CHENNAI: Working overnight on the aborted

, the Indian Space Research Organisation (Isro) teams have pinpointed the

in the GSLV-MkIII

to a ‘

’ of the helium gas bottle that supplies pressure to the fuel and oxidiser. Why it happened remains the crucial question

engineers are trying to answer.

Isro had aborted the Chandrayaan-2 launch 56 minutes before its scheduled lift-off at 2.51am on Monday.

“The good news is that we can fix the leak without dismantling the rocket, since there is an access door to the gas bottle which is atop the oxygen tank,” a senior scientist told TOI. “The bad news is that unless we ascertain the reason for the leak, there is a probability of the problem recurring.” Not having to dismantle means Chandrayaan-2 may be able to fly before the end of the July launch window, but a final failure analysis will be available only in a day or two.

Sources told TOI that the leak wasn’t serious enough to impair the flight, but Isro decided to apply “abundant caution,” given the importance of the Rs 978-crore project that would make India only the fourth country – after the US, Russia and China – to land a craft on the lunar surface.

The helium gas bottle has a capacity of 34 litres and it was to be pressured up to 350 bars before regulating the output to 50 bars. “The leak was bringing down the pressure by four bars per minute. The rocket could’ve still made it, but we didn’t want to take any chances,” a source said.

A veteran of Isro failure analysis said teams would now look at the proximity of the faulty ‘nipple joint’ to the oxidiser tank that stores liquid oxygen at minus 183 degrees Celsius. “If the joint was close to such a low temperature, the reason could be micro shrinkage of the joint. In that case we need to insulate it or shift the joint away from the coldest point,” the scientist said.

Bigger leaks in the gas bottle can, besides affecting combustion and velocity, send the rocket spinning out of control. For now, Isro is confident of rectifying the fault and flying to moon without much delay.

More than 7,000 people from across the country had gone to the Sriharikota spaceport to witness the Monday launch. President Ram Nath Kovind was with senior Isro scientists at the mission control centre when the launch was called off at 1.55am.