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Saturday, April 4, 2015

Orbit raising of IRNSS 1D to its Home ( 111.5 deg East Long )

IRNSS-1D may reach its home today.
We had been eagerly waiting for  updated data about the orbit of IRNSS-1D.  But after 1st ORM on on 29th March the data has not been updated so I can't give the very accurate numerical calculations ( as given about 1st ORM in earlier post ) but still based on their bulletins I have tried to create Graphical representation of ORMs here.

Figure on right shows the two important points A and B.
The rocket PSLV C27 delivered the satellite near point A which is a perigee of Launch Orbit marked as  L.
This launch orbit had an Apogee of 20569 Kms.

As shown in detail this orbit was raised to 1 by firing the LAM near A. This raised the apogee to 35591 Kms.
In this orbit when the satellite was near B on 30th March, LAM was fired to carry out 2nd ORM. This ORM raised the point A of orbit 1 to 8459 Kms from about 300 kms.
Again when the saatellite came near B ( via orbit 2 ), the LAM was fired 3rd time ( on 31st March ) which raised the orbit further ( Represented as 3 ) to 23881 Kms.

Note that all these orbits are in the same plane which is inclined to equator at 19.22 degrees.

 The next ORM  of1st April was a little more complicated. This LAM firing was directed in such a way that the satellite changed its orbital plane from 19.2 deg inclination to 30.46 deg inclination in addition to raising the orbit further to 35556 Kms perigee and 35603 Apogee.
This operation is shown in the figure on left wherein White orbit was changed to Green.

The satellite  in this green orbit takes 23 Hrs 45 minutes to complete.  
We know that Earth makes one rotation in 23Hrs 56 Minutes so it follows that the satellite completing its orbit in 23Hrs 45 Mins  should move ahead of Earth in every orbit.

For a moment we deviate to a ( fictitious ) regular Geosynchronous inclined orbit shown as GSO in adjacent figure. Notice that the orbit forms a regular 'figure of 8' centered around equator.This is due to the fact that the satellite starts its orbit on equator at one point ( about 132 deg Long ) and over a day traverses the '8' path to return to 132 deg again at the same time next day.

Unlike this orbit the IRNSS, due to its 23Hr45 min period moves ahead every day as seen in the 5 orbits and so at the end of the 5th day ( i.e. around 5th April ) it would reach about 111 deg which is its home. As soon as it reaches its home longitude the orbit would be made a circular one with a radius of about 35800 Kms  with aperiod of 23Hrs 56 min.

A word of caution: Notice that I said 'around 5th April' ..  it is due to the fact that latest data ( called State Vector ) is not available in public domain after 29th March.

All the graphics created are based on the post facto 'details' and not the data ..  hence the conclusions are inferences and not actual facts.

Next PSLV Launch ( Tentative ) :

PSLV-XL  C28 in June '15  with following 4 Payloads :

1. Skysat3,  is a part of constellation of 24 Skysat satellites ( 500 Kms Sun synch Orbit )belonging to California based Skybox Imaging ( now acquired by Google ).  being built by Space Systems / Loral ( SSL ) also from California.
2. 3 satellites  ( DMC-3A, 3B and 3C ) from DMC3 constellation ( 650 Kms Sun synch Orbit ). These are built by Surrey Satellite Technology Ltd, ( UK ) for 21st Century Aerospace Technology Ltd ( 21AT).

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  1. tract it on

    1. Yes, it is available on n2yo.
      But it uses the old data of 29th March i.e. after 1st ORM.
      Later 3 more ORMs have been carried out as detailed in this post so what you see in n2yo is not correct real time tracking. ( It is not their fault .. latest data is just not available. As mentioned in the blog I have generated my data base based on INFERENCES from the details of ORMs published by ISRO. It is NOT the ACTUAL data. That is the reason I cautioned the reader in last 2 lines )

  2. Now the updated data is available in public domain. It matches well with my inference in the post. Will update the post soon.