ISRO Approves New Stellite Alloy For Liquid Stage Nozzles After Successful Tests

India’s space agency on 18th April announced that it has approved an alloy called stellite as a material for rocket motors. The move comes as part of India’s drive to develop domestic sources for materials and lower overall rocket costs. ISRO will use the alloy for the nozzle of its Polar Satellite Launch Vehicle (PSLV) rocket. The announcement follows successful hot fire tests.

The PSLV’s rocket fourth stage is powered by liquid fuel, and the Indian Space Research Organisation (ISRO) has been using imported Columbium (C103) material to make the nozzle.

In line with the Indian government led by Prime Minister Narendra Modi’s mission of Make-In-India programme in manufacturing, ISRO was scouting for an alternate material for the nozzle and decided to test Stellite (KC20WN). Cost savings of up to 90% are expected through the use of this alloy, ISRO claimed.

Stellite Survives 665-Second Hot Test

According to ISRO, stellite is a cobalt-based alloy with additions of chromium, nickel, tungsten and iron. It is a material which retains good strength at high temperatures and hence becomes a suitable material for high-temperature applications.

ISRO carried out three hot tests on two pieces of hardware in the first phase and the final qualification hot test was carried out on 8th April 2025 for 665 seconds. The test was carried out at the ISRO Propulsion Complex, Mahendragiri in Tamil Nadu, a state located in South India.

“Stellite series of alloys have been an excellent choice for high temperature structural engineering applications in the aero engine, gas turbine, steam turbine sector and others. They are well known for outstanding resistance to high temperature oxidation and corrosion and thermal fatigue resistance and are used in nozzles and vanes that see hot and harsh conditions,” Dr.Dheepa Srinivasan, Dean, Research and Innovation, MS Ramaiah University of Applied Sciences, Bengaluru told Orbital Today.

“In particular, their durability to wear and erosion owing to their high hardness and thermal stability, owing to the presence of carbides, adding to the exceptional hast resistance, they have been the popular choice as both combustion hardware, such as nozzles and liners, as well as tribological coatings,” Srinivasan added.

Earlier the Indian space agency had developed atomic clocks used in navigation satellites as part of the Make-In-India Programme to save costs as well as improve performance. Imported clocks were failing in some of the Indian navigation satellites, and with each such satellite carrying three clocks, ISRO decided to develop its own atomic clocks saving about Rs.3 crore (about $3.51 lakh) per satellite.