EOS - 09 Satellite launching from ISRO has been unsuccessful. Why?
The Indian Space Research Organisation (ISRO) experienced a setback on May 18, 2025, when the launch of the Earth Observation Satellite EOS-09 aboard the PSLV-C61 rocket failed due to a technical anomaly during the third stage of flight.
🚀 What Went Wrong?
The PSLV-C61 rocket, a four-stage launch vehicle, performed nominally during its first two stages. However, during the third stage, a drop in chamber pressure of the motor case was observed, leading to mission failure. This pressure drop likely resulted from a rupture in the fiber casing of the nearly 8-tonne solid rocket motor, possibly due to hot gases from the burning Hydroxyl-terminated polybutadiene (HTPB) fuel entering sensitive areas.
Additionally, a suspected failure in the flex nozzle control system—a critical component that directs thrust by adjusting the rocket nozzle's orientation—may have contributed to the anomaly.
🛰️ About EOS-09
EOS-09, also known as RISAT-1B, was a radar imaging satellite equipped with a C-band synthetic aperture radar (SAR-C). It was designed to provide continuous and reliable remote sensing data for various operational applications, including agriculture, forestry, soil moisture estimation, and disaster management. The satellite was intended to be placed into a Sun-synchronous orbit at an altitude of approximately 529 km.
🔍 Next Steps
Committee to investigate the anomaly and determine the exact cause of the failure. The committee will analyze flight and telemetry data to identify the root cause and implement corrective measures to prevent similar issues in future missions.
Despite this setback, ISRO's PSLV has a strong track record, with this being only the third failure in over 60 launches since its inception. The organization remains committed to learning from this experience and continuing its advancements in space exploration.
The failure of ISRO’s PSLV-C61 mission carrying EOS-09 was primarily due to an anomaly in the third stage of the rocket. To understand this, let’s break down the components of the PSLV, how they work, and what specifically failed:
Overview of PSLV Launch Vehicle
PSLV (Polar Satellite Launch Vehicle) has four stages:
- First Stage (PS1) – Solid fuel
- Second Stage (PS2) – Liquid fuel (Vikas engine)
- Third Stage (PS3) – Solid fuel (HTPB-based)
- Fourth Stage (PS4) – Liquid fuel (twin engines)
What Went Wrong?
Failure Component: Third Stage (PS3)
- Fuel Type: Solid fuel, specifically HTPB (Hydroxyl-Terminated Polybutadiene).
- Main Structure: Motor casing made of composite materials (usually carbon or Kevlar fiber) to withstand high pressure.
- Thrust Control: Done using a flex nozzle control system.
1. Drop in Chamber Pressure
- The combustion chamber must maintain high pressure to generate thrust.
- During flight, sensors noticed a rapid drop in pressure, indicating a leak or rupture.
- Most likely cause: rupture in the fiber motor casing, allowing hot gases to escape.
2. Cause of Rupture
- A hot gas leak may have eroded the casing from inside.
- This can happen if there’s:
- Improper bonding of the insulating liner
- Material defect in the fiber casing
- Unexpected turbulence or instability in the burning HTPB fuel
3. Flex Nozzle Control System (Suspected failure)
- The nozzle needs to flex to control the rocket's direction during flight.
- Controlled by hydraulic or electromechanical actuators.
- If the flex system fails:
- The nozzle can't steer.
- Thrust may deviate, affecting stability and direction.
Impact of the Failure
- Once the pressure dropped or nozzle control failed:
- The vehicle lost thrust or went off-course.
- It couldn’t reach the required velocity and altitude.
- EOS-09 could not be injected into the correct orbit.
In Summary
| Component | Function | What Failed | How It Affected the Mission |
|---|---|---|---|
| Third Stage (PS3) | Provides thrust after PS2 separation | Drop in chamber pressure (likely casing rupture) | Loss of propulsion |
| Flex Nozzle | Steers the rocket during third stage | Suspected nozzle malfunction | Lost control/stability |
| HTPB Fuel System | Solid fuel burns to generate pressure | May have caused hot gas leak | Burned through casing |
Lessons & Future Action
- ISRO will:
- Conduct detailed failure analysis.
- Recheck structural integrity of motor casings.
- Improve quality checks of the flex nozzle system.
- Simulate the anomaly in ground tests.
If you'd like, I can also illustrate these components in a simple diagram for better understanding.
