Insufficient Pressure Conditions in Fuel Tank Led to the Failure of GSLV Mission in 2021: ISRO

GSLV Mk-II lifts-off with Earth Observation Satellite from Sriharikota. CREDIT: ISROThe Indian rocket that carried the country's first Geo Imaging Satellite (GISAT-1) failed in its mission, owing to damage in the soft seal in a critical valve which resulted in lower pressure in the rocket's liquid hydrogen (LH2) tank, the Indian Space Research Organization (ISRO) said on Friday. According to ISRO’s Failure Analysis Committee (FAC), the failure happened when the Geosynchronous Satellite Launch Vehicle (GSLV) rocket's cryogenic engine was to take the rocket forward. (The GSLV-F10 is a three-stage/engine rocket. The core of the first stage is fired with solid fuel and the four strap-on motors by liquid fuel. The second is the liquid fuel and the third is the cryogenic engine.)

"The FAC concluded that the lower LH2 tank pressure at the time of CUS (cryogenic upper stage) engine ignition, caused by the leakage of Vent and Relief Valve (VRV), resulted in the malfunctioning of the Fuel Booster Turbo Pump (FBTP), leading to mission abort command & subsequent failure of the mission," a spokesperson from the ISRO said. "The most probable reason for the leakage of a VRV valve is attributed to the damage in the soft seal that could have occurred during the valve operations or contamination and valve mounting stresses induced under cryogenic temperature conditions."

On August 12, 2021, the GSLV-F10 lifted off normally from Sriharikota Rocket Port at 5:43 a.m. after a smooth countdown of 26 hours. In the flight, the performances of the first stage, the strap-on stages, and the second stage were satisfactory and in accordance with the pre-flight predictions. The space agency said the FAC observed that a deviation in performance of the cryogenic engine was observed at 297.3 seconds after lift-off, resulting in the onboard computer aborting the mission at 307 seconds. According to the computer, the ground servicing of the cryogenic stage/engine was normal and the required lift-off conditions were achieved.

However, after lift-off, the FAC observed that the build-up of pressure in the propellant (liquid hydrogen or LH2) tank during the flight was not leading to lower tank pressure at the time of ignition of the engine, which is what is normally expected, the ISRO said.

"This resulted in anomalous operation of the Fuel Booster Turbo Pump, mounted inside the LH2 tank and which feeds the main turbopump of the engine, experiencing insufficient flow of liquid hydrogen into the engine thrust chamber," the ISRO said.

Detailed studies by the ISRO indicate that the most likely reason for the observed reduction in LH2 tank pressure is a leak in the respective VRV, which is used for relieving the excess tank pressure during flight. Computer simulations, as well as multiple confirmatory ground tests closely simulating the conditions in the GSLV-F10 flight, validated the analysis by the FAC.

According to the ISRO, the FAC has submitted comprehensive recommendations to enhance the robustness of the cryogenic engine for future GSLV missions. The recommendations include 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 and strengthening of VRV 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.

(In April 2010, the ISRO flew a GSLV with its own cryogenic engine. The mission failed due to a problem in the cryogenic engine's fuel booster turbo-pump; however, it was then stated that a component with a higher dimension than what was designed was fixed and the rocket failed.)

The above article has been published from a wire agency with minimal modifications to the headline and text.

Image:  GSLV Mk-II lifts-off with Earth Observation Satellite from Sriharikota. CREDIT: ISRO

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