Satellite Navigation

SATELLITE NAVIGATION

Satellite Navigation service is an emerging satellite-based system with commercial and strategic applications. ISRO is committed to provide the satellite-based Navigation services to meet the emerging demands of the Civil Aviation requirements and to meet the user requirements of the positioning, navigation and timing based on the independent satellite navigation system. To meet the Civil Aviation requirements, ISRO is working jointly with Airport Authority of India (AAI) in establishing the GPS Aided Geo Augmented Navigation (GAGAN) system. To meet the user requirements of the positioning, navigation and timing services based on the indigenous system, ISRO is establishing a regional satellite navigation system called Indian Regional Navigation Satellite System (IRNSS).

GPS Aided GEO Augmented Navigation (GAGAN)

This is a Satellite Based Augmentation System (SBAS) implemented jointly with Airport Authority of India (AAI). The main objectives of GAGAN are to provide Satellite-based Navigation services with accuracy and integrity required for civil aviation applications and to provide better Air Traffic Management over Indian Airspace. The system will be interoperable with other international SBAS systems and provide seamless navigation across regional boundaries. The GAGAN Signal-In-Space (SIS) is available through GSAT-8 and GSAT-10.

Facts to remember-

• Airports Authority of India (AAI) successfully conducted flight trials using GAGAN based LPV approach procedure.

• India is the first country in the Asia Pacific Region to achieve such a landmark in field of Air Navigation Services (ANS)

• LPV (Localizer Performance with Vertical Guidance) permits aircraft guided approaches that are operationally nearly equivalent to Category 1- Instrument Landing System (Cat-1 ILS), without the need for ground-based navigational infrastructure. In short, GAGAN helps planes to land without ground markers

• GAGAN is an Indian Satellite Based Augmentation System (SBAS) jointly developed by AAI and ISRO for India and neighbouring countries in the equatorial region.

• It is one among the only four Space-Based augmentation systems available in the world which also includes US(WAAS) Europe (EGNOS) and Japan (MSAS)

• Benefits of GAGAN: Air traffic control, manage road and railways transport, help farmers in crop spraying etc.

Indian Regional Navigation Satellite System (IRNSS): NavIC

This is an independent Indian Satellite based positioning system for critical National applications. The main objective is to provide Reliable Position, Navigation and Timing services over India and its neighbourhood, to provide fairly good accuracy to the user. The IRNSS will provide basically two types of services

• Standard Positioning Service (SPS)

• Restricted Service (RS)

To date, ISRO has built a total of nine satellites in the IRNSS series; of which eight are currently in orbit Three of these satellites are in geostationary orbit (GEO) while the remaining in geosynchronous orbits (GSO) that maintain an inclination of 29 to the equatorial plane. The IRNSS constellation was named as “NavIC” (Navigation with Indian Constellation) by the Honourable Prime Minister and dedicated to the nation on the occasion of the successful launch of the IRNSS-1G satellite.

Why satellites do not fall down?

Satellites orbit Earth due to a balance between the gravitational pull of the planet and their forward velocity. This allows them to fall towards Earth due to gravity and move forward at a sufficient speed to miss the planet’s surface. The satellite’s forward velocity creates a centrifugal force, which opposes the pull of gravity. When these forces are balanced, the satellite’s trajectory becomes an elliptical orbit around Earth.

Atmospheric drag, a thin atmosphere at the outer edges of Earth’s atmosphere, slightly slows down satellites over time, causing them to lose altitude. Some satellites have thrusters or propulsion systems to adjust their orbits and counteract atmospheric drag. Satellites in higher orbits, such as geostationary orbit or deep space, experience less drag and can remain in orbit for longer periods without significant adjustments.

Basic Concepts

• Satellite: A satellite is a moon, planet, or machine that orbits a planet or star, such as Earth is a satellite (as it orbits around the sun) and the moon is a satellite (as it orbits around the earth). Natural satellites include Earth and the moon, while thousands of artificial satellites orbit Earth. Some take pictures of the planet to help meteorologists predict weather and track hurricanes, while others take pictures of other planets, black holes, dark matter, or distant galaxies to better understand the solar system and universe. Other satellites are used for communications, such as beaming TV signals and phone calls around the world. The Global Positioning System (GPS) consists of over 20 satellites, which can help determine an individual’s exact location with a GPS receiver.

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Space Shuttle: The Space Shuttle, developed by NASA, was a partially reusable rocket-launched vehicle designed to orbit Earth, transport people and cargo and glide to a runway landing upon return. Originally called the Space Transportation System (STS), it launched its first flight on April 12, 1981 and made 135 flights until its program ended in 2011. Key components of the Space Shuttle system included-

• a winged orbiter that carried both crew and cargo;

• an external tank containing liquid hydrogen (fuel) and liquid oxygen (oxidizer) for the orbiter’s three main rocket engines;

• a pair of large, solid-propellant, strap-on booster rockets - During the launch, the boosters and the orbiter’s main engines ignited simultaneously, increasing thrust. The boosters were ejected after liftoff and returned to Earth for reuse.

• Spacecrafts: A spacecraft is a vehicle designed to fly in outer space, used for various purposes such as communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. Spacecraft require a launch vehicle and can enter space and return to the surface without gaining enough energy or velocity to make a full orbit of Earth. Orbital spaceflights involve entering closed orbits around Earth or other celestial bodies. Human spaceflight uses crew or passengers, while robotic space missions operate autonomously or telerobotically. Space probes support scientific research, while artificial satellites remain in orbit around planetary bodies.

• Launch Vehicle: A launch vehicle is a rocket-powered vehicle used in spaceflight to transport spacecraft beyond Earth’s atmosphere, either into orbit or to outer space. Launch vehicles have been used since the 1950s to send crewed, uncrewed probes and satellites. India’s used launch vehicles are as follows: RLV-TD, SLV, ASLV, PSLV and GSLV.

• Rocket: A rocket is a vehicle that uses Newton’s third law of motion to propel itself by exhaling exhaust gases at high speeds. It operates in space or Earth’s atmosphere, serving various purposes like space exploration, satellite deployment, scientific research, and military applications. Rockets are essential for enabling humans and payloads to reach outer space.

• Missile: A missile is a guided self-propelled weapon system used for various purposes, including military, defense, and scientific research. It is propelled by engines or motors and equipped with guidance systems to ensure accuracy in hitting its intended targets.