Two PSLV failures, one modified rocket stage: How ISRO is trying to restore launch vehicle reliability

The Indian Space Research Organisation (ISRO) is working to restore the reliability of its workhorse Polar Satellite Launch Vehicle (PSLV) after two consecutive mission failures involving its third stage, as per a report by TOI. The space agency on Thursday successfully conducted a ground static test of the rocket's modified third-stage solid motor at the Satish Dhawan Space Centre (SDSC) in Sriharikota, marking a step towards addressing the problems that affected its previous launches.

The test follows setbacks involving PSLV-C61/EOS-09 in May 2025 and PSLV-C62/EOS-N1 in January 2026. Both missions encountered anomalies during the third-stage flight, preventing the launch vehicle from completing its objectives and raising concerns about the reliability of a rocket that has played a central role in India's satellite launch programme.

ISRO said it had undertaken a comprehensive review of the third stage, designated PS3, covering its design margins, raw material acceptance criteria, assembly procedures and quality-control checks before introducing modifications.


The modified solid motor features changes to its nozzle configuration and mechanical interfaces, along with additional redundancy in its sealing systems. The agency has also revised procedures for accepting raw materials, assembling the motor and carrying out non-destructive testing during integration and transportation.

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What changes has ISRO made to the PSLV's third stage?

The modifications are intended to strengthen the third-stage motor and improve the processes involved in its manufacture, assembly and handling.

The nozzle is the component through which hot gases escape from the motor to generate thrust and propel the rocket forward. Changes to its configuration are among the improvements introduced in the modified PS3 motor.

Mechanical interfaces refer to the points where different components connect with one another. ISRO has strengthened these interfaces to improve the mechanical integrity of the system.

The agency has also introduced additional redundancy in the sealing systems. Redundancy means providing backup arrangements so that a system can continue to function even if one component fails. In this case, the additional sealing provisions are intended to improve the reliability of the motor's seals.

ISRO has also revised its non-destructive testing (NDT) procedures. These are inspection methods used to identify defects or weaknesses in materials and components without damaging them. The updated checks will be carried out at different stages of integration and transportation.

The agency said it had reviewed the adequacy of design margins, which refer to the safety allowances built into a system so that it can withstand stresses beyond its expected operating conditions, as reported by TOI.

How two consecutive PSLV failures raised concerns over third stage

The latest modifications follow two consecutive mission setbacks in which problems were reported during the rocket's third stage.

On May 18, 2025, PSLV-C61 lifted off from Sriharikota carrying the 1,696-kg EOS-09 Earth observation satellite. Although the first two stages performed normally, ISRO detected a fall in chamber pressure during the third-stage burn, preventing the rocket from completing its mission.

Chamber pressure refers to the pressure generated inside the motor's combustion chamber as propellant burns and produces hot gases. It is a critical parameter for the motor to generate the required thrust.

Following the failure, a national-level committee was constituted to investigate the incident and recommend corrective measures.

The second setback occurred on January 12, 2026, when PSLV-C62 launched with the EOS-N1 Earth observation satellite and 15 co-passenger payloads. The vehicle encountered an anomaly towards the end of its third-stage operation.

ISRO reported disturbances in the rocket's roll rates, followed by a deviation in its flight path, preventing it from placing the satellites in their intended orbits. Roll rate refers to how quickly a rocket rotates around its longitudinal axis, or the lengthwise axis running from its nose to its tail. An unexpected change in this rotation can affect the vehicle's orientation and flight path.

Although both failures involved the third stage, the reported circumstances were different. ISRO's latest modifications follow a broader review of the PS3 configuration, its design and the processes used to manufacture and inspect it.

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What happens next after the modified PSLV motor test?

ISRO said the performance of the modified solid motor and its subsystems would now be assessed through a detailed analysis of the data collected during the ground test. Further tests will be planned based on the findings.

A ground static test involves firing the rocket motor while it is held securely in a fixed test facility rather than allowing it to fly. This enables engineers to measure its performance, including thrust and pressure, and assess whether the motor and its components function as expected.

The latest test is therefore an important part of the verification process, but the agency will need to complete its analysis and any further testing before the modified stage can be considered ready for operational use.

Why restoring PSLV reliability matters for India's space programme

The PSLV is a four-stage launch vehicle and one of the mainstays of India's space programme. It has been used for a range of missions, including Chandrayaan-1, the Mars Orbiter Mission and Aditya-L1.

Its reliability is important for ISRO's scientific and operational missions as well as India's commercial satellite launch commitments. The successful testing and eventual return of the modified PSLV to flight operations will therefore be significant for the country's broader space programme.