BENGALURU: In an important step towards restoring the reliability of its workhorse Polar Satellite Launch Vehicle (PSLV), Isro Thursday said it successfully conducted a ground static test of the rocket’s modified third stage (PS3) at the Satish Dhawan Space Centre (SDSC) in Sriharikota.The test, conducted on Thursday, follows two consecutive PSLV mission failures in which anomalies were observed in the rocket’s third stage. Isro said it had comprehensively reviewed the stage’s design margins, raw material acceptance criteria, assembly procedures and quality checks before introducing modifications to strengthen the system.Isro said the modified PS3 solid motor incorporates improvements to its nozzle configuration and mechanical interfaces, along with additional redundancy in its sealing systems. The space agency has also revised procedures for accepting raw materials, assembling the motor and conducting non-destructive tests (NDT) during integration and transportation.The mechanical interfaces have also been strengthened, with redundancy introduced in the sealing systems. Isro said the adequacy of design margins had been verified and updated non-destructive testing procedures had been implemented at different stages of integration and transportation.The modifications follow setbacks involving PSLV-C61/EOS-09 in May 2025 and PSLV-C62/EOS-N1 in Jan 2026. Both missions encountered problems during the third stage, raising concerns about the reliability of a launch vehicle that has been central to India’s satellite launch programme.On May 18, 2025, PSLV-C61, carrying the 1,696-kg EOS-09 Earth observation satellite, lifted off from Sriharikota. While 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. A national-level committee was subsequently constituted to investigate the failure and recommend corrective measures.The second setback came on Jan 12, 2026, when PSLV-C62, carrying the EOS-N1 Earth observation satellite and 15 co-passenger payloads, encountered an anomaly towards the end of its third stage. The vehicle experienced disturbances in its roll rates, followed by a deviation in its flight path, and could not place the satellites in their intended orbits.While both failures involved the third stage, the specific circumstances reported were different. The latest modifications, Isro said, followed a comprehensive review of the PS3 configuration and were aimed at improving its design margins and manufacturing and quality-control processes.
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The space agency said the performance of the modified solid motor and its subsystems would now be assessed through a detailed analysis of the test data. Further tests are planned based on the findings.The PSLV, a four-stage launch vehicle, has been a mainstay of India’s space programme, undertaking missions ranging from Chandrayaan-1 and the Mars Orbiter Mission to Aditya-L1. Its return to dependable flight operations is important not only for Isro’s own missions but also for India’s commercial satellite launch commitments.