Satellite communication and India's early satellites

Detail

1. What satellite communication is and why it matters

• Satellite communication: a satellite in space receives a signal from one place on Earth, strengthens it, and sends it back to many places at once.
• Satellites are a mode of communication themselves. They carry phone calls, TV and radio signals and data.
• Satellites also control other modes of communication. Phone networks, TV broadcasting, aircraft and ship navigation and banking networks all use satellite links.
• Synoptic view: a satellite sees a very large area at one time and keeps watching it without a break.
• Satellites watch the weather continuously, which helps weather forecasting.
• They track cyclones, floods and droughts, which helps disaster monitoring.

• They watch remote frontiers, which helps border surveillance.

• Result: satellites matter for both the economy (telecom, TV, weather data for farmers and fishers) and security (strategic use).

• India has two main satellite systems:
• INSAT, for communication and weather.
• IRS, for remote sensing (studying Earth from space).

2. INSAT — Indian National Satellite System

• INSAT was set up in 1983. It is a multipurpose system, which means one system does many jobs:
• telecommunication
• television broadcasting
• meteorology (weather observation)

• disaster warning

• Geostationary orbit: an orbit high above the Equator. A satellite here goes round Earth once a day, which is exactly how long Earth takes to spin once. So from the ground it seems to stay over one fixed spot.

• Why it helps: dish antennas can point at one place in the sky and never need to move.

• INSAT is one of the largest domestic communication satellite systems in the Asia-Pacific region. It had nine operational communication satellites in geostationary orbit, with more than 200 transponders in the C, Extended C and Ku bands [5].

• Transponder: the unit on a satellite that receives a signal, strengthens it and sends it back down.

• C, Extended C and Ku bands: different ranges of radio frequency. Ku-band works well with small dish antennas, as in DTH TV.

• INSAT services [5]:

• telecommunications
• TV broadcasting
• satellite newsgathering
• societal applications (education, health)
• weather forecasting
• disaster warning

• Search and Rescue (picking up distress signals from ships, aircraft and people)

• TV reach (c. 2000): with INSAT, satellite TV covered over 65% of India's land area and over 80% of its population [6].

• Weather role [6]:
• INSAT was the only source of repeated, wide-area (synoptic) weather observations over the Indian Ocean from geostationary orbit.
• Its weather instruments measure cloud motion vectors (wind speed and direction worked out from how clouds move), cloud-top temperature, water vapour, and vertical profiles of temperature and humidity (how they change with height).

• Result: better forecasts, early detection of the genesis (birth) of cyclones, and prediction of each cyclone's track.

• Birth of the system:

• INSAT-1A (1982) failed early.
• INSAT-1B (1983) made the INSAT system work.

3. IRS — Indian Remote Sensing satellites

• Remote sensing: collecting information about Earth's surface from a distance, using sensors on satellites.
• IRS-1A was launched in March 1988 from Baikonur. Baikonur was then in the Soviet Union and is now in Kazakhstan.
• NRSC (National Remote Sensing Centre), Hyderabad, Telangana receives IRS data and processes it.
• India built its own launch vehicle, the PSLV (Polar Satellite Launch Vehicle).
• Polar orbit: an orbit that passes over or near both poles. Earth turns underneath, so the satellite slowly covers the whole planet.

• Result: India no longer needed foreign rockets to launch its IRS satellites.

• (For more detail on IRS, see the remote-sensing-gis note.)

4. Milestones of India's early space programme

Year	Milestone	Rocket and launch site	What it proved
1969	ISRO founded	—	Gave India a national space agency
19 Apr 1975	Aryabhata, first satellite	Soviet rocket, Soviet Union	India could build a satellite
1975-76	SITE	NASA's ATS-6 satellite	Satellite TV could reach villages
18 Jul 1980	Rohini RS-1	India's own SLV-3, Sriharikota	India could launch its own satellites
19 Jun 1981	APPLE, first experimental communication satellite	Ariane, Kourou (French Guiana)	India could build a geostationary communication satellite
1982 / 1983	INSAT-1A fails / INSAT-1B succeeds	—	The INSAT system starts working

ISRO (1969)

• ISRO: Indian Space Research Organisation, India's national space agency. It was founded in 1969.

Aryabhata (1975)

• Aryabhata was India's first satellite. It is named after Aryabhata, the 5th-century astronomer and mathematician.
• It was launched on 19 April 1975 on a Soviet "C-1 Intercosmos" rocket from the Volgograd Launch Station, which is now in Russia [2].
• It was completely designed and built in India by ISRO [2].
• Facts [2]:
• mass 360 kg
• orbit 563 × 619 km, at an inclination of 50.7° (inclination: the angle between the orbit and the Equator)
• 46 watts of power
• VHF band communication

• spin-stabilised (it kept steady by spinning, like a top)

• Science work: X-ray astronomy, aeronomy (the study of the upper atmosphere) and solar physics [2].

• Life [2]:
• It was designed to work for 6 months.
• It kept working until March 1981.
• It came back into the atmosphere on 10 February 1992, after about 17 years in orbit.

SITE — Satellite Instructional Television Experiment (1975-76)

• SITE used NASA's ATS-6 satellite (ATS: Applications Technology Satellite) to show educational TV in about 2,400 villages.
• NASA lent ATS-6 to India for one year, from 1 August 1975 to 31 July 1976 [7].
• Villages: 6 clusters of about 400 villages each (6 × 400 = 2,400), for about 4 hours a day [7].
• India's share of the work [7]:
• 10-foot dish antennas, front-end converters (units that change the satellite signal into a form a TV can use) and TV sets

• making the programmes and transmitting them

• Programme timings [7]:

• Morning, 1.5 hours: for school classrooms.

