbit as well as in Low Earth Orbit.

• Geostationary Earth Orbit (GEO): Communication satellites are generally placed in geostationary Earth orbit (35786 kilometers above Earth's surface) to be used for telecommunication and broadcast as they offer less disturbance or obstacles.
  • GEO has many relative advantages, such as wide area coverage, stable bandwidth and internet connection, and less power consumption.
  • Hence, GSAT series of ISRO has been placed in GEO to provide telecommunication services such as Broadcasting, internet services, etc.
  • However, the service provided by the GEO Communication satellites has the major disadvantage of “highlatency”.
• Low Earth Orbit (LEO): LEO (160 km to 1000 km) offers increased bandwidth of the radio signal with low latency, which facilitates faster transmission of data. Hence, it has become a natural choice to place a constellation of satellites for high speed internet services, such as:
  • Starlink Project of SpaceX: Constellations of 4,200 plus satellites are placed in LEO at a distance of 550 km.

Applications of Communication Satellites

Communication satellites have brought radical changes to modern society due to their diverse applications.

• Communication and Broadcasting Services: Indian National Satellite (INSAT) system is one of the largest communication satellite systems in the Asia-Pacific region.
• Meteorology: Transponders like C, Extended C, and Ku-bands provide services in meteorology, such as weather forecasting, disaster warning, and search and rescue operations.
• High speed internet services: Modern communication satellites are offering exclusive services like high speed internet services.
  • Starlink project, the world's first and largest satellite constellation.
  • OneWeb project: Satellite communications company, One Web has planned to place 648 satellites in LEO.
  • GSAT31 is providing high-speed internet connectivity in India with augmentation ku-band transponders.

Earth Observation Satellites

The Earth Observing Satellites are polar-orbiting and low inclination satellites for long-term observations of the various landscapes on the Earth - atmosphere, biosphere, lithosphere and oceans. These types of satellites monitor our planet from space and report back on any changes they observe.

Orbits of Earth Observation Satellites

• Earth observation satellites mainly follow a synchronous sub-recurrent orbit, a type of polar orbit.
• A synchronous sub-recurrent orbit is a combination of a sun-synchronous orbit and sub-recurrent orbit.
  • sun-synchronous orbit: The angle between an orbit plane and the Sun seen from the Earth is always constant at the same local solar time
  • Sub-recurrent orbit: Flying at the same local solar time and the same location at a fixed period).
• Observational benefit for satellites: It is possible to observe the same region at fixed intervals as the incidence angle of sunlight on the earth’s surface is almost constant in a synchronous sub-recurrent orbit.

Applications of Earth Observation Satellites

Earth Observation Satellites (EOS) provide necessary spatial and temporal data with the help of onboard instruments on the satellites. The data from these satellites is used for several applications, such as land andforest mapping and monitoring, mapping of resources like water or minerals, weather and climate observations, soil assessment, and geospatial contour mapping.

• Mechanism:
  • Remote sensing: It is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance with the help of Earth observation satellites.
  • Geographical information system satellites are a type of remote sensing spacecraft whose main function is to provide images appropriate for GIS mapping and facilitate spatial analysis for town planning and land use change.
• Examples of different EOS satellites:
  • The Cartosat series of satellites (ISRO) are meant to provide data on land topography and the development of maps of geographical areas.
  • Oceanography: Oceansat satellites are meant for oceanography, such asmapping of the ocean topography.
  • Resource management:Resourcesat series of ISRO is dedicated to resource management. For example, EOS-04 (Radar Imaging Satellite) is designed to provide high-quality images under all weather conditions for applications of resource management, such as mineral and forestry resources.
  • Meteorological application: EOS satellites provide meteorologists with a data source unmatched in comparable spatial and temporal coverage by any existing or practical means, which helps in studying ocean and atmospheric dynamics. EUMETSAT is an operational Earth observation satellite of the European Space Agency for monitoring weather, climate, and the environment from space.

Experimental Satellites

ISRO has launched a number of small satellites, primarily for research purposes. These experiment satellites include Remote Sensing, Atmospheric Studies, Payload Development, Orbit control, Recovery technology, etc.

EOS

Indian Regional Navigation Satellite System (IRNSS): NavIC

It is an independent regional navigation satellite system developed by ISRO. NavIC was erstwhile known as the Indian Regional Navigation Satellite System (IRNSS)

• It is intended to provide accurate position, navigation and timing services to users in India and regions extending up to 1500 kilometres from its boundary.
• It provides Standard Positioning Service (SPS) for all users and Restricted Service (RS) for authorised users.

GPS-Aided GEO Augmented Navigation (GAGAN)

It is a satellite-based augmentation system (SBAS) jointly developed by ISRO and the Airport Authority of India (AAI).

• Objectives: Providing accurate satellite-based navigation services for civil aviation applications and improving air traffic management over Indian airspace.
  • The system will be compatible with other international SBAS systems and will allow for seamless navigation across regional borders.
  • GSAT-8 and GSAT-10 provide access to the GAGAN Signal-In-Space (SIS).

Space Explorations of ISRO

ISRO has made significant strides in space science and exploration missions, conducting missions that have expanded our understanding of astronomy, astrophysics, celestial bodies and space.

Future Space Programmes of ISRO

According to ISRO, the following are the upcoming programmes: