Last year in August, the Indian Space Research Organisation (ISRO) lost an important earth observation satellite – EOS-03 – that was expected to remain India’s eye-in-the-sky for at least the next ten years. The GSLV rocket carrying the satellite lifted off normally from the ground, but the mission got aborted mid-flight all of a sudden.
Now, a national-level Failure Analysis Committee (FAC) formed to investigate the cause has submitted its report, detailing what exactly happened on the morning of August 12, 2021.
According to the committee consisting of experts from academia and ISRO, the mission had lifted off normally from Sriharikota on that day at 5:43 am 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) were also found to be satisfactory and in accordance with the pre-flight predictions. However, there was “a deviation in performance of the Cryogenic Upper Stage (CUS)” at exactly 297.3 seconds (4.9 minutes) after the lift-off of GSLV-F10. This is the last stage of a rocket, powered by cryogenic engines that use liquid oxygen and liquid hydrogen to provide a major thrust to the rocket when it’s off the ground.
As soon as the anomaly was detected, the onboard computer immediately aborted the mission at precisely 307 seconds (5.11 minutes) into the flight which led to the mission failure, it said. Scientists at ISRO who immediately examined the post-flight data that day had also indicated an anomaly in the Cryogenic Upper Stage.
EOS-03 was a state-of-the-art agile Earth Observation Satellite with a mission life of ten years, which was to be placed in a geostationary orbit using GSLV-F10. Following the setback, the space agency had to schedule the launch of the next such satellite, EOS-04, in February 2022.
Investigating the cause of the anomaly, the FAC 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. Everything seemed normal on the ground, including the servicing of the Cryogenic Stage, and the required lift-off conditions were also achieved. However, subsequent to lift-off, the committee observed that the build-up of pressure in the propellant (Liquid Hydrogen or LH2) tank was not normal which led to a lower tank pressure just when the Cryogenic Upper Stage engine was fired up.
In its final report, the FAC has concluded that this lower LH2 (Liquid Hydrogen) tank pressure had resulted in the malfunctioning of the Fuel Booster Turbo Pump (FBTP) which led to the mission abort command and subsequent failure of the mission. According to previous studies, this could have happened because of a “leak in the respective Vent & Relief Valve (VRV)”, which is used for relieving the excess tank pressure during flight, it said further. The committee also explained that the most probable reason for the leakage could be “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.”
The committee further validated its findings with a series of computer simulations and multiple confirmatory ground tests closely simulating the conditions in the GSLV-F10 flight scenario and submitted the report.
In its detailed report, the committee has also recommended certain measures to enhance the robustness of the Cryogenic Upper Stage for future GSLV missions. This includes an active LH2 tank pressurisation system to be incorporated to ensure sufficient pressure in the LH2 tank before engine start command, and strengthening of Vent & Relief Valve and associated fluid circuits to avoid the possibility of leakage and automatic monitoring of additional cryogenic stage parameters for giving lift-off clearance.
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