• Evening, 2.5 hours: for adult education in villages.

• Why it matters: it showed that satellites can serve the education needs of rural India. This idea led to INSAT.

Rohini satellites and SLV-3 (1980)

• Rohini is a series of small experimental satellites launched on India's own rocket.
• SLV-3 (Satellite Launch Vehicle-3) was India's first home-built launch vehicle.
• Rohini RS-1 was launched on 18 July 1980 on SLV-3 from SHAR Centre, Sriharikota, a barrier island on the coast of Andhra Pradesh, on the Bay of Bengal [3].
• Result: India became a space-faring nation, able to put its own satellites into orbit with its own rocket.
• Facts [3]:
• mass 35 kg
• spin-stabilised
• orbit 305 × 919 km, inclination 44.7°

• mission life 1.2 years

• Job [3]:

• It sent back data on the fourth stage of SLV-3 during the launch.

• It also carried a digital sun sensor, a magnetometer (it measures magnetic field) and temperature sensors.

• Later flight: SLV-3 carried Rohini RS-D2 successfully on 17 April 1983 [8].

APPLE (1981)

• APPLE stands for Ariane Passenger Payload Experiment. It was ISRO's first home-built experimental communication satellite [4].
• It was launched on 19 June 1981 on Ariane-1 (V-3) from Kourou, French Guiana, on the north-east coast of South America, close to the Equator [4].
• Facts [4]:
• mass 670 kg
• geosynchronous orbit at 102° E longitude, over Indonesia (geosynchronous: an orbit that matches Earth's daily spin)
• 2 C-band transponders

• mission life 2 years

• Tests [4]:

• TV and radio relay (receiving a TV or radio signal and passing it on to other places)
• multiple-access systems: time-, frequency- and code-division, which are ways for many users to share one satellite
• radio networking and computer interconnect (linking computers)

• packet switching (sending data in small blocks)

• Why it matters: it was a test run for India's own communication satellites, which later grew into the GSAT series.

5. Later developments (pointers)

• GSAT series: India's later communication satellites, built on the experience of APPLE and INSAT.
• NavIC (Navigation with Indian Constellation, earlier called IRNSS: Indian Regional Navigation Satellite System) is India's regional navigation system. It works like the American GPS, but for a smaller region [9].
• Coverage: India plus the area up to 1,500 km beyond its borders [9].
• Constellation of 7 satellites [9]:
  • 3 geostationary, at 32.5° E, 83° E and 129.5° E
  • 4 in inclined geosynchronous orbit (orbits tilted to the Equator), at 29°
• Accuracy: better than 20 m in the main service area [9].
• Two services [9]:
  • Standard Positioning Service (SPS) for ordinary users
  • Restricted Service (RS) for strategic users such as the armed forces

• Frequencies: L5 and S band [9].

• Satellite internet licences: private companies are now being given licences to offer internet through satellites. Check the latest status.

Prelims Hooks

• Aryabhata (19 April 1975) was India's first satellite. It was launched on a Soviet rocket from the Soviet Union, not from Sriharikota.
• Rohini RS-1 (18 July 1980) was the first satellite India put into orbit with its own rocket, SLV-3, from Sriharikota (Andhra Pradesh).
• APPLE (19 June 1981) was the first experimental communication satellite. It was launched on Ariane-1 from Kourou, French Guiana, and placed at 102° E.
• SITE (1975-76) used NASA's ATS-6, not an Indian satellite. It reached about 2,400 villages (6 clusters of about 400).
• INSAT is in geostationary orbit, used for telecom, TV, weather and disaster warning. IRS is used for remote sensing, and its data is processed at NRSC Hyderabad.
• IRS-1A was launched in March 1988 from Baikonur (now in Kazakhstan).
• INSAT-1A (1982) failed. INSAT-1B (1983) made the INSAT system work.
• Order of milestones: ISRO (1969) → Aryabhata (1975) → SITE (1975-76) → Rohini RS-1 (1980) → APPLE (1981) → INSAT-1B (1983) → IRS-1A (1988).
• NavIC: 7 satellites (3 geostationary + 4 inclined geosynchronous). It covers India plus 1,500 km beyond its borders.

Mains Points

• Satellites are strategic infrastructure (GS-III).
• Their wide, continuous view supports weather forecasts, cyclone tracking, disaster warning and border surveillance.

• INSAT was once the only geostationary source of weather data over the Indian Ocean, which shows how much India depends on its own satellites.

• Satellites close India's development gap.

• SITE (1975-76) and INSAT took TV and education to remote villages where land networks were weak.
• By about 2000, satellite TV covered over 80% of India's people.

• Today satellite internet can do the same for hilly, island and border areas.

• Self-reliance. India moved step by step from depending on others to launching its own satellites:

• foreign rockets: Aryabhata on a Soviet rocket, APPLE on Ariane
• foreign satellite: SITE on NASA's ATS-6
• own rockets: SLV-3 and then PSLV

• own navigation system: NavIC, which cuts reliance on the American GPS

• Policy response. GSAT, NavIC and private satellite-internet licences extend India's communication network. Together they support Digital India, disaster management and secure communication for the armed forces.