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AIR spotlight summary on ISRO test firing Scramjet Rocket Engine.



AIR spotlight summary on ISRO test firing Scramjet Rocket Engine.



The first experimental mission of ISRO’s Scramjet Engine towards realisation of Air Breathing Propulsion System was carried out successfully. It is a new technology which is not available with many countries. India is the fourth country to demonstrate the flight testing of scramjet engine. Many countries have tested a Scramjet but no country has mastered a Scramjet.

The development of a supersonic combustion Scramjet Engine is a mile stone for ISRO and India. To give a simple analogy, it is trying to light a candle when there is a super cyclone blowing through. This is what ISRO has done. Lighting the rocket engine when it is travelling six times the speed of sound and to sustain the fire for a sufficient time is a big leap forward. ISRO is continuing its Innovation spree.

How is Scramjet Rocket different from Conventional Rocket

  • Conventional rockets have to carry fuel as well as oxidising agent because no fuel can burn without oxygen and in space there is no oxygen. Scramjet rockets draw oxygen from the air and use a compressor to compress the air, ignite it and burn the fuel.
  • The uniqueness of the Scramjet Engine is that it draws oxygen from the air. Here the compression is done during the movement of the rocket itself. Therefore it moves very fast, 6 times the speed of sound.

ISRO’s scramjet engine launch

  • Scramjet was tested with Rohini Rocket, which is a conventional sounding rocket used regularly for scientific studies.
  • Scramjet was fixed to the second stage, the first being conventional rocket which fell off at 11 kms and then the Scramjet was ignited and started.
  • The test-flight is maiden short duration experimental test of ISRO’s scramjet engine with a hypersonic flight at Mach 6 (six times the speed of sound).
  • Scramjet engines designed by ISRO uses hydrogen as fuel and the oxygen from the atmospheric air as the

Uses of Scramjet Engine

  • Scramjet can be used in Rocket Engine and to make more efficient missiles. In the long run in four to five decades we can have planes powered by Scramjets which would make travel faster and cheaper.
  • Services from space will become cheaper and more people will be able to access space services. Banking industry, television broadcasting, and connectivity is dependent on satellites. Launching cost will come down. It will take a long time to have a full fledged Scramjet rocket.
  • Scramjet and Reusable launch vehicle will be of great use because the launch cost will come down.
  • Essentially the endeavour is to lower the cost of rocket launcher. Carrying oxidiser is an unnecessary weight for the rocket during atmospheric phase if we can use the oxygen around it.

Limitations of Scramjet Rocket Engine

  • Scramjet cannot be used to launch the rocket. We have to use the conventional fuel and oxidiser to launch the rocket. We know that oxygen is available till 50 kms from the ground. Scramjet will be into operation till that distance, beyond that it will not work.
  • It has a limited role. Normally in the first or the second stage is when a Scramjet can be deployed.  

Scramjet Engine is different from Cryogenic Engine. Cryogenic Engine functions in the space in near vacuum condition and it provides a specific impulse which is very high.

ISRO says there was the challenge of making the right materials so that at high velocity the engine ignites. Right now it is the mastery of materials which is required for Scramjet.


  • The desire of ISRO is to place the Scramjet below the Reusable Launch Vehicle while launching. This will reduce the launch cost drastically. In Reusable Launch Vehicle 85% of the material cost is saved and by using the oxidiser from the atmosphere would further reduce the cost drastically.
  • The next step is to make it a bigger test flight, make it a prototype, then take it to an experimental flight, and finally to an operational flight. This is a matter of next 20 to 25 years of development and will be an ultra futuristic rocket engine. This is a first step towards realisation of a complex technology and a step in the right direction.