The Indian Regional Navigation Satellite System (IRNSS) with an operational name of NAVIC ("sailor" or "navigator" in Sanskrit, Hindi and many other Indian languages, which also stands for NAVigation with Indian Constellation) is an autonomous regional satellite navigation system, that provides accurate real-time positioning and timing services. It covers India and a region extending 1,500 km (930 mi) around it, with plans for further extension. The system at-present consist of a constellation of 7 satellites, with two additional satellites on ground as stand-by.
The constellation is already in orbit and system was expected to be operational from early 2018 after a system check. NAVIC will provide two levels of service, the 'standard positioning service' will be open for civilian use, and a 'restricted service' (an encrypted one) for authorized users (including military). Due to the failures of one of the satellites and its replacement no new dates for operational status has been set.
In 2017 all rubidium atomic clocks on board IRNSS-1A failed, rendering the satellite redundant. ISRO's attempt to replace it with IRNSS-1H was unsuccessful when PSLV-C39 mission failed to deploy the satellite on 31 August 2017.
There are plans to expand NavIC system by increasing constellation size from 7 to 11.
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 2006.
As part of the project, the Indian Space Research Organisation (ISRO) opened a new satellite navigation center within the campus of ISRO Deep Space Network (DSN) at Byalalu, in Karnataka on 28 May 2013. 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 ₹1,420 crore (US$217 million), with the cost of the ground segment being ₹300 crore (US$46 million). Each satellites costing ₹150 crore (US$23 million) and the PSLV-XL version rocket costs around ₹130 crore (US$20 million). The planned seven rockets would have involved an outlay of around ₹910 crore (US$139 million).
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 ₹2,246 crore (US$344 million)
The NAVIC signal was released for evaluation in September 2014.
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 1 July 2013. IRNSS-1B was launched on 4 April 2014 on-board PSLV-C24 rocket. The satellite has been placed in geosynchronous orbit. IRNSS-1C was launched on 16 October 2014, IRNSS-1D on 28 March 2015, IRNSS-1E on 20 January 2016,IRNSS-1F on 10 March 2016 and IRNSS-1G was launched on 28 April 2016.
The IRNSS system comprises a space segment and a support ground segment.
The constellation consists of 7 satellites. Three of the seven satellites are located in geostationary orbit (GEO) at 32.5° East, 83° East, and 131.5° East longitude, approximately 36,000 km (22,000 mi) above earth surface. Remaining four satellites are in inclined geosynchronous orbit (GSO). Two of them cross equator at 55° East and two at 111.75° East. The four GSO satellites will appear to be moving in the form of an "8".
Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. The Ground segment comprises:
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 ns (2.0×10−9 s) (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 1 August 2013. 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 uplinked to the spacecrafts automatically. The IRDCN has established terrestrial and VSAT links between the ground stations. Seven 7.2 m FCA and two 11 m FMA of IRSCF are currently operational for LEOP and on-orbit phases of IRNSS satellites.
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 1,330 kg and their solar panels generate 1,400 watts.
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.
The system is intended to provide an absolute position accuracy of better than 10 meters throughout Indian landmass and better than 20 meters in the Indian Ocean as well as a region extending approximately 1,500 km (930 mi) 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.
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 (GSO). All satellites launched or proposed for the system are as follows:
In 2017, it was announced that all three rubidium atomic clocks on board IRNSS-1A had failed, mirroring similar failures in the European Union's Galileo constellation. The first failure occurred in July 2016, following which two other clocks also failed. This rendered the satellite somewhat redundant and required replacement. Although the satellite still performs other functions, the data is coarse, and thus cannot be used for accurate measurements. ISRO's attempt to replace it with IRNSS-1H was unsuccessful when PSLV-C39 mission failed on 31 August 2017.. Due to the failure of the replacement satellite launch the system which was expected to go live in August 2017 is currently a degraded / non-operational state. 
Two more clocks in the navigational system had started showing signs of abnormality, thereby taking the total number of failed clocks to five.
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 six satellites. Each satellite has three clocks, therefore a total of 27 clocks for all satellites in the system (including standby satellites). The clocks of both IRNSS and GALILEO were supplied by SpectraTime. ISRO replaced the atomic clocks in two standby NavIC satellites. The setback comes at a time when IRNSS is yet to start commercial operations.
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 for extending coverage. These additional 4 satellites will be made during 12th FYP and will be launched in the beginning of 13th FYP. Also, development of space qualified atomic clocks was initiated, along with study & development initiative for All Optical Atomic Clock (ultra stable for IRNSS and Deep Space Communication).
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 24,000 km (14,913 mi) above Earth. As of 2013[update], the statutory filing for frequency spectrum of GINS satellite orbits in international space, has been completed.
|Satellite||Launch Date||Launch Vehicle||Orbit||Status||Remarks|
|IRNSS-1A||1 July 2013||PSLV-C22||Geosynchronous / 55°E, 29° inclined orbit||Failed in orbit||Atomic clocks failed.|
|IRNSS-1B||4 April 2014||PSLV-C24||Geosynchronous / 55°E, 29° inclined orbit||Operational|
|IRNSS-1C||15 October 2014||PSLV-C26||Geostationary / 83°E, 5° inclined orbit||Operational|
|IRNSS-1D||28 March 2015||PSLV-C27||Geosynchronous / 111.75°E, 31° inclined orbit||Operational|
|IRNSS-1E||20 January 2016||PSLV-C31||Geosynchronous / 111.75°E, 29° inclined orbit||Operational|
|IRNSS-1F||10 March 2016||PSLV-C32||Geostationary / 32.5°E, 5° inclined orbit||Operational|
|IRNSS-1G||28 April 2016||PSLV-C33||Geostationary / 129.5°E, 5.1° inclined orbit||Operational|
|IRNSS-1H||31 August 2017||PSLV-C39||Launch Failed||The payload fairing failed to separate and satellite could not reach the desired orbit. It was meant to replace defunct IRNSS-1A.|
|IRNSS-1I||April 2018||PSLV--C41||Under development|