ISRO PSLV-C61 Mission Failure: Understanding the Third-Stage Nozzle Anomaly

On May 18, 2025, the Indian Space Research Organisation (ISRO) faced a rare setback when its trusted Polar Satellite Launch Vehicle (PSLV) failed to deliver the EOS-09 satellite into orbit. This mission marked the 101st launch for ISRO and the 63rd for the PSLV series.

Launch Overview

The PSLV-C61 lifted off at 5:59 AM IST from the Satish Dhawan Space Centre in Sriharikota. The rocket's first two stages performed as expected, propelling the vehicle along its planned trajectory. However, approximately 203 seconds into the flight, during the third stage, telemetry data indicated a sudden drop in chamber pressure. This anomaly led to the rocket deviating from its intended path, resulting in the mission's failure.

Suspected Cause: Flex Nozzle Malfunction

Initial analyses suggest that the failure may have been due to a malfunction in the third stage's flex nozzle system. The flex nozzle is a critical component that allows for precise steering of the rocket by adjusting the direction of thrust. A malfunction in this system can lead to misalignment of thrust, causing the rocket to veer off course.

Impact on EOS-09 Satellite

The EOS-09 satellite, also known as RISAT-1B, was designed to enhance India's Earth observation capabilities. Equipped with a C-band Synthetic Aperture Radar (SAR), it was intended to provide high-resolution images of Earth's surface, regardless of weather conditions, day or night. The loss of this satellite is a significant setback for applications such as border surveillance, disaster management, and agricultural monitoring.

ISRO's Response

ISRO has established a Failure Analysis Committee to investigate the root cause of the anomaly. The committee will examine manufacturing records, test protocols, and telemetry data to identify the precise reason for the failure. ISRO Chairman V. Narayanan stated, "First two stages performed as expected. In the third stage, we observed less chamber pressure. The mission could not be accomplished."

PSLV's Track Record

Despite this incident, the PSLV remains one of the world's most reliable launch vehicles, with only three failures in 63 launches since its inception. The last failure occurred in 2017 during the PSLV-C39 mission. The PSLV has been instrumental in deploying satellites for various applications, both domestically and internationally.

The PSLV-C61 mission's failure underscores the complexities involved in space missions and the importance of rigorous testing and quality assurance. The findings from the Failure Analysis Committee will be crucial in implementing corrective measures to prevent similar issues in future launches. ISRO's commitment to learning from setbacks and enhancing its systems will be vital in maintaining its position as a leading space agency.