ISRO is developing two LOx methane engines (liquid oxygen oxidiser and methane fuel) engines at Liquid Propulsion Systems Centre at Trivandrum.

About the ISRO’s project

  • Project aims to convert the existing cryogenic engine, which uses liquid hydrogen for fuel, into a LOx methane engine. 
  • The other part of the project is a smaller engine of 3 tonnes thrust, which will feature an electric motor.

About the fuel uses in space missions

  • ISRO currently prefers to use a fuel called Unsymmetrical Di-Methyl Hydrazine, along with Nitrogen tetroxide for oxidiser, in its liquid fuel (Vikas) engines, which are used in the lower stages of its rockets, PSLV and GSLV. 
  • This fuel, like all hydrazine-based fuels, is highly toxic and cancer-causing. Globally, governments are keen on banning hydrazine. 
  • Hydrazine fuels are hypergolic, which means they start burning on their own upon coming in contact with oxygen.

Advantages of Methane over hydrazine

  • Apart from being non-toxic, methane has a higher specific impulse (which means one kg of the gas can life one kg of mass for a longer time), 
  • It is easy to store, does not leave a residue upon burning, less bulky, and, importantly, can be synthesised up in space.
  • Methane can be synthesised with water and carbon dioxide in space. For example, Mars has both water on its land and water in its atmosphere, fuel for a return journey from Mars can be produced right there with these. 


About Cryogenic rocket stage

  • This 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.
  • Cryogenic stage is technically a very complex system compared to solid or earth-storable liquid propellant stages due to its use of propellants at extremely low temperatures and the associated thermal and structural problems. 
  • Cryogenic engines make use of Liquid Oxygen (LOX) and Liquid Hydrogen (LH2) as propellants which liquefy at -183 deg C and -253 deg C respectively.
  • GSLV with indigenous Cryogenic Upper Stage has enabled the launching up to 2 tonne class of communication satellites. The next variant of GSLV is GSLV Mk III, with indigenous high thrust cryogenic engine and stage, having the capability of launching 4 tonne class of communication satellites.

Meanwhile, a few other rocket fuels have emerged on the horizon including Ammonium di Nitramide in Europe and Hydroxyl Ammonium Nitrate in the US.