Indian Regional Navigation Satellite System

The Indian Regional Navigation Satellite System (IRNSS), with an operational name of NavIC (acronym for Navigation with Indian Constellation; also,  'sailor' or 'navigator' in Sanskrit, and many other Indian languages), is an autonomous regional satellite navigation system that provides accurate real-time positioning and timing services. It covers India and a region extending  around it, with plans for further extension. An extended service area lies between the primary service area and a rectangle area enclosed by the 30th parallel south to the 50th parallel north and the 30th meridian east to the 130th meridian east,  beyond borders. The system currently consists of a constellation of seven satellites, with two additional satellites on ground as stand-by.

The constellation is in orbit as of 2018, and the system was expected to be operational from early 2018 after a system check. NavIC will provide two levels of service, the "standard positioning service", which will be open for civilian use, and a "restricted service" (an encrypted one) for authorised users (including the military).

NavIC based trackers are compulsory on commercial vehicles in India and it is planned to become available in consumer mobile phones in the first half of 2020.

There are plans to expand the NavIC system by increasing its constellation size from 7 to 11.

Background 
The system was developed partly because access to foreign government-controlled global navigation satellite systems is not guaranteed in hostile situations, as happened to the Indian military in 1999 when it was dependent on the American Global Positioning System (GPS) during the Kargil War. The Indian government approved the project in May 2013. As per National Defense Authorization Act (NDAA) 2020, United States Secretary of Defense in consultation with Director of National Intelligence will designate NavIC, Galileo and QZSS as allied navigational satellite system.

Development
As part of the project, the Indian Space Research Organisation (ISRO) opened a new satellite navigation centre within the campus of ISRO Deep Space Network (DSN) at Byalalu, in Karnataka on . A network of 21 ranging stations located across the country will provide data for the orbital determination of the satellites and monitoring of the navigation signal.

A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India. Its location in low latitudes facilitates a coverage with low-inclination satellites. Three satellites will be in geostationary orbit over the Indian Ocean. Missile targeting could be an important military application for the constellation.

The total cost of the project was expected to be , with the cost of the ground segment being , each satellite costing  and the PSLV-XL version rocket costing around . The planned seven rockets would have involved an outlay of around . 

The necessity for two replacement satellites, and PSLV-XL launches, has altered the original budget, with the Comptroller and Auditor General of India reporting costs, to March 2017, at 

The NavIC signal was released for evaluation in September 2014.

From 1 April 2019, use of AIS-140 compliant NavIC-based vehicle tracking systems were made compulsory for all commercial vehicles in India.

In January 2020, Qualcomm launched three new chipsets, Snapdragon 720G, 662 and 460 with support for Navigation with Indian Constellation (NavIC). NavIC is planned to be available for civilian use in mobile devices, after Qualcomm and Indian Space Research Organisation signed an agreement.

Time-frame 
In April 2010, it was reported that India plans to start launching satellites by the end of 2011, at a rate of one satellite every six months. This would have made NavIC functional by 2015. But the program was delayed, and India also launched 3 new satellites to supplement this.

Seven satellites with the prefix "IRNSS-1" will constitute the space segment of the IRNSS. IRNSS-1A, the first of the seven satellites, was launched on . IRNSS-1B was launched on  on-board PSLV-C24 rocket. The satellite has been placed in geosynchronous orbit. IRNSS-1C was launched on , IRNSS-1D on , IRNSS-1E on , IRNSS-1F on  and IRNSS-1G was launched on .

The eighth satellite, IRNSS-1H, which was meant to replace IRNSS-1A, failed to deploy on  as the heat shields failed to separate from 4th stage of the rocket. IRNSS-1I was launched on  to replace it.

System description 
The IRNSS system comprises a space segment and a support ground segment.

Space segment 
The constellation consists of 7 satellites. Three of the seven satellites are located in geostationary orbit (GEO) at 32.5° E, 83° E, and 131.5° E longitude, approximately  above earth surface. Remaining four satellites are in inclined geosynchronous orbit (GSO). Two of them cross equator at 55° E and two at 111.75° E. The four GSO satellites will appear to be moving in the form of an "8".

