How Isro’s ‘naughty boy’ cryogenic engine became a ‘smart boy’

Global telecom, news and entertainment all depend on satellites picking up radio signals and bouncing them around the Earth’s curvature. (Image: Pixabay)
Global telecom, news and entertainment all depend on satellites picking up radio signals and bouncing them around the Earth’s curvature. (Image: Pixabay)


  • With the ability to launch over 6,000 kg into Low Earth Orbit, the GSLVF14 is a game-changer for India's space exploration and satellite launch capabilities, opening doors to more direct missions and positioning India as a significant player in the global aerospace market

On 30 March, NASA and ISRO will partner for the launch of the NISAR satellite, which aims to measure the Earth’s changing ecosystems, ice masses to glean information about biomass, natural hazards, sea level rise, among others. The observations will be done every six days in alternating ascending and descending orbits to build up a picture of the Earth over a three-year period.

This collaboration will use ISRO’s GSLVF14 rocket, historically nicknamed the “naughty boy" but now referred to as the “smart boy" after its successful launch of INSAT-3DS on 17 February.

There were four failures and two partial failures in 15 prior launches using the precursors of this engine. However, the engine performed perfectly in the INSAT-3DS launch, indicating the technology has stabilised.

The GSLVF14 is a cryogenic engine using a mix of liquefied gases at super-low temperatures. ISRO had to reverse-engineer this engine by examining six Russian cryogenic engines, which it had received.

It's ironic that this rocket, now set for a joint mission with NASA, was developed after US sanctions prevented ISRO from receiving technology transfers, forcing it to overcome complex engineering challenges independently. The US was reluctant to let India acquire this dual-use technology and prevailed on Russia not to transfer technology. But after several decades of research and development, ISRO has mastered cryogenic technology and India thus becomes the sixth nation to possess reliable cryogenic engines.

The hassle-free performance of the smart boy has huge implications for India’s aerospace industry, apart from possible military applications. Cryogenic engines can deliver greater thrust to weight ratios and thus propel heavier payloads higher.

Cryogenic engines use a mix of liquefied gases, typically liquid hydrogen and liquid oxygen. The liquid hydrogen and oxygen are stored separately at very low temperatures (hydrogen liquefies at below minus 240 degree Celsius) and combust explosively when combined (as in a fuel cell).

Managing temperature differences and storing these liquids safely, requires special alloys and materials which don’t misbehave at these low temperatures. In addition, design must be done very carefully with special valves to ensure is no blowback from the hot combustion chamber into the cold fuel tanks. Designing and fabricating a cryogenic engine also means developing the material science capacity to create those special materials.  

ISRO had to reverse engineer everything and it developed new processes to do so. This engine can push over 6,000 kg into Low Earth Orbit and around half of that into higher geostationary orbits (the INSAT-3DS weighs about 2275 kg). This will make it much easier to plan future missions to the Moon or Mars, or setting up a space station, or putting Gaganauts into orbit. (The Gaganayaan mission will also use a cryogenic engine, the CE20).

ISRO’s Chandrayaan and Mangalayaan missions used the reliable but lower-power PSLV. The agency had to plot complex orbits with slingshot manoeuvres, using Earth’s gravity to accelerate the vehicles. The GSLV14 has enough power to allow for simpler orbits.

Cryogenic engines will make India a bigger player in the global satellite manufacture and launch market. This alone is worth about $25 billion. In totality, the satellite based aerospace economy including the data it garners, and the content it delivers is worth close to $200 billion.

Global telecom, news and entertainment all depend on satellites picking up radio signals and bouncing them around the Earth’s curvature. In consumer terms, Zomato and Swiggy depend on location services from satellites and the news you watch comes via satellite.

India itself is looking at satellite broadband to deliver seamless connectivity in mountainous regions and on islands. Military communications are also heavily dependent on satellites. From Ladakh to Arunachal, both civilian and military communications across India’s Northern frontiers are serviced by ISRO satellites, which also augment terrestrial networks. Cryogenic engines will boost this capacity.

Since ISRO tenders out its designs, and transfers technology to the private sector, India’s defence and aerospace industries have grasped the concerned technologies. Several private sector startups are now trying to develop cryogenic engines.

ISRO had done preliminary tests of a “semi-cryogenic" engine in the Ukraine before the start of the war. This brings us to the question of military applications. Cryogenic engines are not used in missiles since these take several days to fuel up. The Agni range from DRDO uses solid fuel propellants for example.

But sophisticated intercontinental ballistic missiles are powered by semi-cryogenic engines which use a mix of liquid (low-temperature) oxygen and kerosene. Semi-cryogenic technology is even more complex, but allows higher thrusts and missiles can be fuelled quickly. 

Given a grasp of cryogenic technology, India is a critical step further down the road to developing semi-cryogenic engines. ISRO does not do military applications but it would surely transfer technology to the Defence Research and Development Organisation (DRDO). Given geopolitical tensions, this capability would certainly give some comfort to strategic thinkers while the immediate commercial payoffs will of course, boost the revenues of the aerospace sector.

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