PSLV Third Stage: ISRO Tests Strengthened Solid Motor After C61 and C62 Anomalies

The news

The Indian Space Research Organisation (ISRO) successfully carried out a ground static test of the strengthened third-stage solid motor of the Polar Satellite Launch Vehicle (PSLV) on 12 November 2026 at the Static Test Facility in Satish Dhawan Space Centre, Sriharikota. The test follows anomalies observed in the third stage during the PSLV-C61/EOS-09 and PSLV-C62/EOS-N1 missions, which prompted a comprehensive review of the stage's configuration.

ISRO said the configuration of the PS3 stage was revisited with respect to design margins, raw material acceptance criteria, assembly procedures, and quality checks. The nozzle configuration was strengthened to improve design margins, mechanical interfaces were reinforced with redundancy in sealing systems, and the adequacy of design margins was verified. Updated assembly procedures and non-destructive tests during integration and transportation have been implemented, and the new version of the PS3 solid motor stage has been realised and tested successfully. Based on detailed analysis and reviews of the test data, ISRO said further tests are planned.

What is the PSLV third stage and its role?

The Polar Satellite Launch Vehicle (PSLV) is a four-stage launch vehicle developed by the Indian Space Research Organisation (ISRO), with its first and third stages using solid propellant motors. The third stage, designated PS3, is a high-performance solid rocket motor that provides thrust during the vehicle's ascent after the second stage separates. The PSLV had its first successful developmental flight in October 1994 and has since become ISRO's workhorse launcher for a variety of missions. The solid propellant used in the PS3 stage is typically based on Hydroxyl-terminated polybutadiene (HTPB) binder, a formulation standardised for ISRO's large solid motors over decades of development.

What prompted the redesign of the PS3 stage?

The PSLV's third stage, designated PS3, uses a solid rocket motor. Anomalies in that stage during the PSLV-C61/EOS-09 and PSLV-C62/EOS-N1 missions led ISRO to review design margins, raw material acceptance criteria, assembly procedures, and existing quality checks. The review addressed both hardware configuration and the processes used to realise the stage.

What has been achieved and what remains?

ISRO strengthened the nozzle configuration and mechanical interfaces, introduced redundancy in sealing systems, and verified design margins. Updated assembly procedures and non-destructive testing during integration and transportation target potential weaknesses across the production and handling chain. The successful ground test supports evaluation of the revised motor but is not itself proof of a successful flight. A ground static test and a subsequent launch are distinct milestones; the reported test should not be treated as completion of PSLV's return to flight.

What is the next step?

ISRO said further tests are planned based on detailed analysis and reviews of the static-test data. Continued assessment of sealing, interfaces, materials, and assembly quality can help establish confidence in the revised configuration before any flight attempt.