Satellites based on application can be categorized as follows:
Earth Observation satellite->
Starting with IRS-1A in 1988, ISRO has launched many operational remote sensing satellites. Today, India has one of the largest constellations of remote sensing satellites in operation. Currently, *thirteen* operational satellites are in Sun-synchronous orbit – RESOURCESAT-1, 2, 2A CARTOSAT-1, 2, 2A, 2B, RISAT-1 and 2, OCEANSAT-2, Megha-Tropiques, SARAL and SCATSAT-1, and *four* in Geostationary orbit- INSAT-3D, Kalpana & INSAT 3A, INSAT -3DR. Varieties of instruments have been flown onboard these satellites to provide necessary data in a diversified spatial, spectral and temporal resolutions to cater to different user requirements in the country and for global usage. The data from these satellites are used for several applications covering agriculture, water resources, urban planning, rural development, mineral prospecting, environment, forestry, ocean resources and disaster management.
Communication satellite->
The Indian National Satellite (INSAT) system is one of the largest domestic communication satellite systems in Asia-Pacific region with nine operational communication satellites placed in Geo-stationary orbit. Established in 1983 with commissioning of INSAT-1B, it initiated a major revolution in India’s communications sector and sustained the same later. GSAT-18 joins the constellation of INSAT System consisting 14 operational satellites, namely – INSAT-3A, 3C, 4A, 4B, 4CR, 3DR and GSAT-6, 7, 8, 10, 12, 14, 15 and 16.
The INSAT system with more than 200 transponders in the C, Extended C and Ku-bands provides services to telecommunications, television broadcasting, satellite newsgathering, societal applications, weather forecasting, disaster warning and Search and Rescue operations.
Navigation satellite->
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).
(a) 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.
(b) 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)
Space Segment consists of seven satellites, three satellites in GEO stationary orbit (GEO) and four satellites in Geo Synchronous Orbit (GSO) orbit with inclination of 29° to the equatorial plane. This constellation of seven satellites was named as “NavIC” (Navigation Indian Constellation) by the Honourable Prime Minister of India, Mr. Narendra Modi and dedicated to the Nation on the occasion of successful launch of IRNSS-1G, the seventh and last satellite of NavIC. All the satellites will be visible at all times in the Indian region. All the seven Satellites of NavIC, namely, IRNSS-1A, 1B, 1C, ID,1E, 1F and 1G were successfully launched on July 02, 2013, Apr 04, 2014, Oct 16, 2014, Mar 28, 2015, Jan 20, 2016, Mar 10, 2016 and Apr 28, 2016 respectively and all are functioning satisfactorily from their designated orbital positions.
Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. It provides the monitoring of the constellation status, computation of the orbital and clock parameters and navigation data uploading. The Ground segment comprises of TTC & Uplinking Stations, Spacecraft Control Centre, IRNSS Timing Centre, CDMA Ranging Stations, Navigation Control Centre and Data Communication Links. Space segment is compatible with single frequency receiver for Standard Positioning Service (SPS), dual frequency receiver for both SPS & RS service and a multi mode receiver compatible with other GNSS providers.
Experimental satellite->
ISRO has launched many small satellites mainly for the experimental purposes. This experiment include Remote Sensing, Atmospheric Studies, Payload Development, Orbit Controls, recovery technology etc. Example- INS-1A, INS-1B, YOUTHSAT, APPLE