The Indian Navigational Satellite System
T.S. Subramanian*

When India’s Polar Satellite Launch Vehicle (PSLV-C22) rose from its launch pad at 11.41 p.m. on July 1, 2013 from the spaceport at Sriharikota, Andhra Pradesh and put into orbit a navigation satellite called the Indian Regional Navigational Satellite System (IRNSS-1A) 20 minutes later, it signalled that India can build its own navigation satellites for civilian and defence requirements and put them into tricky orbits. The message itself was clear: that India need not depend any more on the U.S.’ Global Positioning System (GPS) or the Russian Global Navigation Satellite System (GLONASS) for the navigation of its civilian ships, aircraft, trucks and cars or its fighter-aircraft, missiles, battle tanks and unmanned aerial vehicles (UAVs) towards their destinations/targets.

The PSLV-C22 mission, which put the satellite IRNSS-1A into orbit, was a special mission on a couple of counts. It was the first time that the Indian Space Research Organisation (ISRO) was attempting a night flight. The launch had to take place at night because the satellite had to be put into a “special, specific orbit.” It was neither a low-earth orbit meant for experimental satellites, nor a polar sun-synchronous orbit for remote-sensing missions nor geo-synchronous transfer orbit (GTO) where the communication satellites are initially slotted, it was a sub-GTO for the IRNSS-1A and ISRO was attempting it for the first time. Yet, the trusty PSLV-C22 billeted the satellite into a perfect elliptical sub-GTO with a perigee of 282 km and an apogee of 20,625 km. From there, it has been boosted into the geosynchronous circular orbit of 36,000 km above the earth.

The IRNSS constellation consists of seven satellites and IRNSS-1A is the first among them. India will put all the seven satellites in orbit by 2015/2016. The IRNSS’ services will be available only after three or four satellites become operational.

India is among the select group of countries including the U.S., Russia, Europe, Japan and China to build its own navigation satellites. They are useful in terrestrial, aerial and sea navigation. They provide accurate information on the position of trucks, cars, battle tanks, aircraft, helicopters, missiles, UAVs, ships, submarines etc.. with precise timing reference. Drivers of trucks or cars, pilots of civilian or combat aircraft and captains of ships can plan their route properly by using the navigation satellites. In other words, the navigation satellites help them to know where they are at a particular point of time and guide them towards their destination with the help of a receiver. It can be an independent receiver or one that is built into a mobile phone, car, truck, ship or a missile.

While the U.S.’ GPS, the Russian GLONASS and the European Galileo are global navigation satellites which can be used by anybody anywhere in the world with the help of a receiver, the IRNSS-1A is a regional navigational satellite which will provide positional information to users only in India and the region extending 1,500 km from its borders.
The IRNSS-1A weighs 1,425 kg. Its sun and star sensors and gyroscopes provide it with orientation reference. An atomic clock is part of the satellite’s navigation payload. This atomic clock will provide the timing reference down to more than nano seconds. The satellite’s mission life is ten years. While the Space Applications Centre, ISRO, Ahmedabad, fabricated the satellite’s payloads, the ISRO Satellite Centre, Bangalore, integrated them into a satellite. It was the Vikram Sarabhai Space Centre, Thiruvananthapuram, which built the rocket PSLV-C22. The lift-off took place from the launch pad situated on the beachhead at the state-of-the-art spaceport on the island of Sriharikota. So it was India’s totally indigenous mission.

In aerial navigation, civilian aircraft can use the IRNSS-1A when they are cruising, approaching an airport to land or during landing. During these phases, the aircraft will know their position and the flight direction accurately. As they approach an airport to land, they will know at what height they are above the runway with an accuracy of 20 metres. Or they can land on the runway within 20 metres of the targeted landing spot.

The IRNSS constellation will help in reducing the distance of separation, both vertical and horizontal, among the aircraft circling over the airports to land. Civilian aircraft need not circle over airports for a long time to get clearance for landing if the air traffic is heavy. The aircraft may have to queque up to land but the waiting time will be reduced. So time and fuel are saved.

In the busy waterways of the world, the IRNSS constellation will help ships to navigate towards their destination through safe and short routes and in guiding them to enter harbours. In terrestrial navigation, drivers of trucks or cars, with the help of a receiver in their mobile phones, can reach their destination through the shortest route available. The constellation will provide visual and voice navigation for drivers. It will help fleet owners to keep a tab on the movement of their trucks. The satellites can act as a navigation aid for hikers and travellers.

In the field of defence, the IRNSS will help missiles in accurately reaching the targets – be it a town, an airport or an installation. The circular error probability (CEP) will be reduced. If the CEP is less and less, it means the missile is more accurate in reaching the target. Indeed, the IRNSS constellation can help missiles in “way-pointing.” If there are hills on a missile’s flight path, the missile, with the help of information received from the constellation, can circumvent the hills and reach the target. The atomic clocks on board the constellation will enable missiles to execute manoeuvres including rolls at the appointed time.

The IRNSS will be a boon for India’s submarine-launched missiles. The boats ought to know their position – where they are and how far away they are from the target – before they fire the missiles. Air-launched missiles can use the navigation satellites to know where they are.

Today, India has an assured access to space. It can build rockets on its own. It can build any kind of satellite, be it a communication, remote-sensing, weather or scientific (Chandrayaan) satellite and put them into their required orbits. The IRNSS-1A demonstrates that India is self-reliant in building navigation satellites too.

(*T.S. Subramanian is Associate Editor of Frontline Magazine and can be contacted at subramsivam@gmail.com)

PSLV-C22 ON THE FIRST LAUNCH PAD WITH MOBILE SERVICE TOWER AT A DISTANCE (Photo Courtesy: ISRO)

IRNSS-1A Satellite in clean room at Satish Dhawan Space Centre, Sriharikota (Photo Courtesy: ISRO)