BENGALURU: Indian Space Research Organisation (ISRO) scientists found helium pressure loss from the gas bottle in the cryogenic engine of the third stage of GSLV MKIII M1 launcher to be the main villain behind the mission being deferred 56 minutes and 24 seconds before the scheduled launch at 2.51 am on July 15.
The helium was meant to provide pressure to the oxidising fuel in this most crucial cryogenic stage engine of the launcher carrying Chandrayaan-2 in its final phase before releasing the spacecraft into the initial earth orbit.
Although they have found the technical snag “simple enough” to rectify now, what has foxed them is the reason for the occurrence of the snag, which is yet to be verified.
“It is likely that it happened because liquid oxygen and liquid hydrogen dropped the temperatures to well below zero (liquid hydrogen to -253 degrees Celsius and liquid oxygen to -183 degrees Celsius).
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That can cause the mechanical apparatus to shrink, which could have caused the pressure to drop,” said a retired ISRO scientist who was closely associated with the Chandrayaan-1 mission, requesting anonymity.
However, that needs to be probed, because the same fuels will have to go into the cryogenic engine when the launcher is being readied for launch on the rescheduled date.
“That would be a big challenge then,” he said.
Space experts said this verification and prevention of recurrence of the snag would prove crucial, and is likely to take time — which poses a big challenge of launching the mission latest by July 20, if the mission is not to be compromised even by a notch.
Initially, after the mission deferment, the scientists were sceptical that the snag could be corrected within ten days.
They had said it was likely that after draining the cryogenic engine of its fuel, it would have to be taken into the assembly shed at Satish Dhawan Space Centre, Sriharikota, for a thorough probe to identify and fix the problem.
What happened? What could have happened?
ISRO scientists explained that the helium gas bottle contained about 34 litres of helium with pressure up to 350 bars (one bar is equal to the atmospheric pressure on Earth at sea level, which is 14.7 pounds per square inch), but regulated to about 50 bars.
However, they found the pressure dropping was at the rate of four bars per minute, which is considered “not that serious”, and they could have allowed the mission to lift off with that.
“But it was only to be on the safe side that the mission was called off 56 minutes and 24 seconds ahead of lift-off.
There was fear that the pressure dropping would aggravate after lift-off, causing the crucial last stage of the rocket to lose thrust and velocity. In such a scenario, the last stage — which is the cryogenic stage — would be unable to achieve the orbital altitude at which Chandrayaan-2 has to be released in earth orbit, and the entire Rs 978 crore mission would have crashed, setting our lunar pursuits back by a couple of years, at least,” an ISRO scientist said.