Achieving a major milestone in the development of new vehicle technologies, the Vikram Sarabhai Space Centre of the Indian Space Research Organisation has successfully carried out tests on the indigenously designed and developed Supersonic Combustion Ramjet.

SCRAMJET was an advanced technology initiative in the area of air-breathing propulsion and such technologies were in a very nascent stage of development the world over.

ISRO, in a release in Bangalore Tuesday, said that through a series of ground tests, a stable supersonic combustion had been demonstrated for nearly seven seconds with an inlet Mach number of six, (ie, six times the speed of sound).

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ISRO considered this achievement as a major technology breakthrough in air-breathing propulsion. Other than the United States, which had recently carried out in-flight demonstration of supersonic combustion for a short duration, work related to supersonic combustor designs in other countries like Japan [Images], China, Australia, Russia [Images] and Europe were either in their initial or ground testing phase.

ISRO, in the coming years, was planning to flight test an integrated SCRAMJET propulsion system comprising air-intake, combustor and nozzle, by using a cost effective two stage RH-560 sounding rocket.

Development of such a high technology system would come in a big way towards meeting the futuristic space transportation needs of India.  

ISRO said currently, the space transportation systems were expendable in nature, and use the conventional chemical rocket systems for their propulsion.

The cost per kg of payload of such expendable systems was quite high; in the range of $12,000 to $15,000 per kg.  

"If we have to make the access to space more affordable, this cost needs to be brought down by something like $500-1,000 per kg," ISRO said adding, this would require a two-pronged approach of systems that were made recoverable and reusable and the adoption of more efficient propulsion systems like air-breathing rockets.  

Air-breathing rocket systems use the atmospheric oxygen from their surroundings and burn it with the stored on-board fuel for producing the forward thrust in contrast to the conventional chemical rocket systems, which carry both the oxygen and the fuel onboard.

As a result, the air-breathing systems become much lighter and more efficient leading to reduced overall costs.  

As the air-breathing systems had the capability to operate only during the atmospheric phase of flight, it always had to be adopted along with the conventional chemical rockets for meeting the final orbital velocity requirements.  

A good example of air-breathing engines was the Turbojet engines used in aircraft. However, it had limitations in operating only up to a maximum of Mach number 3.

To travel beyond these Mach number regimes, SCRAMJET propulsion was the only viable option.

The development of SCRAMJET system was quite complex and it involved a number of technological challenges, especially the ones related to the mixing of very high speed air (velocity around 1.5 km) with fuel, achieving stable ignition and flame holding, in addition to ensuring efficient combustion, within the practical length of the combustor.