Component Manufacturing Error Blamed in GSLV Failure
BANGALORE, India — A committee set up to investigate the July 10 failure of India’s Geostationary Satellite Launch Vehicle (GSLV) has blamed the mishap on a faulty fuel regulator in one of the rocket’s four strap-on booster engines. The panel also characterized as “robust” the GSLV’s design.
Presenting the committee’s findings during a press conference here Sept. 6, G. Madhavan Nair, chairman of the Indian Space Research Organisation (ISRO) said an “inadvertent error in manufacturing, which escaped the subsequent inspection and acceptance test procedures,” led to the accident, which destroyed the Insat 4C telecommunications satellite .
About 55 seconds after liftoff from ISRO’s Satish Dhawan Space Center at Sriharikota , the GSLV started deviating significantly from its planned flight path. It broke up a short time later, with the debris falling into Bay of Bengal.
The failure cost ISRO some 2.5 billion rupees ($54 million), Nair told the press conference . He added that failures are not uncommon in the space business and noted that this was the GSLV’s first.
“We learn as we progress,” he said. “Now that the problem has been identified, the GSLV program will be back on track. ”
The next GSLV launch will take place in June 2007, Nair said. The payload will be Insat-4CR, an identical replacement for the satellite lost in the failure, he said.
Investigators determined the cause of the failure by conducting “simulations and analyses of flight data and verification through calibration tests,” Nair said. While some engine parts have been recovered from the GSLV debris, the search is still on for components of the failed strap-on booster , he said.
The 15-member investigation committee, chaired by K. Narayana, former director of Satish Dhawan Space Centre, deliberated for more than 100 hours in several sessions and was assisted by eight specialist subcommittees, Nair said.
The committee concluded that one of the doomed GSLV’s liquid-propellant strap-on engines lost thrust almost immediately after lift-off . Although the vehicle initially was able to maintain its proper attitude with just three strap-on boosters operating, it could no longer do so after about 50 seconds, and the resulting aerodynamic loads caused the vehicle to break apart, the committee’s report said.
Jaya Shankar, ISRO’s GSLV director, told the press conference that the strap-on booster failed because of a buildup of internal pressure that was well beyond its design limits.
This excessive pressure, Nair said, was caused by the faulty regulator, which fed too much fuel to the engine. The high pressure, in turn, reduced the flow of water that is supposed to cool the engine’s gas generator.
“The combined effect of larger flow of propellants and reduced flow of water led to a very high gas temperature. … The very high operating pressure and temperature resulted in the structural failure of the gas generator,” Nair said. “The consequent abrupt stopping of the turbo pumps that feed propellants at very high pressures to the engines led to loss of thrust of the strap-on engine.”
He said that “water calibration tests simulating the malfunction of the propellant regulator hardware could closely reproduce the flight phenomenon.” Despite the fact that no parts of the failed engine have been recovered, investigators have concluded that the reason for the excessive fuel flow was that the hole in the regulator through which the fuel passes was 17 millimeters rather than the specified 16 millimeters in diameter.
S. Krishnamurthy, a spokesman for ISRO, said technicians were able to reproduce the failure scenario in simulations using a newly fabricated regulator with the faulty dimensions.
Nair noted that the regulator has performed normally on 50 engines built and tested or flown to date . “The company which supplied the faulty regulator has supplied seven more, all of which had worked perfectly.”
He declined to name the company.
Nair said is not ISRO policy to discontinue business with companies that provide faulty hardware because there is always a chance of human error during manufacturing. “On the other hand we will henceforth enforce stricter quality control and include some penalty clauses in the supply contract,” he said. “We already had an interaction with our industry partners and we will have another one this month.”
The investigation committee called for stricter controls on component fabrication, inspection and acceptance procedures and urged ISRO to independently inspect “all critical dimensions of components and subassemblies supplied by contractors,” the report said.
The committee also recommended that long-duration hot-fire tests be conducted on one of every 20 engines produced. In addition, the panel called on ISRO to improve its ability to monitor engine performance parameters in the moments leading up to launch.
Nair said ISRO has accepted the committee’s conclusions and that steps have been taken to implement all of them. “Once implemented we hope such failures will not recur,” Nair said.