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Wednesday, March 25, 2015

IRNSS 1D Launch on 28th using PSLV C27 ... Warming up

A new post has been created showing Orbit Raising of IRNSS 1D to its home.
Fourth ORM has been carried out ..  Quoting ISRO
The fourth and final orbit raising operation of IRNSS-1D is successfully completed by firing the Apogee Motor for 493 seconds, at 06 42 hrs IST, on on April 01, 2015. The orbital parameters are: Perigee Altitude: 35556 km, Apogee Altitude: 35603 km, Inclination: 30.463 degree and Orbit period: 23hr 45min 
Third ORM has been carried out ..  Quoting ISRO
The third orbit raising operation of IRNSS-1D is successfully completed by firing the Apogee Motor for 22 minutes, at 11 37 hrs IST, on March 31, 2015. The orbital parameters are: Perigee Altitude: 23881 km, Apogee Altitude: 35569 km. Orbit period: 18hr 57min.
But, somehow the technical details ( State Vectors ) are not available for 2nd and 3rd ORM till now.
While I am writing ..  ISRO has announced that 2nd ORM has been carried out
The second orbit raising operation of IRNSS-1D is successfully completed by firing the Apogee Motor for 28 min 23 sec at 09 07 hrs IST, on March 30, 2015. The orbital parameters are: Perigee Altitude: 8459 km, Apogee Altitude: 35565 km, Orbit period: 13 hr 13 min.
As soon as we get a new state vector we will plot the changes achieved.
A new set of State Vector ( Numbers defining the orbit ) of IRNSS 1D is now available. It suggests that ISRO has carried out a orbit raising maneuver by operating LAM ( Liquid Apogee Motor ) at Perigee  at about 1205 UT/29th Mar 2015.( These timings and deatils are my inferences based on the State Vector ...  not vetted by ISRO ,  but has somehow not made it public.
The orbit geometry with these State Vectors show that the spacecraft has entered into a 35591Kms Apogee and 310Kms as perigee. and has been plotted hereunder.
Notice the number 35591? ..  does it ring anything? ..  yes, it is the height at which a satellite becomes geosynchronous. So now one end of orbit ( the Apogee point ) is already at the rerquired height and the other point viz. the perigee portion has to be raised to GSO height and this will be achieved by firing LAM at Apogee point instead of Perigee point as was done during this 1st ORM we have described.


1st image shows the Launch orbit ( BLUE ) being raised to Yellow orbit  by firing the LAM at perigee ( Blue small dot ..  nearest point to Earth ).
2nd image shows details of change in path ( Blue path would have been taken had there been no LAM firing while Yellow path to which  it has been directed post LAM operation ) and the third image shows that the plane remains same even after LAM firing.

Let's delve into the Physics involved in ORM:

Here we have zoomed in the situation that was shown in the middle figure above.

First look at the bottom portion. We have computed orbit height and speed against time near the perigee which occurs at 12:08 GMT. Blue square shows values for the Launch orbit and Yellow square shows the same values for intended orbit into which the spacecraft has to be sent. We can see that in launch orbit the velocity ( red hashed circle ) is 9.8 kms/sec and the speed in intended orbit id 10.14 kms/sec.
So it is just a matter of increasing the craft speed from 9.8 to 10.14 kms by the time it reaches perigee. This is achieved by firing the LAM a few minutes before. ISRO has said in its bulletin that LAM firing was started at 1728 IST ( 1158 GMT ).
Due to this the craft velocity started increasing and so its increased centrifugal force it started moving away from Earth. This is shown by the red dashed line in top figure. When the craft speed reached 10.139 kms/sec the LAM firing was stopped an the craft entered in the intended new orbit with this point as Perigee.

Arun Venkataswamy, a hobbyist from Chennai, used his home brewed equipment of Camera and a Astronomical mount to obtained some breathtaking images of PSLV C27 flight from Chennai.

A real rare opportunity utilized to full extent.

1st image is 1st stage with full ignition.
2nd image shows the falling 4 strap on motors and the remaining 2 are seen separated in 3rd picture.
 4th and 5th image are the peak of opportunity ... that fraction of second apart ..  1st stage spent ( not burning ) and 2nd stage ignited ( and do not forget ..this whole drama happening at 57 kms altitude and  100+ kms away  )

Update 28Mar1900Hrs Indianapolis/29Mar0430 IST

Orbit of IRNSS 1D after launch is shown in figures below:
Orbit Shape

Orbit period : 6Hrs 1.2 Min ( 3.98 Orbits /day )
Semimajor Axis : 16807.1 Kms
Semiminor Axis : 13392.8 Kms
Apogee: 20569.1 Kms

Perigee location and Height above Earth
Perigee Height : 278.1 Kms



Update 28th March 1750 IST/0820 Indianapolis

IRNSS1D placed in required orbit successfully via PSLV C27 Launch.

