The project is the Indian counterpart of the Global Positioning system

The Indian Space Research Organisation (ISRO) intends to launch the first in a constellation of seven satellites envisaged for the ambitious Indian Regional Navigation Satellite System (IRNSS) project, GPS' Indian counterpart, by the end of next year.

“The subsystems [of the satellite] are under various stages of fabrication at ISRO's centres. At least four such satellites [each with a life in excess of seven years] are required to make it operational. After launching the first satellite using a PSLV in the last quarter of 2011, periodic launches would take place every six months. Which means by 2014, we would have the IRNSS optimally functional,” said ISRO sources here.

Range of applications

IRNSS, which will have a range of applications including personal navigation, will be India's answer to the U.S.-operated GPS, Russia's Glonass, European Space Agency's under-development Galileo, and China's emerging constellation, Compass.

“The problem with the existing constellations is that they are controlled by defence agencies in those countries. While Galileo is a pay-to-use system, Compass is military-controlled. On completion, IRNSS will have all-weather, round-the-clock coverage over the Indian landmass with an extended coverage of about 1,500 km around it,” said the sources.

Meanwhile, the GPS-Aided Geo Augmented Navigation (GAGAN) payload in GSAT-4 which would be placed into the geosynchronous transfer orbit — before the satellite self-adjusts into its geostationary orbital home at 82 degree east longitude — by the eagerly-awaited April 15 flight of GSLV-D3 with indigenous cryogenic upper stage will provide a position accuracy of better than 7.6 metres required for precision landing of civilian aircraft.

The navigational payload, operating in C, L1 and L5 bands, will form the space segment of GAGAN Satellite-Based Augmentation System (SBAS). “We are planning the launch of GSAT-8, with another GAGAN payload, by this year-end. A third satellite, GSLV 8 or 9, with GAGAN payload would also be launched in succession,” the sources said.

Independent function

GAGAN and IRNSS, once it comes into being, will function independent of each other. The ground segment of GAGAN comprises Indian Reference Stations (INRES) Indian Master Control Centre (INMCC) at Kundanhalli, near Bangalore, and Indian Land Uplink Stations (INLUS). ISRO has already set up eight such reference stations at eight Indian airports in collaboration with Airports Authority of India during the technology demonstration phase of GAGAN and 14 more are in the pipeline.

GAGAN's user segment consists of SBAS receivers capable of receiving GPS signals and corrections from geostationary satellite.

“Data from INRES is transmitted to INMCC. This data is processed by INMCC and sent to INLUS. INLUS transmits the corrected GPS information and time synchronisation signal to a geostationary satellite. It then transmits a GPS-like signal with an accuracy of the order of 3 metre horizontal and 4 metre vertical [which can be accessed by GPS SBAS receivers],” explained an ISRO media hand-out.