The Indian Space Research Organisation (ISRO) has completed qualification tests for a new material used in the fourth stage engine of the Polar Satellite Launch Vehicle (PSLV). The final test, involving a 665-second hot fire, was conducted on April 8, 2025, at the ISRO Propulsion Complex in Mahendragiri, Odisha.
The tested component, a nozzle divergent, was produced using an alloy known as Stellite (KC20WN), which is a cobalt-based alloy containing additions of chromium, nickel, tungsten, and iron. This marks a shift from the previously used imported Columbium (C103) material. ISRO reports that adopting Stellite has resulted in a cost reduction of approximately 90 percent for the part.
Stellite is capable of retaining strength at temperatures up to 1150 degrees Celsius, making it suitable for high-temperature aerospace applications. A total of three hot tests were conducted during the qualification programme, across two hardware units.
In addition to the material change, ISRO has also explored manufacturing advancements for the PSLV’s fourth stage engine. In May 2024, the agency conducted a 665-second hot test of a redesigned engine produced through additive manufacturing. This approach reduced the number of components from 14 to a single piece and eliminated 19 weld joints. The manufacturing process decreased raw material usage from 565 kg to 13.7 kg and reduced production time by 60% .
Furthermore, ISRO has developed a lightweight carbon-carbon (C-C) composite nozzle for rocket engines. This nozzle features a silicon carbide coating to enhance performance in oxidizing environments. Replacing the existing metallic nozzles with the C-C version could reduce mass by approximately 67%, potentially increasing the PSLV’s payload capacity by 15 kg. The C-C nozzle underwent successful hot tests in March and April 2024 at the ISRO Propulsion Complex in Mahendragiri, confirming its performance and hardware integrity.