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Explained: Guardian in the sky

IRNSS 1D, which was launched on Saturday from Sriharikota, is the fourth satellite to be launched.

Written by Sushant Singh |
Updated: March 29, 2015 12:42:09 am
ISRO, ISRO satellite launch Indian Space Research Organisation’s Polar Satellite Launch Vehicle (PSLV-C27) carrying India’s fourth navigation satellite IRNSS-1D, lifts off from Satish Dhawan Space Center in Sriharikota on Saturday. (Source: PTI)

IRNSS-1D, launched on Saturday, is the fourth satellite in a planned seven-satellite Indian navigational system. IRNSS, set to be fully operational by mid-2016, will have a critical application for the Indian armed forces. SUSHANT SINGH explains how:  

What is the Indian Regional Navigation Satellite System (IRNSS)?

It’s a GPS-like regional satellite-based navigation system being developed by India. But unlike the US-operated Global Positioning System (GPS), or the Russian GLONASS, the EU’s Galileo or China’s Beidou Navigation Satellite System (BDS), which have global coverage, IRNSS will focus on the region — up to 1,500 km beyond India’s boundaries, between longitude 40° E and 140° E, and latitude ± 40°. The project will cost around Rs 1,420 crore.

READ: India launches fourth navigation satellite

How many satellites will be part of it?

IRNSS is planned as a constellation of seven satellites. Three will be placed in geostationary orbit located at 34° E, 83° E and 131.5° E; the other four in geosynchronous orbit at an inclination angle of 29°, two each with the equator crossing at 55° E and 111° E. The three geostationary satellites will appear fixed in the sky, while the four geosynchronous satellites will appear to move in the figure of ‘8’ when observed from the ground.

IRNSS 1D, launched on Saturday from Sriharikota, is the fourth in the series. Work to augment the IRNSS system with four additional satellites will begin after the system becomes operational. That will bring the IRNSS to 11 satellites — still be small compared to the Chinese BDS, which will consist of 35.

What will be its ground infrastructure?

A total 20 stations for generation and transmission of navigation parameters, satellite control and monitoring, mostly at airports, along with Indian GPS Aided Geo Augmented Navigation (GAGAN) ground elements. IRNSS will also have two Master Control Stations, likely to be co-located with GAGAN Indian Master Control Centres.

When will IRNSS become operational?

Basic navigational services in limited areas can be provided with four satellites in orbit now. At this stage, ISRO will use the system to test its accuracy. All seven satellites are scheduled to be in orbit by early next year, and IRNSS is scheduled to be fully operational by mid-2016.

How accurate will the coverage be?

IRNSS will provide positional accuracies similar to the GPS: 10 m over the Indian landmass, 20 m over the Indian Ocean. As is the case with GPS and the US military, IRNSS will provide a more accurate restricted service for the Indian armed forces and other special authorised users.

What are the applications of IRNSS?

Terrestrial, aerial and marine navigation, disaster management, vehicle tracking and fleet management, integration with mobile phones, mapping and geodetic data capture. Also, terrestrial navigation aid for hikers; visual and voice navigation for drivers. But the crucial use will be for Indian armed forces, who can rely on assured positional data during hostilities. Most modern weapon systems like guided missiles and bombs use navigation systems for targeting. An indigenous system like the IRNSS will ensure reliable development and execution of such capabilities.

Why is IRNSS so critical to the military?

IRNSS is a strategic requirement for modern war-fighting. Because access to foreign government-controlled navigation satellite systems such as the American GPS or EU’s Galileo is not guaranteed during hostilities — as experienced by India banking on the GPS during the Kargil war — it is critical to have India’s own system in the likely area of military operations.

Does Pakistan have an IRNSS like system?

No. Pakistan’s armed forces currently rely on the US GPS system but are scheduled to switch to China’s Beidou. China may build a network of ground stations in Pakistan to enhance location accuracy.

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