ISRO Achieves Milestone: PSLV’s Fourth-Stage Engine Qualified with Indigenous Satellite Nozzle Divergent

ISRO has successfully qualified the fourth-stage engine of the PSLV with a Satellite Nozzle Divergent made from Stellite (KC20WN), a cobalt-based alloy.

The Indian space agency has successfully tested this new material for the fourth stage engine of its Polar Satellite Launch Vehicle (PSLV). Previously, the nozzle divergent of the engine was made from imported Columbium (C103) material, but ISRO has now developed an alternative material called Stellite (KC20WN), which is a cobalt-based alloy. This new material retains high strength at extreme temperatures (up to 1150°C), making it suitable for rocket engines.

This marks a significant step toward Atmanirbhar Bharat, as it replaces the previously imported Columbium (C103) material, achieving 90% cost savings.

A Satellite Nozzle Divergent is a specialized component used in rocket engines, particularly in the fourth stage of the PSLV (PS4). It helps direct and optimize the exhaust flow to enhance thrust efficiency. Traditionally, ISRO used Columbium (C103) material for this nozzle, but it has now transitioned to Stellite (KC20WN). 

Stellite, the alloy used, is advantageous because it retains high strength at extreme temperatures (up to 1150°C), making it ideal for space applications. This shift to indigenous materials aligns with Atmanirbhar Bharat, reducing reliance on imports and achieving 90% cost savings.

A nozzle divergent is the expanding section of a convergent-divergent (CD) nozzle, commonly used in rocket engines and supersonic jet propulsion. It plays a crucial role in accelerating exhaust gases to supersonic speeds, maximizing thrust efficiency.

How It Works:

1. Convergent Section – The nozzle first narrows, increasing the velocity of the gas while decreasing pressure. 
2. Throat – At the narrowest point, the gas reaches Mach (sonic speed).
3. Divergent Section – The nozzle then expands, allowing the gas to accelerate beyond Mach 1, achieving supersonic flow.

 

Nozzle divergent during the test

The final qualification test was conducted on April 8, 2025, at the ISRO Propulsion Complex, Mahendragiri, with a hot test lasting 665 seconds.

As part of the qualification programme, 3 hot tests were already completed on two hardware in the first phase.

This breakthrough means ISRO can reduce costs while maintaining high-performance standards for future PSLV missions.