An Indian view on history, current affairs and politics

March 27, 2023

GSLV-D5 – Riding India’s own cryogenic engine

GSLV-D5, India’s work horse rocket is set to fly again on January 5th at 16:18 hrs IST. This time using the indigenous cryogenic engine. It took two decades of developmental efforts and 7 launches to reach this stage. GSLV (Geosynchronous satellite launch vehicle) has a chequered past. Of the 7 launches 2 were successful, 2 were claimed partially successful and 3 were failure. GSLV is a vital technology that India needs to master, in order to attain indigenous heavy lift capacity. With a successful launch India will achieve the capability to launch satellites in 1-5 ton weight range. Most of the components in GSLV are from proven PSLV (Polar satellite launch vehicle), yet GSLV has been a challenge because of the extremely complex cryogenic engine stage.

The GSLV project was launched in 1990. India signed a contract with Russia to acquire cryogenic engine technology in 1991. Unfortunately Russia backed out under US pressure prompting India to embark on an indigenous effort. India, however, did get the cryogenic engines from Russia which were used in the Initial GSLV flights. Last GSLV flight in 2010 used the Indian cryogenic engine, however the launch failed when the vernier engines in cryogenic stage failed to ignite.

Cryogenic technology is tough to master as it deals with propellants stored at extremely low temperatures. The Indian engine will be using liquid hydrogen fuel LH2 stored at -253°c and liquid oxygen oxidizer LOX at -180°c. It will be used as third stage engine in GSLV. It’ll provide a nominal thrust of 75kN and will burn for 700 seconds placing the satellite in GTO (geostationary transfer orbit), from where the satellite will be moved to geostationary orbit using satellite’s own propulsion. Developed by Liquid Propulsion systems center, the engine will provide necessary lift for placing the 2 ton GSAT-14 communications satellite into GTO.

cryogenic engine

Fig: Indian cryogenic engine

A Cryogenic rocket stage is more efficient and provides more thrust for every kilogram of propellant it burns compared to solid and earth-storable liquid propellant rocket stages. Specific impulse (a measure of the efficiency) achievable with cryogenic propellants (liquid Hydrogen and liquid Oxygen) is much higher compared to earth storable liquid and solid propellants, giving it a substantial payload advantage. The propellants, at these low temperatures are to be pumped using turbo pumps running at around 40,000 rpm. It also entails complex ground support systems like propellant storage and filling systems, cryo engine and stage test facilities, transportation and handling of cryo fluids and related safety aspects. ISRO’s Cryogenic Upper Stage Project (CUSP) envisaged the design and development of the indigenous Cryogenic engine to replace the stage procured from Russia and used in GSLV flights. The main engine and two smaller steering engines of CUS together develop a nominal thrust of 73.55 kN in vacuum. Liquid Oxygen (LOX) and Liquid Hydrogen (LH2) from the respective tanks are fed by individual booster pumps to the main turbopump to ensure a high flow rate of propellants into the combustion chamber. Thrust control and mixture ratio control are achieved by two independent regulators. Two gimbaled steering engines provide for control of the stage during its thrusting phase.

The technology can, in theory, be used for military purpose. The heavy lift and long range capability of cryogenic engine can be used in achieving intercontinental ballistic missile capability. This is the reason cited behind US pressure on Russia in 1991 preventing transfer of cryogenic engine technology. Interestingly when India embarked on indigenous production, an alleged spy scandal was exposed by IB and kerala police that resulted in arrest of top scientists heading cryogenic development and cases against companies that were assisting the development.The scandal effectively derailed indigenous efforts. A decade later almost everyone was exonerated by the courts. Scientists have alleged the scandal was aimed at sabotaging Indian efforts at the behest of a foreign agency. The allegations do seem to have some merit when chain of events are observed closely.

India is standing at the cusp of a technological leap. The indigenous cryogenic engine if successful in launching GSLV-D5, will fill a major gap between India and future manned missions. This launch was planned in August last year, but at the last minute, a fuel leak was detected in second stage which resulted in the launch being postponed pending investigations. Scientists feel all errors with the vehicle have been fixed and are hopeful of a successful launch. Preparations are already underway for manned missions and lot is riding on this launch.