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The Military Politics

India Successfully Launches Region-Specific Navigation Satellite 86

vasanth writes India has successfully launched IRNSS-1C, the third satellite in the Indian Regional Navigation Satellite System (IRNSS), early on October 16. This is the 27th consecutively successful mission of the PSLV(Polar Satellite Launch Vehicle). The entire constellation of seven satellites is planned to be completed by 2015. The satellite is designed to provide accurate position information service to users in the country as well as in the region extending up to 1,500 km from its boundary, which is its primary service area. In the Kargil war in 1999, the Indian military sought GPS data for the region from the U.S. The space-based navigation system maintained by the U.S. government would have provided vital information, but the U.S. denied it to India. A need for an indigenous satellite navigation system was felt earlier, but the Kargil experience made India realise its inevitability in building its own navigation system. "Geopolitical needs teach you that some countries can deny you the service in times of conflict. It's also a way of arm twisting and a country should protect itself against that," said S Ramakrishnan, director of Vikram Sarabhai Space Centre, Thiruvananthapuram.
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India Successfully Launches Region-Specific Navigation Satellite

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  • So this satellite only orbits above India?

    That must be a tricky orbit.

    You could have one sitting above Sri Lanka (well a little bit to the south) 25,000 miles up.

    • by Anonymous Coward

      It must be great having no idea how anything works. It makes it so much easier to be snarky.

      Satelite navigation systems work by measuring the time difference between signals from more than one satellite. A minimum of 3 for a 2D fix, a minimum of 4 if you want to add a dimension and get altitude information as well. So you make a regional system by setting up the orbits so that there are always 3-4 satellites visible from the region of interest. Occasionally you will be able to get a fix elsewhere in the

      • So you make a regional system by setting up the orbits so that there are always 3-4 satellites visible from the region of interest. Occasionally you will be able to get a fix elsewhere in the world, but usually not.

        Actually, while it's generally pretty trivial to make sure 3-4 (5+ would be better) are visible from any given point on Earth, it's rather harder (read: nearly impossible) to make sure 3-4 are visible from any point in India but NOT from any point outside India.

        Unless the satellites are in geosy

        • "Unless the satellites are in geosynchronous orbits, of course, but then you're not going to have the separations you need for a good solution."

          The satellites are at geosynchronous altitude but located off the Clarke Belt. This results in a constellation of satellites which appear to move north/south or in a figure 8 above a fixed point on earth.

          The japanese system is setup the same way - in that case resulting in rather good australian coverage, but other than Sri Lanka there's nothing due south of India e

    • by Rich0 ( 548339 )

      Agree. It isn't clear to me how one implements a "regional GPS." You could certainly implement a global one and then disable it outside of the region (ie satellites don't broadcast when they're not near India). Maybe a few in geosync might work - they would all lie on the equator so the solution to the problem would allow for a position in either India or the Indian ocean, and if it is "regional" they could just exclude the southern solution. I'm not sure what the accuracy would be like since all your f

      • IRNSS sats are geostationary, they are positioned above india and dont move.
        • Re:Region-Specific (Score:5, Informative)

          by Anonymous Coward on Saturday October 18, 2014 @10:42AM (#48175807)

          Three of them yes. 3:4 in geostationary vs geosynchronous orbit of 1 sidereal day.
          So, three will always be visible over india. Two of the other other four will be timed such that they are over India in a 24 hour period.
          So, 5 satellites will provide a fix.
          Hope that helps.

        • by AHuxley ( 892839 )
          Great link, ty.
          The "Such an arrangement would mean all seven satellites would have continuous radio visibility with Indian control stations." and "A network of 21 ranging stations located across the country will provide data for the orbit determination of the satellites and monitoring of the navigation signal." should help most readers understand the navigation system.
          Great news from India and it shows the long term design efforts. Fully understanding the science and been able to build the needed system
        • by Rich0 ( 548339 )

          Thanks. The geosynchronous orbits are probably the key - at any time one would be far enough above the equator to provide the necessary angular separation to improve accuracy.

  • by BlackPignouf ( 1017012 ) on Saturday October 18, 2014 @10:11AM (#48175699)

    director of Vikram Sarabhai Space Centre, Thiruvananthapuram

    With the added benefit that saying "8.460N,76.963E" is much faster than pronouncing this city name!

  • How do they stop the service at the borders? Do the sats turn around?
    They are in polar orbits, so they cover the whole planet. How can that be considered regional?

Long computations which yield zero are probably all for naught.