CHENNAI: Failure analysis of the aborted Monday launch of Chandrayaan-2 has presented the Indian Space Research Organisation (Isro) with some “unexpected learning curves” that may lead to tweaks in the cryogenic upper stage of GSLV-MkIII.As it was first reported by TOI on Tuesday , Isro teams had found a leak in one of the ‘nipple joints’ of a helium gas bottle that supplies pressure to several systems including fuel injection. The reason turns out to be the proximity of the joint to the tank that stores oxygen at minus 183 degrees Celsius; the extreme cold must have strained the joint, causing the leak.“Now we have to seal and insulate the joint from the cold or shift it away. The second option is tough if we were to work on the engine without dismantling the rocket. Now efforts are on to plug the leak without moving the rocket from the launchpad, so we can launch it sometime early next week,” said a source. A senior scientist said the Chandrayaan-2 setback has presented some learnings for the indigenous cryogenic engine CE-20, which was developed after studying Russian cryogenic engines. The joint that now presents a problem is defined as a rigid joint.“That’s something Russians do all the time, while the Americans use flexible joints. The rigid joints have lesser chances of leak, but if there is one, they have to be discarded and made again. During their heydays, the Russians produced cryogenic engines by the dozen and they could afford it. They were also supremely confident of their engineering skills. Flexible joints can be repaired,” explained the scientist.Having worked with seven Russian engines in the past, Isro adopted the rigid joint concept in several places, but it doesn’t have the luxury to discard and use another engine in short notice.“We may not entirely drop rigid joints, but now we may think of having some add-ons like an ‘S’ loop or a ‘U’ loop that can help deal with such anomalies. This latest setback has been an unexpected learning curve,” he said.India, which has been using Russian cryogenic engines (KVD-1) for its GSLV launches, developed an indigenous engine (CE-7.5) for its GSLV-MkII and later the more powerful CE-20 for its GSLV-MkIII. Chandrayaan-2 was to be the third flight of GSLV-MIII using CE-20 (the first was in June 2017 and the second in November 2018).Isro makes not more than a couple of cryogenic engines at a time, one for ground tests and one for flying, and every time one fails, the mission gets delayed for months till a new engine is fabricated. The Chandrayaan-2 experience may force Isro to make some changes in the cryogenic stage.