PSLV-C61/EOS-09 Mission: A Setback in India’s Space Journey

By Hansika Namdeo, Budding Forensic Club

On May 18th, 2025, at 05:59 a.m., the Indian Space Research Organization (ISRO) launched its 101st mission, the Polar Satellite Launch Vehicle (PSLV-C61), carrying the Earth Observation Satellite (EOS-09), also known as RISAT-1B. This satellite marked the 63rd flight of the Polar Satellite Launch Vehicle and the 27th using the PSLV-XL configuration.

The PSLV-C61, a 44.5-meter-tall rocket weighing 321 tonnes at liftoff, with a four-stage and six solid strap-on booster configuration, was launched from the Satish Dhawan Space Centre in Srihari Kota, Andhra Pradesh.

However, the aim to place the 1,696.24 kg satellite into a Sun Synchronous Polar Orbit (SSPO) at an altitude of approximately 524km cannot be marked as “accomplished” due to a glitch during the third stage of the vehicle, resulting in the failure to deploy EOS-09 as planned.

Technical Anomaly in the Third Stage

The launch proceeded smoothly for the first two stages, with the PS1 (first stage) and strap-on engines performing as expected, followed by proper ignition of the second stage. Around 203 seconds into the flight, during the third stage (PS3), a serious anomaly occurred. The solid rocket motor, fueled by hydroxyl-terminated polybutadiene (HTPB) and capable of delivering 240 kilonewtons of thrust, suffered an unexpected drop in chamber pressure. This malfunction eliminated the thrust required to place EOS-09 into the planned orbit.

“The PSLV is a four-stage vehicle, and second-stage performance was quite normal. The third stage’s motor started perfectly, but during the functioning of the stage, we are seeing an observation, and the mission could not be accomplished. After analysis, we shall come back,” said ISRO’s chief V. Narayanan during the livestream.

Narayanan further explained that there was a fall in the chamber pressure of the motor case, and the mission couldn’t be accomplished. He added, “We are studying the entire performance; we shall come back at the earliest.”

Reflections from ISRO Leadership

Former ISRO Chairman S. Somanath, in a post on X, stated:

“I am aware of the formidable challenges we faced during the development of the third-stage solid motor — an endeavour marked by multiple failures. It is indeed unusual to witness such anomalies resurfacing at this stage. Nevertheless, I have complete confidence that the team will identify the root cause both swiftly and effectively.”

Historical Context of PSLV Missions

Historically, failures in PSLV missions have been rare. Including PSLV-C61, only three failures have been recorded out of 63 missions. The first setback was noted in 1993 (PSLV-D1), where PSLV failed to place the IRS-1E satellite into orbit, and another in 2017, the 41st launch. Since 2017, PSLV maintained an impressive track record with 58 consecutive successes, earning a reputation as one of the world’s most reliable launch vehicles.

A Reminder of Space Exploration’s Challenges

Though this failure is a setback, it serves as a reminder of the inherent challenges in space exploration. As ISRO Chief Narayanan noted, “Space is tough, but India is tougher,” reflecting India’s resilience and capabilities.

While the EOS-09 mission faced a hiccup, it is not the end of India’s journey to expand its space-based capabilities.

ISRO PSLV-C61 EOS-09 Space Exploration Satellite Launch

References

• PSLV-C61/EOS-09 mission could not be accomplished: ISRO - The Hindu
• Why did ISRO's PSLV-C61 mission fail after launching from Srihari Kota? - India Today
• PSLV-C61 / EOS-09 Mission - ISRO