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Monday, July 14, 2014

A look at five satellites launched by PSLV C23

A PSLV ( Flight PSLV C23 )   launch on 30th June carried 5 satellites from various nations:

SPOT 7 is a French satellite weighing 714 Kgs. This is the main payload that C23 is has carried. The other 4 satellites are what are called as ' piggybacks'.  - PSLV can carry more than SPOT's weight so a few lightweight satellites are also carried along and hence they are also referred as co-passengers.

In this C23 flight ( Incidentally  C stands for commercial !!!   yes  c o m m e r c i a l ..  ISRO earns some cash to reduce your and my tax contribution burden to ISRO  )
    - AISAT is a German satellite weighing 14 Kgs,
    -  CAN X4  and CAN X5 are canadian satellites each weighing 15 Kgs,  and the smallest is
    -  VELOX 1 from Singapore weighing 7 Kgs,

All these five satellites were released from the rocket almost at the same time ( within just over 2 minutes period ) and in the same order as listed above.

The adjacent figure shows the positions of these satellites at about 01:15 AM  ( IST ) on 15th July 2014. Note that they are now separated significantly from each other ( use your maths skills ..  radius = 6371 average earth radius ,  Satellite height = about 650 kms from Earth surface ,  seperation between SPOT7 and Velox is about 1/2 a circumference,  sepeartion between SPOT7 and AISAT is about 1/4th of circumference. )

Presently heights of the satellites are as follows:

SPOT 7  698 Kms

AISAT 653 Kms

CANX 4/5   654 Kms

VELOX 654 Kms

Notice that there is one 6th body in the drawing. Is it a mistake?  NO.....   this a part of the same launch. It is the 'womb' - the last stage of PSLV C23 which carried the satellites upto their ejection height and has the 'release' mechanism  which ejects the satellite into space.  In fact spacecraft release itself is a very complex procedure which , if not designed and executed properly can make the released satellite to collide with the launcher and cause damage/crippling of both. A wrongly released satellite may go astray and loose forever ; it could start spinning ..  and several possibilities of malfunction exist. So, launcher is a very important ( but rarely praised ) part. Unfortunately as soon as the last satellite is released this very important part ( VIP ;) ) turns into the most unwanted DEBRIS. One of the thousands of 'useless' man-made objects that circle around Earth creating a threat of collision with useful satellites.

Of late therefore,  the 'good' launch operators make changes in the launcher orbit ( at the cost of a lot of money  which they could have simply saved) so that the launcher falls towards Earth and burns itself. This de-orbitting slows down the debris speed and it gets deflected to successive lower orbits.

At the time when these orbits were computed the PSLV C23 launcher was slowly coming down and its orbital height was 624 Kms ( compared to 650 and 700 kms of satellites that it launched ).

A small observation: SPOT7 orbit is higher ( 694 Kms )  than the other satellites ( about 654 Kms ) so spot should have lagged behind the rest .. but it appears to be leading the lot..  how?

Actually SPOT is lower and was in 218th  orbit from launch when this graphic was generated whereas the others were in their 219th orbit, lagging thereby by more than one orbit.

The launcher was slowed down for de-orbitting and so was in its 216th orbit.

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