Ground segment 
Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. The Ground segment comprises:
 IRNSS Spacecraft Control Facility (IRSCF)
 ISRO Navigation Centre (INC)
 IRNSS Range and Integrity Monitoring Stations (IRIMS)
 IRNSS Network Timing Centre (IRNWT)
 IRNSS CDMA Ranging Stations (IRCDR)
 Laser Ranging Stations
 IRNSS Data Communication Network(IRDCN)

The INC established at Byalalu performs remote operations and data collection with all the ground stations. 14 IRIMS are currently operational and are supporting IRNSS operations. CDMA ranging is being carried out by the four IRCDR stations on regular basis for all the IRNSS satellites. The IRNWT has been established and is providing IRNSS system time with an accuracy of  (2 sigma) w.r.t UTC. Laser ranging is being carried out with the support of ILRS stations around the world. Navigation Software is operational at INC since . All the navigation parameters viz. satellite ephemeris, clock corrections, integrity parameters and secondary parameters viz. iono-delay corrections, time offsets w.r.t UTC and other GNSS, almanac, text message and earth orientation parameters are generated and uploaded to the spacecraft automatically. The IRDCN has established terrestrial and VSAT links between the ground stations. Seven  FCA and two  FMA of IRSCF are currently operational for LEOP and on-orbit phases of IRNSS satellites.

Signal 
NavIC signals will consist of a Standard Positioning Service and a Precision Service. Both will be carried on L5 (1176.45 MHz) and S band (2492.028 MHz). The SPS signal will be modulated by a 1 MHz BPSK signal. The Precision Service will use BOC(5,2). The navigation signals themselves would be transmitted in the S-band frequency (2–4 GHz) and broadcast through a phased array antenna to maintain required coverage and signal strength. The satellites would weigh approximately  and their solar panels generate 1,400 W.

A messaging interface is embedded in the NavIC system. This feature allows the command center to send warnings to a specific geographic area. For example, fishermen using the system can be warned about a cyclone.

Accuracy 
The system is intended to provide an absolute position accuracy of better than  throughout Indian landmass and better than  in the Indian Ocean as well as a region extending approximately  around India. The Space Applications Centre in 2017 said NavIC will provide standard positioning service to all users with a position accuracy up to 5 m. The GPS, for comparison, had a position accuracy of 20–30 m. Unlike GPS which is dependent only on L-band, NavIC has dual frequency (S and L bands). When low frequency signal travels through atmosphere, its velocity changes due to atmospheric disturbances. US banks on atmospheric model to assess frequency error and it has to update this model from time to time to assess the exact error. In India's case, the actual delay is assessed by measuring the difference in delay of dual frequency (S and L bands). Therefore, NavIC is not dependent on any model to find the frequency error and is more accurate than GPS.

List of satellites
The constellation consists of 7 active satellites. Three of the seven satellites in constellation are located in geostationary orbit (GEO) and four in inclined geosynchronous orbit (IGSO). All satellites launched or proposed for the system are as follows:

Clock failure 
In 2017, it was announced that all three SpectraTime supplied rubidium atomic clocks on board IRNSS-1A had failed, mirroring similar failures in the European Union's Galileo constellation. The first failure occurred in , followed soon after by the two other clocks on IRNSS-1A. This rendered the satellite non-functional and required replacement. ISRO reported it had replaced the atomic clocks in the two standby satellites, IRNSS-1H and IRNSS-1I., in June 2017 The subsequent launch of IRNSS-1H, as a replacement for IRNSS-1A, was unsuccessful when PSLV-C39 mission failed on .  The second standby satellite, IRNSS-1I, was successfully placed into orbit on 12 April 2018.

In July 2017, it was reported that two more clocks in the navigational system had also started showing signs of abnormality, thereby taking the total number of failed clocks to five, in May 2018 a failure of a further 4 clocks was reported, taking the count to 9 of the 24 in orbit. 

As a precaution to extend the operational life of navigation satellite, ISRO is running only one rubidium atomic clock instead of two in the remaining  satellites.

Future developments
India's Department of Space in their 12th Five Year Plan (FYP) (2012–17) stated increasing the number of satellites in the constellation from 7 to 11 to extend coverage. These additional four satellites will be made during 12th FYP and will be launched in the beginning of 13th FYP in geosynchronous orbit of 42° inclination. Also, the development of space-qualified Indian made atomic clocks was initiated, along with a study and development initiative for an all optical atomic clock (ultra stable for IRNSS and deep space communication).

IRNSS-1J, IRNSS-1K, IRNSS-1L, IRNSS-1M and IRNSS-1N are next batch of spacecrafts in development.

Global Indian Navigational System (GINS) 
Study and analysis for Global Indian Navigational System (GINS) was initiated as part of the technology and policy initiatives in the 12th FYP (2012–17). The system is supposed to have a constellation of 24 satellites, positioned  above Earth. , the statutory filing for frequency spectrum of GINS satellite orbits in international space, has been completed.

See also

References

Footnotes
  SATNAV Industry Meet 2006. ISRO Space India Newsletter. April – September 2006 Issue.

External links 
 View the satellites in real time

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Category:Space programme of India
Category:ISRO programs
Category:Satellite navigation systems
Category:Satellite constellations
Category:2013 establishments in India