Malfunctioning of regulator led to GSLV failure: ISRO chief

Malfunctioning of regulator led to GSLV failure: ISRO chief

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Bangalore, India, 7 September 2006 : The primary cause for the failure of the Geosynchronous Solar Launch Vehicle-F02 (GSLV-F02) was the sudden loss of thrust in one of the four liquid propellant strap-on stages immediately after lift-off, said G. Madhavan Nair, Chairman, Indian Space Research Organisation.

He was speaking to presspersons here on the findings of the 15-member Failure Analysis Committee (FAC), set up to investigate the failure of the GSLV-F02 mission on July 10. The FAC submitted its report to ISRO on September 5.

The committee, chaired by K. Narayana, former Director of the Satish Dhawan Space Centre, Sriharikota, along with experts from academic and research institutions, besides ISRO, reviewed a huge volume of data and concluded that the failure was due to the malfunctioning of a regulator in the fourth liquid propellant strap-on motor. “With only three strap-on stages working, there was significant reduction in the control capability,” Dr. Nair said.

The thrust of the liquid engines used in the strap-on stages is controlled by a set of regulators. Analysis indicated that in S4 engine, the thrust control was not effective and the engine failed at 0.2 seconds after lift-off, which is five seconds after ignition. “Instead of stabilising at 5.85 mega pascal (MPs) chamber pressure, it reached 7.11 MPs at 2.8 seconds. This was much beyond the design limit and the engine failed.”

The defect appeared in a component that could not be tested on the ground. Hence, an innovative testing methodology must be put in place to ensure that such defects were avoided in future launches. A critical review had been put in place for the PSLV launch, scheduled to take place from Sriharikota in mid-October.

According to the FAC report, the performance of all sub-systems of the vehicle, except the fourth strap-on, was normal until 56.4 seconds. “It was a hidden problem that led to the failure of the vehicle 62 seconds into the flight,” Dr. Nair said.

The reason for the failure could be an inadvertent error in manufacturing, which escaped subsequent inspection and acceptance test procedures. The regulator functioned satisfactorily in all the 50 previous engines manufactured and tested so far. Dr. Nair said the FAC concluded that the GSLV design was robust and recommended the implementation of strict control on fabrication, inspection and acceptance procedures.

It recommended fabrication processes to be critically reviewed and updated. ISRO had also been asked to go in for independent inspection of all critical dimensions of components and sub-assemblies by in-house agencies.

The report also recommended long duration hot test on one out of every 20 engines fabricated to ensure that the production process was under control. It was also for the strengthening of the process of clearance of launch during the Automatic Launch Sequence phase.

The committee’s recommendations had been accepted and action initiated to implement them, the ISRO chief said.