The Indian Space Research Organisation successfully ground-tested a revised third stage for its Polar Satellite Launch Vehicle on November 12, 2026. The static firing took place at the Satish Dhawan Space Centre in Sriharikota, according to ISRO’s test announcement.
The test followed third-stage anomalies during the PSLV-C61/EOS-09 and PSLV-C62/EOS-N1 missions. ISRO reviewed the motor’s design margins, raw-material acceptance criteria, assembly procedures and quality checks before producing the revised configuration.
Changes included an updated nozzle, strengthened mechanical interfaces and redundant sealing. The agency also revised nondestructive testing during integration and transportation. These inspections assess components without destroying the hardware being examined.
The Third Stage’s Role
The PSLV’s four-stage design alternates solid and liquid propulsion. Its third stage, designated PS3, is a solid rocket motor that supplies thrust after the atmospheric portion of ascent. The liquid-powered fourth stage subsequently places the payload into its intended orbit.
ISRO identifies the third-stage motor as S7 and lists its maximum thrust as 240 kilonewtons. Its propellant uses hydroxyl-terminated polybutadiene, commonly abbreviated HTPB. This material serves as the binder in the solid propellant mixture.
A solid rocket motor contains fuel and oxidizer together in a solid propellant. After ignition, combustion progresses across the exposed propellant surface, producing hot gas under pressure. The gas expands through a nozzle and accelerates outward, generating thrust.
The nozzle’s narrowest section, called the throat, influences the gas flow rate. The expansion between the throat and the outlet affects exhaust velocity and pressure. Nozzle geometry is a direct part of the motor’s propulsion performance, alongside the propellant and combustion chamber.
Because a rocket carries its oxidizer, it can operate outside the atmosphere. That is the operating environment relevant to a launch vehicle’s upper stages, which continue adding speed after the earlier stages have completed their burns.
Ground Testing in the Flight Recovery Program
A static firing operates the motor on a ground test installation. Engineers can examine its behavior under firing conditions and compare the resulting measurements with the design.
The revised PS3 work addresses the stage involved in the two mission anomalies. Those events form part of the recent history of India’s launch capacity, including the role of PSLV in transporting national and commercial spacecraft.
PSLV has carried Indian and foreign satellites and launched the Chandrayaan-1 and Mars Orbiter spacecraft. Its variants change the number of solid strap-on boosters to match mission requirements, retaining the four-stage central vehicle.
ISRO said it will analyze and review the November 12 test data before conducting further tests.
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