

India Launches Its Second Navigation Satellite - middleclick
http://www.space.com/25373-india-navigation-satellite-launch.html

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ljd
"Preliminary data showed the rocket placed the spacecraft in an orbit with a
high point of 12,807 miles, a low point of 176 miles and an inclination of
19.2 degrees."

Maybe I'm reading this wrong, but this appears to be a very elliptical orbit
with a the difference between the high and the low being more than 70x.

Does someone here know what the purpose of such an orbit is? Obviously it
states navigation but I guess that's not enough for me to understand why they
would pick such an orbit.

~~~
swatkat
Geostationary satellites have a circular equatorial orbit, at 35,786 km above
the Earth. Launch vehicles can only place satellites in an elliptical orbit
with some degree of inclination from equator. So, geostationary satellites are
placed in elliptical "geostationary transfer orbits". And, satellite's onboard
propulsion system is used to:

1) Gradually raise the apogee

2) Transform elliptical orbit into circular orbit

3) Reduce inclination to zero degree with respect to equator.

Orbit's apogee is raised by firing onboard motor at perigee. Circular
transformation is done by firing onboard motor at apogee.

~~~
swatkat
If a launch vehicle can place satellite in a geostationary transfer orbit with
calculated apogee of 35, 786 km itself, the the apogee raising operation (i.e.
perigee firing) is not required. Satellite can just start firing at apogee to
transfrom elliptical orbit to circular orbit.

ISRO's PSLV-XL placed IRNSS-1B at an apogee of 20,630 km. So, ISRO needs to do
apogee raising before transforming into circular orbit.

~~~
swatkat
ISRO's bigger rocket GSLV Mk2 can launch satellites directly to geostationary
transfer orbit (calculated apogee of 35,786 km), so there's no need to do
orbit raising manoeuvres.

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swatkat
Launch video:
[http://www.youtube.com/watch?v=LtdgrcF1nFg](http://www.youtube.com/watch?v=LtdgrcF1nFg)

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dalek2point3
As an indian citizen I've never understood how these technologies ever reach
me. I know GPS is by the US government, is any one commercializing these
technologies in India?

"Indian officials say the independent navigation service will aid marine
traffic, emergency response officials, vehicle tracking applications, mobile
communications, mapping, and civilian drivers."

~~~
swatkat
IRNSS wiki page[1] sums up nicely, on _why_ indigenous navigation system is
required:

    
    
      The requirement of such a navigation system is driven by the fact that access to foreign government-controlled global navigation satellite systems is not guaranteed in hostile situations.
    
    

Two more IRNSS satellites will be launched by the end of 2014, and remaining
three will be launched by mid 2015. So, the 7 satellite constellation will be
ready by 2015. IRNSS receivers (akin to GPS receivers) can be tested by 2014
itself (4 satellites are sufficient for determining position). I've come
across few vendors who already have industrial/commercial grade IRNSS
receivers[2]. So, it's only a matter of time until we start seeing IRNSS
receiver chips in consumer electronic devices.

Missiles use satellite navigation to determine their targets. So, relying on
external navigation systems is undesirable.

[1]
[http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Sa...](http://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_System)

[2] [http://gpsworld.com/novatel-supplies-reference-receivers-
for...](http://gpsworld.com/novatel-supplies-reference-receivers-for-irnss-
ground-segment/)

~~~
quanticle
Do we know if IRNSS will be backwards compatible with GPS (like the Galileo
system that the Europeans are launching)?

~~~
swatkat
No. IRNSS is not compatible with GPS.

[https://www.quora.com/Indian-Space-Research-Organisation-
ISR...](https://www.quora.com/Indian-Space-Research-Organisation-ISRO/Is-
IRNSS-1-aimed-at-augmenting-the-GPS-or-is-it-entirely-inaccessible-by-
existing-GPS-receivers?share=1)

