Bangalore, Sep 6 (IANS) A defective propellant regulator of the fourth strap-on motor caused the INSAT-4C-carrying vehicle to crash a minute after lift-off from Sriharikota on the Andhra Pradesh coast July 10, a top Indian space agency official said here Wednesday.
'The failure analysis committee (FAC), set up to investigate the crash of GSLV (Geosynchronous Satellite Launch Vehicle)-FO2, has concluded the primary cause was the sudden loss of thrust in the fourth strap-on motor (S4) due to the malfunctioning of the propellant regulator of the gas generator system,' Indian Space Research Organisation (ISRO) chairman G. Madhavan Nair told reporters.
The 15-member FAC, headed by former ISRO director K. Narayana, attributed the malfunctioning to an inadvertent manufacturing error resulting in the deviation in dimension, which had escaped established inspection and calibration process. The deviation was found to be 1 mm instead of the specified dimension of 16 mm.
'Other than this anomaly, performance of all other launch vehicle systems like solid core booster, three liquid strap-on motors, navigation guidance and control system, structural elements were quite satisfactory until the vehicle broke up,' the inquiry report said.
Simulations and analyses of flight data and verification through calibration tests have led the FAC to conclude the propellant regulator in the failed engine (S4) had much higher discharge co-efficient in its closed condition.
'The larger flow of propellant led to very high operating pressure and temperature resulting in the structural failure of the gas generator. Instead of stabilising at 5.85 MPa (mega Pascal) chamber pressure, the flow reached 7.11 MPa at 2.8 seconds. As it was beyond the design specification of 3.6 MPa, the engine failed at 0.2 seconds after lift-off and five seconds after its ignition,' Nair said quoting from the FAC findings.
The 49-metre tall and 414-ton GSLV comprises three stages. The first stage consists of a solid propellant motor and four liquid propellant strap-ons. The second stage is also a liquid propellant stage and the third a cryogenic stage.
To prevent recurrence of such failures, the FAC has recommended additional tests for the critical engine components like regulators and valves to check their performance adequacy.
The Rs 1.6-billion GSLV-F02 was the fourth in the INSAT (Indian satellite) series. All the three earlier missions - GSLV-D1, D2 and F01 were launched successfully between 2001 and 2004.
The aborted GSLV mission was to launch the heaviest and powerful INSAT-4C satellite, weighing about 2.2 tonnes and costing Rs 960 million, into the geo-synchronous orbit, around 36,000 km from the earth. The payload consisted of 12Ku band transponders for direct-to-home (DTH) broadcasting and communications services for Indian operators.
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