IRNSS is an independent regional navigation satellite system being developed by India. It is designed to provide accurate position information service to users in India as well as the region extending up to 1500 km from its boundary, which is its primary service area.
An Extended Service Area lies between primary service area and area enclosed by the rectangle from Latitude 30 deg South to 50 deg North, Longitude 30 deg East to 130 deg East.
IRNSS will provide two types of services, namely, Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorised users.
The IRNSS System is expected to provide a position accuracy of better than 20 m in the primary service area.
IRNSS will be using a combination of GEO and GSO spacecrafts and state-of-the-art ground systems.
IRNSS provides Standard Positioning Service (SPS) and Restricted Service (RS) to the users on dual frequencies in L5 and S band.
NavIC is based on eight satellites. IRNSS- 1 A, 1B, 1C, 1D, 1E, 1F, 1G and 1 I
The IRNSS system architecture mainly consists of:
The space segment consists of the IRNSS constellation of eight satellites, NavIC. Three satellites are located in suitable orbital slots in the geostationary orbit and the remaining four are located in geosynchronous orbits with the required inclination and equatorial crossings in two different planes.
All the satellites of the constellation are configured identically with I-1K Bus to be compatible for launch on-board PSLV.
The IRNSS space segment consists of 8 satellites (4 GEO and 4 GSO). The 3 GEOs are located at 32.5o E, 83oE and 131o E and the 4 GSOs have their longitude crossings 55o E and 111.75o E (two in each plane).
IRNSS-1A spacecraft was launched on 1 July 2013. It was followed by launch of 5 more spacecrafts upto IRNSS-1F in the years 2014-16. IRNSS-1G was launched on 28th April, 2016. IRNSS-1I was launched on 12th April, 2018 to replace IRNSS-1A. IRNSS- 1I carried refurbished Atomic clocks. IRNSS 1A had failure of three Rubidium atomic clocks and IRNSS constellation was functioning with only six satellites.
PROJECT LAUNCH DATE LAUNCH VEHICLE
IRNSS-1I 12-April-2018 PSLV-C41
IRNSS-1H 31-AUG-2017 PSLV-C39
IRNSS-1G 28-APR-2016 PSLV-C33
IRNSS-1F 10-MAR-2016 PSLV-C32
IRNSS-1E 20-JAN-2016 PSLV-C31
IRNSS-1D 28-MAR-2015 PSLV-C27
IRNSS-1C 15-OCT-2014 PSLV-C26
IRNSS-1B 04-APR-2014 PSLV-C24
IRNSS-1A 01-JUL-2013 PSLV-C22
The IRNSS Satellites are designed around I-1K bus with a dry mass of 600 Kg & a Lift off mass of 1425 Kg. It has a power generation capability of 1600 W. Three-axis control of the satellite with Yaw steering capability to optimize the use of Solar Panels and to support the thermal control of the satellite.
The navigation payload transmits SPS & RS signals in L5 & S Bands. Highly stable Rubidium Atomic Frequency Standards (RAFS) are used on-board for generation of Navigation Signals.
The latest satellite in the series, IRNSS-1I also had a lift-off mass of 1425 kg. Like its other IRNSS predecessors, IRNSS-1I also carried two types of payloads – navigation payload and ranging payload.
The navigation payload of IRNSS-1I transmits signals for the determination of position, velocity and time. This payload is operating in L5-band and S-band. Rubidium atomic clocks are part of the navigation payload of the satellite. The ranging payload of IRNSS-1I consists of a C-band transponder, which facilitates accurate determination of the range of the satellite. It also carries Corner Cube Retro Reflectors for LASER Ranging as per the ISRO.
Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. The Ground segment comprises of:
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 20ns (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 Aug 1st 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 the spacecrafts automatically.
The IRDCN has established terrestrial and VSAT links between the ground stations. seven 7.2m FCA and two 11m FMA of IRSCF are currently operational for LEOP and on-orbit phases of IRNSS satellites.
The User segment mainly consists of:
Single frequency IRNSS receiver capable of receiving SPS/RS signal at L5 or S band frequency.
A dual frequency IRNSS receiver capable of receiving SPS/RS signal in both L5 and S band frequencies.