Lower pressure in fuel tank led to failure GSLV-F10/EOS-03 mission in August 2021, says ISRO

The 52m tall GSLV-F10, carrying EOS-03, at the launch pad in Sriharikota, shortly before it lifted off on August 12, 2021. (ISRO)

Lower pressure in fuel tank led to failure GSLV-F10/EOS-03 mission in August 2021, says ISRO

Bengaluru, March 25, 2022

A committee set up by Indian Space Research Organisation (ISRO) to identify the causes that led to the abort of the GSLV-F10/EOS-03 flight on August 21, 2021 has concluded that the lower LH2 tank pressure at the time of cryogenic upper stage (CUS) engine ignition had led to the failure of the mission.

The national-level Failure Analysis Committee (FAC) said that the lower tank pressure, caused by the leakage of Vent & Relief Valve (VRV), had resulted in the malfunctioning of the Fuel Booster Turbo Pump (FBTP), leading to mission abort command and 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," a statement from ISRO said.

The GSLV-F10/EOS-03 Mission had lifted-off normally from Sriharikota on August 12,2021 at 0543 hrs after a smooth countdown of 26 hours.

In the flight, the performance of the first stage (GS1), the strap-on stages (L40) and the second stage (GS2) was satisfactory and in accordance with the pre-flight predictions. However, the onboard computer aborted the mission at 307 seconds into the flight, leading to mission failure.

According to ISRO, initial investigations with the post-flight data conducted immediately after the launch indicated that an anomaly in the Cryogenic Upper Stage led to the mission abort.

The Failure Analysis Committee (FAC), consisting of experts from academia and ISRO, was constituted to identify the causes of the anomaly and to recommend corrective actions for future missions.

"The FAC has thoroughly reviewed the flight data along with all data related to the activities ranging from the stage preparation at the launch complex, countdown to lift-off. The committee recommended a series of computer simulations and confirmatory ground tests to simulate the conditions very close to the GSLV-F10 flight scenario and validate the findings of the committee. Subsequently, the respective teams have completed the simulations and 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 statement said.

"The timeline of flight events and major observations on the Cryogenic Upper Stage in the GSLV-F10 mission along with all previous GSLV missions, were thoroughly discussed and deliberated. FAC observed that a deviation in performance of the Cryogenic Upper Stage (CUS) was observed at 297.3 sec after lift-off due to which the onboard computer aborted the mission at 307 sec.

"The ground servicing of the Cryogenic Stage was normal and the required lift-off conditions were achieved. However, subsequent to lift-off, the committee observed that the build-up of pressure in the propellant (Liquid Hydrogen or LH2) tank during the flight was not normal, leading to a lower tank pressure at the time of ignition of the engine. This resulted in anomalous operation of the Fuel Booster Turbo Pump (FBTP) mounted inside the LH2 tank which feeds the main turbopump of the engine resulting in insufficient flow of Liquid Hydrogen into the engine thrust chamber.

"Detailed studies indicate that the most likely reason for the observed reduction in LH2 tank pressure is a leak in the respective Vent and Relief Valve (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," the statement said.

The committee has submitted comprehensive recommendations to enhance the robustness of the Cryogenic Upper Stage for future GSLV missions, which 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, 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.

The 2,268 kg earth observation satellite EOS-03, originally named GISAT-1, was to have provided a real-time image of a large area of region of interest at frequent intervals. It was also meant to enable quick monitoring of natural disasters, episodic events, and any short-term events.

The satellite had a payload of imaging sensors of six band multi-spectral visible and near infra-red with 42 metres resolution, 158 bands hyper-spectral visible and near infra-red with 318 metres resolution, and 256 bands hyper-spectral short wave infra-red with 191 metres resolution.

It was originally slated for launch on March 5, 2020, but hours before lift-offthe launch, ISRO announced postponement of the mission owing to some technical glitch.

Soon after, the COVID-19 pandemic and the lockdown delayed the mission. The rocket had to be dismantled and cleaned up.

Subsequently, the launch was slated for March 2021 but due to problems in the satellite's battery side, the flight got delayed again.

With the replacement of the battery, the satellite and the rocket were being readied for their flight at Sriharikota when the second wave of COVID-19 swept in, affecting many at the rocket launch centre.


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