The Failure Analysis Committee submits conclusions of ISRO's GSLV MkII mid-flight Rapid Unscheduled Disassembly due to upper stage inadequate LH2 tank pressure.
INDIA; On August 12, 2021, ISRO's GSLV-F10 rocket lifted-off at T-0 at 0013 UTC, into the Geo Synchronous Orbit trajectory, on board with agency's Earth Observation Satellite (EOS-03) from Satish Dhawan Space Center, Sriharikota.
In the flight, the performance of the first stage (GS1), the strap-on stages (L40) and the second stage (GS2) were nominal. Per contra, the onboard computer aborted the mission at 307 seconds into the flight, leading to mission failure
Post flight failure: The FAC has thoroughly reviewed the flight data and Simulated the GSLV-F10 flight scenario and validate the findings of the Committee. Subsequently, the respective teams have completed the simulations & ground tests and presented the results, based on which FAC has completed its deliberations and presented its findings and conclusion on March 24, 2022.
The FAC concluded that the lower LH2 (liquid Hydrogen) tank pressure at the time of CUS engine ignition, caused by the leakage of Vent & Relief Valve (VRV) resulted in the malfunctioning of the Fuel Booster Turbo Pump (FBTP) leading to mission abort command & subsequent failure of the mission. The most probable reason for the leakage of VRV valve is attributed to the damage in the soft seal that could have occurred during the valve operations or due to contamination and valve mounting stresses induced under cryogenic temperature conditions.
In Conclusion; The committee has submitted comprehensive recommendations to enhance the robustness of the Cryogenic Upper Stage for future GSLV missions, which includes an active LH2 tank pressurization system to be incorporated to ensure sufficient pressure in the LH2 tank at the appropriate time before engine start command, strengthening of Vent & Relief Valve and associated fluid circuits to avoid the possibility of leakage along with the automatic monitoring of additional cryogenic stage parameters for giving lift-off clearance.