IRNSS is an independent regional navigation satellite system being developed by India. It is an autonomous regional satellite navigation system which is designed to provide accurate real-time positioning and timing services 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.
Indian Regional Navigation Satellite System (IRNSS), with an operational name of NavIC (“sailor” or “navigator” in Sanskrit, Hindi and many other Indian languages and also standing for NAVigation with Indian Constellation) is 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, 1,500–6,000 km beyond borders. The system at present consists of a constellation of seven satellites, with two additional satellites on the ground as stand-by.
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 authorized users. The IRNSS System is expected to provide a position accuracy of better than 20 m in the primary service area. The IRNSS is being developed parallel to the GAGAN (GPS Aided GEO Augmented Satellite Navigation) program, the ISRO SBAS (Satellite Based Augmentation System) version of an overlay system for GNSS signal corrections.
Architecture:
The IRNSS constellation architecture consists of the following elements:
• Space segment: The IRNSS satellites carry a navigation payload in a redundant configuration. A separate C-band transponder for precise CDMA ranging is included in the payload configuration. The important functions of the IRNSS payload are- Transmission of the navigational timing information in the L5 bands; the transmission of navigation, timing information in S-band. The navigation payload will have the following subsystems: NSGU (Navigation Signal Generation Unit), Atomic clock unit, comprising of Rubidium atomic clocks, clock management, and control unit, frequency generation unit, modulation unit, high power amplifier unit, power combining unit and navigation antenna.
• Ground segment: The ground segment is responsible for the maintenance and operation of the IRNSS constellation. Seventeen IRIMS sites will be distributed across the country for orbit determination and ionospheric modeling. Four ranging stations, separated by wide and long baselines, will provide two-way CDMA (Code Division Multiple Access) ranging. The IRNSS timing center will consist of highly stable clocks. The navigation center will receive all this data through communication links, then process and transmit the information to the satellites.
• User segment: Specially designed receivers and antennas are needed to receive the IRNSS signals. The receivers are also planned for receiving multi-constellation signals inclusive of GPS, GLONASS, Galileo, and IRNSS.
Spacecraft:
The IRNSS satellites are configured around the spacecraft bus I-1K, which is similar to ISRO’s meteorological satellite, Kalpana-1, with a dry mass of ~600 kg and a launch mass of 1,425 kg. The solar panels are generating power of 1600 W (with a payload power requirement of 900 W. The spacecraft are 3-axis stabilized. Attitude control of the satellite is provided with yaw steering, a capability to optimize the use of the solar panels, and to support the thermal control of the satellite.
Space Segment:
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. The satellites are configured with I-1K Bus to be compatible for launch onboard PSLV.
IRNSS-1A | IRNSS-1B | IRNSS-1C | IRNSS-1D | IRNSS-1E | IRNSS-1F | IRNSS-1G | IRNSS-1H | IRNSS-1I
Ground Segment:
Ground Segment is responsible for the maintenance and operation of the IRNSS constellation. The Ground segment comprises of:
1. IRNSS Spacecraft Control Facility (IRSCF)
2. ISRO Navigation Centre (INC)
3. IRNSS Range and Integrity Monitoring Stations (IRIMS)
4. IRNSS Network Timing Centre (IRNWT)
5. IRNSS CDMA Ranging Stations (IRCDR)
6. Laser Ranging Stations
7. IRNSS Data Communication Network (IRDCN)
User Segment:
The user segment consists of IRNSS receivers operating in:
• Single frequency (L5 at 1176.45 MHz or S-band at 2492.028 MHz)
• Dual-frequency (L5 and S-band)
The single frequency and dual-frequency receivers shall receive both SPS (Special Positioning System), which is provided to all users and RS (Restricted/Authorized Service) signals, which is an encrypted service provided only to authorized users. The IRNSS user receiver calculates its position using the timing information embedded in the navigation signal, transmitted from the IRNSS satellites. The timing information being broadcast in the navigation signal is derived from the atomic clock on board the IRNSS satellite.
