Development of semi-cryogenic engine to power ISRO’s future launches in final stages

The semi-cryogenic engine, which will do much-needed heavy lifting for ISRO’s future launch programs, is currently under the last phases of development

The Indian Space Research Organisation (ISRO)'s endeavour towards developing the next generation of advanced rocket engines is steadily gathering momentum, after facing disruption due to the pandemic in the last two years. The semi-cryogenic engine, which will do much-needed heavy lifting for ISRO’s future launch programs, is currently under the last phases of development.

The semi-cryogenic engine is an advancement in rocket technology over the cryogenic engine, which ISRO currently uses for the Geosynchronous Satellite Launch Vehicle (GSLV), which can carry up to 4 tons of payload into higher earth orbit. For increased payload, a cryogenic engine would not be enough and hence the development of semi-cryogenic engines is a key stage in India’s space program.

“The semi-cryo (engine)…more than 40-45% of the subsystems have been qualified, tested and found satisfactory and we are now working on to the major assembly of these subsystems called thrust chamber where the actual firing is going to take place and the thrust will get developed. So, it is in the last stages of development,” Surendra M. Vaidya, Executive Vice President and Business Head, Godrej Aerospace, said.

Godrej Aerospace, an arm of Rs 11,500-crore Godrej & Boyce and the flagship company of Godrej Group, has been ISRO’s key technology partner since 1985 for both for Polar Satellite Launch Vehicle (PSLV) and GSLV, and is now engaged in the development and manufacturing of the semi-cryogenic engine.

Need For Semi-Cryogenic Engine

Cryogenic engines are mostly used in the last stages of space launch vehicles and are based on use of rocket propellant at extremely low temperatures. The propellant comprises liquid hydrogen and liquid oxygen as the oxidizer. Oxygen is liquified at minus 183 degree Celsius and hydrogen at minus 253 degree Celsius.

According to ISRO, cryogenic engines are more efficient and provide more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellant rocket engines.

However, the use of liquid hydrogen at extremely low temperatures comes with many challenges.

“The difficulty with liquid hydrogen is that hydrogen is the smallest gas and very difficult to store because the storage temperature for liquid hydrogen is minus 253 degree Celsius or around that. So, handling liquid hydrogen is most difficult,” said Vaidya.

In a semi-cryogenic engine, the liquid hydrogen is replaced by civil aviation fuel, which is mostly kerosene or even compressed natural gas or CNG.

While resources are not constrained, the cost of producing liquid hydrogen is also a prohibitive factor. The production of propellants for semi-cryogenic engines on the other hand is much more cost effective and environmentally friendly.

“CNG is typically Rs 50-60 a kg, whereas when you produce liquid hydrogen, even though it can be produced through water that means the resources are not very difficult, but the cost of producing and storing liquid hydrogen is 100 times costlier than the normal CNG and that is where the semi-cryo engine comes in,” said Vaidya.

The combination of kerosene/ CNG and liquid oxygen also gives much higher thrust to the launch vehicle compared to liquid hydrogen and liquid oxygen.

Vaidya outlined that the full development of the semi-cryogenic engine is expected to be completed in the next one or two years and the thrust chamber of the engine is expected to be ready in the next couple of months.

“Once the thrust chamber is tested, I think then we can really think of integrating into an engine and test the engine itself,” he added.