Cryogenic is the science pertaining to very low temperatures and includes super-low temperatures of-150°C to-273°C.
The cryogenic engine which is crucial to the development of GSLV uses such technology of sub zero temperature. The cryogenic engines use liquid oxygen as the oxidizer and liquid hydrogen as the fuel.
The use liquefied fuel instead of solid fuels or earth-stroke liquid fuels like kerosene helps the engine in producing greater thrust for the same quantity of propellant. The engine’s capability is thus of placing a for heavier load. The American Atlas-Centaur rocket, thirty year ago, was the first to use cryogenic technology.
The technology of cryogenic engine is very complicated one because the use of special insulation and materials that can withstand temperatures of minus 200°c. The turbines and pumps delivering the propellants to the combustion chamber in the cryogenic engine are also designed with special materials.
India was to acquire the cryogenic engine and technology from the Russian space agency, Glavkosmos but a hitch developed when under USA pressure and the missile technology control regime restrictions, Russia refused to honor the contract under which India had to gain three cryogenic boosters and the entire know knowhow by 1995. This force ISRO to go ahead on its own to develop a cryogenic engine. But renewed negotiation between ISRO and Glavkosmos resulted in resettlement.
This resettlement provided for four mock up models in lieu of the technology, besides the three boosters. However, ISRO scientists managed to design a small cryogenic engine. In February 1998, ISRO successfully tested an indigenously designed cryogenic engine from its Mahendragiri test facility in Tamil Nadu. The test showed that ISRO has mastered the process for firing a cryogenic engine.
On February 16, 2000, ISRO crossed and important milestone in the development of indigenous cryogenic Upper stage for the GSLV when the first cryogenic engine was ignited at the liquid propulsion systems. This engine had employed liquid hydrogen and liquid oxygen.