BANGALORE: As part of its advanced technology initiative in air-breathing propulsion, the Thiruvananthapuram-based Vikram Sarabhai Space Centre of the Indian Space Research Organisation (ISRO) has designed and developed a Supersonic Combustion Ramjet, recording a major technological breakthrough. With this, ISRO has taken a big step forward in its search for reduced launch costs, a key factor in emerging competitive in the global satellite launch market.

The SCRAMJET technology is still in a nascent stage of development the world over. India is the second country after the U.S. to have advanced this far. "Other than the U.S., which has recently carried out in-flight demonstration of supersonic combustion for a short duration, work related to supersonic designs in other countries such as Japan, China, Russia, Australia, Europe and others are either in their initial or ground testing phase," ISRO said in a release. Through a series of ground tests, a stable supersonic combustion was demonstrated at the VSSC for nearly seven seconds with an inlet Mach number of six (six times the speed of sound), the release said.

Integrated propulsion

It is learnt that an in-flight test SCRAMJET using a rocket was likely to take place in 2007. "In the coming years, ISRO is 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 will come in a big way towards meeting the futuristic space transportation needs of our country." The cost of the current test was about 15 times lower than a similar test in the U.S.

The space transportation systems were now expendable in nature and used conventional chemical rocket systems for their propulsion. "The cost per kg of payload of such expendable systems is in the range of $12,000 to $15,000 per kg. To make access to space more affordable, this needs to be brought down to about $500 to $1,000 per kg, the release said.

Air-breathing rocket systems used atmospheric oxygen from their surroundings and burnt it with the stored on-board fuel to produce the forward thrust. In contrast, conventional chemical rocket systems carried both the oxygen and fuel on board. Air-breathing systems were thus much lighter and more efficient, leading to a reduction in overall costs. But since air-breathing systems could operate only during the atmospheric phase of flight, they had to be adopted along with conventional chemical rockets to meet the final orbital velocity requirements.

Turbojet engines were air-breathing engines, but had limitations in operating only up to a maximum of Mach number 3. "To travel beyond these Mach number regimes, SCRAMJET propulsion is the only viable option.''

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