The Russians have pointed their fingers at the rocket's bigger heat shield (4 metre) as the proximate cause for high atmospheric load on the rocket that broke it. Refuting that theory, Indian officials cited an earlier GSLV rocket that went up with a heat shield of similar size.
The Indian Space Research Organisation's (ISRO) 418-tonne Geosynchronous Satellite Launch Vehicle (GSLV) rocket (cost Rs.175 crore) carrying advanced communication satellite GSAT-5P (weight 2,310 kg, cost Rs.150 crore) veered off its flight path and began disintegrating within one minute after lift-off from Sriharikota in Andhra Pradesh Dec 25, 2010.
"The Russians have attributed the failure to bigger heat shield. However, we have established why it can't be," former ISRO chief G. Madhavan Nair, who heads the failure analysis committee (FAC), told a news agency.
Till date the FAC has met thrice - the first meeting was in January and the subsequent two meetings were held Feb 7 and Feb 14 at Thiruvanathapurm in Kerala.
According to the ISRO, the rocket's failure was due to the snapping of 10 connectors that carry command signals from the onboard computer to the control electronics of the four strap-on motors in the first stage.
The German made connectors are fixed on a metal plate. The plate, in turn, is fixed to a shroud or cylindrical cover that comes between the cryogenic engine and the lower stage (engine).
The shroud made of composites is part of the Russian cryogenic engine and it got deformed due to the flight load which in turn led to the snapping of the connectors.
Experts said that the first 15 kilometres of a rocket's flight is a very crucial time as it is subjected to heavy atmospheric loads. It is more so when the rocket is escaping the earth's gravitational pull at 330 metres per second.
The flow of air along the rocket will be turbulent at the transonic speed - when the rocket crosses the speed of sound. At that point the air will attach to the rocket at some places and detach at some spots in a haphazard manner.
According to Nair, there is no divergence of views between the ISRO and the Russians on the reasons for the connectors demating, that is, the shroud deforming during the rocket's flight.
At the Feb 7 meeting, the Russians after analysing the data and the pictures provided by ISRO, agreed that the connectors snapped due to deformation of the shroud.
However, they said the rocket suffered heavy atmospheric loads due to its bigger heat shield which in turn resulted in the deformation of the shroud.
The Dec 25 GSLV's heat shield measured 4 metre diametre as against 3.4 metre diametre most of the earlier GSLV rockets had.
ISRO officials argue that a rocket with a 4 metre diametre heat shield was flown in April 2010.
Though the April 2010 rocket too went down into the sea as the Indian made cryogenic engine failed to power the rocket, ISRO officials said the failure happened only after the first two stages performed well.
According to them, necessary calibrations have been carried out in the rocket's navigational systems, control dynamics and aerodynamics factoring the bigger heat shield carried by the GSLV rocket.
Nair said ISRO's different teams are carrying out various experiments to arrive at the cause of load on the rocket.
The Russians, on their part, told ISRO that they would revert after studying the data provided to them.
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