New Delhi: The Indian Space Research Organisation (Isro) will be testing an air-breathing propulsion system this month which will allow rockets to use atmospheric oxygen for fuel, reducing costs and fuel weight in the future. The technology is an important step towards developing reusable launch vehicles.

“Basically, of the total launch vehicle mass, 86% is propellant mass in the launch vehicle. That is huge, say if you’re looking at a 400-tonne rocket. Out of that propellant, 70% is oxidiser. Instead of carrying that much load, why not take it from the atmosphere. That way the vehicle will be lighter and it will be much more efficient," explains K. Sivan, director of the Thiruvananthapuram-based Vikram Sarabhai Space Centre.

Launch vehicles use a combination of propellants consisting of oxidiser and fuel for energy. Air-breathing propulsion systems use atmospheric oxygen, which is available up to a height of 50km from the earth’s surface, to burn the fuel stored on board.

“We are planning a test some time in July in the second half. When you use an air-breathing propulsion system, you need a compressor so that the air automatically gets compressed and then it gets ignited," says Sivan.

There are several challenges in using atmospheric oxygen as the launch vehicle speeds through the atmosphere at supersonic speeds, which is why the national space agency will be developing a supersonic combustion ramjet or a scramjet engine. This engine will also be tested this month by Isro.

Air-breathing propulsion is a key technology that will be involved in space shuttles. “Of course if vehicle mass is less, costs will be less and more payload can be carried," says Sivan.

As part of the development of its own space shuttle, Isro in May carried out a test in which scientists developed a model that was one-fifth the size of the planned shuttle. This scaled model, capable of climbing to an altitude of 70 km, made a smooth landing on the Bay of Bengal, after taking off from the Satish Dhawan Space Centre at Sriharikota. Called the hypersonic flight experiment (HEX), there are several steps left till the final reusable launch vehicle is ready.

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