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Isro joins elite group with successful scramjet test

Business Standard:  August 29, 2016

Chennai: The Indian Space Research Organisation (Isro) on Sunday successfully tested its own scramjets, or air breathing engines, which would help in reducing launch costs.

Two scramjet engines were tested at 06:00 am from the Satish Dhawan Space Centre in Sriharikota, Andhra Pradesh. The two engines were ignited 55 seconds after the rocket took off.

Vikram Sarabhai Space Centre Director K Sivan (VSSC) said scramjet engines would make rocket launches cheaper by reducing the amount of oxidiser to be carried along with the fuel on rockets. “This is a baby step but a major milestone in history and it aligns with the Prime Minister’sMake in India initiative, as Isro goes for more indigenisation. We are currently using technologies which are around 50 years old.”

Isro’s Sunday test was of the engine was for five seconds. In flight, however, the engine has to work for 1000 seconds.

It might take a decade before this this technology can be used in a rocket. The US, China and Russia have this technology, Sivan said, but have not used it in rockets as it is complicated and has to be mastered completely.

The technology will significantly reduce the weight of a rocket. GSLV rockets, for instance, weight around 400 tonnes, of which 200 tonnes is oxygen. But scramjet technology does not require a rocket to carry oxygen, reducing weight. As a result, the payload capacity of the rocket can be increased.

Theoretically this technology can be used to reach the US in two to three hours using a space plane.

Development of the technology started in 2005-06 and was developed for Rs 35 crore. Sunday’s flight demonstration of a hypersonic combustion ramjet engine using atmospheric oxygen in a portion of its journey is a major step for Isro in its pursuit of a space transportation system.

The experimental mission was the first experiment of Isro’s Dual Mode Ramjet (DMRJ) engine, which uses hydrogen as fuel and air from the atmosphere as the oxidiser, at hypersonic (Mach 5 or more — speeds of five times the speed of sound and more) conditions. The programme, with an ongoing one for developing a re-usable launch vehicle, would position the organisation as a major space fare agency, with the ability to offer low-cost access to space in the long term.

Most of the current launch vehicles are designed for one-time use and are expensive. Further, their efficiency, in terms of payload to lift-off mass, is barely two to four per cent. In current rocket technology, 85 per cent of the lift-off mass is the propellant. And, 70 per cent of the latter is the oxidiser. The next generation of launch vehicles will have to use propulsion systems which can utilise atmospheric air.

The ultimate goal is developing a single stage-to-orbit (SSTO) launch vehicle configuration, to finally make access to space a routine affair.

One of the concepts for air-breathing technology being studied worldwide is a ramjet. This uses the vehicle’s forward motion to compress incoming air for combustion. Fuel is injected in the combustion chamber where it mixes with the hot compressed air and ignites. Ramjets cannot move an aircraft from a standstill. Such a vehicle still needs an assisted take-off like a rocket assist to accelerate to a speed where it begins to produce thrust. Another concept is the scramjet. A scramjet engine is an improvement over the ramjet engine as it operates at hypersonic speeds and allows supersonic combustion, which gives it its name — supersonic combustion ramjet or scramjet. The exhaust gases are then accelerated to hypersonic speeds.

While this is conceptually simple, implementation is limited by extreme technical challenges. When the vehicle is within the atmosphere, fuel must be injected, mixed, ignited, and burned within milliseconds. Worldwide efforts are on to achieve powered flight using scramjet engines.

The third concept is a mix of ramjet and scramjet, called DMRJ. There is a need for an engine which can operate at both supersonic and hypersonic speeds. A DMRJ is an engine design where a ramjet transforms into a scramjet over Mach 4-8 range.

Most of the research on air breathing engines is kept secret. Flight testing is the only tool available to master all the key technologies.

Disclaimer: This information has been collected through secondary research and IBEF is not responsible for any errors in the same.