ISRO Team Says Cable Rupture Caused Rocket Failure

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BANGALORE — A preliminary analysis of data from the failed launch of India’s Geostationary Satellite Launch Vehicle (GSLV) Dec. 25 has led an expert team to conclude that the primary cause of the mishap was the “untimely and inadvertent snapping” of a group of 10 connectors located at the bottom of the rocket’s Russian-supplied upper stage.

The Indian Space Research Organisation (ISRO) said in a Dec. 31 statement that the vehicle’s performance was normal up to 47.5 seconds after liftoff. It then began to stray from its planned orientation angle, which resulted in higher structural loads than the vehicle was designed to handle. The rocket, which was carrying the GSAT-5P telecommunications satellite, began to break apart about 58 seconds into the flight and was destroyed by command at 64 seconds.

It was the second consecutive failure of the GSLV. On April 15 a GSLV failed to place a communications satellite into orbit in a mishap that was attributed to a failure of India’s domestically developed cryogenic upper-stage engine, which was making its debut. The latest GSLV failure came during the first stage of flight.

ISRO said some of the connectors that snapped carried command signals from the onboard computer near the top of the vehicle to the control systems for the four L40 strap-on boosters that augment the rocket’s first stage. These connectors are intended to be separated by command 292 seconds after liftoff but their “premature” rupture stopped the flow of control commands to the boosters, resulting in the loss of control of the vehicle, ISRO said.

“The exact cause of snapping of the set of connectors — whether due to external forces like vibration or dynamic pressure — is to be analyzed further and pin-pointed,” ISRO said.

GSAT-5P, at 2,310 kilograms, was the heaviest payload ever placed aboard a GSLV, and one source had speculated that this was a factor in the failure. “It is possible the analysis by our scientists to look at vehicle stability after increasing the payload weight had gone wrong somewhere,” said this source, who has been associated with ISRO’s launch vehicle program for two decades.

In its statement, ISRO said it has formed a committee to carry out an in-depth analysis of the failed flight as well as of the previous six GSLV missions and recommend corrective actions. The committee is chaired by G. Madhavan Nair, former chairman of ISRO, and has 11 experts drawn from within and outside ISRO.

Of the six previous launches of GSLV only two were totally successful, with two partial successes.

ISRO also has created a panel led by K. Kasturirangan, also a former ISRO chairman, to look into the future of the GSLV program and the vehicle’s reliability for upcoming missions including the Chandrayaan-2 mission to the Moon, which is slated for launch in 2013. ISRO plans to complete these reviews by the end of February, the statement said.

The GSLV rocket is 51 meters tall, weighs 418 tons and has three stages. The first stage is powered by a solid-fuel motor with four strap-on boosters providing additional thrust during lift-off and the initial phase of flight. The second stage is powered by a liquid-fueled engine, while the third stage uses liquid hydrogen as fuel and liquid oxygen as oxidizer.

All but one of the GSLV’s flights to date have used a Russian-built cryogenic upper stage, but only one of those engines remains. An ISRO domestically developed version is not yet considered operational.

ISRO spokesman S. Satish told Space News that telecommunications services in India will not be affected by the launch failure as there are eight Insat communications satellites in operation. Another satellite, GSAT-8, with 24 transponders, is to be launched by the European Ariane 5 rocket in March or April 2011, he said.