A composite image of GSLV-MKIII, Chandrayaan-2 Lander, Orbiter and the Rover

Five sources independently confirmed to TOI that the launch was put off because of a leak in the cryogenic stage. “After filling liquid oxygen (oxidiser) and liquid hydrogen (fuel), helium was being filled. After filling helium, we found the pressure was dropping, indicating there was a leak,” a senior scientist told TOI. The launch of Chandrayaan-2 on July 15 was postponed because of “a technical snag,” officials said

SRIHARIKOTA: A leak in the helium bottle of the cryogenic engine of GSLV-MK-III forced the Indian Space Research Organisation (ISRO) to abort the launch of Chandrayaan-2 early on Monday. The launch was called off just 56 minutes before the scheduled lift-off at 2.51 am. 

While ISRO officially confirmed “a technical snag” in GSLV-MK-III, five sources independently confirmed to TOI that the launch was put off because of a leak in the cryogenic stage. “As a measure of abundant precaution, Chandrayaan-2 launch has been called off for today. Revised launch date will be announced later,” ISRO tweeted.

“After filling liquid oxygen (oxidiser) and liquid hydrogen (fuel), helium was being filled. The procedure is to pressure the helium bottle up to 350 bars and regulate the output to 50 bars. After filling helium, we found the pressure was dropping, indicating there was a leak,” a senior scientist told TOI. “The team is yet to pinpoint the exact spot of the leak in the gas bottle; there could be multiple leaks.”

Significantly, a leak of the oxygen tank was detected during a ground test of an identical cryogenic engine on June 22, but ISRO decided to go ahead with the launch. A senior scientist told TOI that ISRO would “come back soon”, indicating the agency is trying to get the rocket off ground before the present launch window ends on July 31. The next best launch window (which ensures full 14 Earth days for the lander and the rover on Moon) comes in September. 

For some 5,000 spectators who had gathered from across the country for the first ever public viewing of a rocket launch in Sriharikota, it was a disappointing end to a night-out of patriotism and revelry of science. Among those in the VIP gallery of the mission control centre was President Ram Nath Kovind. 

The ₹978-crore Chandrayaan-2 project is to use GSLV-MK-III, a three-stage launch vehicle with an indigenous cryogenic stage powered by a C-25 engine as its upper stage. The cryogenic stage uses liquid hydrogen (LH2) as fuel and liquid oxygen (LOX) as oxidiser. 

Glitch During June 22 Test

As a practice for all big missions, ISRO had built two C-25 engines and one is tested rigorously on ground. During the ground test on June 22, a source said, a leak of liquid oxygen was detected. The team decided to “waive off” the anomaly and go ahead with the launch as scheduled. “It didn’t mean that the flying engine would have the same problem, but there was always a probability. It was a calculated risk,” said a scientist. 

A source said the leak could have happened at a weak joint of the chambers. “In layman terms, this works like a pressure cooker. When your gasket is weak, as the steam builds, you see water getting out of the lid instead of the ‘weight’ going up because of the pressure. Here, it could be possible that some welded joints were weak, causing a leak,” he said. 

Another scientist said the ‘failure analysis board’ may be ready with an initial report as early as Tuesday. “The final report may take a few weeks,” he said.