What went wrong with the Chandrayaan-2 launch

Published : July 17, 2019 17:09 IST

The Geosynchronous Satellite Launch Vehicle Mark III (GSLV-Mk III) at the assembly building ahead of the launch of Chandrayaan-2 in Sriharikota. Photo: PTI

A leak of helium gas from a bottle in the cryogenic upper stage of the rocket was the villain of the piece on July 15. The leak forced the Indian Space Research Organisation (ISRO) to cancel the launch of its Geo-synchronous Satellite Launch Vehicle-Mark III (GSLV-Mk III). It was a prestigious mission for ISRO because it involved putting the spacecraft Chandrayaan-2, with the lander, called Vikram, and a rover, named Pragyan, into an orbit around the moon.

For thousands of people gathered at the newly-built viewers’ gallery at Sriharikota (SHAR), the media contingent that had converged at the Satish Dhawan Space Centre (SDSC) inside SHAR and for crores of space buffs across the country, it was a big let-down. The GSLV-Mk III was to lift off at 2.56 a.m. from the second launch pad at Sriharikota and put the composite module of Chandrayaan-2 into its initial earth-parking orbit about 17 minutes later. It was a highly complex mission, but it had caught the imagination of the people in the country. It was India’s second shot at the moon. The first had taken place in October 2008 when India put Chandrayaan-1 in a 100-km circular orbit around the moon. The mission also involved crash-landing an instrument called the Moon Impact Probe on the moon. But Chandrayaan-2 involved soft-landing the lander on the South Pole of the moon, where the United States, Russia and China had not dared venture until now (“Giant leap, Frontline, July 19).

The countdown for the Chandrayaan-2 mission was progressing smoothly when, 56 minutes before the GSLV-Mk III’s scheduled lift-off, a glitch occurred in the launch vehicle system. The sensors showed that helium gas was leaking from a bottle in the cryogenic upper stage of the rocket (helium is used to maintain pressure in the cryogenic chamber). The leak occurred after the propellant tanks in the cryogenic stage had been filled with liquid hydrogen, the fuel, and liquid oxygen, the oxidiser. With the pressure not holding in the cryogenic chamber, mission control had no option but to call off the lift-off.

An informed source in ISRO said there was “an anomaly” in the pressurisation of the chamber and that “the pressure was not holding” because of the leak of the helium gas from the bottle. “This will affect the nearby systems”, thereby endangering the flight after lift-off. Another ISRO rocket engineer told Frontline that the launch was called off because “one of the high pressure [helium] gas systems started leaking and there will be no gas left.”

He explained: “If there is no gas, all the other systems cannot function. The valves, the pneumatic systems, the hydraulic systems and the electro-voltage systems will not function. The [entire] system will fail. The rocket will fail. Or it will put the spacecraft into a lower orbit than intended.”

The leak could have occurred in one of the “manual joints” in the metal bottle, but it was not a quality control problem, he said. For, the bottle had undergone a series of checks. “What is puzzling is that the leak did not occur up to a certain pressure. It did not occur when the cryogenic fluids were being filled up. It occurred at a certain pressure. They are assessing why it happened. A clear assessment will be available by the afternoon of July 17. A committee has been set up to investigate what led to the leak.”

ISRO engineers are confident that the problem could be tackled without dismantling the huge 640-tonne, 44-metre long GSLV-Mk III vehicle. However, the cryogenic fluids have been drained out.

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