In early 1990s, India had approached the US, Soviet Union, Japan and France for cryo technology. Only Soviet Union came forward, but then stepped back when the US cited a violation of the international MTCR. ISRO needed cryo engine rockets to lift heavier payloads

SRIHARIKOTA: A technical snag in the cryogenic stage of the GSLV-MK-III rocket carrying Chandrayaan-2 module had stalled ISRO’s launch of the moon mission on July 15. Though the space agency successfully launched the mission in its second attempt on Monday after taking great efforts to fix the snag, the moot question is why it is so difficult to deal with a snag in the cryogenic upper stage of GSLV-MK-III, popular as 'Bahubali'.

To know about the cryo stage snag, first an understanding of the art of cryogenics is needed. Among all rocket fuels, hydrogen is known to provide enormous thrust as compared to solid and earth-storable liquid propellants. But hydrogen in its natural gaseous form is difficult to store and handle, and is, therefore, not used in normal engines like that of PSLV. However, hydrogen in liquid form can be stored in a rocket engine but that requires it to be maintained at a very low temperature — minus 253 degrees Celsius. And to burn the liquid fuel, oxygen too needs to be in liquid form — minus 187 degrees Celsius. Creating an atmosphere of such low temperatures in the rocket is quite challenging as it creates problem for other materials.


Over 25-30 years ago, ISRO was desperate to develop the cryogenic technology for its GSLV rocket in order to lift heavier payload of over 3-4 tons into the Geo orbit at 36,000 km altitude, from where it could send its spacecraft to deep space or other planets. This was because ISRO’s mainstay rocket PSLV without a cryogenic engine, could deliver payload only up to 1.7 tonne to the lower earth orbit up to an altitude of 600 km. It could go to Geo transfer orbit but at reduced payload. Though PSLV was used for launching India’s first moon mission Chandrayaan-1 in 2008 and Mars Orbiter Mission in 2014, in both the cases the payload was not above 1.4 ton,

In early 1990s, India had approached the US, Soviet Union, Japan and France for cryo technology. Only Soviet Union came forward. But Moscow too stepped back when the US cited a violation of the international Missile Technology Control Regime (MTCR) to threaten it and imposed sanctions on ISRO and Soviet Union's launch service provider Glavkosmos. Though the US threat stalled the transfer of Russian cryo technology, India still managed to import seven such engines from Glavkosmos. The engines were used to launch initial versions of GSLV rockets. But desperate to have an indigenous technology, ISRO scientists worked tirelessly for over two decades to develop its own cryo engine. Being a complex system, ISRO still faces some hiccups in its cryo stage like the July 15 snag.

The July 15 glitch was due to a leak in helium bottle joint in the cryo upper stage (Helium is used to maintain pressure in the cryogenic chamber). The leak occurred after the propellant tanks were filled with liquid hydrogen, the fuel, and liquid oxygen, the oxidiser. With the pressure not holding in the cryogenic chamber, the mission control centre had no option but to call off the liftoff.