A flaw in the fuel booster turbo pump was the cause of the failed 15 April launch of India's three-stage geosynchronous satellite launch vehicle (GSLV), according to an investigative committee.

The broken pump prevented adequate liquid hydrogen supply from making it to the thrust chamber of the main cryogenic engine, starving the GSLV of hydrogen and ultimately plunging to vehicle and its satellite payload into the Bay of Bengal, according to the Failure Analysis Committee set up by the Indian Space Research Organisation.

The failed launch was the first time the GSLV was flight-tested equipped with a home-grown cryogenic engine stage. The five previous successful GSLV flights were powered by Russian-supplied cryogenic engine stages. As part of an agreement signed in 1990s, India has seven Russian seven cryogenic engines to use while ISRO which launched its own cryogenic engine project.

During the April launch attempt, the GSLV-D3 performance was normal through the second stage. After a 293s burn of the first two stages, the cryogenic stage was supposed to ignite for 720s, sending the GSAT-4 satellite into the intended geosynchronous transfer orbit. The failure committee found that acceleration build-up was comparable with that of earlier GSLV flights up to 2.2s from the start of the third, cryogenic stage. Without being properly fuelled, the third stage ignited but could not burn properly.

"The start up of the fuel booster turbo pump was normal," says ISRO. "It reached a maximum speed of 34,800RPM and continued to function as predicted after the start of the cryogenic upper stage." However, it says that the speed of the pump started dipping down after 0.9s and its stopped within the next 0.6s.

The committee hinted at two possible scenarios for the failure: gripping at one of the seal locations and seizure of rotor, or the rupture of turbine casing due to excessive pressure increases and thermal stress.

"The vehicle had a perfect lift off at 16:27 and the performance of the four liquid strap-on motors, the first stage and the second stage were normal. Everything went well until the burn out of the second stage, that is 293s from lift-off," says the ISRO. "The rocket's altitude, velocity and acceleration took place as per prediction. The navigation, guidance and control system using the indigenously developed onboard computer called Vikram 1601 and the sophisticated telemetry system functioned flawlessly. The initial conditions required for the ignition of the cryogenic upper stage were attained as expected and the cryogenic stage ignited at 294.06s."

In the light of the committee's findings, ISRO is planning for a series of ground tests to validate the cryogenic engine stage. After incorporating the required corrective measures, the GSLV will be flight-tested within a year. According to ISRO, the next two scheduled GSLV flights will be powered by the available Russian cryogenic engine stages.

ISRO chairman K Radhakrishnan says India continues to move forward with plans for the country's second lunar mission, Chandrayaan-II in 2013.

Source: Flight International