Sriharikota: The PSLV mission launched by the Indian Space Research Organisation (ISRO) on Monday encountered an anomaly during flight, with early indications pointing to a deviation observed after the third stage of the launch vehicle. While ISRO is still analysing flight data, understanding the role of the PSLV’s third stage (PS3) helps explain why even small disturbances at this phase can have mission-level consequences.
How PSLV flight stages work
The Polar Satellite Launch Vehicle is a four-stage rocket designed for precision orbital insertion, particularly for earth observation and multi-satellite missions.
- First stage (PS1): A solid rocket booster that provides the initial thrust to lift the vehicle off the launch pad.
- Second stage (PS2): A liquid-fuelled stage that stabilises ascent and refines trajectory.
- Third stage (PS3): A solid-fuel stage that significantly boosts velocity and places the vehicle on a near-orbital path.
- Fourth stage (PS4): A liquid-fuel, restartable stage responsible for fine orbital insertion and precise satellite deployment.
Each stage must perform within tight margins, but PS3 plays a uniquely critical role.
Why the third stage is critical
The third stage acts as the bridge between ascent and orbital precision. By the time PS3 ignites:
- The rocket is already outside dense atmosphere
- Guidance corrections are minimal
- Any error directly affects velocity, altitude, and orbital geometry
Unlike liquid stages, solid rocket motors cannot be throttled or shut down once ignited. This makes PS3 inherently less forgiving.
What kind of anomalies can occur in PS3
ISRO has not yet disclosed the exact issue, but historically, third-stage anomalies can arise from:
- Combustion instability: Irregular burning of solid propellant can cause thrust oscillations
- Nozzle or insulation issues: Even microscopic defects can alter thrust vectoring
- Structural or thermal stress: High vibration loads at this phase can affect alignment
- Guidance propagation errors: Small deviations become amplified before PS4 correction
If PS3 under-performs or deviates even slightly, the fourth stage may not have sufficient propellant margin to correct the orbit.
Why satellites may not reach intended orbit
In a nominal mission, PS4 fine-tunes the orbit for satellite separation. However, if:
- Velocity is lower than planned
- Apogee or inclination is off-target
PS4 may be unable to compensate fully. In such cases, satellites may:
- Enter a lower-than-intended orbit
- Be placed in an unstable trajectory
- Fail to separate safely
This is why ISRO typically withholds confirmation of mission success until post-flight orbit determination is completed.
How ISRO responds to such anomalies
ISRO follows a structured process:
- Telemetry reconstruction from onboard sensors
- Stage-wise performance analysis
- Simulation replay against expected profiles
- Root cause identification by a Failure Analysis Committee
This process is data-driven and corrective, not punitive, and has historically strengthened the PSLV programme.
Why this does not undermine PSLV’s reliability
The PSLV remains one of the world’s most reliable medium-lift launch vehicles, with decades of operational heritage. Occasional anomalies—especially in solid propulsion stages—are not uncommon even among mature launch systems.
Importantly, ISRO’s transparency and conservative validation approach ensure that:
- Future missions incorporate corrective design or process changes
- System reliability improves over time
What to watch next
ISRO is expected to clarify:
- Whether any payloads achieved partial or stable orbit
- The exact subsystem involved in the anomaly
- Corrective actions before the next PSLV flight
Until then, the mission remains under technical review, not categorised as a failure.
PSLV mission hits second consecutive setback as trajectory deviates after third stage
India’s workhorse launch vehicle suffered a setback on Monday after the PSLV-C62 mission deviated from its planned flight path following third-stage separation, prompting the Indian Space Research Organisation (ISRO) to initiate a detailed analysis of flight data.
Confirming the anomaly, ISRO chairman V. Narayanan said the launch proceeded normally until the end of the third stage.
“PSLV-C62 was launched as scheduled, and everything proceeded as planned until the third stage separation. Disturbances were observed at the end of the third stage. The flight path deviated from the plan. We are analysing the data,” he said.
The PSLV-C62 mission was carrying EOS-N1, also known as Anvesha, an advanced earth observation satellite developed by the Defence Research and Development Organisation (DRDO). The satellite is intended to strengthen India’s strategic surveillance and defence capabilities, while also supporting civilian applications such as agriculture, urban mapping, environmental monitoring and disaster management.
Mission profile and objectives
This was the 64th flight of the Polar Satellite Launch Vehicle (PSLV) and the fifth mission of the PSLV-DL configuration, which uses dual strap-on boosters. ISRO had also planned to mark its 101st orbital launch with this mission.
The rocket, with a lift-off mass of 260 tonnes and a height of 44.4 metres, was scheduled to place EOS-N1 into a Sun-synchronous orbit at an altitude of 505.291 km.
In addition to the primary payload, the mission carried 15 co-passenger satellites from commercial and international agencies. Among them was the Kestrel Initial Technology Demonstrator (KID), developed by a Spanish startup. KID is a prototype re-entry capsule designed to demonstrate controlled atmospheric re-entry, with a planned splashdown in the South Pacific Ocean following deployment.
Under the mission plan, EOS-N1 and 14 co-passenger satellites were to be injected into Sun-synchronous orbit, after which the fourth stage of the PSLV would de-boost the KID capsule into its re-entry trajectory. The observed deviation after the third stage prevented confirmation of successful orbital insertion.
Why the third stage matters
The third stage of the PSLV is a solid-fuel motor that plays a critical role in imparting velocity and shaping the vehicle’s near-orbital trajectory. Any disturbance at this phase can significantly affect altitude, inclination and velocity, limiting the ability of the fourth stage to correct the orbit.
ISRO is now examining telemetry, propulsion behaviour and guidance data to determine the exact cause of the deviation and its impact on payload deployment.
A rare stumble for a proven launcher
The PSLV has long been regarded as one of the world’s most reliable medium-lift launch vehicles, with 63 previous successful missions. Its record includes landmark launches such as Chandrayaan-1, the Mars Orbiter Mission, Aditya-L1, Astrosat, and the 2017 world-record mission deploying 104 satellites in a single flight.
However, this mission marks the second consecutive setback, underscoring the inherent complexity of space missions—even for mature and extensively proven launch systems. Solid propulsion stages, while robust, offer limited scope for in-flight correction once anomalies arise.
What happens next
ISRO is expected to constitute a failure analysis committee to reconstruct the flight sequence, identify root causes and recommend corrective actions before future PSLV missions. Officials are likely to provide clarity on the status of EOS-N1 and the co-passenger payloads once the analysis is complete.
Despite the setback, ISRO has historically demonstrated resilience and transparency in addressing anomalies, often emerging with strengthened systems and improved mission assurance.
For now, the PSLV-C62 mission stands as a reminder that spaceflight remains an exacting endeavour, where even established platforms demand continual scrutiny and refinement.
