The Hindu : ISRO working on air-breathing rocket engines

Online edition of India's National Newspaper
Monday, Mar 01, 2004

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ISRO working on air-breathing rocket engines

By T.S. Subramanian

CHENNAI, FEB. 29. The Indian Space Research Organisation is working on air-breathing rocket engines that will use hydrogen as fuel and the air from the atmosphere as the oxidiser to burn that hydrogen. This is a frontier technology, especially because it involves the use of hydrogen — a clean source of fuel.

The ISRO Chairman, G. Madhavan Nair, told The Hindu: "We have initiated work on air-breathing rocket-propulsion systems. They will use hydrogen as fuel and air as the oxidiser. One of the engines for this mission has been conceived." Plans are under way to conduct tests of this engine. "In another three months, we will be able to show some results. If we have a good result, it will be a breakthrough. We are really considering to hold the flame at Mach 6," he said. Mach 6 is six times the speed of sound that travels at 1,100 km an hour.

All conventional aircraft engines are air-breathing. They carry fuel (aviation kerosene) with them, and take in the air from the atmosphere as oxidiser to burn the fuel. They can do this because the aircraft fly in the earth's atmosphere. For a rocket (a launch vehicle), which travels much beyond, there is no atmospheric air. The rockets carry oxygen, for example, in the form of ammonium perchlorate for burning the fuel in a solid propellant.

But when an air-breathing rocket propulsion system flies within the atmosphere, it sucks in the oxygen from the atmosphere for burning the fuel and does not have to carry an oxidiser separately.

Mr. Nair said: "The air-breathing rocket propulsion systems basically collect air from the atmosphere. As they do that, the drag increases considerably. Then, using this air, we are burning the hydrogen. So the thrust we have to develop should be more than the drag. This is really a million-dollar question, especially in hypersonic regime. I don't think many people have solved this. We are trying to make a start in this field and some experiments in the next few months will give us a feel of this problem. We are really considering to hold the flame at Mach 6.

The best of air-breathing engines used in aircraft can go up to (only) Mach 3."

An air-breathing rocket engine collecting the air from the atmosphere at hypersonic speeds and using it to burn fuel is not every nation's cup of tea. For, it involves high-end technology.

When fully developed, the air-breathing rocket propulsion system can place satellites in orbit more efficiently.

In a conventional launch vehicle, the oxidiser (ammonium perchlorate) accounts for 70 per cent of the weight of the solid propellants or 50 per cent of the vehicle's lift-off weight.

Mr. Nair said that even if 20 per cent of the oxidiser could be collected from the atmosphere, it would be "a tremendous advantage" for putting heavier satellites in orbit.

The air-breathing rocket propulsion system would ultimately reach the upper atmosphere from where it would orbit the satellite, using a conventional rocket system, he added.

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