Navigating NAVIC

NAVIC is very useful for positioning in urban canyons where other systems fail. Also, its immediate users will be the armed forces who will have access to the very accurate restricted service signals.

- Prof. Arup Dasgupta

On April 28, 2016, Indian Regional Navigation Satellite, IRNSS-1G went into geosynchronous transfer orbit and by May 3 it had taken up its position in the geostationary orbit at 129.5 degree East. With this, the IRNSS constellations of seven satellites are in position. Since then, there has been an intriguing silence on the availability of the system. The initial euphoria about an Indian GPS has subsided. This may be a good time to take stock.

IRNSS constellation consists of three Geostationary Earth Orbit (GEO) spacecraft and four spacecraft in Geosynchronous orbit (GSO) inclined at 29 degree to the equator. IRNSS will provide two types of services, namely, Standard Positioning Services (SPS) — provided to all users — and Restricted Services (RS), provided to authorize users.

Three satellites IRNSS-1C, 1F and 1G at 5-degree inclination are called GEO satellites. IRNSS-1F is placed at 32 degree East, 1C at 83 degree East and 1G at 129.5 degree East. The four GSO satellites, IRNSS-1A, B, D and E are placed in inclined orbit with longitude crossover of an equatorial plane at 55 degree East and 111.75 degree East. GSO satellites are placed in two planes with the planes being 180 degree apart. These seven satellites will cover a service area of 1,500 Km around India with an SPS accuracy of 20 m or better.

The IRNSS satellites carry two types of payloads — navigation payload and CDMA payload. The navigation payload operating in L5-band and S-band will transmit navigation service signals to the users. It also has a highly accurate Rubidium atomic clock. The ranging (CDMA) payload consists of a C-band transponder which facilitates accurate determination of the range of the satellite. It also carries Corner Cube Retro Reflectors (CCRR) for laser ranging.