The Hindu : National : Scramjet on the drawing board

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Friday, Nov 19, 2004

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National

Scramjet on the drawing board

By Our Special Correspondent

THIRUVANANTHAPURAM, NOV. 18. India's supersonic combustion ramjet (scramjet) is on the drawing board.

The Indian Space Research Organisation (ISRO) is working on a range of technologies, including scramjet that could be used for exploration of deep space and planets. A small model of scramjet has been ground-tested at the Vikram Sarabhai Space Centre (VSSC) here. A bigger model is being designed.

It was only on Tuesday that the United States test-fired its scramjet that set a speed record by flying at nearly 10 times the speed of sound. India may take years to catch up with the technology.

NAL collaboration

The VSSC is carrying out the ramjet combustor development programme in collaboration with the National Aerospace Laboratories (NAL), Bangalore. The system under development is one that can typically operate in different modes such as ramjet, scramjet and rocket.

NAL has built a large database for the design and development of advanced high-speed combustors and setting up facilities for combustion heated testing facilities.

The Defence Research and Development Laboratory, Hyderabad, has a programme for the development of hydrogen-fuelled, supersonic combustion ramjet/scramjet for hyperplane.

This will be a fully reusable, single-stage hypersonic vehicle. The laboratory has already designed and tested a supersonic combustor.

Reduces amount of fuel

Ramjet and scramjet are basically air-breathing engines that suck up and store oxygen needed for combustion as they climb though the atmosphere. This reduces the amount of fuel that the rocket should carry at lift-off, resulting in considerable cost savings.

In ramjets, the high pressure required for propulsion is produced by "ramming" external air into the combustor using the forward speed of the vehicle. Ramjets are lighter and simpler than the conventional turbojet used in jet planes. They cannot produce thrust when the engine is stationary or static. So, a minimum speed in the range of two to five times the speed of sound is to be achieved before ramjets can be used.

Scramjet is a variant of the ramjet that works at higher speeds. The air comes in at supersonic speeds, mixes with fuel, ignites and the flames exit at supersonic speed. The near term goal of the VSSC is the development of a two-stage-to-orbit reusable Launch Vehicle. Its booster stage flies back to base after separating the sustainer stage at a speed of about four km per second. Initially, these vehicles would use semi-cryogenic engines. Later on, advanced airbreathing propulsion will play an important role.

Effort is on to develop a powerful 100 to 150 tonne semi-cryogenic system employing cost-effective, eco-friendly and easy-to-handle propellants as the United States and Russia have done. Development of these would take 15 to 20 years.

Semi-cryogenic propulsion uses liquid oxygen as oxidiser and one of the earth storable fuels such as alcohol, kerosene unsymmetric dimethyl hydrazene and propane. According to V. Gnana Gandhi, Liquid Propulsion Systems Centre (LPSC), Thiruvananthapuram, semi-cryogenic propulsion has many advantages.

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