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Sunday, October 19, 2014

Indian Regional Navigation Satellite System (IRNSS)


The Indian Regional Navigation Satellite System ( IRNSS ) is an independent, ingenuously developed  satellite Navigation system.

It has  been fully planned, established and controlled by the Indian Space Research Organization (ISRO).

The Space Segment of IRNSS consists of 7 satellites and  ( when  fully configured by end 2015 ), will consist of : 

The 3 satellites in Geo-synchronous Orbits ( GSOs )  parked  at :

                    32.5º E, 83º E and 131.5º E 

The remaining 4 IGSO  ( Inclined Geo-synchronous Orbit ) satellites  are :

with longitude crossings 55º E and 111.75º E (two in each plane). 

The overall final configuration is depicted in the images below.

Ground Traces of all 7 satellites over
the target area intended to be served by IRNSS
Sequence showing 3 positions of constellation
at 1 hr interval

Goal of IRNSS SERVICES is twofold : 

1. Standard Position Services (SPS), an open service without encryption
2. Restricted Service (RS), an authorized service with encryption 

First, i.e. SPS service, will be accessible to anyone having a IRNSS receiver. Regular GPS receivers will not be useful to access IRNSS.

The 2nd one  ( RS )   will  be a special purpose high accuracy service available to classified users only.

The satellites have these signal characteristics:

 Carrier frequency        Bandwidth       Nominal received signal strength

  1176.45 MHz                24 MHz                    - 127 dbm

  2492.028 MHz              16.5MHz                  - 130 dbm

As on date ( mid October 2014 ) 3 satellites have been launched and the current configuration with these satellites is shown below:

IRNSS 1A and 1B satellites ( launched in July 2013 and April 2014 respectively ) are already in their designated slot of 55º E Longitude. 

As can be seen in the figure on right that the orbits of these satellites are inclined at 29 deg with equator.

The Last satellite IRNSS 1C is in Equatorial GSO and will finally be placed at 83º E. 

It was launched by PSLV C26 rocket on 16th Oct 2014.  What you see here is the orbit  after 1st orbit raising on 17th Oct 2014. 

Figure on right is the snapshot of what was seen in the figure above but  as seen from  a point above North pole.

Both 1A and 1B are at the same longitude hence they overlap each other. 1B being in Northern hemisphere is only seen.  1A is below it so it is not visible. 

The two inclined satellites  1A and 1B are geosynchronous so they will always be on the same longitude but will oscillate N-S at that longitude making a figure of 8 in 24 hours

This is seen in the figure on left.

The inclination of 29 degrees means the figure of 8 will span +/- 29 degrees latitudes.

Also notice that just these 3 satellites will provide 3 distinct points for triangulation for location fixing throughout day except for a very small duration when 1A and 1B are at equator. But in full configuration the other 2 similar satellites at 111.75 E will provide the other 2 points spread in two hemispheres.

Current GPS will not be able to provide 3 points throughout 24 hours with just 3 satellites.

 That is the beauty of IRNSS.

Update : 18Aug2016

Now that all sats are in place here is a final overall coverage map:

Notice that it covers African, Asian and Australian Subcontinents fully.

But there's a catch!  For location fixation we require at least four satellites to be visible.  Next figure shows the approximate area which is covered almost always by at least 4 satellites simultaneously.

The dashed RED area shows 4 satellite coverage

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