A clear weather over SHAR gave an opportunity to view the physical separation  of 4 Groundlit PSOM-XL motors.

Ejection of 4 PSOMs

The 2 of 4 add-on rockets are clearly visible lagging behind the advancing PSLV

Update 27th March night.

1st and 3rd stages of PSLV are solid stages fabricated along with the propellants. So when they are assembled they are already loaded.
2nd and 4th stages are Liquid engines and they have to be charged after assembly just before the actual launch with two components: Fuel and Oxidizer.

On 26th morning Fuel component viz. Mono Methyl Hydrazine (MMH) filling of 4th stage was commenced and was completed by Noon.
In evening this stage was filled with Mixed Oxides of Nitrogen (MON-3) which is an oxidizer to supply oxygen during stage operation.
Propellant filling of 2nd stage would be taken up soon.

Live telecast of launch will commence at 1650 IST on Doordarshan

IRNSS 1D is set to  Launch on 28th using a PSLV rocket at 17:19 IST ( 11:49 UTC ).

The rocket to be used is a XL version ..  meaning it will have 6 extra large Strap On Motors added to central core of PSLV to boost the thrust created by central core.

( We have covered PSLV XL in detail  in an earlier post )

This will be the 4th satellite in the 7 satellite constellation which we had covered here.

PSLV C27 will be ignited at05:49 IST.

1st stage will burn for 1 min 50 sec and carry the rocket to 56 kms height and its speed would be 2.4 Kms/sec.

2nd stage will burn for 2 min 33 sec and carry the rocket to 131 kms height and its speed would be 5.38 Kms/sec.

3rd stage will burn for about 6 min  and carry the rocket to 184 kms height and its speed would be 7.7 Kms/sec.

Between the 3rd stage seperation and 4th stage ignition there is small Coast for about 10 seconds
during which the rocket would be moving only under the influence of attained Kinetic energy. There is no active force ( excluding gravity ) driving the 4th stage and satellite.

4th stage will burn for 8 and a half  minute and carry the rocket to 454 kms height and its speed would be 9.6 Kms/sec. In fact the 4th stage would shut down as soon as the targeted orbit of 284kms Perigee, 20650 Kms Apogee with an inclination of 19.2 degrees is achieved.

After the 4th stage shutdown ( yes .. only shutdown .. the stage is still connected to satellite ) the rocket would continue to travel to the precise location in the orbit ( at a height of about 507 kms ) where the speed of satellite would be 9.6 Kms/sec.
This is the 2nd Coasting and after this point the satellite will be gently separated from 4th stage.

( In the regular orbit satellite speed at perigee would be  about 9.8 kms/sec  and it would reduce as the satellite travels towards apogee. In between, after the perigee, there would be a location where the satellite would travel with a speed of 9.6 kms/sec. ..  the satellite would be separated from rocket at this location ).

We like to watch the Launch of PSLV video.

You may enjoy more if you know what and why of the events being shown.
We have a quick brush-up  here   about actual launch process ..  go through and we assure you that your experience of video will multiply several fold.

We will continue with this post after the launch with actual data.


  1. Nice informative article! One question - why is the satellite decoupled from the spent fourth stage only when it will be at a height of 507 km and 9.6 km/s orbital speed ?

    Also, for a geosynchronous satellite, how is the satellite finally placed in its target slot, in this case over the 111.75°E longitude?

    1. I mean, how is the satellite exactly drifted to its target orbital slot of 111.75°E in this case?

    2. Thanks for the interest.
      I am currently midway in covering that topic. May be tomorrow or a day after .. along with updates post launch.

    3. Regarding 4th stage ..

      1. The 4th stage shutdown specified here is only tentative. Launch System ( which is an autonomous process .. all decisions are by computer itself without human intervention ) will decide when to shut off based on realtime requirements.
      2. ( My guess ) .. 4th stage is not separated because the system has to continue to rise to 507 kms from 454 kms with the kinetic energy that has been achieved till 4th stage was burning. Now sudden removal of 4th stage would reduce the 'm' significantly from 1/2mv^2 formula and so there is a loss of momentum which will not allow the satellite to climb.