Rocket failure: ISRO awaits data from Russia

An 11-member expert committee was set up to study the reasons for the disintegration of the heavy rocket Dec 25, 2010, shortly after lift-off.

"We are expecting some data from the Russians who had supplied the cryogenic engine. The Russians are expected to provide the data by the end of this month," former ISRO chief G.Madhavan Nair, who heads the committee, told IANS.

"We have scheduled another meeting of the failure analysis committee (FAC) Feb 7 at Thiruvananthapuram where we hope to come to a conclusion as to the cause of the GSLV's loss," he said.

The 418-tonne 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.

According to the ISRO, the primary cause for the rocket's failure was 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 committee is examining why the connectors snapped. It has met once in Thiruvananthapuram early January.

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).

According to Nair, the shroud made of composites is part of the Russian cryogenic engine and it got deformed due to the flight load. The committee is yet to conclude why the shroud was not able to bear the load.

Experts told IANS 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, the experts said, preferring anonymity.

The deformation of the cylindrical shroud is a structural failure and the reasons for that is what FAC is looking into.

Nair said some tests are being conducted in that connection.
ISRO has set up various sub-teams to study and analyse the flight data.
Compared to the other Russian cryogenic engines that powered the earlier GSLV's, the one that was fixed to the ill-fated Dec 25 rocket was 1.3 metres longer to contain higher fuel.

According to a retired ISRO official, the GSLV broke most likely due to the instability caused by the heavy satellite it carried.

Dismissing the contention, another ISRO official said: "The increase in the satellite GSAT-5P's weight is just 90 kg as compared to the GSLV rocket that carried the GSAT-4, weighing 2,220 kg in April. Such marginal increase in weight will make no difference."
He also discounted the possibility of the rocket becoming unstable because of the two-tonne increase in its overall weight as compared to the April GSLV rocket that weighed 416 tonnes.

"The rocket would have burned around 100 tonnes of first stage fuel by the time the problem started. So a mere addition of two tonnes to the rocket's weight would not make it unstable," he added.

R.V. Perumal, a retired ISRO rocket scientist, said: "When the rocket configuration changes, necessary calibrations will be carried out in its navigational systems, control dynamics and aerodynamics to make the mission successful."

ISRO officials say the rocket's capability will be improved continuously so as to arrive at optimum level.

The GSLV rocket that blasted off in April 2010, powered by an indigenous cryogenic engine, stood 50 metres tall and had a lift-off weight of 416 tonnes. That mission too failed as there was a problem in the cryogenic stage built by the ISRO.

The standard configuration for GSLV is a height of 49 metres and a weight of 414 tonnes at lift-off whereas the rocket that went up in flames was taller by two metres and heavier by four tonnes.

Queried about the ISRO getting GSLV technology right, Nair said that the space agency has got the technology right for individual systems and the problem seems to arise when the systems are integrated into a single rocket.